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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

Showing 3 responses by zd542

zd542
5,339 posts
 
You said that you sent the amp back to the factory and they couldn't find anything wrong with it. Assuming the amp is OK, I would try 2 things. The first would be to connect a different pair of speakers just to rule them out as the problem. If the hum is still there, try the amp in a different location. Maybe in a friends system. That will tell you a lot about what is causing the hum.

One thing you really need to do before making any decisions or spend money is to hear the amp working without the hum. If not, you can't rule it out. The thing you say about the AC being the problem that gives me pause is that you tried different power products and there was no change whatsoever. If your AC is at fault, I would expect you to hear something if you tried different solutions, like a line conditioner. Even if it didn't fix the problem, I would expect to hear some difference; whether it be better, different or worse. I could be wrong, of course, and maybe the AC is the problem, but I would need to hear the amp working properly before I tried fixing anything else.
zd542
5,339 posts
 
"I then tried changing the inputs on the amp (not that I have anything plugged in aside from my XLR and speaker cables), and ran through them all, with each remote outlet (with extension cord attached), and then again with amp plugged into the power strip I've been using. NO CHANGE on any input."

Just to be clear, when you were swapping out components, did you leave the IC's plugged into the amp? Because if you left them in the amp but not connected to anything on the other end, that can produce a hum like you are describing. Especially if open ends happen to be touching something. Also, does the amp have a way to go back and forth between balanced and single ended operation? Having that on the wrong setting can also cause a hum if its not in the right mode. Last, if the amp allows you to adjust the level of each input individually, along with a global volume control, try reducing the level on the individual input.
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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