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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
bifwynne
2,069 posts
 
Please report back tomorrow after you short the inputs. There's a couple of other switch-outs you can try, but I caution you that if everything else fails ... its the tin foil hat for you.
almarg's avatar
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almarg
8,673 posts
 
Do either or both of the upgraded outlets have a small triangle symbol on them, signifying that they are isolated ground types? Did you install the upgraded outlets yourself, or did an electrician install them? Is there a basis for confidence that their safety ground connections are wired correctly?

If you are uncertain as to any of that, while you are at Radio Shack consider purchasing a multimeter, which might help to diagnose any outlet-related issues. Also, consider stopping at a Home Depot-type place and purchasing an extension cord that is long enough to allow you to connect the amp to a different outlet on a different AC run.

Re your other questions and comments, I doubt that "dirty power" could produce this symptom, and I wouldn't assume that the cause of the volume-dependent hum problem with the other amp was the same as the cause of this problem.

Beyond that, the tin foil hat suggestion is probably as good as anything else I can think of :-)

Regards,
-- Al
pbnaudio's avatar
pbnaudio
1,534 posts
 
Have you tried to move the amp to different location in your house along with the speakers to see if the problem persists ?

Best of Luck

Peter
kjweisner's avatar
kjweisner
291 posts
 
I would double check the outlet wiring--if you don't have one already you can get an outlet checker for about 6 bucks at nearly any hardware or home improvement store. It verifies that hot, neutral, and ground are all correct. If no fault in the wiring of the outlet, I would second the idea of a long extension cord and trying a few other outlets. If nothing else, it rules out a variable. Then I'd swap out speaker cables as the next experiment, again, to rule out a variable. If none of that has a positive outcome. . .then I'm out of ideas, but plenty of smart people here! Good luck.
justlisten's avatar
justlisten
489 posts
 
If I were in your shoes, I'd ask my neighbor if I could bring my amp and speakers to his home.

No hum there, you know you have an ac issue at home

If hum there, you know one of two pieces are bad

From there would swap different speaker with same amp, ...you get the picture.
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