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Speaker hum problem - need help

I've searched the forums and have seen past posts for this topic, however, I've yet to find an answer that fits my situation.

First, here's my equipment:
Coda CSib integrated amp
Ayre QB-9 DSD DAC
Auraliti PK-90 USB server
Dynaudio Focus 380 speakers
Audience Au-24 speaker cables
Cardas Clear XLR interconnects
Cardas Clear & Grover Huffman power cords
Wireworld Platinum Starlight USB

Here's the problem:

With only the amp plugged into power and the speakers connected, I get a 38 db invariant hum coming out of the speakers. The hum does not change no matter what the volume is on the amp. The hum does not change regardless of whether I have the amp plugged into the: wall, a power strip, or a power conditioner. The hum does not change regardless of power cord connected to it. The hum does not change when I plug in the remainder of components and cords into my system.....it is invariant.

I have tried to "lift the ground" with a 3/2 cheater plug, but this had no impact. I sent the amp back to the factory to be checked out and slightly upgraded; they could not reproduce the hum at the factory. A previous amp (tube) produced the same issue, however, with the tube amp, the hum got worse as the volume was raised.

I love the overall sound of this system, but this hum is definitely getting in the way of my enjoyment. Any thoughts out there about what is causing this problem and how to correct this issue?

Many thanks,

Matt
mwsl
mwsl OP
52 posts
 
Went over to fellow Audiogoner drubin earlier today (thanks Dan!!) to try my amp in his system. Had the same exact problem occur in his system that I do in mine; hum coming through speakers when as little as (any) power cord and speaker cables are plugged in. He heard it too!!

Looks like my amp has a problem. I just contacted Coda and am waiting for a response. Odd that they claimed to have not heard it when it was at the factory less than a month ago. This time, I'll bring it in myself, and make sure that I have someone there listen to it with me. Fortunately, they're only about an hour away.

(As a complete aside.....I almost bought a highly regarded integrated from a european manufacturer before I purchased the Coda. They were offering a screaming deal (I know it was legit). I kept on musing about "if there are any problems with this, how am I going to get this fixed?" Glad I listened to that little inner voice and bought domestically (and, locally, as it turned out).

I'll keep you apprised as this saga continues. Kudos to those that thought it was an amp problem all along. You get extra points for that call :-)

Matt
grannyring's avatar
grannyring
6,471 posts
 
Power supply cap:-) been there, done that and your comments point
straight to it. I would be most surprised if it was anything else. Can't say
with 100% certainty, but perhaps 80% certainty!
mwsl OP
52 posts
 
I got a response from Coda within 2 hours. They want the amp back at the factory, and will pay for shipping both directions. They verified that they had listened to the amp through their speakers, and could not hear the hum.

The hum is stable at about 37 db, and is audible in my listening position 9 feet away from the speakers when there are quiet passages in the music (or when no music is playing). Is this level of hum normal in quality sound systems?
mwsl OP
52 posts
 
Jim (Jea-48) - just curious if you could say more about what/how to do the AM radio experiment. Should I actually tune into a station......or just set it to the very beginning or end of the band? What am I listening for if I set it to the station....I have very poor reception around here as I'm in a very hilly location?

Just curious about this suggestion.

Matt
zd542
5,339 posts
 
"06-06-14: Mwsl
I got a response from Coda within 2 hours. They want the amp back at the factory, and will pay for shipping both directions. They verified that they had listened to the amp through their speakers, and could not hear the hum."

I think that's good news. Fixing the problem at no cost to you is the best solution. I suspect that when they had your amp the first time, they were just careless. They probably tested it to see if it worked, but didn't do any critical listening. Yes, that's not good, but I think you'll get your amp back working properly.
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