Katz's Corner Episode 11: The Oppo Explosion

This is the most comprehensive equipment review I've published in Innerfidelity, as the quality of the gear under test and its astounding price/performance ratio warrant our full attention.

The Oppo HA-2 is a compact DAC/headphone amp about the size of an iPhone 6, a little heavier, but that includes a high-current rechargeable battery which can be used as auxiliary power for your cell phone. It's finished in brushed aluminum covered with a smart stitched genuine leather cover which evokes the look of a classic carry-round diary. Its features are well-considered: It has two flavors of USB jacks, and comes with accessory cables needed to interface with iPhone, Android, or desktop computer. Though intended for portable use, it can also be a DAC interface for your computer or recording engineers can bring it on location to use as a reference headphone amplifier from an analog source (via a 1/8" TRS jack).

The Oppo PM-3 headphones (which I reviewed en passant in Episode 10) come with two premium, flexible headphone cables, a one-meter with a remote control for portable use, and a three-meter for desktop use. (Source: PM-3, personal purchase. HA-2 amp, reviewer's loan.) I tested the HA-2 both in portable use with an iPhone 6 and desktop use with JRiver Media player. Retail price: HA-2 amp, $299; PM-3 phones, $399. So for about $700 plus the cost of a cell phone you can have high resolution 192 kHz/24-bit or DSD portable playback.

The more I discover about Oppo, the more I admire the company, its forward thinking, and attention to detail. I already own an Oppo Blu-Ray player, which is solidly built and great sounding. The build of the PM-3 phones is clean and first rate. The controls on the HA-2 amplifier are easy to use and if you can read fine-print, each button, switch and connector is carefully marked so you do not need to refer to the instruction manual after you have read it once. Even if you cannot read the fine print, the switches are quick to learn just by feel.

The included 4 inch lightning to USB cable is designed to pair an iPhone with the DAC. Oppo thoughtfully includes two rubber bands to physically tie the two together, however, they block part of the LCD screen, so I keep them separate and replaced the cable with a longer Apple version. I use a belt pouch to carry both, or a pair of Banana Republic cargo pants! Even together, the two units are less bulky than a single Pono, which does not fit in your pocket (sorry, Neil)! The Astell and Kearn player is stylish and compact, but it doesn't answer phone calls, give you driving directions or flight times. So I like this two-box solution, and for jogging or non-critical listening, you can leave the DAC home and plug your cans into the iPhone. Clearly it would be better if the iPhone itself had a superior DAC and headphone driver, but this two-box solution is worth the trouble for the great improvement in sound quality.

I found when the iPhone went to sleep and then reawakened, sometimes the connection to the DAC was lost and the sound reverted to the iPhone's speakers. You can wake up the connection either by power-cycling the DAC or momentarily disconnecting the USB cable. Other than that small glitch, everything worked flawlessly and never crashed: Thanks Apple, thanks, Oppo!

Audio Connections
The fixed level line output, on 1/8" TRS, is designed to feed an external amplifier. The headphone output, also on 1/8" TRS, is controllable by the rotary analog volume control.

Resolution Galore
To play high resolution files (including DSD files and FLAC at high sample rates) from your iPhone, you need a special app. Oppo recommends the Onkyo HF player, which is full-featured, as rich as iTunes and includes a 64-bit high resolution equalizer. Thanks, Onkyo! I found it as easy to use as iTunes and just as pleasurable if not more. The file list is conveniently divided between high-res tracks and the iTunes database to make it easy to find the high res files. Being an Onkyo product, there are EQ presets for different Onkyo headphones. To use the Oppo phones, set the phones type to "other". However, I found Onkyo introduces an interesting subtle widening effect with the setting for the Onkyo H500M phones. You might like to try that. But the Onkyo phone presets cannot be used in conjunction with the equalizer. Engaging the EQ bypasses any headphone preset.

According to Oppo and Onkyo, the data exchanged between the app and the Oppo DAC is 32-bit fixed point. We already know that the ESS Sabre chip can use 32-bit data, so for all practical purposes, all of the resolution of the source music file is retained, even after digital equalization. Here's a bit of math explaining how I arrive at that conclusion: Truncation distortion in 24-bit calculations (if the calculation is not dithered) is potentially audible as it produces unmasked distortion products higher than the lowest level which the ear can hear (approximately -120 dB). However, 32-bit integer can encode 192 dB of dynamic range, so the distortion due to truncation would be so far below perception to be completely inaudible, assuming that the DAC chip itself does not truncate the 32-bit data, or that the remaining errors are far enough below the DAC's noise floor to be inaudible. The ESS chip's dynamic range is spec'ed at a remarkably high 127 dB, and its noise is lower than 21-bit noise. The Onkyo high-res equalizer is 64-bit (double precision), in order to handle the complex calculations without generating significant errors. This is then handed off to the DAC at 32 bits, which is a truncation and does cause distortion or errors of some magnitude. There are other errors along the way, but let's consider: even if cumulative errors might be as high as 40 dB above the LSB (a conservative, extremely high estimate), then the error might be as high as -152 dBFS, which is still completely inaudible, and also immeasurable at the analog output. Even if errors approach 50 dB above the LSB they would still be inaudible! Conclusion: Single precision 32-bit is a powerful format; the double-precision equalizer is icing on the cake. What's left is to determine how much analog resolution is lost due to noise when attenuating in front of the DAC chip, and whether the DAC chip audibly truncates any of the data. I'm betting that it is unnecessary to dither the signal going to the DAC. What remains to be proved is how well that all works, which can only be confirmed through measurements and listening tests.

All About That Bass
My experience with the sound of the highest model Astell and Kearn portable player introduced me to the warm quality of the ESS Sabre DAC chip, but it did not prepare me for the thrill of this portable system: the incredibly microdynamic HA-2 with the well-tuned PM-3 headphones, driven digitally by the iPhone. Every dynamic cut I own plays with amazing impact! I found drums and percussion to be clean, punchy, and snappy (when the recording itself had snap to deliver). The battery-driven HA-2 never seems to run out of steam so clearly Oppo have engineered a regulated, tight power supply.

On the PM-3's, well-recorded acoustic upright bass sounds full, deep, and punchy with perfectly even notes (but read on). With my desktop AMB M3 amp and the Slim Devices DAC, I felt that a half dB drop circa 60 Hz would perceptually flatten the bass response, but on the HA-2/PM-3 combination, flat sounds correct to my ears down to about 60. Perhaps this is because the M3 amp is DC coupled and/or the HA-2 has a slight rolloff. I'll look for this issue when I measure. The bass response seems to go down to the center of the earth; deeper and cleaner than any moving coil headphone in my experience, and rivaling my equalized Audeze LCD-X and Stax cans driven by the world's best desktop amps. In general, not a single note stands out too far to expose a resonance, but there's a little devil is in these details.

Judging bass response in headphones is an imprecise science. According to Harman research, listeners prefer some kind of bass boost. I prefer less boost than typical consumers, because I listen a bit louder, which would bring the perceived bass up due to the equal loudness contours. So, for me, flat to 60 Hz sounds just right on these phones with the HA-2. After study of many cuts I know well, I concluded that there is a subtle rise in the PM-3's low frequency response below about 60 Hz. This includes the notes A, G, F, E, and D (36.7 Hz). The latter is used on occasion by the 4-string electric bass in hard rock with "Drop D" tuning or the five string in fusion jazz. So the residual resonance of the PM-3 lives below 60 Hz. Well, if there has to be an anomaly, let's put it below most of the musically significant bass notes! The reason we don't initially notice a resonance with these cans is that there is rarely a bass note to excite it, and when there is one, our ear's natural insensitivity in this region makes it sound very musical. Good choice, Oppo: These are very linear headphones!

To complicate the matter, a lot of what we hear with bass notes are the harmonics, and a lot of recordings which seem to have good fundamental are fooling us, as for a low B (61.7 Hz), they are actually taking advantage of the second and third harmonic (123 and 185 Hz), the frequencies which help give the note its definition. Typical open-headed kick drums' primary frequency is 60 Hz. Below 60 Hz is the frequency range occupied by the bottom end of the thumps of the bass drum. Below 60 is where the upright bass instrument's "rumble" and "solidity" live; it's the part of the acoustic bass that is felt as much as heard, however, typical stereo systems are weak in or incapable of reproducing this range. Obviously it's the least important range, but when a loudspeaker can reproduce it, it can enhance our sense of reality and enjoyment of sound reproduction. On headphones, subsonic is rarely a problem range, because most phones don't go down that far, but the advent of the planars has reawakened our interest in this range. I can tell that the PM-3's have that rare response down to the lowest octave, since I can hear a sonic difference when equalizing the 31.5 range.

It's difficult to subjectively judge how much subsonic information to permit when equalizing headphones. With loudspeakers, you feel subsonics in your chest and body as well as your ears. Headphones do not deliver that total sensation, plus they literally press the bass drum onto your eardrum. It's unnatural and fatiguing to hear too much subsonic information in a transducer a few inches from your ear drums, although it can be terrific on loudspeakers like mine which are flat (0 dB) to 20 Hz, minus 3 dB at 17 and then the response drops off a cliff.

In the days of LPs, you almost never heard fundamental bass below 70 Hz because it ate up the groove spacing and reduced the playing time of a side. Most popular music recordings are still rolled off in this range, as engineers often remove mud from the bass drum and bass, but my recording of Joachim Palden's band is an intentional exception. This recording is particularly problematic on the PM-3's because it has distinct and intentional subsonics to below 20 Hz. We wanted the power and rumble of the bass and bass drum to extend to their deepest potential, but this is problematic when reproduced that close to the eardrum. The EQ which I arrived at for perceptual flatness with most recordings is flat at 1 k, down -0.1 at 63, -0.8 at 46 and -1.5 at 31.5. But this EQ is simply too heavy below 60 for the Palden recording, producing ear fatigue. So I created a second EQ for programs with extra subsonics that's an additional 1/2 to 1 db down at the two lowest bands. This yields an analogous sensation to the loudspeakers without fatiguing pressure on the eardrums.

I advise caution when dealing with subsonics because the ears are very insensitive to pressure at extreme low frequencies! I'm reminded of my high resolution recording of a shuttle launch. March 8, 2001, I was invited to attend the launch of Space Shuttle Discovery at the press box, so I brought some very special recording gear to capture the launch without any distortion. This recording is available at no cost on my website, www.digido.com. The sound goes down to 8 Hz but this cannot be appreciated in the home unless you have one of those expensive fan-driver subwoofers with response down to DC, and then it would be purely felt and not heard. So 8 Hz response would be useless in phones, and probably would cause serious vibrations if they could reproduce this frequency. During the launch I felt the 8 Hz-centered noise, 127 dB SPL, multi-kilowatt wave deep in my chest without any ear pain whatsoever. It was an amazing experience that I can never repeat since after 9/11/2001 us civilians are not permitted within the 3 mile limit during a launch. Only government officials, congressmen and dignitaries can enjoy a launch from the press box after 9/11. Especially since the shuttle program is no more and the only rockets coming out of Canaveral are military satellite launches.

I'll tell you more about fine-tuning the EQ after our listening report.

Listening Report: Portable Use, IPhone with Onkyo HF Player, Oppo HA-2 Amp and PM-3 Headphones
During the making of this review I've had to "recalibrate" my ears more than once! Some products which I formerly have given an A grade have been reduced to B. New products of higher quality than I have previously heard have replaced them, so let's see what has developed.

We'll start by listening to some notable musical examples, auditioned portably all over my house because they sound so infectious I couldn't put the phones down! Later I will try substituting the HA-2 for the Slim Devices DAC in the desktop system feeding my M3 amp, try to see how much of the magic is in the amp and how much in the DAC. These recordings were auditioned some with a flat EQ and some with the custom EQ, but really the custom EQ is an icing on the cake, it's not necessary to appreciate the virtues of the PM-3 phones.

From HD Tracks: Arthur Fiedler and the Boston Pops, Hi-Fi Fiedler, at 88.2 kHz (upsampled in the Onkyo player to 176.4). My dad had this LP and passed on the love to his son. The glorious Hungarian Rhapsody...when the orchestra hit its sforzando I nearly jumped! An experimental early stereo LP, made from 1957-1960 to 30 IPS 3-track tape, this recording has stood the test of time. It is bright and saturated on the peaks, but there's so much romance, bloom, depth, richness, beauty, and expression that I quickly forgive it. Some of the cuts are quite fuzzy on the peaks, but others are glorious with just a bit of tape saturation, regardless of which, this is one of my top reference pleasure orchestral recordings.

From HD Tracks: Cat Stevens' Tea for the Tillerman. Lovingly restored from the 15 ips 1/4" analog to 2496. But I never would have guessed it was "only" a 15 ips because of its fabulous macro- and microdynamics which come through so well on this portable playback system. This classic 1970 release sounds as clear as if it had been made yesterday, pure, and amazingly dynamic. They don't make 'em like they used to. Cat's voice sounds just like it does from the reference loudspeakers, with a lot of presence but never unpleasant. Wikipedia calls Cat Stevens one of the most important musical performers of the 20th century. Whether or not you were around when the recording came out, you'll love this 2496 file from HD tracks; it took me right back to my youth and the carefree feeling that Stevens portrays throughout the album. The residual tape distortion is very tolerable.

Joachim Palden Trio: Guilty, 2496 BK master. I highly recommend this CD for traditional blues lovers. This is one of my best-sounding blues recordings. Joachim is a master on the keyboards. On the portable system it sounds exactly as Joachim and I intended: fat, impacting, big, punchy, just right with the headphone EQ designed for extra subsonic rolloff (described later in this review). The bass from the organ and bass instrument is purposely larger than life, perfect for electric blues. The HA-2 with the PM-3 phones produces a palpable sound, so impacting you can practically touch it. I'm sure a lot of that has to do with the deep, punchy feel of the bass. Dana Gillespie's sexy contralto voice is a real turn on. I passed the phones to Mary to enjoy Flip Flop and Fly and she sat mesmerized through the whole cut. Despite not being an audiophile, she immediately remarked on the focus of the center image and the palpability of the sound. I hope someday to see the 2496 version released for sale as it sounds even warmer, deeper and purer than the 1644 reduction.

You may be familiar with the Buena Vista Social Club, a very pure acoustic performance available in high resolution on HD Tracks. The classic traditional Afro-Cuban performance with soaring vocal harmonies puts chills up my latin-loving latissimus*. This recording is warm, beautiful, and spacious with a deep bass resonance that may require the extra "anti-subsonic" EQ for the PM-3s.

*That's the broad muscle in your spinal area!

From HD Tracks: 2496, 52nd Street, headlined by bass player Andy Gonzalez. The upright bass is holographically real on the Oppo phones. The instruments sound so alive you can touch them. Great stereo image and depth. This is another one of my references, highly recommended if you like Latin Jazz played by a small acoustic ensemble.

The center image from these phones is perfectly focused, so the left and right channels, right down to the Oppo transducers themselves, must be very well matched. Raising or lowering the little analog volume control on the top of the HA-2 does not seem to shift the image, which is a remarkable achievement considering how difficult it is to manufacture a matched volume control in this size. I still can't believe it's true since I've never before encountered a consumer-grade analog volume control that matches left-right gains this well, down to the lowest level. This is further evidence of Oppo's attention to detail. Could this be a DC-level controlling an analog gain cell? I wouldn't be surprised.

Fine Tuning the EQ

According to Onkyo, this equalizer is a linear-phase, FIR EQ. As a mastering engineer, I've found a linear phase high frequency boost for program EQ sounds greatly superior to minimum phase. Linear phase EQ preserves the depth image, while minimum phase EQ brings the image forward when the high frequencies are boosted. There is no distortion or image warping with linear phase. However, linear phase may not be is superior for transducer compensation. Transducer errors, which are typically minimum phase, should be corrected with a minimum phase EQ, which produces the inverse of the transducer error. In fact, I've found when the program is already perfect but the transducer needs some high frequency help, a minimum phase high frequency boost sounds a little better. So in a perfect world, Onkyo should give the user a choice of which characteristic to use. Regardless, the Onkyo EQ is very sweet and capable of the most subtle corrections and I would not kick it out of bed! Keep in mind that the EQ operates in the PCM domain and is bypassed when playing DSD files.

The ergonomics of this equalizer are good but one function puzzles me. You can start with a flat response by loading a preset. Tapping your thumb on any point in the frequency graph produces a new dot which can be dragged up and down. But there is no way to erase a dot, so if you're not careful, the graph will quickly become littered with dots that you have to move to the 0 dB line if you don't want an active filter at those points. But I beat the system, and you can, too! I found a way to precisely set the EQ in 0.1 dB increments or less if you want and place dots precisely anywhere on the graph: Using an OSX App called iMazing allows me to exchange files between my iPhone and my Mac. I extracted an EQ document from the iPhone and found the EQ settings are written in XML, which can be directly edited with a text editor! For example:


(Ed Note: "<" and ">" symbols have been replaced by "[" and "]" so they can be seen in an HTML web page.

This means that 1 kHz is set to flat and 32000 Hz is boosted 1.1 dB (expressed to 16 decimal places if you want!), producing a gentle rise in the high end. So you can edit this file to produce exactly the curve that you'd like. Thanks, Onkyo! Even if you're all thumbs on the iPhone touchscreen you can precisely edit this file on the desktop Mac and send it back to the iPhone. Later when measuring I found the EQ circuit drops level 3 dB, so if you don't boost any frequency more than 3 dB, you won't have to worry about digital overload. Hints: You'll have to explicitly flatten each octave by adding more dots or it will draw a slight dip in the curve between 31.25 Hz and 1000, unless you're looking for a dip.

As I reported in Episode 10, on my desktop system (JRiver, Lynx interface, AES/EBU into Slim Devices DAC, M3 headphone amp), the Oppo PM-3 cans seem to need some high frequency boost. But I found the HA-2 DAC has much more audible definition and resolution than my desktop DAC: On the portable player I found the PM-3 hardly needs any high frequency boost. With well-recorded music, the HA-2/PM-3 combination sounds so open that you don't feel deprived when playing it flat. I finally decided on + 1.1 at 32 kHz, up from 0 dB at 1 kHz using a straight line tilt. If I turn up the high end even 0.1 dB more, it noticeably dips the fundamentals of vocals in the lower midrange, so this must be optimum tilt, the icing on a very nice-tasting cake. Hey, Tyll, you can write up about EQ since your readers will be interested in these player apps. So that's fair game for you to review. I look forward to Tyll getting an iPhone and a Mac soon (insert smiley face here). You may be able to extract these files on a PC as well, though I have not tried.

(Ed Note: I'll work on it, Bob. Got a few irons in the fire to flesh out my understanding of EQ on headphones, but it's something I'll definately do when I get my ducks in a row.)

Clearly Onkyo has put great attention to detail into this application and it has already received numerous user-driven revisions. I hope they will consider my suggestions: I'd like to find a way to let the user delete a dot. I'd like to see the position of a dot displayed with more precision by adding 1/2 dB step graph lines, and also display the overall gain in dB. I'd like to see the main digital volume control displayed in dB as well.

I didn't spend much time comparing upsampled to 1x rate. On a simple comparison, the difference was quite subtle but I think the upsampled version has a bit more depth. After that I just let the app do its upsampled thing.

Gain Staging The HA-2
Everything about this software and hardware has been optimized for high resolution sound. The digital volume control in the app directly controls the built-in 32-bit volume control in the ESS chip. Oppo recommends setting the digital volume control at full and then making final adjustments through the analog volume control. But the errors (distortions) from 32-bit fixed-point (integer) communication are so far below the noise of the DAC that it hardly matters whether you attenuate via the digital control or not. So feel free to use the digital volume control if it's more convenient than the analog.

Beats the iPhone's Amp
I did a quick switch between the built-in amp/dac in the iPhone and the HA-2. It's no contest: The HA-2 has much better resolution. On the iPhone's own amp, bass is soggy and wimpy, and the sound is just not as clear. But for jogging and casual playback I have no problem just taking the iPhone out with these incredible Oppo phones.

Listening Report: On the Desktop, HA-2 as a Line-level DAC
I'm no stranger to asynchronous USB as I have the excellent portable Centrance DAC-port/headphone amplifier, which is self-powered from USB. But it doesn't have a connection suitable for use with the iPhone and so it mostly sits idle unless I take my MacBook Pro on location. In the mastering studio I've not used USB. I depend on AES/EBU for a multichannel connection to 10 channels of DAC! But there is no reason why I cannot employ asynchronous USB for a headphone connection and so I was very curious to try the HA-2 as a desktop DAC for headphones, either feeding its headphone output, or into my custom-build AMB M3 headphone amp.

The first thing I discovered, moving the PM-3s into my quiet studio (NC-20 rated) was that I can feel the pulse in my temples when I put on the cans with nothing playing! It's easy to ignore, but quite disconcerting at first. That's how quiet my room is and how good are the seal and isolation on these comfortable little headphones.

The desktop amp I chose to compare with the HA-2 is my custom-built AMB M3, which I felt was the best-sounding standard headphone amplifier at Big Sound 2015, and the equal in resolution, punch, definition, and channel separation to Tyll's custom KGSS electrostatic amplifier. In the studio I compared five options:

1) JRiver ---> USB ---> HA-2 ---> Headphone output ---> PM-3 phones.

2) JRiver ---> USB ---> HA-2 Line output ---> AMB M3 amp ---> PM-3 phones

3) JRiver ---> USB ---> HA-2 Headphone output used as a line driver ---> AMB M3 amp ---> PM-3 phones

4) JRiver ---> Lynx AES-16 Card ---> AES/EBU ---> Slim Devices DAC ---> AMB M3 amp ---> PM-3 phones

5) iPhone HF Player ---> HA-2 ---> Headphone output used as line driver ---> AMB M3 amp ---> PM-3 phones

That's a lot to swallow so I concentrated on playing the same song each time. I used the song "Flip Flop and Fly" from the Joachim Palden album, which has bass and bass drum that go down into the subsonic range. The double-time boogie woogie piano is a perfect test for left hand definition, complemented by a breathy tenor, a big upright bass, and punchy drum set. The star is Dana Gillespie, a charismatic blues vocalist whose contralto voice has great body and presence. The overall sound of this recording is authentically "blues phat" but with plenty of presence and natural high end on the cymbals. This song is rhythmically infectious; sonically it has excellent low and high frequency extension, excellent separation, dynamic impact, power and purity of tone. It makes a great demo track and besides, I know this song cold, having mastered the track.

To cut to the chase, four out of five of these options sound nice; it's a matter of degree and polish, with the first place finisher getting a definite A+ and the third place a B grade. One option, however, got a C grade for sound. Let's find out which one.

First I listened to option 1, JRiver feeding the HA-2 amp directly driving the PM-3 phones. In this case, JRiver is outputting 32-bit fixed point through the USB. This seems a bit dark and a bit thick (or warm as some would say), not very extended at the high end. I felt the need for some high frequency boost EQ. Grade: A- (without EQ).

Then I tried option 2: I patched the line output of the HA-2 into the M3 amp, which fed the PM-3 headphones. Levels to the cans were matched as closely as I could using the stepped analog attenuator. With a 1 kHz test tone and a 20 ohm load, I was able to get the AMB to match the HA-2's headphone output within 0.6 dB. Upon listening, to be honest, I was underwhelmed with the sound of the HA-2's line output. It seemed wimpy in the bottom, a bit thin and uninvolving with less stereo separation. I conclude that the 15 k ohm load of the M3 amp might be a little heavy for the HA-2's line output. It might like to see something closer to an open circuit, perhaps 47k ohms or higher. Regardless, I did not like the sound quality of the line output. I took it out of the running and would give it a C grade if I had to use it. I was never able to prove that the issue is load impedance, but regardless, I suggest you exercise caution when considering the HA-2's line output.

Option 3: Fortunately, we have the option of using the HA-2's headphone output as a line driver. This proved to be a completely different sonic story! The HA-2's headphone output stage obviously has more active components than the line output, which could degrade the sound, but it has a much lower output impedance and can drive any load to well below 600 ohms. In my studio experience, line drivers that can feed real current into a low impedance load generally sound more robust and clearer than those which require a high impedance load. That was definitely the case with the HA-2 amp. With this connection I found the AMB amp to have considerably more presence, subjectively brighter than the HA-2 direct. In fact, I felt much less need to add any EQ: it sounds great flat. Does this mean that the AMB amp is bright-sounding or has a bit of edge to it? If it does, then it's euphonic distortion, a perfect match for these slightly dark PM-3 phones. It does not sound harsh or edgy or "transistory". At Big Sound 2015 Tyll and I did not find the AMB to be bright, just that it sounded distinctly open and clearer than the very darkest commercial competitors but attractive without any edge or harshness. At Big Sound the AMB was driven either by the Prism or the Antelope DAC, and both sounded similar. I have to spend much more time with the HA-2, the AMB and various DACs and phones to reach a definitive conclusion, but this is an A grade playback.

Option 4: AES/EBU to the Slim Devices Transporter DAC and into the AMB amp. This is (was) my standard headphone playback method until I got the HA-2. In this case, JRiver is dithered to 24 bits to accomodate the wordlength limit of AES/EBU. The verdict: No contest. This has been downgraded to grade B. Compared to the HA-2 DAC, the Slim Devices is less resolved, with less depth, smaller soundstage, veiled. It requires considerable HF boost to try to overcome its veil, but it can't improve the loss of resolution. Could this be the dreaded j*tter? The 24-bit interface versus the 32-bit interface? The outdated chip in the Slim Devices DAC? In any case I will have to abandon the Slim Devices DAC for critical headphone listening. We have a new winner and established a whole new standard.

Option 5: iPhone with HF Player ---> USB ---> HA-2 amp headphone output as a line driver ---> M3 amp ---> PM-3 phones. This sounds very similar to JRiver but superior! The HF player sounds a little warmer than the desktop JRiver, and perceptually goes down a bit deeper in the low end. In other words, the HF Player has a warmer and deeper output through USB through the same DAC. This is very puzzling. Theoretically both software players are sending the same digital information...or are they? Without EQ, the HF Player sounds darker than JRiver, but it is very pure, resolved, rhythmically impactive, and involving. In fact I feel the HF Player has better sub-bass impact. How can a portable playback system get a better grade than a desktop? But it does! This is definitely an A grade system or A+ with a little HF boost applied.

What's going on? Does this mean that the HF Player has less distortion than JRiver? Does the portable USB interface perform better than the desktop? Why would that be? Keep in mind that interface jitter is irrelevant with asynchronous USB, and regardless of the player, the internal clock of the HA-2 is always the master, so I can only chalk up these differences to the mysteries of the universe. I will try to get to the bottom of this puzzle with measurements, but cannot promise a definitive explanation. Please don't send me any jitterbugs or other magic USB cures, I'm not ready for voodoo yet.

Listening conclusions
How much of the magic is in the amp, and how much in the DAC? Answer: a little of both. The M3 amp seems to have the perfect definition and clarity for the PM-3 phones, but it may be because it's a little on the bright side or has a bit of euphonic distortion, to be determined. Comparing the HA-2 DAC to a classic AES/EBU DAC is no contest: USB rules! The slight sonic differences I found between software players are a bit of a mystery and will require considerable further investigation.

Measurements and Objective Tests
Frequency Response - I measured both JRiver and the HF Player using discrete sine wave tones, identical 24-bit dithered -20 dBFS FLAC files that I created. I was able to switch between software players in an instant by simply switching the USB input on the bottom of the HA-2. I normalized the HA-2's analog gain to produce an integer dBu value at 1 kHz for easy comparison. I was unable to match channels to better than 0.1 dB, so at 1 kHz, HF player produced -11.0/-11.1 dBu (left channel/right). Then when switching to JRiver, the identical test tone read -10.8/-10.9 dBu, so JRiver produces 0.2 dB higher level at 1 kHz than HF player, and this was consistent. What's going on? The player engines are measurably different!

What are the possible causes of these level differences? Firstly, I confirmed that both apps were set to full (0 dB) gain and not doing any EQ or other processing. However, Onkyo is upsampling the 96 kHz signal to 192 kHz, but it produces identical output at 1 kHz with or without upsampling. Anyway, I was curious to see the high frequency response with the upsampler engaged. JRiver has an upsampling filter available but my past distortion measurements show that it does not like non-integer ratios, so I have not used its upsampler. Another possible cause of the level differences is that JRiver's native engine is 64-bit float, and it therefore truncates to 32-bit fixed. I doubted one could measure this effect on an analog output, but I did find some distortion differences between the two players (see below). In contrast, the HF Player is native 32-bit fixed with a 64-bit fixed equalizer. So this difference could be rounding or truncation error within JRiver, or some other factor that I cannot determine. For frequency response, I determined all levels relative to each player's response at 1 kHz, which by definition is 0 dB.

Both player's frequency responses match within 0.1 dB or less at all frequencies up to 20 kHz when normalized to 1 kHz. 20 kHz measures -0.1/0 in HF Player and -0.1/+0.1 in JRiver, which could easily be due to a digit rounding error in my Fluke 199C, so I discount any differences unless they are greater than 0.1 dB. All frequencies in the mid band of both players are flat within 0.1 dB or less, with losses only at the extremes. 20 Hz response is effectively flat, measuring -0.1/-0.2 dB in both players. 10 Hz is only 1 dB down! This is an exemplary, very rare bass response for a portable player, indicating either the use of very large capacitors or DC servo circuits.

The "smoking gun" (if there is one) is the difference in 30 kHz response (the highest frequency I measured). At 30 kHz, the HF Player measures -0.5/-0.3 and JRiver measures -0.1/+0.1, an 0.4 dB difference. So the HF Player begins dropping its HF response where JRiver remains flat. This probably reflects the characteristics of the upsampling filter in the HF player. I regret not having measured the 30 kHz response with upsampling turned off, or tried even higher frequencies, so this must remain a conjecture.

Onkyo's one-sheet for the HF Player tells us:

"When designing the HF Player's digital filter, our engineering team took the unique characteristics of your device's D/A converter and other associated hardware into consideration in order to achieve outstanding performance. Each filter coefficient is individually tuned according to sampling frequency for sound quality that surpasses theoretical signal-to-noise ratios, not only for Studio Master-quality Hi-Res Audio, but also for compressed audio files such as AAC and MP3. With HF Player, you can experience a clarity and vibrancy previously unobtainable on your mobile device."

Translation: This may be marketing talk. Or it could refer to the high resolution of its filtering engine, which keeps digital distortion and noise below the floor of any DAC. But at least there is a measurable frequency response difference. Although the HF Player produces slightly less output at 30 kHz than JRiver, it is clearly flat to 20 k. Is this the reason why the HF Player sounds a bit warmer and appears to go down lower than JRiver? I doubt it.

Distortion and Noise
I have not yet measured THD, but many authorities consider this to be a meaningless figure. Instead I looked at an FFT of the headphone output. Due to an attenuator in the circuit, I was not able to get a peak level higher than -10 dBFS into my Prism ADC, so the noise of the Prism ADC itself is a factor, but we can still see differences and conclude that the HA-2 is a very quiet amp indeed.

For example, Fig. 1 shows the noise floor of the HA-2 amp with no signal (green) vs. power off (blue). The measurement is only about 4 dB quieter with the amp turned off than on. Some of the residual noise is the instrument amp input of the Prism and the Prism's ADC itself, but in this measurement we can see that the HA-2 is nearly as quiet turned off as on!

KatzCorner_Ep11_Plot_Fig1 Fig. 1: HA-2 amp with no signal (green) vs. HA-2 amp powered off (blue).

Next we look at distortion at 1 kHz, at 0 dBFs and at -10 dBFs, comparing JRiver to HF Player. I hesitate to show these graphs because they will be misinterpreted because the magnitudes of this distortion are so low in any case as to probably be inaudible. What makes the graphs interesting is to see visible evidence of different digital engines doing the calculation, so let's look at them for that purpose.

In Fig. 2 we compare each player's distortion at 0 dBFS, 1 kHz. JRiver is in orange, HF Player (iPhone) in turquoise. JRiver exhibits between 2 and 12 dB more high frequency distortion at some frequencies than HF Player, and has up to an 18 dB lower noise floor than HF player at low frequencies. I chalk up the noise difference to the noise of the upsampling/anti-image filter in the HF Player, which is obviously measurable, though certainly below audibility. I wager the distortion differences are due to JRiver's rounding of 64-bit floating point to 32-bit fixed, while HF Player is 32-bit fixed native. Let me repeat that these measured differences are for academicians, not for listeners. I strongly doubt they contribute to any sonic difference.

KatzCorner_Ep11_Plot_Fig2 Fig. 2: HA-2 amp driven to 0 dBFS at 1 kHz. JRiver player (orange), HF Player (turquoize).

Figure 3 compares the players with a more sensible -10 dBFS 1 kHz signal. Here we can see that JRiver's distortion has greatly reduced and is much closer to that of HF Player. The noise floor differences have not changed.

KatzCorner_Ep11_Plot_Fig3 Fig. 3: HA-2 amp driven to -10 dBFS at 1 kHz. JRiver player (turquoize), HF Player (magenta).

I wanted to see if JRiver was uncomfortable feeding a 32-bit fixed point signal, so I engaged its 24-bit TPDF dither, thereby limiting the signal to the HA-2 to 24 bits. In this case the distortion went up, not down, so I conclude that the ESS DAC chip loves to get low level information below the 24th bit.

Volume Control
Note that the HF Player is capable of controlling the ESS chip's volume control via commands over USB, so the signal can remain at high level, 32-bit fixed all the way from the HF player through the chip's circuitry up to just before the oversampling filter. The ESS Sabre chip's volume control is located just before the oversampling filter. The idea of having a volume control at this late point is to maintain digital resolution for as long as possible in the chain. However, JRiver must perform its digital attenuation at 64 bits floating point, and then convert that signal to 32-bit fixed on the way to the DAC. In theory, using JRiver's digital volume control is inferior to computing in fixed point and/or using the chip's own volume control. But in practice I think we are trying to count the number of angels on a pin head. The noise generated within a 32-bit data path is so far below that of the DAC that it does not deteriorate signal to noise ratio. And the DAC noise itself is so low it is inaudible, even at full gain of the HA-2's analog control. In fact, if implemented well, both 32-bit fixed point and 64-bit floating point have such low inherent noise and distortion that either volume control approach is probably audibly indistinguishable, with reasonable amounts of attenuation. All PC-based players are floating point, to my knowledge. The only fixed-point players are on mobile devices.

I think the chip's digital volume control shines in applications like the Raspberry Pi, which does not have enough calculation power to perform a good volume control, but it can easily send control commands to the chip for a "perfect" volume control experience. To equal the quality of any of these digital volume controls, an analog control would have to be extremely well designed and quiet. Ironically, the analog volume control in the HA-2 DAC seems to qualify, so take your choice or exercise your prejudices and adjust whichever one your heart desires.

Clipping points: I verified with measurements and listening to sine wave tones that it is impossible to clip the DAC chip. A 1 kHz, 0 dBFS 24-bit dithered test tone does not clip the DAC, provided that the equalizer in the HF Player is bypassed. However, I could hear the circuitry in the DAC just going into clipping when boosting the 1 kHz EQ band by more than 3 dB, clearly clipping with a 3.6 dB boost. This correlates well with my measurement showing that the EQ drops overall level by 3 dB. So if you want to boost any band more than 3 dB, turn down the EQ gain by dragging your thumb downward until the highest boost level at any frequency is below the 0 dB line, which puts all material safe from digital clipping by 3 dB. However, if the equalizer is clipping, dropping the digital volume control will not fix the problem, making it clear that the digital volume control comes after the digital output signal of the App, and in fact it controls the built-in 32-bit volume control in the DAC chip itself. The app sends control commands for digital volume over USB to the HA-2. The digital volume control can be touch-screen adjusted to 0.1 dB precision if you are careful, or incremented in precise 4 dB steps by pushing on the iPhone's up and down volume controls.

The HA-2 has what I would call a perfect analog gain structure, neither too little nor too much analog gain at the high gain setting. With a 0 dBFS 1 kHz test tone, the headphone output does not visibly clip on the oscilloscope, even at maximum gain, into a high-impedance load. However, when loaded by 20 ohms, the output drops about 0.6 dB and goes into clipping, which is easily rectified by turning down the analog (headphone) gain about a dB. But no sane practitioner (who isn't already deaf) would ever need to turn the analog gain up this far! I measured 2.18 volts across 20 ohms just before clipping, which is 238 mW. Given the stated 102 dB/mW sensitivity of the cans, turning the analog gain up to just below amp clipping would produce 125.8 dB SPL level with a full scale signal. Ouch! A more normal (but still loud) situation would be to turn the analog gain down by 20 dB, which with a more normal level -20 dBFS RMS signal would produce 85.8 dB SPL. Most of you will run the analog control 7 to 10 dB lower than that. However, at maximum analog gain before clipping, there is only enough voltage to drive a pair of insensitive high impedance phones like the Sennheiser HD 600 to about 77 dB SPL with a -20 dBFS signal. The open-back HD 600 should do fairly well in a quiet room with pop music and jazz, but may be a bit low for wide dynamic-range classical music played in a normal or noisy environment.

Output Impedance and Level
Headphone amp output level drops about 0.6 dB when the output is terminated by 20 ohms, which calculates to approximately 1.5 ohms at 1 kHz, quite low for a battery-powered device. Just for laughs, I tried a 20 ohm load on the HA-2's line output and the level dropped precipitously. I did not try to determine the line output impedance, but I did measure a voltage level at 0 dBFS, 1 kHz, of +1.82/+1.62 dBu with HF Player into a 10 k ohm test load (right channel measures 0.2 dB lower than the left). This translates to 0.93 v RMS, about 6 dB lower than the standard output of a CD player. Plugging into the headphone jack disables the line output.

Analog Volume Control Tracking
I suspected that the analog volume control might be a DC level controlling an active circuit because the interchannel tracking was so good. But I was wrong, measurements indicate enough interchannel errors to imply the tiny analog volume control in the HA-2 must be a superior dual-channel model with excellent tracking. At low amounts of attenuation, channel differences are within 0.1 dB. However, at 10 dB of attenuation, this increases to 1 dB but never gets worse than 1 dB at any further attenuation down to 20 dB where I stopped measuring. Given production variances, it's possible that each HA-2 analog control will perform differently, but hopefully no worse than a dB error.

Switching to low gain drops the level about 9 dB, and the volume control will travel nearer the top of its range where the channels will track better. Low gain is sufficient for most musical sources I encountered. Or you can always attenuate with the digital control if you want a perfectly centered image, with no concerns unless you are a digiphobe.

Audible DAC Resolution
The HA-2 analog gain structure is so well-designed that there is no audible hiss with these cans, even at full analog gain! The noise floor of the DAC with high gain measures only a few dB higher than the noise floor of my Prism converter's instrument level input, which I used to view noise and distortion with a Spectrafoo FFT analyzer, so we are close to the limits of the measurement gear itself.

The lowest level single frequency tone which I can hear in the phones with analog gain turned up just below the clipping point is a 1 kHz -120 dBFS dithered test tone, give or take a couple of dB. This is audible only in a quiet room, very faintly, but it establishes the low level resolution of the DAC. An FFT measurement confirmed that -120 dBFS is about the lowest visible tone before it disappears into the noise. I don't know which ESS chip is used in the HA-2, but ESS specs 122 to 127 dB dynamic range for their chips so this correlates well with my measurement.

What does this resolution mean in practical terms? It does not mean we can hear discrete signals down to -120 dBFS because this tone was only heard with the analog gain maxed out. In practice, we could be using 20 dB less analog gain, which means that in a quiet room we should still be able to hear, at normal analog gains, a -100 dBFS tone, which is a fantastic achievement. At normal analog gain, that tone would produce 6 dB SPL, only 6 dB above the nominal threshold of hearing! Only audible in the most quiet room. There is no recording on earth with that low a noise floor; most recordings exhibit noise floors 40 dB or more higher. So this DAC and amp can handle anything we want to put into it.

Bottom line
Oppo PM-3 headphones plus Oppo HA-2 DAC/amp plus iPhone is the best-sounding, most accurate, reference-quality portable playback that I have experienced in many years of this audio business. The bass response is most impressive. The portable experience rivals the best desktop headphone amplifiers and DACs and the HA-2 can be used as a desktop DAC rivaling the best line-powered beasts. We're living in exciting times!

Oppo Digital
2629 Terminal Blvd., Ste B
Mountain View, CA 94043
(650) 961-1118

Defguy's picture

Great Review,Bob! I had just waded through the comments on your mid price sealed shootout so I wasn't expecting to see this so soon. My only issues are that I steer far from the i universe so some of the Apple centric stuff doesn't have too much relevance to me personally and because I travel a lot and use my phone for work, using it as a transport isn't ideal. If you look at the price of these 2 products though, they do seem like shockingly good value for the money after reading this review!

guerillaw's picture

With little effort you can get an iphone or iPod touch on the used market to use as a portable player. Now that we are on iphone "6s" an iphone 5 which is a great transport is 3 generations behind and thus quite affordable on the used market. You can even seek out a broken screen and get it fixed for 75 bucks if you are in a large city.

tony's picture

All this started in 1877 or 1878, didn't it?

I came in as 78s were still selling but 33s took over and lasted until the mid 1980s. ( despite rumors to the contrary )

Finally, we have wonderful music reproduction to fit in a pocket, to accompany a SunSet over Lake Michigan or anywhere on the Planet.

I've owned portable gear for the last few years, I won't leave home without it but it's been pricy, too pricy for most folks and too cumbersome. ( and not as high a quality as my big Base Station system)

We had to see this coming, the Apple people were taking over Consumer Audio with the iPod, now with the iPhone and probably soon they'll have a proper DAC in their phones.

But we can lead them out with this OPPO system, we don't have to wait for em! and we don't have to spend thousands of $,$$$.00 any longer. Plus, you report, it can be our Big Base Station system! Phew.

I wonder how well these OPPO devices will drive a pair of Genelec 8040b?

I think I'm reading you saying something profound: We have a new Benchmark Standard of Performance!, one that hits home with Consumer friendly pricing and availability, from a Mainstream Outfit that sells at places like Best Buy, designed for the "Everyman" marketplace, a real McCoy "Pedestrian" Audiophile quality Music System for well under $1,000 !

If we consider the Mojo, we might have two such systems.

Tony in Michigan

ps. the Record Player guy just presented a review of "Magnetic" interconnect adaptors for $299.
Bob Katz gives us a break thru product for $299 ( look out JDS Labs)

Bob Katz's picture

I think you mean the 8040A. I can make up a set of cables for you going from TRS to the 8040s, no trouble. I would recommend the headphone output just in case the input impedance is too low, and it's just no big deal, considering the great performance I was getting from the headphone output. And the HA-2 will feed the 8040s, no problem at all from the headphone output at least. Plus you get a volume control with the headphone output so that's cool. In fact the 8040s are among the more neutral of the Genelec models out of the box. Hint: there are screwdriver trims on the back of the 8040s that control the tweeter and the woofer level. Still, I would recommend adding a subwoofer to the 8040s, and pretty soon it would pay to plug the HA-2 into some kind of a preamp so you can distribute audio to the mains and the subs. Also, you must be using the 8040s kind of nearfield, right, Tony? Because they really don't play very loud and their virtues are best appreciated say 3 to 4 feet away plus a sub.

tony's picture

I was grabbing for any Active. ( my Wife's decorator wants me to hide some loudspeakers in the base of Table lamps, I thought of using little Genelecs, I don't know where she'll let me hide some Subs )

I've owned many Meridian Active Loudspeakers, I even Imported em. I sorta love the concept.

I suppose my point would and could be that the cheap OPPO system can interface with Room filling Loudspeakers. Any Civilian could own the OPPO stuff and use it as a basis for a full satisfaction Hi-Fi System by simply buying some Actives!

I wouldn't suggest this to be a solution for a Mastering Studio but certainly adequate for the Majority of folks.

Back in 2011, at RMAF, where our Tyll, Steve G. and Jude were having a headphone Seminar ( video available on Google ). I failed to imagine the headphone world revolutionizing Home Audio, as it has done in just 4 or 5 years. I looked at Tyll's book of headphone performance as a technical manual about various transducers. Now I see headphone Audio devices as being the very DNA of successful Consumer Audio.

We've come a very long way. In 1985 an "A" level Phono Cartridge ( Koetsu Rosewood ) cost in the $750 Range. Today, a complete "A" level Music System costs $700. Phew!

I can't imagine the costs lowering further.

Thank you for your Insights,

Tony in Michigan

poleepkwa's picture

If you use the Genelec sub 7060 with the 8040's you do not need preamp.
Feed the HA-2 into the subwoofer as it has a built in crossover for the 8040's

Bob Katz's picture

Right, Poleepkwa. I was thinking on the lines that the more complex the system gets, the more silly it becomes to use an HA-2 and a set of cables to feed your playback system. You also want to have a computer to play back files, maybe some analog sources, etc. A more accessible volume control. so sooner or later a more sophisticated setup is warranted, a "line stage preamp with switching" or something else you can rig up.

poleepkwa's picture

Good point Bob. You are of course correct. Start to get bit silly from functional point of view. Just because you could do not mean you should.

ADU's picture

Some of the tech-talk gets a little too in depth for me, but it's clear from your comments that you've found the Oppo HA-2 and PM-3 an excellent fit for your portable listening needs. I imagine it's quite an upgrade to your ears from the old Senn 280's. ;)

I've never owned any Oppo products, but have been aware of them since the release of their first upscaling DVD player quite a few years ago. And they have a reputation for paying attention to the small details that can turn a good product into a great one. I was a little surprised when I heard they were moving into the audio/headphone market, but knew they'd bring something interesting to the table there as well.

I use a lower-cost Sony BD player for most of my home video viewing and listening. It's basic, but it has decent up-conversion, accurate color decoding, and pretty ok sound (to my ears anyway) on its RCA phono outs. I run the analog audio directly into a DBX 31-band 231s graphic EQ, thru an attenuator to my new AKG K553s. So I guess that now makes me a "Harman man". :) All pure analog btw (which is the best way to go on my very tight budget, I think). I'm still working a few kinks out of the arrangement, but am reasonably pleased with the results so far. And the AKGs can also be easily driven by portables.

If I had a grand or so to spend for my portable listening needs though, I'd probably be looking very closely at the kind of arrangement you've outlined above.

Bob Katz's picture

$700 (not counting the phone) is still expensive in the overall scheme of things, but if you love portable audio, this is the best price/performance I've ever seen. Sorry for the length of the article. I can't help myself. You could stop just before the measurement section and breathe a sigh of relief. :-)

ADU's picture

And your (and Tyll's) follow-ups to the questions and comments here are also much appreciated, Bob. I just wish I could give you a nice lengthy comment to reciprocate. :)

I was thinkin about some of your remarks in the article related to bass and the Harman study though, while rewatching this Floyd Toole presentation over the weekend...


This is basically a long advertisement for JBL's M2 speaker. But it contains a lot of useful info re room acoustics and how those effect the sound you hear from a speaker as well.

The very last slide in the presentation (after the audience applauds) is actually one of the most interesting, because it shows how the M2 measured in several different spaces, ranging in size from a small home theater to a large auditorium. The differences in the bass response are particularly noteworthy imo.

barun432's picture

Hey Bob,

A very enjoyable read as always. I really admire the way you get into all the details of what you did with the gear when you review the product, as a reader, enthusiast and a consumer it is very helpful, so thank you.

I had only one thing to add, you could have used the Neutron Player with the setup, as it is the most tweakable and neutral sounding software across both iOS and Android platform. Hope you give it a try sometime.



Phoniac's picture

+1. Neutron beats the shit out of Onkyo's not well maintained app. It might have an edge on DSD, though...if you believe in that...

Bob Katz's picture

I have no experience with the Neutron, but I detected lots of care in the build of the Onkyo App. Don't know what generation HF Player you looked at, but I found the Onkyo ergonomics to be first-rate and lots of care and attention to detail in its software design. A good piece of user-software should not require more than a little experiment to figure out how things work, and the Onkyo HF Player fits right into that. And include an easily-found FAQ on how to do things... again, right there in the HF Player. As far as maintenance goes, I never hit a single bug, and only one annoyance, the EQ dot thingy I described. But that's real nit picking, folks. So for me the Onkyo app is big thumbs up, even if Neutron is incredible. And I'm very picky about software so I have no idea what you mean by "not well maintained". It's as if you and I are on different planets...

Bob Katz's picture

Thanks for you kind words, Barun. My only concerns about the Android are the questions I asked in the article: Does it have the same resolution and performance as the HF Player on the iPhone?

barun432's picture

Hi again Bob,

Thanks for replying. I have not used the Neutron player with an iPhone but I've used it in the iOS platform. I personally have used the Neutron Player with HTC One M8 and an iPad 3 with and without a DAC and I have found the Neutron Player to be better in performance and resolution (Subjective Interpretation). I use the Resonessence Labs Concero HP as the DAC in most occasions. The following are few of the features of Neutron. BTW I switched from fooBar2000/Audirvana to JRiver because of you in Windows/Mac and I find it better in almost every aspect.

• 32/64-bit audio processing
• OS independent decoding and audio processing
• Direct output to USB DAC without format limitation
• Parametric equalizer DSP
• Crossfeed DSP
• Rumble Filter DSP
• Dithering DSP
• Pitch and Tempo DSP
• Phase inversion



Bob Katz's picture

Dear Barun: I'm glad you like JRiver. By the way, JRiver on Mac seems to always lag compared to the PC version on Windows. Windows version provides optional 24 bit dither. The Mac version does not. I use Izotope or other plugin to dither to 24 bits on the Mac side when I'm not using the HA-2. I've done the resolution and distortion testing to confirm it all works.

As for Neutron Player, I'm intrigued. I have a lot on my plate right now but I guess sooner or later I'm going to have to test Neutron. How much is the product for iPhone?

barun432's picture

Hi Bob,

Neutron goes for $6 (Approximately) in the Apple App Store. Thanks for the JRiver tip in MAC, I'll try that. You have a great weekend.



neo's picture

This was an amazing in depth review. Would love to read more like these..
Also its interesting to read Bob's impressions, someone who you know you can trust (cough cough unlike sm1 from cnet), have a somewhat different take on these. I remember Tyll loving them as well but describing them as a bit boring

Bob Katz's picture

if he tries that EQ, cause it makes all the difference. I'm jumping up and down and everyone I put these phones on wants to dance out of the room with them. And I'm talking pro listeners who should be jaded by now. Nothing boring about this setup.

avens's picture

What DAC/amp would you recommend for desktop use, with the PM-3's?

And just to be sure, is the HA-2 without EQ a good pair with the Oppos?

Bob Katz's picture

Hi, Avens! I think an EQ is kind of essential unless you have a pair of the Audeze LCD-4s, which sound just about right without any EQ at all. The HA-2 without EQ is still an A with the Oppos in my opinion but I just would not feel right without that last polish, if you are a perfectionist.

For a DAC, what's your price range? The Antelope, the Benchmark, the Prism Lyra 2 and the Weiss I have personally experienced at three wildly different price ranges. There are now many good DACs at different price ranges... Let's see what Tyll recommends as I'll bet he's heard more of the Consumer models than I. I own an older model Benchmark and it has always been very good, but it does not have USB.

avens's picture

Since they pair so well, would it be a good idea to get the HA-2's for desktop use?

BTW, last time I tried my PM-3's was with the e10 from Fiio, and it was a horrible pairing.

HAE's picture

Great review.
How is the desktop USB audio powered? I remember Stereophile once published bad jitter results for one of Cambridge Audio products and the company responded saying that the USB interface performed much better when powered from battery powered laptops and presented a great jitter graph. My guess it could be a combination of the desktop USB connection injecting some noise through its power lines, may be also some jitter/variable latency? in response to the commands from the clock master and what else the PC is doing in the background.

Bob Katz's picture

Yes, it's possible that the power line makes a difference. It's very hard to find reasons or if it's jitter or interference. Since the clock in the HA-2 is the master, I think the slight differences I heard could be small ground loops through the power.... In the case of desktop the HA-2 is being constantly charged through the USB line which receives its power from a line-powered computer and all the garbage in that. A well-isolated and regulated charge circuit in the HA-2 should isolate it from that. But clearly the portable battery-powered system is isolated from the power line. It takes a real measurement expert to isolate the variables because the measurement ADC is powered from the power line and small ground loops can lead to hum or RFI injection. This is a very very difficult subject to isolate. We can measure possible distortion differences at 20 kHz, which can show possible jitter artifacts. We can look for RF-induced artifacts. But then showing what route the interference takes to get into the device requires PHD-level engineering expertise, which I do not have.

I have some friends who do and who do not live very far, but I'd have to bribe them with a lot of money to spend the time to try to find the causes, and it can take days to be sure. So if you hear a difference, try different variables and listen. Unscientific, but that may be the only way us mortals can make judgments.

Seth195208's picture

Tuning it was amazingly painstaking process. Literally hundreds of hours for one guy. The beta team provided feedback and consensus along the way. An amazing experience!

Bob Katz's picture

I believe it, Seth. That's why I put my heart and soul into this review, as a kind of thank you to the incredible folks at Oppo.

potterpastor's picture

Great review, very thorough. Makes me want to buy a pair.
Has Tyll told you about the HiFiMan HE400S? it is not as portable or as nice-looking as the OPPO PM3, but it is probably as good as you could ever expect a $300 open back headphone to be. I actually like it better than the Sennheiser HD 600 or 650, and Wirecutter picked it as its favourite headphone under $500, or at least the headphone that the most people would like or something like that. it sounds fantastic. It sounds so clear! It just needs a little bit of a treble boost and it sounds perfect.

Bob Katz's picture

Dear pottpastor. So much time for me, so little to do :-). Thanks for your kind words. I'll put a note about the Hifi man. Tyll mentioned another headset rival to the PM-3s he wants me to check out and it was not the Hifi man. Can't remember, 99x or something like that?

potterpastor's picture

The Meze 99 classics. They are supposed to be really good, and they look really really classy. But I've never heard them myself. Maybe next month at Axpona

@custic's picture

Can't wait for your opinion on these headphones! You're doing such a fantastic job with your posts. Invaluable competence. Passion emerges everywhere even after such a long time in this business. Hat off!

Dr Zingo's picture

Thanks for the interesting review. Actually, the way to "erase" dots in the Onkyo HF Player is to simply drag one dot into another and they will merge.

JL77's picture

Bob, I'm waiting for a DAC with 160dB of dynamic range. Until then, will keep using my old 16 bit jobby :-)

austinpop's picture

Hi Bob,

I'm going to sound like a Luddite, even though I'm a SW engineer and work on computers for a living. But when it comes to my headphone rig, I work hard to get the laptop out of the mix. My current system is:

Synology NAS ----> wifi ---> Aries Mini streamer ---> USB ---> Ayre Codex DAC/Amp ----> HD800

I can control this from an iOS device of my choice. All hunky-dory, but then along comes Bob, preaching his seductive EQ gospel.

Damn you, Katz! Now I have to get JRiver with DMG Equilibrium and Izotope plugins to achieve nirvana? Or is it a descent into madness??!!


Bob Katz's picture

Dear Austin:

Glad to help you descend into madness. If the Synology has the features and resolution then there's no need to change to JRiver. I have a stable OS8 PC running from SSD. It didn't take me too long to make it stable and dependable running JRiver. But it has a lot more power (6 core Intel i7) and memory (16 GB) than your NAS. But clearly a streamer in an NAS with embedded Linux OS is potentially more stable than a Windoze PC. Go for which one has the features and whether you don't mind the slight increased headache in maintaining a Windoze machine. I like the ability to run VST plugins in JRiver. Can you do that with the Aries Mini Streamer?

austinpop's picture


In a typical streaming ecosystem, constituting UPnP server, renderer, and player, the "traditional" EQ approach like what you used is to do EQ in the renderer running on a PC with software like JRiver.

Now - running an embedded renderer like the Aries Mini limits your options. I know the Aries doesn't support plugins for EQ.

What I do wonder is whether one can run EQ plugins in a DLNA server, and if so, whether any support NAS implementations. I suspect the answer is no.

Maybe someone reading this knows of solutions.

bernardperu's picture

I use pono via balanced and the pm-3s. I get really good sound but now i wonder how it compares to te one you described.

Bob Katz's picture

How do you run balanced with the PM-3s? The jack on the side is a 3 pin to my knowledge.

I think it will come down to whether the EQ makes a difference to you. I haven't tried the Pono balanced and don't have one so I can't do the shootout. To repeat, I'm puzzled how you can run the PM-3's balanced. You don't want to parallel a common of the left and right channels in any way or it could burn out the active drivers in the Pono and the jack on the side of the cans is a TRS to my knowledge.

bernardperu's picture

Hi Bob, the PONO in balanced mode is a true miracle and I have tested it with all kinds of hi-end headphones including: Pono PM-1 and PM-3; Senn HD-600 and HD-650; Audeze LCD-X

The PM-3 is factory balanced via TRRS 3.5 mm, so connecting it to the Pono is really simple as long as you have the balanced cables TRRS -> Pono balanced.

The sound of the above combo is really good.

In my opinion, the Pono balanced should be considered a benchmark for portability. I do some hiking and I love it. I guess the whole point of portability is actually moving or commuting (moving and, then, taking a break for conscious listening).

Bob Katz's picture

Thanks, Bernard. Well, I'll be a monkey's uncle. Oppo does not go out of their way to publicize the connections on that unit and since they did not offer balanced cables at their website I assumed (wrongly) that the headphone could not be balanced.

Bob Katz's picture

Well, I'll be darned, there are after-market PM-3 balanced cables listed, although Oppo does not offer one. I hate those awkward 4 pin 1/8" jacks, very unreliable. Soldering to one is nearly impossible.... I will need a magnifying glass and I have myopic eyes and can read the label on a penny normally without my glasses! Anyway, I just tried measuring my PM-3's with a 4-pin plug and an ohmmeter and could not get a reading below 400 ohms any which way but with a TRS I've measured 24 ohms, which is much more in line with what I would expect with planars. So I'm very confused and question that a PM-3 is really ready for balanced. Would someone please supply a valid schematic for PM-3 balanced and at the least I'll check that with an ohmeter and a 4-pin plug.

jagwap's picture

not to you with the TRRS connection. But here are some details.

I have been using the PM-3s with my Pono balanced for months. I took the cable with the microphone and modified it, so the 4 way TRRS is now the headphone end, and added another 3 way TRS to plug into the Pono.

The connection details are here: http://www.head-fi.org/t/629454/pono-neil-youngs-portable-hi-res-music-p...

Not the neatest job, but it works well, and the lack of silver plated OFFC is out shone by the balanced connection.

That Pono is quite the bargain: 4 DC coupled discrete amplifiers with ESS DA, configurable in balanced mode.

bernardperu's picture

Contact Oppo for asistance, Bob. They are very nice. Or even better (though this may go against your principles :-) Buy the cable, then, listen.

I would would strongly urge you to listen to the Pono in balanced with all kinds of balanced phones (such as the Senn HD-650 and the Oppo PM-1s). The sound is wonderful and you get real portability.

I get my cables from these guys https://customcans.co.uk/s/s/index.php/pono-player.html

(I live in Peru and they are good at shipping them).


jagwap's picture
Bob Katz's picture

Thank you, Jagwap! Now I know something I did not know before.

jagwap's picture

It can be satisfying to learn, especially when it leads to better sound.

But I suspect you are last person who needs to learn this.

norb's picture

May I ask: can there be really heard a difference in the audio quality when balanced compared to unbalanced. I know that in live situations balanced XLR cables are used, because there is so many crossfeed from other signals as lights or electrical sockets, but why do you need a balanced wiring when using a portable player? I mean, how can there be any crossfeed problems from other electrical signals when I´m outside?

jagwap's picture

It is not about cancelling external signals like it would be for a balanced microphone cable. It is more to do with not sharing a common ground connection for both headphone drivers.

Also given the same peak voltage level on each amplifier and no other limitations, balanced gives four times the power in each channel.

I posted a short list of them on HeadFi: http://www.head-fi.org/t/756828/oppo-pm-3-the-portable-planar-impression...

There is more to it than that, but it's a start.

norb's picture

Thanks, that makes sense!

Bob Katz's picture

Dear Norb: Comparing balanced to unbalanced. Well first of all I think the word "balanced" with respect to headphones should be abolished. We should use "push-pull", which is what's happening. Because as the other poster replied, there is nothing which is being "balanced"... the headphone is fully floating and has no ground reference. Secondly, since switching an amplifier over from single ended to push-pull doubles the signal (it will be 6 dB up), matching levels is very critical.

Lastly there may be no fair comparison, but the Pono is probably the fairest as he uses nearly the identical circuitry. So all you have to do is try to match the levels, which is never easy. In a battery-powered device the additional headroom can be very significant as Pono and Charles Ayre point out. But in a line-powered device with a stiff high-voltage power supply there may be no advantage whatsoever to running push-pull and don't let anyone tell you differently. And if you try to compare two different amplifier topologies, one single-ended and one push-pull, it's apples versus oranges. Pick the one which sounds better to you at matched levels. That's all you can do.

norb's picture

I got it! Thanks Bob!

Ed G's picture

I thought the review was excellent and I appreciated the in depth analysis. I struggled with some of the technical details but that made me re-read it several times for a better understanding. I am still slightly confused about sound quality issues. I have a Galaxy S6 phone. Would the Onkyo HF player app for Android diminish the sound quality? Would I have to purchase a set of "after market" cables to get a balanced signal?

Bob Katz's picture

Thanks for the kind words, Ed, about my review. You'll have to send a message to the guys at Onkyo inquiring if there are any technical differences to the implementation in Android than in Apple. If they have the same resolution in the same player App for the different platforms and use the same code base it's likely the two apps will sound alike.

You would have to purchase a set of aftermarket cables to get a balanced signal but anyway, I do not believe the HA-2 has a balanced (push-pull) out.

Defguy's picture

I spent some time playing with HF player on a couple of android devices (Note 3 and TAb Pro)yesterday and got pretty exciting results,even without using an out board dac. With careful eq, I was able to get both devices sounding considerably better than the Fiio stack I had with me. This was with Dunu 2000 iems, The illusion would probably fall apart with anything at all challenging to drive

dayvo's picture

Thank you, Mr. Katz, for this great review. Based largely on this, I purchased an Oppo HA-2. It sounds great. I'm using it to drive a HiFi Man HE 400S and a Sennheiser HD600 from either my MacBook Pro or iPhone 6S+. The HA-2 has impressive power for a portable amp.

As an aside, have you tried the Mac app BitPerfect? I've been using it for a couple of years with a couple of other DACs and it plays nicely with the HA-2. BitPerfect runs in the background behind iTunes. It takes control of the audio path to support higher bit rate files and bit length / rate up-conversion of standard files. The BitPerfect web site explains the numerous set up options and provides good customer support. Just thought I'd pass it along.

Thanks again,
Dave O.

tony's picture

Push-pull !

Geez Bob, you keep bringing these insights.

All this headphone fanfare for Balanced never made any sense.

You are the first person, in the headphone context, to clarify this silliness.

I can understand the Balanced output of the Yggy DAC if it's intended to be a Professional use DAC ( maybe ), because Balanced is Professional and Pro folks think Balanced.

I suppose "Sizzle" sells the Steak so we need our headphone Amps to have something special for folks to buy them but I feel disappointed to read so many folks talking-up "Balanced" as a
"Sound Quality" enhancer, where is this coming from?

Probably not from the Engineering world where 2 + 2 = 4!

Nice work.

Tony in Michigan

zobel's picture

*Its interesting to think our audiophile ancestors used to live in the trees, like apes. Finally they got the nerve to head out onto the planes, where some were probably hit by cars. Fortunately some survived, and.....well.....here we are!

*Research here by Jack Handy.

tony's picture

Blaming Cars is a bit much. iPhones keeping folks connected instead of paying proper attention is whats thinning out the herd.

Still, we "Responsible" Auto Industry folks are about to fix the problem by taking the keys away from all you reckless drivers and letting the Responsible/Clear thinking Car do the driving ( and the decision making ). Expect a $75,000 sticker price but it'll be worth it. Climb in, settle down, open a beer and tell the car to take you where you wanna go. Presto ! Once again we can rate our car trips by how many beers it takes to get there : Hmm, that's a 6-Pack trip!

Kinda harkens back to the good old days, don't it?

Tony in Michigan

ps, we'll even be able to shoot at road signs with our .22s like we used to do in the 1950s

zobel's picture

When will it be coming out in hard cover?

gnahra's picture

Thanks for the comprehensive review. I have both the PM-3 and HA-2, and love them both. Just came across Audeze's new Cipher lightening cable, which I believe includes an inline amp and DAC. Any experience with this (their EL-8, specifically, is the model I was thinking of, as it's a closed-back planar magnetic)? The price ($799) is comparable to the combo of the PM-3 and HA-2...thanks!

poleepkwa's picture

Do you think the Oppo HA2 is a viable replacement for a desktop setup?
I am currently using an Xonar Muses Essence One and would like to know how well does the Oppo drive more difficult loads?I have the 300ohm HD650 and the rest are all pretty easy to drive.

Bob Katz's picture

I didn't do any measurements of the Ha-2 with high impedance loads but it seems to drive my 650's more than satisfactorily. The Ha-2 is a surprisingly all-inclusive amplifier that should satisfy all but the most demanding of headphones. For a battery-operated product this is very promising.

rroman's picture

You mentioned some fantastic albums for critical auditioning. Do you have a list of any additional albums you consider exceptional for critical auditioning of head-fi equipment. Let me vote for Portraits of Cuba which I think edges out Buena Vista Social Club for outstanding soul and fidelity. Curious, did you ever work with a Puerto Rican pianist named Mario Roman? Great review. Absolutely world class.

Bob Katz's picture

señor roman: Is Mario one of your relatives? sorry, my keyboard's right shift key has gone bad. anyway, I'm trying to introduce you to additional reference recordings of mine gradually in later reviews, as in the review of the Oppo PM-3 (love affair as tyll puts it).... some day I may get around to giving a list, but in the meantime I hope I've intrigued you with some nice new stuff to get, like Joachim Palden's great album, if you like fat, somewhat dirty, electric blues. I love the buena vista recording... I think both my Paquito and the buena vista have different virtues and both lovely to listen to. the buena vista recording is warm and enveloping, while my Paquito recording has more detail and transparency. both recordings are oozing with musicality!

Silvertrees's picture

Hi Bob,

First let me thank you for your wonderfully detailed review! Like all of your writing, this reignites my passion for understanding on so many levels. As a previous owner of the HA-2 and one who very much values your opinions, I wanted to hear your thoughts on my experiences with the Oppo as well as hopefully, eventually, to read your impressions/review of the unit I chose to replace it.

A few months back, my living situation changed; I wasn't able to spend as much time with my HiFi as I'd like; and I began a lengthy and epic journey into the new-to-me world of portable audio. My decidedly-circuitous route through DACs/DAPs went, more or less, like this: IBasso DX90, Cowon Plenue 1, Celsus Sound Companion One, Astell & Kern AK120 II, Oppo HA-2 and finally, Sony NW-ZX2 (yes, you read correctly, Sony; please don't stop reading!).

Like so many before me, I had totally fallen in love with the HA-2 and easily considered it the best sounding of all the units I had tried up to that point. It managed this (and still does) while simultaneously being priced so competitively that one has to wonder how such obscenely overpriced jewelry from the likes of A&K still sells. The only possible competitor worth mentioning, though costing nearly double the HA-2's price, was the uniquely-featured Celsus Sound Companion One, another ESS-powered unit. Alas, this suffered from a distractingly audible hiss in one channel with some cans, specifically mine. In response to this, the manufacturer (the original designer behind the well-regarded NuFOrce DAC/amps) assured me that this design flaw would be taken care of in the C1's next iteration and graciously offered me a future-proof 20% discount, which I'm pretty sure we both knew would never be used.

Then, however, I was relatively certain that I had, in the Oppo, already found my portable audio life-mate. Nevertheless, as a dedicated completionist with only one name remaining to cross off my short-list, along came the Sony NW-ZX2. After its recommended 100 hours of burn-in (a process I previously chalked up to voodoo but now consider obligatory), I settled in to listen to what I unwaveringly expected to be overpriced crap and instead had my brain exploded clear out of my skull. Everything I had previously known about detail, dynamics and musicality was suddenly rendered obsolete. I discovered a new standard all wrapped up in a brand I'd long dismissed as "mid-fi" and "consumer-grade". With a sigh and some soul-searching, it was time for me to rethink my prejudices, something I imagine we all should do from time to time.

I really didn't want to like the Sony. My vanity wanted to fall in love with some obscure, limited-release boutique beauty about which I'd proudly answer the many inquiries this theoretical masterpiece would illicit. Not that most of their products are of particularly cheap build quality, but the word "Sony" is hardly synonymous with either top-tier audio nor indestructible reliability. Not so with the ZX2. It is a tank and I can't help but love the feeling of its weight resting reassuringly in my hand.

I can't pretend to have anywhere near the technical know-how or skill to design or build a DAC or headphone amp myself; even so, with what little knowledge I do possess, I've become convinced that the ZX2's one-of-a-kind internal design is nothing short of brilliant. Most portable audio products currently in production use off-the-shelf DAC chips, the ESS Sabre (like the one found in the HA-2) enjoying particular notoriety of late. A few others, like the Chord Hugo, create their own D-to-A algorithms in-house and implement them via FPGAs. The analog signal from any of these DACs then needs to be amplified via one or more magical doo-dads beyond my comprehension. This is a time-honored concept mirroring what we so often see in the open-air HiFi realm: source to DAC to preamp to amp to speakers. Problem is, each component along the way adds its own peculiarities to the sound, thus, with many exceptions (most of them expensive), the shorter the audio path, the less distorted the signal. Sigma-delta DACs first metamorphose a PWM to a bitstream (sometimes a "couple-of-bitstream") much like what's encoded in Sony's weirdly desperate Betamax, err.... DSD format. Ones and zeroes, processed at unfathomable speeds, the lowest frequencies of which comprise the human audible range. Sony cleverly realized that this is almost exactly the same way the increasingly-popular class-D amps work, specifically those of the digital (quantized) variety. I have no idea how this is accomplished, but the ZX2 completely does away with additional amplification stages, and instead found a way to use the same components that function as a DAC to also function as a digital class-D amp. All that remains is a short trip through a low-pass filter, then the analog signal from the DAC runs straight into your ears.

In short: the DAC IS the amp.

Such elegant simplicity of design is a thing of beauty and, if you think about it, there are very few places other than a DAP where this could work. Perhaps someone will invent some powered monitors with digital inputs that could somehow pull off this trick, but almost any other situation would require additional amplification to power the load. Brilliant. Fortunately, the benefits of this design don't just work in concept; in practice, it's as detailed, clear, dynamic and musical a presentation of digital audio as I've ever heard. I'd venture a guess that, on many albums, I'm now hearing subtleties that were veiled even to the original engineer.

So, what specifically is it about the HA-2 that, to my ears, the ZX-2 presents with such superiority?

I was originally going to keep the Oppo alongside the Sony, and for several months, I did. Finances eventually conspired to force the Oppo and me to part ways, but in the interim, I had several months with which to conduct a multitude of home-brewed tests and one-on-one comparisons. In addition to being an insanely anal audiophile/gearslut/Nerdlord Supreme, I'm also a musician and occasional engineer. I track, mix, and (with extra thanks to a little book called "Mastering Audio: The Art and Science" - you may have heard of it ;)) master my own tracks as well as some of my friends'. While listening to just such a track, something I have probably heard literally thousands of times on countless systems, I slowly started to understand what I was hearing in the HA-2 that, for lack of a more forgiving word, I found... unnerving.

Dynamics. Not the obvious dynamics that epitomize a dB boost for a chorus or an excitable drummer's lead-in thereof, but subtle, visceral dynamics. Microdynamics, the sort of sound that doesn't let you hear so much as feel a guitarist's thumb unleash a string ever-so-slightly firmer than the last, and suddenly you know, in your bones, that NOW they're really feeling it. Microdynamics that let you know how excited the upbeat is to drive the downbeat by the way a percussionist's hand slips off a skin, not back onto it. Microdynamics that reveal the meaning behind a singer’s breath, held in anticipation and subsequently released. All this is at the very heart of musicality and, of course, should be presented to the listener given the fidelity to do so. But it should be done as true to the original recording as possible. Those subtleties, to no small extent, define the emotional content of a performance and, whether intentional or not, convey a great deal of information to the listener. If these subtleties are exaggerated, as I hear with the HA-2, one is presented with some unholy mad science/dark magic robo-interpretation of emotion, exaggerated for maximum titillation and twisting beautiful, subtle, human art into a machine's sarcastic recreation thereof. As I spent more time with the Oppo, I couldn't deny feeling a continual and increasingly unnatural creepiness, as though some malevolent force was trying to trick me, replacing musicians I've known all my life, or worse, my own voice, with automatons. I started to feel genuinely uncomfortable with how artificial, yet eerily close-to-life things sounded: the uncanny valley of HiFi.

This hyperemphasized sound is analogous to the distortion and warping of a visual image as seen through a fisheye lens or the intensification of light passing through a magnifying glass. While this does zoom and shed light upon corners of the music that would otherwise be overlooked, the image as a whole is distorted, and, importantly, no longer representative of the original form. Having previously-unheard nuances so starkly exposed is sure to be both exciting and enticing to many listeners. Upon first listening, the sound truly does impress, so might it be possible that such emphasis is deliberate, something designed first to define, then to popularize the "Sabre sound"? I don't know if it's a logical possibility, but I'd very much like to find out if, somewhere in the math used by ESS during sigma-delta modulation, the dynamics from a PCM source could somehow be altered through its transformation to a bitstream.

However it's accomplished, the HA-2 offers gobs of detail. That said, the ZX2 offers more. Additionally, in the latter case, detail effortlessly shines through; its balanced, musical, nuanced subtleties leave me surprised by how vulnerable I remain to certain long-loved songs I thought played out long ago, but instead, upon their rediscovery, I find myself totally overwhelmed. Unlike the eerily roboticized recreations of the HA-2, I can only describe the Sony as... Human. Beautiful, flawed humanity, ironically recreated through modern digital perfection.

I know the Sony is currently priced at three times that of the Oppo, but, despite the fact that I'm now on food stamps (sadly, this is not a joke; I'm that far gone when it comes to my desire for quality audio), I consider the added expense well worth it and now count my ZX2 among my most valued possessions. Another bowl of ramen seems a whole lot more palatable when it's served alongside music reproduction of this caliber...

Thank you so much for reading this, I know it's been long-winded, but, like you, I'm obviously very passionate about this subject. I'd really appreciate your thoughts on what I'm hearing regarding HA-2's interpretation of microdynamics, especially in contrast with the ZX2. If at all possible, please consider getting your hands on one and giving it some serious time and attention. You might love it as much as I do mine, which could only translate to even more love of music in your future! I think the Sony name could lead more than a few people to overlook this amazing device, as I nearly did. Don't let that happen to you, you deserve to hear it! In every way for the better, it has changed my life.

Many thanks for all your fantastic work, and have a wonder-filled day!

-Jesse Silvertrees

Bob Katz's picture

You had me at "hello", Jesse. My only concern is the exact meaning of "the sony has more detail". As detail without accuracy or musicality doesn't make it in my book. I hope you got good money for selling your Ha-2, I would have been sad to see it go. I am intrigued by the concept of a dac that also performs as a class d amplifier and since there is no such thing as a free lunch, I'll leave your sony unit on my short list of things to investigate! according to bruno Putseyz, class d expert, it's not economical or efficient to make a low powered class d amp that sounds as good as any Hypex, which is why Hypex hasn't made a headphone amp. all the previous class d amp products that I've seen that have headphone sections cheat by putting in a separate driver to feed the cans. cheating! so this sony, if it sounds as good as you say, is a rare exception.

fbczar's picture

Bob, Can you compare the Oppo HA-2 to the HA-1 as a line out DAC, relative to sound quality, with an emphasis on DSD playback? I will be using one device or the other in my main system primarily as a DAC. In my case headphone usage is secondary.

fbczar's picture

Could you offer an opinion as to whether the synergy of the HA-2 / PM-3 combo would offer better sound quality than the combination of the HA-2 and a HiFiMan HE 400i? Your article was exceptionally helpful. The information on equalization was is excellent.

abelian's picture

Hi Bob,

Sorry to hijack this thread, but John Grandberg informed me that IF writers don't actually get notified of new comments in their threads, and you probably don't check you Big Sound 2015 impressions thread anymore.

Just want to ask: was there a reason you picked an M3 build over the Beta-22? I understand from my browsing that the Beta-22 is designed to be (and apparently is) better than the M3.

ladjack's picture

Hi Bob,

Thank you for such great review - it was a pleasure to read it. Although I wanted to ask you is there any chance you can share EQ preset for Onkyo HF Player you use for pm-3 with ha-2?

Fuzzywallz's picture

I would also love to see this

DevOpsProDude's picture

Hi Bob,

Great review. Was looking forward to Innerfidelity reviewing the HA-2 and you didn't disappoint.

Will the HA-2 be a waste if I mostly listen to Spotify at max quality?

I've had the PM-3s for a few months now based on the review here and love them.



Fuzzywallz's picture

Great review and coverage guys!!! I recently ordered a pair of these Oppo PM-3, as recommended by Bob Katz on this site (and his own). I had been looking for a set of headphones with FLATTEST frequency response possible, especially in the low-range. These quickly replaced my AKG 702 fas my main (headphone) mastering reference. I honestly have almost nothing bad to say about these PM-3's so far- they sound as flat as anything i have ever heard!...Well, maybe not quite as flat as the Lipinksi Monitors at Universal Mastering, (but that's unfair). Most "pro" headphones (including the AKG 702, for sure) sound overly bright and very thin in the lower sub frequencies, forcing me to second-guess constantly. These Oppo(s) present everything honestly and don't even try to "hype" the sound at all. the only thing I am missing is the deep and wide soundstage of the (open-backed) AKG 702, and that's why i'll keep the 702 to check soundstage every so often. It also is great that the Oppo PM-3 are great for traveling because they're closed back (with a good seal) and the carrying case is functional, slim and even beautiful! So the box it came in isn't wood.... i could care less that i don't have a "nice box" to throw away.
In summary, these Oppo PM-3 are about a 4.9 out of 5 stars...Here is a link to a past blog where i compare the AKG 702 to the Audio Technica ATH-m50 and Bose Triports- http://www.fuzzywallz.com/ath-m50-headphones-review/ I'll be doing a full review of the Oppo PM-3 once I have had them for a year or so. Thanks for the awesome info and site!

chet.d's picture

Thanks Bob.
I got the PM3 / HA2 combination for listening & studio mix work.

My only concern is wondering if (other than inserting eq) there may be another solution, such as a moderate priced CABLE upgrade to achieve "Slightly" better top end extension…..?

Curious for any thoughts.

MarkyM's picture

Thank you Mr. Katz!

The PM-3 ends a years-long search for new personal reference headphones for both home and my pro audio work! I have been through a lot of them and this one is a keeper! I am shuttling it in its case between home & work daily. Finally a closed headphone with deep bass, smooth mids and no harsh, brittle treble peak!

I don't use my (Andriod) phone for music and the combo of that, EQ plugins and a separate headphone amp seemed too clunky to carry around for me.

So I looked around for an all-in-one solution to replace my aging iPod Classic. I think I have found it in the Shanling M5 DAP from Hong Kong. It has a nice relatively high power headphone amp that is fed from the new AKM AK4490 series DAC chip. The highs sound buttery smooth to my ear, pairing nicely (IMHO) with the PM-3, taming its slight "edge" at 8kHz. And I have my entire library on a 200GB MicroSD card.

I also like a little EQ with the PM-3 and a 2dB boost of the M5's 16kHz slider adds the missing "air" to my ear. I also like a little more bass slam when just listening to music so I boost the 31 & 63 Hz bands by 3 dB or so. I was worried that a simple 10-Band graphic EQ wouldn't be enough or would get the mids muddy but the M5 EQ works well with the PM-3 to my ear and sounds transparent. The PM-3 really takes EQ well!

Elen Kras's picture

What about difference between iPhone6 and iPad mini retina?

ScaryFatKidGT's picture

Would the HF player also work 32bit with the dragonfly?

JJT's picture

Hi, Bob. Based on your recommendation, I plan to buy these cans, but I´m worried about the possibility of not getting an optimal marriage with my studio interface (Apogee Symphony I/O, first generation), because of their impedances: PM-3 is 26 Ohm and the headphone amp on the Symphony is 30 Ohm. I´m concerned not about "loudness”, but frecuency response, because of something I read:

"If the output impedance is greater than an 1/8th of the headphone impedance, there will be undesirable variations in frecuency response: weaker bass, glaring mid-range emphasis, muted high frecuencies, odd phase characteristics. The greater the output impedance, the more likely there will be a discrepancy in the way your headphones receive the sound. This can manifest erratically depending on the headphone. Basically they will not sound as they are meant to”. Is this… true? Does it apply to the PM-3?

According to this, when using the PM-3, the output impedance of the amp should NOT be greater than 3.25 ohm (26/8 = 3.25). But the headphone amp on my interface is 30 ohm. Will this compromise the performance of the PM-3? I think they´ll work well with my Astell & Kern portable player (2 ohm), but I´m choosing the PM-3 because of your recommendation as a (secondary) reference tool, and if they lose accuracy when paired with my interface, I feel like making a bad purchase decision, as I want to upgrade my headphones mainly for studio work (checking mixes & masters), personal entertainment is just a (very) exciting bonus, a bonus that will help me “calibrate my ears” while I´m having fun.

Any assistance will be greatly appreciated.
Best regards.