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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 5 responses by bifwynne

bifwynne
2,206 posts
 
Good point Drubin. I wonder if the OP's problem might be helped if he used shorting caps on all of the amp's inputs, except for source inputs that are being used. Almost seems like the amp, through ambient inductance, is picking up a 60 cycle signal at the inputs and the signal is getting amplified. Heck ... maybe he should short all the inputs to see if the problem is ameliorated.

The other alternative is that maybe the OP should fashion a tin foil hat when he listens to his rig. LOL :)

Please report back.

Best.
bifwynne
2,206 posts
 
Al, ... any thoughts about the tin foil hat idea? :)

@Matt, Al's suggestion to check the ground socket hole is a cheap and quick way to confirm that your socket is properly grounded. If Al's idea is negative, I'd move on to his other suggestions. But if still negative, move on to the next least expensive test.

You said that "[w]ith only the amp plugged into power and the speakers connected," you still get the hum. Does that mean the other source components were also disconnected from the amp? If not, disconnect them.

What Al said about the hum not changing with volume probably eliminates my thought about shorting the inputs, but what the hay, I'd give it a whirl. All you have to do is buy some cheapy shorting caps from Radio Shack.

If still no solution, try borrowing another amp from a friend, or maybe a friendly local dealer. If you're still stuck, try the tin foil hat idea.

Please report back.

Regards,

BIF

Have a great weekend.

BIF
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.
bifwynne
2,206 posts
 
Mwsl, picking up on Zd542's suggestion. If your integrated amp has both XLR and SE input capability, can you use a shorting shunt on unused XLR inputs?

I had a hum problem with my former ARC power amp, which had both XLR and SE inputs. I'd get a hum if I used the SE inputs and forgot to shunt the XLR inputs.

Other than that, I think Zd542 and Al are leaving you with the best straws to grasp at for now. I gotta say that if your amp was checked out by Coda and they missed bad power supply or coupling caps, I'd be extremely surprised. But, as Forrest Gump said, "sh*t happens."

Please let us know how you make out, especially if the dealer comes out.

Cheers,

BIF
bifwynne
2,206 posts
 
Zd and Mwsl ... yes that's good news indeed. Not sure how to put this, so please do not take it as me being snippy.

Mwsl's unfortuante experience is one of the reasons why I love ARC. My personal experience is also consistent with what I have read on ARC's web site and in various audio articles. Specifically, no unit leaves ARC's shipping dock (new or repaired) until William Gehl, ARC's offical live tester, plugs the unit into a system gives it a good listen. Mr. Gehl initials a QC card which accompanies the unit, and only then is the unit shipped out. Every ARC unit I own or have owned has a QC card with his initials. Mr. Gehl must have an incredible auditory memory.

Is the systen perfect? Does a chicken have lips? Same answer .... after all, it's run by human beings.

Anyway ... I sincerely hope that Coda puts your amp back in 100% operating condition and this is the end of your aggravation.

Best,

BIF
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