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I hadn't used my PA50 in several years, and when I turned it on yesterday, there was a lot of noise when using the internal speakers (there's no noise on the line or headphone outputs). The noise sounded like typical 60Hz power supply noise, so I tried using different 12V wall warts (including Yamahas designed for musical instruments) and while there might have been a little bit of difference, all were about equally noisy. The noise is loudest when the master volume is set to minimum (off) and noise decreases as I turn the master volume up - the internal speakers are almost usable if I turn master volume all the way up and, using the assign volume for instrument volume, keep assign and acc/seq volumes very low. So it seems like it must be related to the power supply or amplifier board (since headphone and line outs use the same signal that is sent to the amplifier board, and they are OK). Has anyone had this kind of problem? Was the original PA50 power supply a linear supply? All of the supplies I had were switching power supplies - could that be the problem?

OK, in case anybody else has this problem in the future: the noise went away after I disconnected and reconnected all the connectors on the amplifier PCB (to remove it and check for burnt-out components), and had done the same with some of the connectors on the front panel PCBs. The noise could have been caused by a dirty / corroded contact (ground?) on one of the connectors.

I've also noticed that the power supply has to be able to supply 12V at the full 26W, too (OK, 12V @2A will work). A ferrite bead on the DC line doesn't seem to make any difference. An argument for using "only the Korg-supplied power supply", maybe?

While I had the PA50 apart, I replaced the floppy disk drive with one of those cheap Gotek USB floppy disk emulators that you can get on eBay. It works just fine, and USB flash drives are a lot more convenient that floppy disks these days.

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