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
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
I had an opportunity today to go to a local audio store. Brought in the integrated, thinking, if I can still hear the hum, and the staff can hear it, then we've isolated the problem. And, fortunately, the problem remained, obvious to all ears. It was interesting to me that after listening to my integrated hum away, the salesperson plugged in a $1000 integrated into the exact same cords, cables and connects......and all I heard was a blissful silence. For those of you who thought my amp was problematic, you are correct. Alas, I'm still waiting for the word from CODA for when they'll be ready to receive my amp for repair; the owner/founder has been out due to a severe injury, so I'm biding my time waiting for his return.
Mwsl,
Thanks for the update, I wondered what was happening.
When you get the issue resolved please let us know what needed to be replaced.
Thanks,
After much delay, I finally got my problem resolved.....and quite nicely!

Doug Dale, the owner of Coda, had been severely injured many months ago and has been off work until last week. Much of the delay that I experienced was due to Doug's absence. He was apologetic for the delay.

As soon as he got back to work, he decided to simply swap out my unit for a new one that he had tested and was sure worked to spec....with no noise. I brought my amp in today. We listened to it in his listening room and (thankfully) heard the noise....although it was MUCH quieter in his room with his Legacy speakers that it was in my room with my speakers. We then listened to the new amp that he had selected to replace mine.....it wasn't dead quiet, but the noise was of a much less obtrusive nature that he said was normal and (I believe) related to the volume control used.

I brought the amp back to my house, plugged it in and......it's lovely...no noise. Again, not dead quiet, but WAY more quiet than my previous unit. Since the replacement unit is new I'll have to break it in again, but, frankly, that's not that bad a prospect :-)

Doug did say that very infrequently, generally due to shipping issues (dropping, rough treatment) some wires get slightly loose and may cause the issue I have been having. Oh well, just bad luck on my part.

It was cool seeing the Coda facility.....there's only 4 employees (that I saw) including Doug, so it's a small operation. But they're producing some neat products.

OK, I'll check back in in a few weeks....but I'm VERY heartened with today's news. Thanks again to all of you for your support and help.