How to Eliminate Hum? CDP + Pass Preamp + Amp Setup.

@88man 

Hum is a very specific sound. You can't hear it in the midrange or tweeter. I am assuming this is what you are hearing with the following comments.


Don't worry about hum if you can only hear it 6" from the speaker. That is pretty common. But the fact that the addition of the preamp causes the hum to be so much more audible is an important clue. Another important clue is the fact that the hum is affected by the volume control. If this were a ground loop problem or anything caused by the AC line you would be hearing a buzz, which is audible in the tweeter.


You did not mention if the CDP was connected or not when the hum was noticed with the preamp. If it was connected, disconnect it and see if the hum is still there. If yes, return the preamp for service- the hum should not increase with the volume; this suggests a filter capacitor problem in the power supply of the preamp.

If the hum goes away when the CDP is disconnected, have the CDP serviced out. Digital devices can make all sorts of sounds including hum when things go awry.

The CDP has makes no contribution to to hum. It’s only between the Preamp and Amp. The hum is audible from across the room. Nothing is connected in the room. I even turned off the lights, hum still present.

My $200 receiver (2-conductor PC) is dead silent at max volume on the same outlet. The house has never had noise/hum issues on any equipment. I’m going to order Hum X and Emotiva CMX-2. I’m discouraged and worried since I only have 8 days to sort this out.

@88man The preamp is having a problem. If you can send it back I would do so. If your integrated amp is alright, its pretty safe to assume that there are no problems with the AC line.

Try a different outlet on a different circuit completely it cold be that something on the line is affecting the setup.

I’d suggest calling Pass Labs directly or drop them an email sooner than later. Doesn’t surprise me you’re integrated isn’t having a ground hum as it’s one device not two on the same circuit. For the fun of it, off another electrical circuit such as another part of your home, run a long extension cord to the preamp and see if that changes things... make sure it’s indeed a separate circuit so you might have to flip some panel breakers. Are you sure the receptacles are indeed grounded and not just an outlet with a ground socket and the ground is only floating? I wouldn’t suggest it long term but go to any hardware store and buy two cheaters to float the ground on both the preamp and amp; if the buzz is gone it’s likely an electrical issue and then call a electrician for the fix. That preamp and amp should be dead quiet even with very efficient speakers.

Are you running balanced IC’s or single end? If single ended are the pins in the XLR sockets on the amp? If you’re running single ended you might want to try balanced.