Originally Posted by runeight
So, would this mean that the hiss is dependent on the impedance of the heaphones and not their sensitivity? That is, high Z sensitive heaphones have less hiss than low Z not-so-sensitive headphones?
If so, then the hiss would have to be buffer related somehow.
I'll have to double check, but my IEMs have the hiss really loud and I believe it's sensitivity is around 120dB (crossroads mylarone x3). I have some other IEMs I can try.
I know I tested it with my other headphones, and heard a slight hiss with the K81DJ (32 ohm, 115dB/mW) and ATH-ANC7 (260ohm, 109dB) and DT-660 (32 ohm, 96dB). I have tested, but can't recall how loud it was with my M-Audio Q40 (64 ohm, 116dB/mW). I don't hear it with my DT-990, HD650, and K240 Sextett.
The sensitivity ratings don't list the reference points for all the headphones, so it's hard to say if it's dB/V or dB/mW. Anyhow, it does seem to be more closely related to sensitivity, as the ATH-ANC7 is up there in impedance as well as sensitivity.
I think it's in agreement with FA.
Tubes removed, I hear no hiss. It definitely is something in the VAS stage, but where exactly it's hard to say. I did try turning down to 55V and it was quieter, and turned it back up to 95V and it was noticeably noiser. The regulator is worse at noise rejection in the higher voltages. So, it could still be the HV.
I have pics of my reg I can upload in a few days.