As I am about to enter into the world of headphone amps, This thread caught my eye and I've read all the replies so far.
Before I get going, excuse the low post count here. I have a long obsession with all things audio and used to test/review for a car stereo magazine, and have a M. Eng, so know a few things (and also don't know a lot of things).
Originally Posted by streetfighter
Would like to bump this thread again, as I have the same question. Not sure which way is right or wrong?
Possibly important enough to be a sticky if some sort of definitive answer can be found.
Originally Posted by c64
Low volume on pc/soundcard and adjust headphone amp is the way to go.
No idea why people go around saying put pc volume at 100% and adjust amp, they are just wrong.
You will get distortion and clipping the higher you go.
I'm going to disagree quite strongly (although actually 100% output may be slightly too high, perhaps around 95%), and part of the reason is based on the loading of the circuit.
When using a headphone jack (due to there being no line-out), that headphone jack needs to be taken up to near the maximum output to get near the voltage levels of a line out. Most amplifiers are designed to work with that level as their input. anything lower and you need to take the amplifier up to near its maximum to get the level you want (because you made the input level too low).
HiFlight's quote is spot on as it comes down to S/N ratio, continued below the quote...
Originally Posted by HiFlight
Although this topic could be argued pro and con endlessly, I have always run the source near max for best s/n ratio as well as for maximum dynamic range. Below is an excerpt from a professional sound recording site that may be of value in understanding the rationale for a high source level. Although we are considering a headphone amplifier, for all practical purposes, it can be considered the equivalent of a mixer.
Maximising the dynamic range
All equipment has dynamic range. This is the range between the quietest and loudest signals it can accommodate, or between the noise floor (beneath which a sound cannot be heard) and distortion. A signal entering a mixer needs to be as loud as possible without overloading the circuitry and causing distortion.
Setting the best signal to noise ratio
All circuits produce a fixed level of noise (hiss). If the source signal is loud enough this noise will be less noticeable.
So, whatever your view might be, your final stage amplification will be amplifying everything from the input. All devices have some noise, so noise cannot be ignored. If the amplifier is taken to near to its top end of amplification, it will be making that input noise the loudest possible level it can be, so you WILL hear it.
This means that you definitely do want the strongest 'clean' input signal with the highest S/N ratio you can get without distortion.
The critical factor here is with a headphone output, it is designed to run a high load (low impedance) so can deliver current to drive the coils of the speaker. When connected to the input of an amplifier, the impedance is much much higher (~10kOhm), so it draws very little current (the lower current the better) and is better able to avoid voltage sag and clipping.
There is no way to determine the correct level to set the headphone output using headphones to 'listen' for distortion, because as soon as you remove the load, and perhaps use an oscilloscope to monitor the output for clipping, the output will recover and no longer clip.
One could argue that the characteristics of the headphone output's amplifier can be avoided if running it at a very low level, but you definitely will end up with a low S/N ratio and you will hear hissing.
Using a headphone jack as a source is often the only option, but these can remain distortion free to a far higher level when connected to a line-in than when they drive a low impedance load.
Interestingly there is an analogy to the source/amp level configuration in the car hifi world as all power-amps are designed to sit at a fixed gain and the volume is then controlled by the source components, However, a critical point in this case is that all the components are designed specifically to run like this. (Of course so are pre/power-amp HiFi systems). IF, and I really mean IF, a headphone amp was supposed to be used like this, then it would not have a volume knob on it; there would be a relatively inaccessible 'gain' control that you set once and leave.
I am open minded about this, but reviewing these facts, I just can't see a good argument for using the headphone amp at maximum volume and using the source to control the output level.
(A small note regarding 100% settings - generally I would avoid ever using something at 100% as fully loaded you are more likely to see/hear the subtle differences in some components. I would go with 90-95% as a practical maximum in most cases.)
Edited by subwoofer - 8/24/16 at 1:09am