Korg Forums

[stratus2000]

Hello, when I hook up the self powered speakers I get an unbelievable amount of noise, while they still play the keyboards sound. When running off a UPS supply all's OK, until I plug in the UPS, noise comes back. I could blame this on a ground loop, or some AC shorting, but why isn't the noise coming into my headphones, which have no noise?

[voip]

It does seem like a ground loop, or a ground wiring fault, based on the description.

The M3's headphone and line outs pass through different amplifier stages, each optimised for their respective output loading, so there's a substantial amount of buffering between them. The headphones are not connected to any ground, so no ground currents can flow through them back into the M3. It also suggests that the M3's internal earthing arrangements are probably in good shape, else the headphone output would also have been affected when the UPS was plugged in. What happens when the UPS is left out, and M3 and amplifier are both connected to the mains directly?

Connecting the M3 and amplfier to the same mains extension block, and keeping the mains leads close to each other and the signal leads following a similar path to the mains cables, but not right next to them, may reduce the interference. Another possibility is that the amplifier may have developed a grounding system fault.

Further investigation by a qualified electrician/electronics engineer, to establish the cause, is recommended.
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