Questyle CMA 800R Good? Not Good?

[Sylafari]

So a few years ago, I was looking for a headphone amplifier for my HD 800, and I stumbled across this amplifier the Questyle CMA 800R (http://www.questyleaudio.com/index.php/product/CMA800R). It seemed to tick off all the requirements for me at the time (based on the manufacturer specifications it seems to measure very well, looks to have good components in it, and subjective impressions from 'professional' reviewers seemed to be positive as well). It also had a strong marketing buzzword to me in that it has something called Current Mode Amplification (I don't wanna pretend I know what it is so I'll leave a link: http://www.questyleaudio.com/index.php/technology#电流膜技术 ).

Anyways I was curious to if there were actually any quality parts inside so I took it apart (very easy to uses some torx bits and the top cover comes off). The build is very nice as it uses very thick aluminum panels and the inside seems to look good. I'm not too sure but I have posted some pictures.

Supposedly it has a measured THD+N of 0.00038% and 114 dB SNR.

I was wondering since you guys seem to analyze PCBs on amplifiers and numerous other things to see if things are actually designed well on your insights into this amplifier (design and part quality) and if it is crap feel free to let me know (better than to know if I been duped than to keep getting duped!). My only subjective impression is that the HD 800 produces sound when used with it and doesn't sound awful.

Maybe one day I can send it in for measurements too!

A few pictures:

Hmm pictures came out too big. Not sure what to do about that...

 

[amirm]

Seems like a well made product backed by proper measurements using professional equipment (Audio Precision). There are Japanese parts in there which is always a good sign.

It also looks over designed with that large bank of capacitors, tons of power transistors, etc.

All in all I think you have done well!

 

[RayDunzl]

Hmm pictures came out too big.

They'll shrink on a small screen.

 

[amirm]

Just followed the link and that is one nice quality case work!

The only downer is the high price of $2000. I would have liked to see a price less than half of that.

 

[Sylafari]

Sort of luckily for me, I bought it a while ago near mint second hand for about $1200 if I remember correctly. I believe the new price back than was $1400ish and now it is $2000

 

[amirm]

For that price, you did well then. It is the kind of unit that you should not have to replace in the future.

 

[Sylafari]

I'm guessing you would prefer a stepped potentiometer?

 

[Dialectic]

I'm guessing you would prefer a stepped potentiometer?

Yes, a stepped attenuator, whether on an IC or comprising discrete components, would offer better measured performance, I think. Even better would be a high-quality digital volume control, which, of course, is not possible in an analog product like this.

I'm just picking nits. I'm sure the volume control on the Questyle sounds fine.

 

[trl]

I very much like the GOSS outer-shield from the toroid, it will definitely decrease the mains hum induced on the surrounding components. Also, i'm impressed by the AP measurements. I like the multitude of reservoir caps from the PSU, German style (Meyer Corda, Violectric).

I'm not sure I love the 2 x Red MKP caps from signal path, at this price I was hoping to see DC-servo. I don't understand the single 3-pin XLR balanced-out plug from the front (not shown in your pics), this amp is not balanced, it only has 2 x push-pull output buffers inside, also a 2-gang potentiometer.

However, a bit too price for my taste, but seems very well built and I really like when I see a device built after a bit of R&D, not just a simply copy-paste of schematic from a datasheet and...voila.

 

[solderdude]

The 3 pin XLR is a direct feedthough from the rear. The goal for this is to connect it to a second CMA800 and use each CMA800 as a mono-block.
This way you can use a balanced headphone 'truly balanced'.

When you have 1 CMA800R you basically have a single ended amplifier that has single ended inputs and a balanced input. That input is just a differential opamp converting the balanced signal to single ended.
The design seems nice and appears to be DC coupled.
The used IC for on/off switching delay also has inputs for DC protection which is a good thing when something goes wrong.

I think the big MKP cap is for decoupling the power supply lines and is not in the audio path.

The RK27 pot is fine.
I have never had one turn scratchy and have used some for over 25 years (still in daily duty till this day)

 

[BurritoJustice]

The 3 pin XLR is a feedthough from the front. The goal for this is to connect it to a second CMA800 and use each CMA800 as a mono-block.
This way you can use a balanced headphone 'truly balanced'.

When you have 1 CMA800R you basically have a single ended amplifier that has single ended inputs and a balanced input. That input is just a differential opamp converting the balanced signal to single ended.
The design seems nice and appears to be DC coupled.
The used IC for on/off switching delay also has inputs for DC protection which is a good thing when something goes wrong.

I think the big MKP cap is for decoupling the power supply lines and is not in the audio path.

The RK27 pot is fine.
I have never had one turn scratchy and have used some for over 25 years (still in daily duty till this day)

It's worth noting that there is a separate XLR input for monoblock operation that isn't just summed to SE.

Also, a photo for the curious.

 

[Veri]

I don't understand the single 3-pin XLR balanced-out plug from the front (not shown in your pics), this amp is not balanced, it only has 2 x push-pull output buffers inside, also a 2-gang potentiometer.

That does seem odd indeed.

The 3 pin XLR is a feedthough from the front. The goal for this is to connect it to a second CMA800 and use each CMA800 as a mono-block.
This way you can use a balanced headphone 'truly balanced'.

When you have 1 CMA800R you basically have a single ended amplifier that has single ended inputs and a balanced input. That input is just a differential opamp converting the balanced signal to single ended.
The design seems nice and appears to be DC coupled.
The used IC for on/off switching delay also has inputs for DC protection which is a good thing when something goes wrong.

I think the big MKP cap is for decoupling the power supply lines and is not in the audio path.

The RK27 pot is fine.
I have never had one turn scratchy and have used some for over 25 years (still in daily duty till this day)

That was quick! That clears things up.

 

[Veri]

Just saw they offer a "special" studio version with ceramic PCB:

Besides the strict procedure in manufacturing, Questyle Audio Golden Reference System's one more unique point is it's the world's first audio device to use Rogers Ceramic PCBs. Rogers ceramic PCBs, a top level PCB mainly applied in military applications, allow the system to achieve an even more outstanding sound performance and specifications, some of the advantage are:
- Ultra-low distortion: 0.00022% (20Hz-20kHz)
- Dielectric constant and dielectric loss are both the lowest available in audio devices
- Ultra-stable dielectric constant in ultra-wide frequency (up to 10GHz) ensures ultra-low loss and stable signal transmission
- Ultra-low thermal expansion , ensures stable operation up to 280 ° C temperature
- Selected components, ceramic packages, provide superior performance in terms of system sound quality and technical specifications

 

[trl]

Thank you Frans for your experienced eagle eye and explanations!

Great looking ceramic board indeed, not willing to find out the price for the finished unit.

 

[BurritoJustice]

Thank you Frans for your experienced eagle eye and explanations!

Great looking ceramic board indeed, not willing to find out the price for the finished unit.

$2999 for each of the amps, $2999 for the DAC, $3499 for the preamp (no fucking clue why this is the most expensive component considering it's minor role). $12,495 for the stack in the image above.

I'd love to see these measured together, though I doubt we ever will. The DAC uses a curious chip, Wolfson WM874, which I've not seen before.

E: Fun extra fact, the "Golden Reference System" specified here was launched with the Focal Utopia as the recommended source to pair with the headphones.

 

[solderdude]

Its the WM8741 a well known chip

Agreed that it is a bit expensive for what it offers.

 

[trl]

$2999 for each of the amps, $2999 for the DAC, $3499 for the preamp (no fucking clue why this is the most expensive component considering it's minor role). $12,495 for the stack in the image above.

I'd love to see these measured together, though I doubt we ever will. The DAC uses a curious chip, Wolfson WM874, which I've not seen before.

E: Fun extra fact, the "Golden Reference System" specified here was launched with the Focal Utopia as the recommended source to pair with the headphones.

The non-ceramic amp was sold for about $1500; now on eBay can be found at $700, quite a good price.
Technically, WM8741 measures about the same with ES9038Q2M, in regard with SNR, but many folks consider this DAC as sounding more natural and musical vd. ESS chips that sound more "non-analogue" and clinical. I can't comment on that. However, this is a great DAC for sure:
- http://www.lampizator.eu/lampizator/REFERENCES/wolfsondac/WolfsonWM8742DAC.html
- http://hifiduino.blogspot.com/2009/11/testing-wm8741-filter-setting.html
- http://www.itsonlyaudio.com/audio-hardware/wm8741_vs_ess9023/
- http://hifiduino.blogspot.com/2009/05/wm8741-digital-filters.html

@Sylafari, it's a great headamp definitely, I'm sure it drives all your cans with ease.

 

[Sanlitun]

This amp was the first thing I bought on Massdrop back when they were actually doing group buys and weren't just a retailer. I hadn't used it in some time as I have gravitated away from dynamic phones and the HD 800S. Recently I had decided to put together a system using a lot of hyped components like the THX 789 and the SMSL SU9. I did like the DAC but it has been a struggle with the THX and I had ended up doing a shoot out and comparing it to the amps I already owned including the CMA800R.

To cut a long story short I can say this is a fantastic amp. It has a broad smooth resolution rather than just at high end. I'm not saying anything bad about the THX 789 as it is a great buy for $250.

I realize I am bumping an old thread but if you can find one of these used it will probably be a better deal than many of the popular amps A90 or SA-1 available now.