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I just bought a GEM RP-X piano module, which has amazing acoustic piano sounds, but I noticed, when I'm not playing, there is a background buzz that phases on a 1-2Hz cycle.
I tried all the usual experiments to determine if something in my environment was causing the problem: different interconnects, house circuits, amps, etc...: no difference.
I then noticed that I heard the noise even if the unit itself was powered off--until I unplugged its wall-wart type 12VDC power supply. Only then did the noise stop completely. I hooked my 'scope up to the end of the wall-wart and could see a sawtooth waveform in the audio range.
The adapter is rated 2.2 Amps and is the switching type. I've never had big problems with wall-warts before, but I think most of the lower-current ones are linear, not switching.
Do you think I got a bad adapter, or are they all this way? Will I have to build my own supply?
David Anderson
Follow Ups:
Quite simple
You have a ground loop
There are a few ways to address this issue
Lift the ground on your mixer with a ground lift
Lift the ground on your amplifier with a ground lift adaptor
You can try one at a time
Or you can go through the process in RANE NOTES
at Ranes site
I should have posted back earlier--I did, in fact, already discover the ground loop problem and used a 3-2 prong adapter to lift the ground of the module.
All is well.
David A.
I think the lower-current ones are probably conventional supplies, but they're not linear (I don't know of any AC to DC supplies in common usage that are).
I'd look for a better-quality power supply. How much current does your module require?
The module's current rating is 500mA--I'm not sure why they sell it with a 2.2 amp supply.
Is there a company that makes high-quality/low noise 12VDC/1000mA supplies?
David Anderson
all-analog regulated lab power supply and built like a tank. Adjust and go....
Cheers,
David
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