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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
 
Thanks for all your thoughts, suggestions and quips :-)

So, first, yes, the amp makes this hum with ONLY it plugged in with the speakers connected. All other equipment was disconnected for this experiment. This same hum occurs in two different outlets (which, to be fair, are likely on the same "line" in my house). Each outlet has a different high quality audiophile outlet.

Second, didn't mention this, but prior to purchasing this amp, I auditioned a tube amp, and it too created a hum through the speakers....it, however, got louder when volume was increased. For the Coda amp, the hum "volume" stays the same regardless of output volume on the amp.

Third, I have tried different power cords, and have plugged different power cords into: the power outlet (wall), a high quality power strip, and/or a line conditioner. Nothing has impacted the hum.

Fourth, I am aware of possibility that speaker cables over power cords might create hum and have moved all cables/cords around to no effect (doesn't seem to change anything).

I have not tried shorting the inputs.....thought about it, but not done it yet. Maybe that'll be tomorrow's experiment if i can get to RS before it closes.

Any other ideas would be appreciated.

Maybe I just have exceptionally "dirty" power? If so, would that explain this symptom? And then, what the heck would I do about it?

Thanks again!

matt
bifwynne
2,206 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
Ag insider logo xs@2x
almarg
9,670 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
1,610 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
293 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.
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