I don't care what you or other people have heard. I'm saying on my unit - I hear no hum. I have my TH-900 on right now. Music off. L / M gain volume turned all the way up - nothing. With the H gain - I do get a slight hum - very slight. But why would I have it on H gain with these headphones???
So Yes when listening to music on M / L gain with the TH-900s - I don't hear any hums..
WOW I was just reporting I'm not getting this hum. Now something must be seriously wrong with my hearing. ha ha ha you guys make me laugh..
I get noise at high gain & high volume too (which sounds more like a hiss than hum) but the noise I've been referring to is an electrical hum, sort of like the buzzing that large electrical systems manifest but on a much smaller scale, directly in line with Justin's earlier post: "The transformers are also 66% larger so there is a larger magnetic field. To get the benefits of the separate PSU the amp needs to be placed away from the power supply; either side by side or at least 8" of vertical separation." If you can hear the high gain/high volume hiss, I'm not sure why you wouldn't also hear the transformer hum (which was audible to me at any gain setting or volume level down to Low gain and zero volume).
Perhaps it was out of line for me to say that something has to be wrong with your hearing (and for that I now apologize) if you didn't hear the effect of said magnetic field on the amp, but that magnetic field applies to every MK2, not just mine or 1 other person's. My earlier post was merely a counterargument for your statement that you didn't hear it - just because you didn't hear it, doesn't mean that it's not there, because the electromagnetic interference is there as a scientific fact (no this isn't the Sound Science forum, but that merits pointing out). I guess some people just can't hear it for whatever reason.
Update: I did some experimenting and found that the transformer hum lessens when the PSU is placed on top of the amp, so that could be a solution for anyone else that's bothered by it and doesn't have space to separate them. However, I'm not sure stacking the PSU on the amp is a good idea because the amp gets hotter than the PSU and probably needs ventilation more as a result. I'd highly suggest risers for anyone who intends on stacking the PSU on top of the amp. (Don't listen to this advice, see Justin's post below!)
Update #2: I also found that the AD2K is actually more sensitive to the transformer hum than the TH900. The AD2K seems to be about 150% louder than the TH900 on the transformer hum, and I can actually say that the hum is almost completely inaudible on the TH900 at low gain (but I can still still hear it faintly), but clearly audible on the AD2K. So I guess whether one can hear it or not also depends on which headphones are used.
The hum went completely inaudible on the TH900 only when the PSU was on top of the amp (configured to low gain), but that's the only way I got it to be completely inaudible. I heard it on the TH900 with every other gain setting and/or with the amp on top. And I still heard it on the AD2K even with the PSU on top, at low gain, so I still have to use the MK2 separated in order for it to not distract me.
Note: I deleted previous references to volume settings, because volume didn't affect the level of the transformer hum, only hiss on high gain.
Edited by Asr - 3/17/13 at 4:50pm