[DIY] RE: PAIA multiplying DAC, was My new VCO

[jh]

Is this online somewhere ?

JH.

PS.: For monophonic keyboards, basically 3 fixed resistor values (unlike
one value for V/Oct) works - there is a Korg patent for that.

-----Original Message-----
From:	Donald Johnson [SMTP:djohnson at mdsi.bc.ca]
Sent:	Thursday, June 03, 1999 3:31 AM
To:	synth-diy at mailhost.bpa.nl
Subject:	PAIA multiplying DAC, was My new VCO

jh <jhaible at primus-online.de> wrote:
>>Very interesting stuff. Now all we need is a 14/16 bit multiplexed DAC.
>
>Not sure about that. There was an interesting article from Paia's John
>Simonton in Electronotes (#61, if memory serves) where he shows
>how to do it with a (very special) discrete 6-bit DAC. 
>The idea looks brilliant: changing the gain of 3 opamp stages with
>6 electronic switches, so you get a scaled multiplication
>(where you have addition in a normal DAC). John ?

 Sure, the 4700 replaced the keyboard CV trimmer array with a diode
 'matrix' which drove a 6 bit multiplying DAC. The DAC circuit used a
 laser-trimmed (?) resistor set. Cool idea. Works well. My 37+ trimmer
 key 'exponential-keyboard' became trimmer-less.

 don.


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