Small and Mighty: The Resonessence Labs Concero HP
Resonessence Labs made a name for themselves selling their $3,999 Invicta DAC which has an excellent integrated headphone stage. The recent refresh of that model brings it up to $4,999 and forks it into two versionsone keeping the headphone section and one going without. On the other end of the spectrum, their little Concero DAC ($599) came out last year and offered supreme bang for the buck, and their new Herus ($350) is a tiny USB stick in the same vein as the Audioquest Dragonfly. With the higher and lower price points covered, Resonessence hasn't forgotten the middle, giving use the new Concero HD and the Concero HP ($850 each).
I'm not sure how many times I've already mentioned this, so forgive me if you've read this from me several times by now...but I feel the need to once again (briefly) explain the history of the company. Resonessence Labs top dog Mark Mallinson was formerly the operations manager at ESS. He left there to form Resonessence Labs, along with a group of engineers who were directly responsible for the creation of the Sabre DACs. Worthy of note is that Mark's brother Martin remains high up on the ESS roster. The Sabre chips are notoriously difficult to work with compared to alternatives from Wolfson, Cirrus, Texas Instruments, or Analog Devices. So if anyone should be able to extract maximum performance out of them, it's the team responsible for their very existence.
Now, with that out of the way (it's the last time I'll say it, I swear).... I reviewed the Concero HD over at Part Time Audiophile recently and found it to be extremely worthy of a recommendation. That model has RCA outs and is basically a stand alone DAC unless we count the USB to SPDIF functionality (which it also handles quite well). The Concero HP, however, does not have RCA outputs. It's strictly a headphone only device. How often do you find that outside of portable amps?
Resonesense Labs Concero HP ($899)
Like its brethren, the Concero HP is tiny but dense. The satisfying heft is courtesy of the CNC machined enclosure which to these eyes is subtle yet very attractive. The minimalist front panel design consists of a single 1/4" headphone jack, a volume knob, and an LED lit "R" logo which shows different colors based on system status. Around back is a USB input and a hybrid coaxial SPDIF input/output jack. Input and output? Yep. For now it can take signals from a CD transport or other source (in which case a USB power adapter will be needed), but Resonessence will soon offer a software method for transforming the port into an output jack whenever the user desires. That means the same USB to SPDIF functionality found in the original Concero and Concero HD will work here as well.
The heart of the device is the new ES9018K2M DAC chip which is the top dog in the new ESS SABRE-2M line. Perhaps you've heard of the flagship ES9018 DAC as used in numerous expensive DACs and disc-players? That's an 8-channel design, typically summed for quad-mono operation or else used for 7.1 surround devices (see Oppo for example). The ES9018K2M makes its debut with the Concero HP/HD and is a completely new chip that seems ideally suited for this type of device. A 2-channel design, it draws less power and comes in a significantly smaller package than its sibling. It costs less too, which is a plus since the ES9018 is the most expensive DAC chip on the market right now (the possible exception being out-of-production R2R DACs like the TI PCM1704 which are getting harder to come by). I predict we'll see more of the 2M DACs in the coming monthsESS seems focused on getting them into devices such as smartphones and tablets, as well as higher-end Blu-Ray players and other consumer electronics. But Resonessence Labs had the exclusive from the very start.
The new SABRE-2M chip may be the star of the show, but it's got a nice supporting cast behind it. Important players include a Xilinx Spartan 6 FPGA, a USB implementation from Cypress Semiconductor, and a pair of Analog Designs AD8397 op-amps. Jitter reduction is tackled by the FPGA DSP core which also holds the custom Resonessence Labs apodizing and IIR filters. These optional filters upsample 44.1kHz and 48kHz material while leaving higher-resolution streams to their native sample rate. I've heard many upsampling implementations that seemed like little more than marketing fluff, but in this particular case it does seem quite effectiveI nearly always choose one or the other as opposed to using pass-through mode.
The LED logo starts out showing red in color when USB power is connected but no signal is present. Introduce a signal, either SPDIF or USB, and the LED changes to blue for standard playback. Press the volume knob once to engage the IIR upsampling filter and watch the LED switch to a lovely shade of magenta. So far so good right? Press the knob once more to select the linear-phase apodizing filter, and the LED turns from magenta to...magenta? Again? That's right, the LED doesn't differentiate between the two filters. One must keep track of button presses or else repeat the cycle to find their bearings. It would really have made sense to have one more color available. Sounds like I'm nitpicking but that's the level of achievement we're dealing with herethe biggest issues I can find to complain about are fairly trivial.
The HP is the first Concero product with a volume knob. This is more of a trick feature than it would initially seem. Turning the physical knob results in Audirvana (Mac) showing the software knob rotate, or Foobar (PC) moving the volume sliderbut it is not a software volume implementation. The internal Sabre 32-bit volume control is actually doing the legwork, while "talking" with the system to present as a software function. Resonessence has a more detailed explanation here, and I'll only add that this solution works brilliantly and seamlessly. Use the software control or the physical knob and you get the same results without throwing away nearly as many bits as software solutions. Very clever.
In actual use, the Concero HP couldn't be simpler. As usual, PC users will need to install the special driver while their counterparts running OS X will be ready to go immediately. You'll want to turn down the volume when using Concero HP for the very first time, as it tends to default to 100%. From there on out it remembers your last setting so that's a one time deal. Load up any music from lowly CD quality to high-res PCM, DSD64, DSD128, or even DXD which is really just 24-bit PCM with a super high sample rate (352.8kHz to be exact). The Concero HP plays pretty much anything you can throw at it without batting an eyelash. Output impedance is a suitably-low 2.2 ohms meaning just about any headphone or IEM is fair game. On paper the select few exceptions would be multi-driver balanced armature or hybrid armature/dynamic designs with wild low-impedance swings. In practice I don't think it's much of an issue at all"2 ohms remains a good target" says Mr. Hertsens and that's good enough for me. Output is 270mW into 32 ohms, meaning the little HP is no slouch and able to drive most typical headphones fairly well.
So much for the design, now on to the sound.