Circuit Bending a Yamaha PSS 470 - PSS 560

PSS470_1

PSS560_1

PSS470_2

PSS560_2

PSS470_3

PSS560_3

PSS470_4

PSS560_4

PSS470_5

PSS560_5

The Yamaha PSS470/560/360 keyboards are my favorite ones to bent. They are full of beautyful glitches and random streams. While I destroyed two of them during the process of bending, I now have three working ones with the similar enhancements. Some of the modifications I made in the 470/560 also work on a 360 but have to be soldered to different points on the board. The following text considers only the 470 and the 560. At the bottom of this page there is also some information on the 360.

A good point to start with is the 3 to 8 line decoder, the chip named TC40H138P. Connecting some of the pins gives very satisfaying results.

Connections among the pins of the DAC Y3014B, the TC74H175, the YM3812 and the CPU are worth to do.

(see all connections on the diagram below).

The clock frequency of the instrument is controlled by an external circuit with a voltage controlled oscillator. Therefor I use a 74LS629 or similar. There is a potentiometer for tune and one for finetune and an array of switches to choose among four capacitors determining the tuning range. See the notes below for the diagram of the circuit. I learned about this by the postings of Sam Samshuijzen at electro-music.com. You could also alter the clock frequency by crystal swapping but there you always have to reset the instrument and you only get fixed steps of frequencies.

`Connection-Diagram`	`Connections On YM3812`	`74LS629 Oscillator`

So now here some information on the Yamaha Pss360 keyboard. As mentionned it has almost the same technical architecture like the 470/560. Here I describe what I did with the 360 only. This family of keyboards has a synthesizer section. the parameters on that synthesizer are changed by sliders. this sliders are no potentiometers, but 5 position switches. It makes a nice effect to play a note and to change the sliders while still holding down the key. I wanted to have the changing of the sliders automated. I used a squarewave oscillator that drives a counter upwards in a loop (1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, ...). The counter controls an array of analog switches. The pins of the switches are soldered to the points on the pcb, where the sliders would have closed the connections. It sounds like a kind of arpeggiator.