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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
 
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.
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
jea48
4,446 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.
06-06-14: Mwsl
Mwsl,

Earlier in one of your posts you said you tried a ground cheater on the AC power plug of the amp. Doing so ruled out the safety equipment ground being the problem.


If by chance somewhere in the 120V circuit that is feeding the amp there is a loose and or corroded connection, that could possibly cause an RFI interference in the amp and cause a buzz heard through the speakers. If there is a loose and or corroded connection an AM radio plugged into the same receptacle as the amp could/would cause a buzzing sound in the speaker of the radio because of the RFI interference being generated.

As for the AM station used, set the tuner on a moderate signal strength station. No buzz, then try a weaker AM station.

Like others have said in this thread, the problem is more than likely the amp.
Jim
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