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Power available and distortion

post #1 of 30
Thread Starter 

Ok, lets say you have two amp of different power output rating.  One outputs twice as much power.  Also the max voltage much greater with greater headroom for swing.

 

The one that is less has enough according to specs to give sufficient loudness output for power in.  The other have more than sufficient.  Would one of these output significantly more distortion than the other?  As far as to cause significant affect on the sound output of the headphones?

post #2 of 30

Look you need more specifics if you are really looking for an answer.  Is amp A specified as having the same distortion level as amp B?  For instance a SS amp might be spec'd as 100 watts at .02% distortion.  Yeah, you can be sure at higher power the distortion goes up.  Though without more details of the amp and its load you don't know how much.  A tube amp might be spec'd at 100 watts at 2% distortion.  It too will go up with higher power.

 

2% might be audible, anything below .1% usually can be considered inaudible even with test tones.  With music even 2% might be inaudible or inaudible most of the time. 

 

So what really is your question?  Distortion below .1% under use is not audible.  With music you pretty well can consider 1% or less inaudible under use. 

 

Going back to your question.  If amp A, the lower powered one is nevertheless capable of playing your headphones to full volume level you use at low enough distortion to be transparent, then amp B with even more power won't sound any better, worse or different assuming your output impedances and such are handled well with both amps, and both have flat frequency response over the audible bandwidth.

post #3 of 30
Quote:
Originally Posted by SilverEars View Post
 

Ok, lets say you have two amp of different power output rating.  One outputs twice as much power.  Also the max voltage much greater with greater headroom for swing.

 

The one that is less has enough according to specs to give sufficient loudness output for power in.  The other have more than sufficient.  Would one of these output significantly more distortion than the other?  As far as to cause significant affect on the sound output of the headphones?

 

There's no way to tell without much more detailed measurements. Ideally, you want a distortion vs output level plot at several different load impedance values. It's possible that the higher peak output amplifier has higher distortion at all output levels, or it might have lower distortion than the lower output amp. It might be better at driving low impedance loads, or it might be better at driving high impedance loads. All you can say based on what you said above is that it has a higher peak voltage capability and a higher peak power output (which, if they're from different manufacturers or specified differently, might still not mean much - maybe one amp's peak power is specified at 0.1% THD, and one at 10% THD).

 

For an example of this, look at the specs on the Denon AVR-X3000. It can put out 105 watts per channel full spectrum (20-20000Hz) at 0.08% THD at 8 ohms, 135 watts per channel at 1kHz and 0.7% THD into 6 ohms, and 215 watts per channel peak (no distortion or impedance figure specified). So does this mean that this is a 105 watt amp? 135? 215? You could argue that the 105 number is the most realistic, since it is full spectrum into a normal speaker load, but the way some headphone amp manufacturers rate their output, this would be a 215 watt/channel amp. At the end of the day, unless the power output of the amp is specified at a specific impedance, distortion level, and frequency, it's impossible to know.

 

Oh, and as for the final question, any two competently designed amps that can both drive a pair of headphones to adequate volume will sound identical. If a pair of headphones requires 0.5 watts at the peak volume you will ever listen, a good 0.75 watt amp and a good 25 watt amp should both sound the same. If anything, you might have some problems with the 25 watt amp unless you have an adjustable gain structure, since you will be down at the very bottom of the volume range. If it uses an analog volume potentiometer, this can lead to channel imbalance issues. Also, most amplifiers have more THD+N at extremely low output (mostly due to the electrical noise) than they do at moderate output.


Edited by cjl - 5/19/14 at 9:51am
post #4 of 30

Distortion is not usually an issue with decent solid state amps. Power and features are what count.

post #5 of 30

What about IMD? Doesn't that matter too? 

post #6 of 30
Quote:
Originally Posted by davidsh View Post
 

What about IMD? Doesn't that matter too? 


That falls under the category of "distortion", which, as bigshot said, is usually pretty negligible in any decently designed modern solid state amp (which does leave out some audiophile designs, as well as a great many headphone amps, but pretty much any speaker amp from a reputable company should fit that description).

post #7 of 30
Quote:
Originally Posted by cjl View Post
 
Quote:
Originally Posted by davidsh View Post
 

What about IMD? Doesn't that matter too? 


That falls under the category of "distortion", which, as bigshot said, is usually pretty negligible in any decently designed modern solid state amp (which does leave out some audiophile designs, as well as a great many headphone amps, but pretty much any speaker amp from a reputable company should fit that description).

IMD isn't part of THD to my knowledge? 

 

Again, IMD is pretty hard to measure with real music playing so I guess you can't know for sure that IMD doesn't play a role with a specific amp?

post #8 of 30
Quote:
Originally Posted by davidsh View Post
 

IMD isn't part of THD to my knowledge? 

 

Again, IMD is pretty hard to measure with real music playing so I guess you can't know for sure that IMD doesn't play a role with a specific amp?

It isn't part of THD, no, but it is distortion. As for measuring distortion with music playing, sure, that's hard. That's why you measure it with test tones instead. Pretty much every decent modern solid-state speaker amp passes this test easily.

post #9 of 30
Quote:
Originally Posted by cjl View Post
 

It isn't part of THD, no, but it is distortion. As for measuring distortion with music playing, sure, that's hard. That's why you measure it with test tones instead. Pretty much every decent modern solid-state speaker amp passes this test easily.

I don't quite like taking your word for it, though I *believe* you are right on that one ;)

 

In general, there's THD, IMD and the noise floor/SNR. Anything else of importance (not considering stuff like radio waves, grounding problems, whatever, introducing distortion etc.)?

post #10 of 30

Well, there's also output impedance and crosstalk, though both are more of a problem with headphone amps than speaker amps. There's probably another spec or two that I'm forgetting about (but I'll edit this post or add another if I remember).

post #11 of 30

Why do so many headphone amps perform so poorly? I have a little Altoids tin cmoy and it works with whatever I throw at it just fine. It seems to me it should be easier to design a transparent headphone amp than it is an amp for speakers.

post #12 of 30
Quote:
Originally Posted by bigshot View Post
 

Why do so many headphone amps perform so poorly? I have a little Altoids tin cmoy and it works with whatever I throw at it just fine. It seems to me it should be easier to design a transparent headphone amp than it is an amp for speakers.

I think because the lower cost of entry into the market allows for a lot of relatively untested designs, often designed by someone who doesn't fully understand what they're doing. There are also a lot of great, inexpensive headphone amp designs out there, you just have to be careful when buying one to make sure you get one of the good ones, not one of the bad ones (which does not require spending a ton of money).

 

As for the cmoy, from what I've seen, it actually measures quite well - some of them might have a very slight channel imbalance issue at lower volume, but that's both normal and pretty negligible. Also, the measurements I saw showed that at least some Cmoy amps have unity gain at full volume, which could be problematic if you want to drive hard-to-drive or high impedance headphones, or if you have a quiet source. That seems to depend on the layout used to build the cmoy though - changing out a couple resistors results in plenty of gain, so again, this isn't a huge problem unless you both get a version of a cmoy without gain and are unable to swap out a couple resistors. Overall, the cmoy seems to measure better than several "high-end" headphone amps, so as long as you aren't trying to drive any particularly difficult to drive headphones with it (peak power isn't that high with the cmoy, especially for a low-impedance headphone), it should work great, and sound basically audibly perfect.

post #13 of 30
Quote:
Originally Posted by bigshot View Post
 

Why do so many headphone amps perform so poorly? I have a little Altoids tin cmoy and it works with whatever I throw at it just fine. It seems to me it should be easier to design a transparent headphone amp than it is an amp for speakers.

Solution: Use a speaker amp with headphones ;)

 

Possibility of lowering the gain and a circuit with low noise figures might get you there? Then use the O2 for the sensitive stuff that the speaker amp is too noisy for.

 

Any thoughts on 'stat amps and transformers, that sorta stuff? With 'stat amps the output voltage is actually an issue with regards to headroom it seems to me..

post #14 of 30
Quote:
Originally Posted by davidsh View Post
 

Solution: Use a speaker amp with headphones ;)

 

Possibility of lowering the gain and a circuit with low noise figures might get you there? Then use the O2 for the sensitive stuff that the speaker amp is too noisy for.

 

Any thoughts on 'stat amps and transformers, that sorta stuff? With 'stat amps the output voltage is actually an issue with regards to headroom it seems to me..

 

That might not be a bad solution, so long as the speaker amp doesn't mind the shared ground and the noise floor is low enough.

post #15 of 30
Quote:
Originally Posted by davidsh View Post
 

Solution: Use a speaker amp with headphones

 

Actually, I do that... and I use the headphone jack on my iMac unamped with no problem.

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