Curiously Strong CMOY Headphone Amp Review

[amirm]

Can I ask how you came up with the 100mW figure?

Empirically from testing probably 50 headphone amplifiers with HD-650.

 

[JohnYang1997]

Can I ask how you came up with the 100mW figure?
Also, you mentioned that 100mW of output was your standard for desktop products. I think most people would agree that the CMoy is a portable product?


Can you clarify what you meant by this? Unless I'm interpreting your THD+N vs. Power chart incorrectly, the CMoy's THD+N is the same at 0.1 mW (100 microW) as it is at 1mW.

With 9V battery it's easy to create +-9V supply which will give tremendous boost in output power for high impedance. Or use Li-ion battery and 65131 to create +-12V.
No, just no.

 

[audio_tony]

I would say that the OPA2227 is wholly unsuited to the application here. Even the datasheet suggests using two opamps in parallel for a headphone amp (admittedly at -/+ 15v)

 

[JohnYang1997]

I would say that the OPA2227 is wholly unsuited to the application here. Even the datasheet suggests using two opamps in parallel for a headphone amp (admittedly at -/+ 15v)

View attachment 86757

With a rail of only 9V or +-4.5V. I don't think there's a lot of opamp that can work well. Perhaps those that convert rail internally. Definitely not normal opamps.

 

[audio_tony]

<snip>
27 mW into 300 ohms is 8.0 Vpp, which is realistic to expect out of a 12 V supply. (14 mW would mean 5.7 Vpp, again a fairly typical value out of 9 V.) You could probably get 9-9.6 Vpp out of the thing with an OPA2132/34 or NJM4556AD. Those serious about output power into higher-impedance loads (250+ ohms) would have been building a dual 9 V (split supply) cMoy, which may have provided up to 4-5 Vrms out and as such close to 80 mW into 300 ohms..
<snip>

A while back I ran some load tests (with headphone usage in mind) on a group of opamps and the OPA2134 didn't do very well.

All tests were run with a 15-0-15 psu.

Surprisingly, the NJM2068 was second to the LM4562 which came out on top.

NJM2068

LM4562NA (I think the 4562 was oscillating a little which went unnoticed at the time but that's why the LF region is so noisy).

NE5532

 

[frogmeat69]

Gotta slow down on trying to eat all of your harvest, no wonder your septic tank is full, that's a lot of fiber. Don't you have neighbors?? lol

 

[raindance]

If someone is looking for a project to do with a young person, I'd highly recommend the Pete Millett headphone amp, the Butte. It sounds very good.

 

[Milesian]

Good look with the septic tank. I had to replace a whole system a few years ago. $25000 and I had to cut down 70 cedar trees to clear an area for the new raised bed.

 

[infinitesymphony]

Some people were running these with two 9V batteries in series (18V). Would this impact power handling?

 

[Count Arthur]

Has anyone got a Grado RA-1 heaphone amp? It would be interesting to see how it compares to the Cmoy and some of the really well performing amps from Topping and JDS Labs, etc..

I remember there being a bit of a scandal about these a while back when it was revealed that they were little more than a Cmoy, and maybe $20.00 worth of components, in a wooden box with a ~$300 price tag.

 

[audio_tony]

Some people were running these with two 9V batteries in series (18V). Would this impact power handling?

More power supply voltage will provide a greater output 'swing' (more output voltage) into a given load, which will mean lower distortion for a given level, as the amplifier is not being pushed to it's limits.

 

[preload]

Unless it's intended to measure poorly, no device should be treated differently. It does not matter if it's designed for high impedance.
In fact, there's literally no design almost at all. No sign of optimizing for high impedance load.

The chart you gave is very old. Fiio, topping etc have several portable devices measured with way higher power than 14mW.

I think you're right John. I'd like to suggest that we test the Topping NX4 DSD unit at an output of 100mW (Amir's standard) while driving 300 ohm headphones. That should give us a THD+N around 1%? Maybe 2%? 10%? Anyone know?

No device should be treated differently.

 

[infinitesymphony]

More power supply voltage will provide a greater output 'swing' (more output voltage) into a given load, which will mean lower distortion for a given level, as the amplifier is not being pushed to it's limits.

I wonder how a CMoy with 18V, decoupling capacitors, and LM4562 would compare. Maybe I'll dig mine up.

Here's a link to my parts list. The gain ended up at around 5.5.

 

[amirm]

I think you're right John. I'd like to suggest that we test the Topping NX4 DSD unit at an output of 100mW (Amir's standard) while driving 300 ohm headphones. That should give us a THD+N around 1%? Maybe 2%? 10%? Anyone know?

No device should be treated differently.

??? The 100 milliwatt is not a pass or fail criteria. It is my target that I like to see amplifiers meet. The NX4 DSD gets 60 milliwatts which is very good for a portable product. It is hugely better than the product tested here seeing how at the point it produces no distortion. It is also very capable with 33 ohm load producing 147 milliwatts whereas the CMOY tested here has no usable response with that load.

Anyway, my subjective remarks are from my overall experience and feeling about a product. It is an additional data point above and beyond what the measurements say. If all you want to go by is measurements as you ask, then you should just ignore my opinion/recommendation and do just that.

 

[jasonhanjk]

My target amp should achieve 0.001% or less at 32 ohm 4mW; 0.0009% or less at 16mW.
With output reaching 1Vrms without clip.

Too much gain will increase it's noise level and also push the THD to a higher power level; which I don't listen to.

 

[xarkkon]

I might be wrong, but is this the first ever decapitated recommendation? Cool!

 

[solderdude]

I have tested some different opamps in a simple circuit as well (using a scope) about 8 years ago.
It uses a TL2426 rail splitter, has 4 Ohm output R and is measured at 9V and 18V.
Measured with 30, 60, 120, 300, 600 and 10k loads.

 

[audio_tony]

I have tested some different opamps in a simple circuit as well (using a scope) about 8 years ago.
It uses a TL2426 rail splitter, has 4 Ohm output R and is measured at 9V and 18V.
Measured with 30, 60, 120, 300, 600 and 10k loads.

It's interesting to note you had oscillation issues with some opamps.

In my standard test jig, all the opamps I have work just fine with one exception - the LM4562 which oscillates at about 380kHz when connected to any cable longer than about 40cm. Even series resistors in the output don't help.

This is at a low gain of around 2x as well - even a cap across the feedback resistor doesn't help. So although it may be a good opamp, it seems to be difficult to stabilise.

I first suspected an issue when I used a pair of them in my CD player - and I noticed the sound became sibilant and bright. Putting NE5532s back in solved that problem!

 

[solderdude]

Most problems occur when clipping (current- or voltage-clipping also makes a difference).
People may be doing this sooner than they think.
At 9V and 300 Ohm headphones won't play impressively loud and even decently loud may have some voltage clipping.
For lower impedance headphones current clipping is right around the corner.

For 'normal' listening levels these amps will probably stay below problematic behavior and actually sound quite good.
When using high impedance headphones 18V (+/-9V) is about the minimum required for louder listening levels.

 

[JohnYang1997]

Most problems occur when clipping (current- or voltage-clipping also makes a difference).
People may be doing this sooner than they think.
At 9V and 300 Ohm headphones won't play impressively loud and even decently loud may have some voltage clipping.
For lower impedance headphones current clipping is right around the corner.

For 'normal' listening levels these amps will probably stay below problematic behavior and actually sound quite good.
When using high impedance headphones 18V (+/-9V) is about the minimum required for louder listening levels.

I decided to make an upgrade to the NX1s. Though practical speaking 2V into hd600 and dt880 600ohm should be very loud. Whats important is to make sure there's no distortion before clipping.