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

HELP! How do I eliminate Hum? I just bought a demo, Pass XP-22 and X250.8. 60Hz hum is audible across the room at no volume. It’s only a 60Hz hum, not 120Hz/buzz. Here’s the setup into same AC wall plug.

Amp only (no Preamp): Very slight hum audible inches from speaker
Amp + Preamp: 0 Volume: Slight hum audible 6 ft away
Amp + Preamp: 01 Volume: Slight hum audible across room.
Amp + Preamp: 99 Volume: Moderate hum audible across room

I tried the following without any success:
- Connecting CDP
- Used different interconnects
- No cables touch nor cross.
- Separated the preamp from the power supply module.
- Used different AC outlets
- Used different AC Power strips for testing
- Each unit on different rack.

My integrated amp doesn’t have this problem.  The sonics are great, except for the annoying hum. I have 9 more days of trial period... How do I solve the hum issue without killing the sonics?


88man
88man OP
28 posts
 
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.

atmasphere's avatar
atmasphere
11,760 posts
 
@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.
speakermaster
738 posts
 
Try a different outlet on a different circuit completely it cold be that something on the line is affecting the setup.
adg101
1,062 posts
 
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.
88man OP
28 posts
 
I’m going to relocate the Pass XP-22 to another room. I’m using unbalanced RCA IC. I’m going to call Mark @ Reno.
I used the Pass X250.8 with my D. Sachs 6SN7 Tube Preamp - Dead quiet!
I ordered an Emotiva CMX-2 (Humdinger was out of stock). I’ll try the Cheaters too tonight.
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