maybe-i use shielded ic from bluejeanscables.com. inexpensive, custom built and good quality.
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Are both speakers plugged into the same outlet? If not, try using an extension cord and plugging them into the same outlet. This fixed a hum problem in my active speakers. It could be a ground potential problem between the two different outlets, or between the speaker outlets for the active speakers vs the outlet for the pre-amp/processor. You can also try 2-prong cheater plugs if the speaker PCs are 3-prong.
Thanks all. After some experimentation it seems it may not be the IC after all - or the grounding, for that matter. The ICs (with its current routing maintained) when connected directly to the line level source which normally goes into the MC preamp results in no hum coming from the speakers. Since all my sources are connected to the same power conditioner I figured it also isn't a grounding problem, but for kicks I lifted the ground on the MC preamp - no difference. Since my MC preamp has both analog and digital inputs I tried one of the digitals for this source - hum went away.
So if this source's analog out produces no hum when connected directly to the speakers, and it does when connected to the MC preamp's analog (but not digital) inputs - and it doesn't appear to be a ground problem - I've decided to contact the manufacturer and see what they have to say.
Reubent, I did also try your suggestions and there was no change.
- and it doesn't appear to be a ground problem -
...buuutt it is. It's the new power cord I'm using on my PS Audio PWD. I was previously using a cord where I lifted the wire to the ground pin because of a ground hum problem with this DAC. I completely forgot about that when I replaced it with a different cord - the ground hum is only audible on my front speakers when you're right up in front of them. Apparently on the active rears it's much more audible. Sigh.