Shim if you are talking about an expression pedal I bought a Korg EXP2 pedal and it is neither "good nor bad" for my PSR, actually the arranger does not recognize it at all. My Roland expression pedal works fine with Korg but with Yamaha does not work properly even changing the polarity. If you are talking about a foot pedal switch you can use any brand and adapt the polarity if if is necessary.
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Victor
Korg Pa3x 61 - Mediastation X76 - Yamaha Psr s900 - Korg Tr61 - Roland PK5A - NanoKontrol - Ensoniq SQ1 - Yamaha D85 organ