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Just purchased a new Commander Plus. I find that it has quite the ground hum when using the balanced outputs to American Audio powered speakers. The hum remains if I disconnect all inputs, lift the ground on the incoming power and isolate the unit from the equipment rack. I bought this unit as a quieter replacement to a ****** EM-460, but have found it to be quite a bit noisier due to the grounding issues.

Has anyone else had similar issues?

Another strange note (which makes this ground hum demon hard to find and destroy): the hum disappears when using unbalanced outputs, when running the balanced inputs through a nice SR mixer, when running the mixer through a new AA V5000 amplifier. The hum is strongest (comprimises ~ half of the total amp output) when running balanced through an older V3000 (slightly quiets to ~10% of total amp output when V3000 ground is lifted), quieter (but present) when running through Crest CA and LT power amps (completely disappears when ground is lifted).

We tested other (non-commander & consequently non-grounded) AA mixers out of the box with no ground hum (all other variables held constant). When we got a second new Commander Plus, It had the same hum.

I would rather not lift the ground on all my power amplifiers (safety issues), I would rather not run unbalanced (I have ~200 foot runs at times). I would rather not buy another mixer (this one is new - I like the features of individual channel metering and dual XLR mic inputs on the face, etc). I would rather not send the unit in for repair since:
It is new; we also tested another new unit that had the same issue - I think it is a general design flaw
The last time I had an American Audio unit serviced it took 2-3 months to get it back in usable condition (it also had an intermittent/hard to isolate problem; but was happy to receive a working unit after all was said and done)

What are my options?

Thanks in advance.
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hmm try this

disconnect all wires to the mixer. plug in your headphones. can you hear the hum through the (cue set to listen to "program out") headphones??

if the answer is yes then:
try this again after lifting the ground on the power coming to the mixer. (of course isolate the mixer from the rack for these tests)

did the hum go away?

if so then it would seem to be a manufacturing flaw.

*****
when you hook up the mixer to the amps with balanced cables and hear a hum, it sounds like the shield from the balanced cables are just trasnferring the ground problem to the amps which is why it sounds louder when using balanced cables.

just speculation right now but i would really like to find out the cause of this problem
DJ Utah,

Sounds like you've done all the obvious troubleshooting, you say you've swapped out the commander with another mixer but, same cabling but with different results. Some mixers behave differently in the way they handle their shield/grounding, I would have a closer look at your XLR connection between the commander and amp. Ensure you are using high quality (professional) and properly shielded signal cable. The manual for the commander should explain how to properly terminate your balanced output cables. Once you've eliminated that but still getting hum I would then consider calling tech support. Hope this helps.

ROQ out.
I don't think the cabling is an issue (we used 3 different cables - all manufactured by CBI with BELDEN Ultimate 20 AWG wire and NEUTRIK ends - At other times have used 22AWG Mogami cable with Canari ends with the same results).

I get no hum through the unbalanced outs or the headphones. I think I have properly troubleshot this.

In other circles people say that this is an overall design flaw in the commander plus and the reason why a new commander plus (in black) will soon be available (with this flaw repaired).

Apparently the new V5000 has built in ground filtering (cleans up the grounding issue from "low quality" mixers).

My expensive sound reinforcement mixing boards utilize the same technology, which is why the noise disappears when running the commander's outs trough those mixers.

My best bet may be to lift the shield off my balanced cable and then to await the purchase of the new commander plus (in black - although I much prefer the silver due to its higher contrast in dark environs).

Thanks

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