I have stated this question on another thread, but it has gotten locked, and hopefully I can get a good explanation this time. I'll try to be clearer with my question this time.
I was curious why my tube amp(Elekit TU882) would cause hiss even at it's lowest impedance setting( 4-32ohm), but my Audinst HUD-mx1(DAC/SS amp) would not. In addition, my JDS labs CMOY would output hiss at null volume. Hiss is outputted on what I believe to be very sensitive IEMs such as UM3X, 1964-T customs, or ER4P. My Sony X1051 outputs hiss at null volume, but my Sony NWZ S636F does not, even with sensitive IEMs.
All are audio sources so I assume the parts used are audio grade. So far, what I believe has to do with hiss is output impedance being much greater than the impedance of the headphones. Another poster have stated that too much current going through the transducer(probably because the low impedance of the IEM), but I don't think that makes much sense. What doesn't make sense is adding a impedance adaptor for ER4P supresses hiss(which adds to output impedance), but output impedance close to 0 is ideal. It contradicts the theory that high output impedance causing hiss, although the adaptor is resistive. I know sensitivity has to do with hiss because obviously all the IEMs that I have listed have high sensitivity, but I really don't know the relationship with the different signal sources. I know that thermal noise is picked up by the conductors and resistors in the circuit(my CMOY hisses even with metal shield, it's just not picking up RFI or other nearby noises), but what I am trying to get an understanding of is is what type of circuit configuration will create hiss with sensitive IEMs. My amps and CMOY have audio grade parts. I'm looking for an explanation on this so that I would be more knowledgable in what kind of specs to look for when I pick out my sources for sensitive IEMs.
Edited by High_Q - 6/19/11 at 7:48am