I wouldn't call it a veil, but they do tend to sound less of what they should when they are under powered.
I just tested at low volume (Magni 3 amp on lo-gain setting, volume pot at 8 o'clock). I don't hear anything like that, the sound is still very detailed and I can hear everything clearly. Turning the volume up just makes it louder. I don't know what gear you are using but here are a couple of thoughts about low level veiling:
How are you controlling volume? A DAC should be used at full output or at least not attenuated too much or it may lose bits (resolution). For every six decibels dropped, you lose 1 bit. If a DAC is 16 bits this can become a problem quickly. Most current DAC's use 24 or 32 bits, so should not be a problem, but worth considering.
I have a Topping TP21 chip amp that has a potentiometer on the input for level control. There is no buffered preamp section. The pot acts like a passive preamp ahead of the power amp section. IME, passive preamps are very transparent but they suck the life out of music. The Topping sounds best with the pot fully open, basically out of the circuit. Trading PRaT for transparency is a bad deal. The Magni 3 has a proper buffered preamp. Input impedance does not change with frequency, nor does the sound.
Thanks for your replies!
I was using two systems:
1) DFR >> Bottlehead Quickie+Quicksand
2) RasPi+HiFiBerry DAC+ Pro >> Peachtree nova65SE
I think I was getting similar result with both systems...
On the DFR Bottlehead system, I do a combination of volume control through the computer and using the (stock) pot on the Quickie. I believe the DFR uses a lossless digital volume control, so I don't think that's causing any problems (when I use it by itself with other headphones, I don't hear any degradation of sound).
On the Peachtree, I wouldn't be surprised if the volume pot is just a relatively cheap one.
My main reason for asking is that I did a minor mod to the Quicksand so that it's more compatible with headphones, but I almost immediately noticed something like a veil at less-than-too-loud volumes. At first I thought it was the mod I'd done, but then I realized it might just be that it was always too loud before the mod, so I wouldn't have noticed a problem that occurs at somewhat lower volumes. I'm thinking of upgrading the pot on the Quickie to either a fancier pot or a stepped (ladder?) attenuator, but I don't want to throw money and parts at it until I know it's going to solve the problem. I'm asking here to eliminate the possibility that it's the headphones causing the problem... Which I'm willing to accept as being eliminated.
Now I just need to narrow down whether it's my ears or the equipment.
I hadn't thought of testing it with just the DFR, but maybe I'll do that, too. Maybe I'll test it with some other 'phones too. (sorry, just thinking aloud here)
PS-- I want to repeat myself: thank you guys for the answers! Honestly! I tried asking at the Bottlehead forum and they seemed less than enthusiastic about answering. At least the BH staff did. Just kind of a "learn by doing not asking" (a.k.a., "I don't feel like answering your questions") type of answer. Maybe my questions were vague or stupid seeming... But I think there's a saying about stupid questions and stupid answers...
Anyway, it often takes a negative experience to make one realize precisely how good a positive experience actually is. So THANK YOU (again) for putting some effort into your answers. I really do appreciate it!