[sdiy] Polyphonic keyboard scanner

Mike Gorman mikegorman at btinternet.com
Fri Jul 31 22:24:42 CEST 2009


There are at least 3 designs from ETI that should fit the bill here.

The Polyphonic keyboard from July 1979,
The Transcendent DPX from August to November 1979 (I think this was the one
that Tony mentioned)
The ETI Polysynth from December 1980 to March 1981

The last one might be the best bet, as I know this could be expanded to 8
voices (Mostly CEM based voice modules IIRC).

I think the ETI articles are all available on CAG, though the scans may only
be monochrome, which can be awkward at times.


Mike Gorman

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of David G. Dixon
Sent: 31 July 2009 17:53
To: 'synth diy'
Subject: [sdiy] Polyphonic keyboard scanner

I know this will earn the scorn and derision of the programmers on the list,
but I'm wondering:  Does anyone here know of a polyphonic keyboard scanner
circuit based on logic IC's (non-programmable)?  Is this even feasible
without a massive pile of chips?  If so, I'd be very interested to learn
what the algorithm is.  The approaches I've been thinking about are all
fairly complicated (one scanner (counter + 2 multiplexers), but 8 separate
latches and ladders with data comparators to compare the count to the
latched data for preventing double latching and controlling note-off -- I
haven't worked out all the gory details yet).  I'd like to design something
that will send out 8 CV's, 8 triggers, and one gate.

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