The Polysix-M S/H (analog) board

The S/H (sample-and-hold) Analog Board enables the Bend and Mod wheels to be interfaced via MIDI. The nice poeple at Korg have actually provided a lot of the circuitry on the Polysix boards, and only a couple of hold amplifiers and a VCA need to be added. The schematics show the electronics on the board. It is connected to the Polysix via an 8-pin connector (to the KLM-367 circuit board), and a single wire to the Bend Range pot (VR3 on the KLM-369 circuit board). No pin numbers for the IC's have been given. Instead, refer to the pictures below.

Veroboard-based design

This is what the S/H board looks like from the top ...

Top view of S/H board

...and this is what the wiring on the underside looks like.

Bottom view of S/H board

The black arrow points to the connection point for the BEND CV output from the board (TL072 pins 1 and 2, connected to the BEND RANGE pot CW terminal).

The trimpot on the board is set up after everything has been mounted, and is set so that there is a reasonable (i.e. same as before the modification was installed) amount of LFO modulation when the mod wheel is fully advanced. Alternatively, it can be replaced, together with the series-connected 22k resistor, with a single 68k resistor.

The board is mounted just to the left of the two main Polysix boards as shown below.

S/H board mounted in Polysix

(The strange cable emanating from the EPROM socket on the CPU board is for my Z80 development system).

PCB-based design

To build the S/H board using Martin Wise's PCB design, you'll have to download a .zip file of the artworks. Within the .zip archive, you'll find images of the copper traces and silk screen for the board, a circuit diagram to replace the one above, and some notes on how to assemble it all. Once completed, it will look like this.

S/H board PCB

This page is (c) Copyright 1999 by Ricard Wolf

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