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Review and Measurements of Massdrop Alex Cavalli Tube Hybrid (CTH) and JDS O2 Headphone Amps

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This just shows that the amplifiers are different. :facepalm:
If you actually looked at the blog article instead of the image, later down the page they cover DAC differences, so... maybe you should actually look into the article before commenting just on the image linked.

Screenshot 2018-08-08 16.35.05.png
 

Grave

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If you actually looked at the blog article instead of the image, later down the page they cover DAC differences, so... maybe you should actually look into the article before commenting just on the image linked.

View attachment 14628
I can comment on the insufficient evidence posted all I want. Although the Element DAC does seem to be better in some ways and worse in some ways, I am sure it sounds the same. If the ODAC RevB is not the ODAC it should not be called the ODAC because that would be plagiarizing NwAvGuy. :|
 
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I can comment on the insufficient evidence posted all I want. Although the Element DAC does seem to be better in some ways and worse in some ways, I am sure it sounds the same. If the ODAC RevB is not the ODAC it should not be called the ODAC because that would be plagiarizing NwAvGuy. :|
YoYoDyne holds most of the rights to the ODAC.

From NwAvGuy's blog:

PARTNERS REVEALED: Because of the above requirements, the ODAC development has been a joint effort with YoYoDyne Consulting. George has supplied other open source USB DAC boards at reasonable prices and seems to be well respected on diyAudio. He’s taking considerable financial risk having a large batch of ODAC boards assembled and hence is coordinating all the manufacturing and distribution. I conducted all the measurements, refined the design, and helped optimize the PCB layout.

Further information from the Blog post JDS Labs made on working with Yoyodyne to release the Rev.B
 

DuxServit

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Sorry, I meant the JDS Labs version of ODAC.

I have the slim ODAC-only box, with the manual stating it is v1.0.0 ODAC.

I can ship this to you if it helps comparison with the new RevB ODAC.
 

Jimster480

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At the time I purchased JDS had "B stock" available. B stock is only cosmetic - electronics are new and can be customized. So the lettering on my O2 is somewhat faint and uneven, but the price was US$116 shipped. No regrets - it's worked just fine for me.

My one complaint was that because it is essentially hand made, the circuit board rattled inside the case. On something like this that isn't unexpected. I put a few small pieces of sticky backed foam on the two 9V batteries and it completely solved the issue.

The board is hand made and my example was constructed properly, but I wouldn't say I was in awe of the soldering. So I'd simply say the device is "properly made".
I also have a B-stock JDS O2, but mine i customized to have 1x/3.2x gain and no batteries and all the inputs on the back.
I think it was around $120 shipped? I use it almost every day.
 

JJB70

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The O2 was never going to be well received by certain parts of the hobby as it posed an existential threat to high end equipment and the whole cottage industry around it by demonstrating that a well executed low cost product could perform extremely well. The designer applied sound engineering principles and clearly understood that performance is about design and not just buying the fashionable component of the moment. It wasn't just the O2, he also demonstrated that cheap and cheerful products from China and Behringer are often very good. I have a few interests and I am not sure there is anything like the same absence of a link between price and performance as in hifi. I remember when he called Schiit out over the Asgard, rather than thanking him many decided to shoot the messenger. Sadly I made the mistake of giving Schiit the benefit of doubt and assuming that they had learnt a lesson until I read the review of the Jotunheim here which seems to have an even more serious problem.
I see this site as sort of like a spiritual successor of nwavguy, applying rational analysis and measurement and opting out of the whole mutual back scratching world of certain magazines and websites with their almost incestuous relationships. Amir's reviews are first class, if only more were like his.
 

wadec22

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With the CTH being such a poor performer, would you guys anticipate the Liquid Carbon X to also disappoint? Or are they different enough that you would make no connected assumptions?
 

AnalogSteph

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There's one measurement of the O2 I've been pestering people about for years but nobody has ever bothered to conduct: Distortion vs. input level (especially high-frequency / IMD) of just the input (gain) stage, i.e. with volume turned reasonably far down and no load so that the output amps have negligible impact. The JDS Labs O2 comes with gain settings of 1X and 2.5X, if memory serves? Now I'm not sure how much there'll be to see at 2.5X, but at 6.5X one should be able to see crossover distortion coming in quite clearly, as the NJM2068 increasing struggles to drive its feedback network. (There should be no irregularities at 1X, since an opamp that couldn't drive a load consisting of nothing but a 10k pot properly at unity gain would have to be quite pathetic. Even a 4558 can do that.)

NwAvGuy himself found lower distortion and higher clipping level at 7X when using an NE5532 instead, which - surprise! - is a better load driver. Unfortunately he never tried some different feedback network resistor values - increasing those by about a factor of 2 should address this issue if you need high gains like 6.5X. I'm talking about R16/17/19 and R21-23. Ideally C19/20 values should be reduced by the same factor as well. I would also suggest doing the same or perhaps even more when building the low-power version - low power opamps invariably are not good load drivers, so why torture them needlessly? Even the TL072 (shown to be a sad loser in default configuration, being a notoriously poor load driver and preferring at least 10 kOhms or so) might perform acceptably then.
Besides, one motivation for low resistor values - aside from keeping impedance mismatch and resulting distortion low - was keeping gain stage noise down, but in practice chances are that source noise is going to swamp this anyway, so that's kind of silly. (How many sources have you seen that had less than, say, 5 µV of output noise? That's 106 dB below 1 V or 112 dB below 2 V, much like the ODAC actually. Quite respectable and more than sufficient for a source followed by another volume control, yet still almost 20 dB noisier than the suggested gain stage config at 6.5X with NJM2068. Most anything short of an LM358 - heresy! - would be adequate noise wise. Using one of those for the lulz might be worth it to those curious enough, but don't forget hacking in the obligatory output pull-down resistors to -15 V, typically 10k, which is the usual trick to avoid this part's terrible crossover distortion.)

I think this is an important test because you might have a source with a fixed output level, like a traditional CD player, and gain stage distortion solely depends on input level with nothing the user can do about it.
 
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amirm

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I think this is an important test because you might have a source with a fixed output level, like a traditional CD player, and gain stage distortion solely depends on input level with nothing the user can do about it.
I have experimented with input levels and it definitely has an impact on performance as does the volume position. There are infinite possibilities here unfortunately so a hard problem to solve. I do play with a few values to get the best numbers I can in the dashboard.

So to be clear, you want a sweep of input values? With what volume and output level so that everything is fair from product to product?

Welcome aboard by the way.
 

AnalogSteph

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So to be clear, you want a sweep of input values? With what volume and output level so that everything is fair from product to product?
To clarify, this test only makes sense for amps like the O2 with a gain stage up front, not so much for those with a volume pot first (which can take silly levels). I think the Lake People / Violectric amps are another example.

First you'd have to determine input clipping level with the volume turned down.
Then set up the volume for input clipping level to occur at a moderate output level, maybe 1 Vrms?
Then do your HF distortion / IMD sweep up to input clipping level.
It'll be noise-limited eventually, so if you want to get fancy, I'd suggest stitching the graph together:
Sweep from 100 mV to 1 V out, then adjust volume up by 20 dB, repeat, until you max out the volume.
OK, maybe that order is stupid - I think you better max out the volume first, do a full sweep up to 1 V out, then set volume to -20 dB, do a sweep of 100 mV .. 1 V out, and repeat until input clipping occurs inside that range. Et voilà, the entire input level range is covered. Rinse and repeat for all gain setting options if desired.
Or can the AP shoot for a desired level automatically, perhaps? Then you could step through a range of volume settings and interpolate. Don't like this quite as much though.

I'd have to think about how to determine whether 1 V is too much... I guess it's seeing the stitched graph go up and then jump down at the stitching points. Should be different from what noise would do.
Welcome aboard by the way.
Thanks. :)
 

Roen

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Also, if we could see if the measurements different significantly when the O2 is solely operated on battery power, that would be interesting.
 
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I like it very loud! :) Actually I did not know I wanted it that loud until I played the iFi. The sensation of the cups physically moving back and forth is something else. :)

But yes, by most standards, the O2 was loud enough. It just couldn't make the headphones cry. :D
I do wonder how loud you actually listen to your cans. :eek: If I'd use my O2 amp it'd set my sound card volume to 28% (I want at least some breathing room and the channel imbalance would be a problem otherwise) and then O2 to around 10 o'clock... and 1x gain. Similarly I have to use Zx's vol pot when using the AE-5's headphone out because otherwise I'd have to use single digit % volume when using the lowest gain.

I have the Massdrop version and there are few things that are really puzzling me. Right off the bat it sounded definitely worse than straight from the AE-5's headphone out (originally plannes to use O2 with Zx but while waiting for O2 to arrive I ended up getting AE-5 to replace Zx). Especially stereo imaging took a very clear hit and things sounded more compressed. The difference was so obvious that I did a quick RMAA test to see if that could show anything. Since the ADC in AE-5 is pretty ****** (integrated in the SoundCore3D chip) I didn't expect to see any difference. However, I got these:
resultsa8s7r.png

Seems to make sense why I though that O2 sounded worse. Some of those are within margin of error but I just don't understand why there's such a massive differences in dynamic range for example or even in the noise level. I didn't expect to see any real differences considering the ADC quality. I do have hunch why the crosstalk if better on AE-5, considering the amp design. The ADC is totally the limiting factor in AE-5's case so in reality the differences are larger. The only difference was that O2 got the signal from line out instead of headphone out (both used the low gain mode which seemed to give similar levels).

I have sensitive ear so I actually use quite low volume when listening to stuff. I don't know if that makes those differences even larger in practice - probably? Doesn't matter where I plug it, it seems to just craptalise the original signal. There's a chance that for some reason the line out give crap signal - after all the headphone out is handles differently (doesn't touch the backbracket for example) - but I really, really doubt that.

Did I get a dud from Massdrop or is the somewhat high crosstalk just the way O2 is? One of the screws just self destructed when I tried to open it so now it's forever shut too... In any case tough, it felt like I wasted a quite a bit of money for a paper weight. I also bought proper EU power adapter since the bundled one was a bit dangerous looking (also it wouldn't fit without an adapter).

Meh, I don't really get this... :rolleyes:
 
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