Monday, December 12, 2011

Yamaha PSS-270 Modifications

I usually post finished circuit-bent creations, but here's a work in progress and some documentation. The Yamaha PSS-270 is a FM keyboard with a multitude of cool presets and an analog chorus. Here's the first round of discoveries: an octave drop, randomize function, chorus depth, chorus morph feedback, overdrive, and a sustain twister. The connections are marked with colored circles, with an explanation of the connection provided for each color.

I found a chorus speed modification and added it to the diagram above. A randomize function was also added, as well as information on limiting resistors. Limiting resistors are placed in the circuit between the potentiometer and the contact points to protect the circuit. They are also used to tune control ranges.

New controls fitted to the hand-painted faceplate

BaumDerProllige says similiar chorus modifications also work with the Yamaha PSS-570.


  1. many thanks for sharing man. tried on a pss-270 works awesome! Realy great to be able to tweak the chorus! Only one thing on mine tho, the "chorus depth" mod don't seem to do anything, is it supposed to be realy subtle? or i did something wrong? thanks

  2. As far as I can remember, it's pretty subtle. Did you use a 500K potentiometer?

  3. Nice page, I've had one of these for a while and am just getting into bending more or less, going to try this mod. quick question- should i use 2 limiting resistors per pot? one on each connection? Thanks

  4. Yes. It seems to interact a little with the oscillations of the chorus and the "sustwist" but it does'nt sound like it's doing anything to the chorus depth. Just wanted to know if it's supposed to be like that or if i screwed something. A chorus depth control would be awesome.

  5. Yes, please use two separate resistors, one for each potentiometer.

    For sustwist, did you use the proper limiting resistor? If so, maybe try a slightly different value?