CanJam at RMAF 2013: JDS Labs to begin...

Back in early 2011, NwAvGuy made a huge splash in the headphone enthusiast world. Huge. As a very competent analog electronics engineer he had the chops to deeply investigate circuit designs of numerous headphone amplifiers in the trade, an embarked on a one-man crusade railing against the poor design practices he found. Well...long story short, he found himself banned from most every important headphone and DIY audio site out there. His blog remains as an interesting source of technical information, but NwAvGuy no longer posts, and has essentially disappeared from the scene. I'm all for knowledgable people having an influence in the market, but generally I think applauding good performers is more productive than trying to destroy poor performers.

Anyhow, one of his contributions is an open-source design headphone amp called the O2. NwAvGuy designed the amp in an effort to show that a high-performance headphone amp doesn't need to be expensive. I've measured this amp and, true to his word, it indeed does measure spectacularly. To my ears, it's a very good amp for the asking price.

John Seaber is a super nice guy, and runs a nice little company, JPS Labs, dedicated to bringing enthusiasts low cost and DIY headphone amps. There you'll find a dandly little array of amps including the CMoy, C5, and, as of a year or so ago, the NwAvGuy O2 and Objective DAC. All are available both in kit form and pre-built at reasonable prices.

You'll find JDS Labs here. I'll let John tell you about the O2 in the video.

donunus's picture

First let me say that I am not one of those O2 fanatics that worship NWAVGUY as a God. I don't like the idea of people arguing on forums that the o2 is as good as great high end amps out there because it definitely has its limitations but what I can say is that it is a great value. For people that want an amp tuned to sound neutral and work as a portable at the same time, I can't think of anything else in its price range that can do the same thing. Simple as that.

JIGF's picture

What about Schiit?

donunus's picture

schiit doesn't have a portable amp

zowki's picture

What are the O2 limitations? It is powerful enough to drive nearly any headphone, has almost no noise, and a completely neutral frequency response.

Can you give an example of a high end amp and the audible differences compared to an O2?

donunus's picture

Have you tried a t1 out of the o2? :D

Limp's picture

I don't have a T1, but going by the numbers I see no reason why the O2 shouldn't be able to drive them, even running on batteries.

A 0.5Vrms source and a gain of 7 gives 3.5Vrms output. 
3.5Vrms into a 600Ω load gives 20mW.

With the T1s sensitivity of 102 dB/mW that will give you 115dBSPL. Quite loud enough.

zowki's picture

Yes, I have and it was more than loud enough.

donunus's picture

It wasn't a matter of volume with the T1. It was a matter of bad synergy, or lack of power... whatever it was, the t1 didn't sound good at all.

dalethorn's picture

That's great Don, except that you're getting a handful of views while NwAvGuy gets millions of views.

donunus's picture

? I don't get what that has to do with my comment :D

xnor's picture

What do you suggest? A tube amp that smears transients and distorts treble and has a high output impedance (basically a bass boosting EQ) so that the T1 will not pierce your eardrums?

donunus's picture

Thats just it though, it seems that the o2 was smearing the transients of the t1. I mean they sounded so dead it was unbelievable. With my dt250-250s the O2 is great, With HD600s, I couldn't expect much more especially for the price. So it is either the t1s are totally void of dynamics or the o2 just can't drive them right. Anyways, I am curious as to what others have observed with the T1 and the o2.

donunus's picture

I want to say that John Seaber is awesome about answering emails regarding product details. Very good customer service indeed!

paul's picture

Bad idea using Jude Mansilla as the camera man. :-)

Why is there a caveat when reviewing less expensive equipment, ie, sounds good at the price ...  It sounds good or it doesn't sound good. Saying "It sounds good for the price" just begs the question. 

This is not to say price doesn't matter. Saying it is one of the best portable amps in the under such and such a price is more helpful - This is one of the best sounding amps in the under $500.00 range.

donunus's picture

I did say that there was no other option in the price level when talking about portable amps that sound good. And yah, I do slightly prefer the o2 compared to a lot of much more expensive portables too. But if we were talking about amps regardless of price, the o2 first of all is not loud enough for AKGs like the k500 since I don't use the flawed and distorted high gain mode so I assume it won't drive the k1000, the HE6, and also felt lacking with the t1. 

But be realistic, even though higher price doesn't always equal better sound. Higher price does make it easier for manufacturer's to get things right and not cut corners. 

Limp's picture

"…the flawed and distorted high gain mode…"

You need to expound on this.

donunus's picture

When using high gain, the sound clips and gets severely distorted when: 

1)Either the music is very loudly mastered (basically almost all music produced today)

2)The dac being used with the o2 has a high voltage output. With loudness war stuff though, even a relatively low output dac can cause the o2's input to clip. 

Using Batteries, the O2 is also more prone to clipping vs when using a wall plug.


I only use high gain when the music playing is mastered with low volume levels, I am using a DAC with a low output voltage, and the headphones being used is not that sensitive. Otherwise, I keep the amp at low gain at all times.

Limp's picture

That's not really anything you can fault the O2 for.

It demands some attention to gain, source voltage levels and power voltages relations, but the intricacies have been covered extensively.

What gain levels do you use?

donunus's picture

So you want to decide for me what I can fault the O2 for and what i can't? Of course it is a flaw. Sometimes when the headphones are not too sensitive ex. AKGs, using high gain would make the volume right but the sound wrong. 

Your Philosophy basically forces me to listen at volume levels that I find boring because even full volume at low gain with the k500 for example is plainly not loud enough. This is a non issue with many other amps. 

Limp's picture

Any amplifier will clip if it is asked to amplify beyond what its rails can supply.

Do you fault the GS-1 for not being able to drive Sextetts sufficiently?

It is a matter of asking for more than what is reasonable to expect. 

With a 2V source and a gain of 2 the K500 should be able to get plenty loud, but this is pushing the limits of what is reasonable to expect from a portable amp.
Plug in the power and anything short of an HE-5 should no problem, unless you've hamstrung it with poorly chosen gain settings.

donunus's picture

Hence, why I said I like the O2. Not everything I like has to be perfect and for the money there is nothing to complain about. That comment was a complaint if the o2 was a product to be reviewed regardless of price which people seem to say doesn't matter.


About the GS1, If the sextetts are your primary headphone then yes I can fault them. I mean why would I buy an amp that doesn't match my current cans? If they have a hard time with them then they are not the perfect amp like a lot of people make the o2 out to be :)

Limp's picture

I'd say it was my fault, for not finding out beforehand if the amplifier would be up to the task. After all, it's right there, printed on the tin.

If I want unsaltet tomato juice I don't go on random and buy the carton that looks the nicest, and then complain if it tastes salty. I look for those with "no salt added" or similar printed on the label. If when I taste the juice find that it tastes rotten, I can fault the manufacturer, because it didn't say "made from rotten tomatoes" on the label.

donunus's picture

So what is your take on the o2? Best amp in the world?

Limp's picture

Without defining what 'best' constitutes, that is a question without an answer, and then there's the wole problem of induction.
That being said, I think it does what it does admirably.

donunus's picture

Definitely a good amp. I like them quite a bit which is why I am keeping them. 

donunus's picture

Like I said, its not a power thing, and even if we are using the most sensitive cans out there it doesn't matter, The clipping in high gain mode is independent of power output capability. It is a design flaw.

donunus's picture

The clipping is not due to a question of power by the way. It is due to the input getting overloaded. So at any volume level (even at the lowest volumes), you can hear that clipping. It's not a distortion thing due to maxxing the power capability of the amp.

Limp's picture

The two are essentially the same thing.

If it is set to a gain of 2 it will try to double the amplitude of whatever signal it is given. On batteries it can't output more than 4.5V (a bit less with rechargeables), that's how far the rails will go. Therefore if you have a gain of 2, max source voltage before clipping is 2.25. If you have a source voltage of 2, then the max gain is 2.25. If you have a source voltage of 2 and a gain of 2.5, of course it will clip. Any amplifier with a 4.5V power supply would.

donunus's picture

I am apparently not as technically literate about this stuff as you are but all I know is that the o2 is the only amp i have ever had this problem with. Ive had amps with less power that can output more yet not have any input clipping problems. 

You are saying it is the same thing as output power hmmm so basically even though I am driving grados at 9 o clock, I still get distortion so let me ask if that is a normal amplifier trait to you. Even the FiiO E9 at the high gain setting which is extremely loud and much higher gain than the o2, the input doesn't distort. I think you have to read more into this before inventing things and talking up your bleep. 

Limp's picture

Maybe not a normal trait, but it ceirtainly isn't unheard of either, and the reason is where the pot have been placed. In the O2 it is placed between the gain stage and the parallel buffer stage, while in most commercial amps it is placed before the gain stage. 
A pot is a variable voltage divider, it shaves off some of the signal and sends the rest onward. This creates noise. When you have the pot in front of the gain stage both the noise and the signal is amplified. If the pot is placed after the gain stage only the signal is amplified, while the noise remains at unity.
I'm far from proficient in this subject, but in all honesty it isn't really rocket science either. If you had just read up a bit on the intricacies of this amplifier you could have saved yourself a lot of bother. You know where to find the blog.

donunus's picture

Alright, these are what we call compromises. Anyway, I don't use high gain mode so it doesn't matter. I would rather have a little bit of noise than clipping. If the gain stage was made like other amps, I may have used the high gain on the o2 more.

Limp's picture

Have you tried using software on your computer to control the volume?
That way you can adjust the output of your source so that it is just below the clipping point of the input stage. I assume high gain on your amp is 6.5x, which makes max source voltage just a shade over 1V when running on AC. Also assuming your DAC outputs ~2V, that should make a 6dB reduction in software sufficient to escape distortion. At that point you can either use the pot to adjust volume further, or you can just leave it completely open and adjust further in software.

If you're a bit sceptical towards software volume controls, then don't be.
At least give it a try.

donunus's picture

Thanks. For computer use, the volume control is my friend. As for connecting directly to a CD player, thats a different story. Still, low gain is fine most of the time with a higher voltage input anyways.

donunus's picture

Anyway, I am willing to admit I am wrong about the math since I am not a technical person but if it was just about power output being exactly the same as to why the input distorts then why does it happen only with the o2 and not on other amps? Can someone else with a good grasp of the technicalities explain why this is so? Why is a FiiO E9 which is about similar in power output to the o2 not having clipping problems even when switched to high gain which is by the way, waaay louder and higher in gain than the o2s high gain mode.

tdockweiler's picture

Not enough volume with the O2 and K500? Are you using a weaker portable source? I used my K400 which is pretty power hungry and the O2 with Modi had zero volume issues. Nowhere near half volume on low gain. No headphone ever had to be past 50%. No volume problems with the HD-650 or Q701.

I had the K501 before and both the K400 and K501 are pretty hard to drive.

donunus's picture

Yah I was talking about it with a weak source

sgrossklass's picture

With a truly weak source, you ought to be able to use high gain mode though. That can take up to ~600 mVrms even on batteries with the default 6.5x high gain, and something like a volume-limited iPod Classic/Touch outputs about 400 mVrms. And once you're getting into unlimited iPod Classic/Touch line-out territory of ~1.2 Vrms, the default low gain of 2.5x should be good for a really decent amount of output, not that much short of what the amp could deliver.

What sort of source with a fixed output level do you have that would fall in between these two cases? If the high gain mode currently isn't of use to you anywhere, swapping out its gain setting resistors would be worth considering.

Anyway, I do agree that this version of gain staging isn't all that user-friendly, actually this was one of my concerns even at the time. Compared to the straightforward approach with the volume pot at the input, it sits on the opposite end in terms of both noise and input overload handling. But this is part of what makes the amp as good as it is in terms of noise and distortion even without any high-strung parts. I guess the reasoning was that audiophiles are used to jumping through all kinds of hoops for best sound anyway, and it would be for a good cause this time. That's tradeoffs for ya.