[RichardS]

I need help with a buzz that's only there when my new DAC is inserted into the system.
I recently purchased an Audio Logic 24 MXL DAC and it sounds really, really nice, except for the buzz. Specifically, there is a buzz/hum (more of a buzz, though) that comes through the speakers when the DAC is inserted. It's loud enough to hear from my listening seat and bothers me when the system's on and I'm reading without any music playing. I don't hear it when music's playing.

I have tried disconnecting my cable TV feed, and I used a cheater plug to every component in the system with no success. I've changed the tubes with new ones. I've inserted a different amp (two actually, both SS) and another CD transport and the buzz is still there. I've used different digital inputs on my Tact preamp.

I've tried every input and both RCA and XLR outputs. If I change the input on the Audio Logic front panel to 'aux' the sound changes slightly but doesn't go away (the highs in the buzz are reduced, but not in the mids). Only when I insert my Tact 2150 in place of the Audio Logic and amp, does the buzz go away--completely. Totally silent without the Audio Logic DAC in. Also, when putting another DAC in place of the Audio Logic, the buzz goes away. So, it's some weird interaction between the Only when I insert my Tact 2150 in place of the Audio Logic and amp, does the buzz go away--completely. Totally silent without the Audio Logic DAC in. Also, when putting another DAC in place of the Audio Logic, the buzz goes away. and the rest of my system.

It is slightly louder in the right speaker than the left. When I put my ear to the tweeters it is definitely a buzz sound. At the mid/woofers it's a bit of a cross between the two.
It's really not all that loud, but if I'm sitting in the room reading with the equipment on, but no music, it's a bit irritating; and I feel a sense of relief when I turn the equipment off.

Frustrated, I sent the DAC to Jerry at Audio Logic. He kept it for a week and went over it with a fine-tooth-comb, and checked all connections. He was unable to reproduce any buzz. Worked perfectly in his system. I got it back and the buzz remains. IMS, it's there anytime I put the DAC in.

Any ideas???? I love the sound of this DAC, but if I can't resolve my buzz problem I'll probably sell it.

[ckoffend]

Sounds like a ground loop hum.  Surprised the cheater plug did not work (at least for testing). 

There are two things you may want to try (having just gone through a similar process, but with an amp):

#1:  Are you connecting the interconnects that have directional arrows on them?  If so, this is a grounding related arrow (the direction only applies to the ground).  Try running these backward - pointing in the opposite direction of the music.

#2A:  Disconnect any inputs from the dac and just keep the output from the dac to the pre-amp.  Is the hum still there?  If so, try a direct chasis ground from the pre-amp to the dac (unscrew a chasis plug on each and connect a wire between the two before re-installing the chassis screw).  This is safe, you are fine.

#2B: If the hum goes away when you unplug any inputs to the dac, then you have a loop with one or more of your source components, plug them into the dac one at a time until you hear the hum (note, only plug one it at a time - unplug the previous one if there is no hum).  If you plug them all in, but only one at a time and there is no hum, then plug in one source to the dac and keep that one plugged.  Then plug in the one at a time other sources.  It could be as simple as a ground loop between these sources.  Have you tried the cheater plug on any of the source components?

I have a PDF file on a sure fire way of finding ground loop hums.  You need a volt meter and it takes maybe two hours, but you will find the source of the problem.  If you want me to e-mail it to you I can (ckoffend@getechaus.com).

Hope this helps.

FYI - cheater plugs are not designed to be a permanent fix, just a good source to help identify the problem.