[sdiy] Approximate linear 2164 scheme using zeners

Roman Sowa modular at go2.pl
Mon Mar 21 12:23:21 CET 2022

The lower Zener voltage, the softer is transition knee, more suitable 
for quick and dirty linearisation. But you may get better results using 
diodes in forward direction, just add more of them.
You might also try multi-linear aproximation (not sure how to call it in 
English) with a series of diodes and resistors. I've used 4 red LEDs 
with 4 different resistors to make not so bad expo converter. It was 
tracking almost good enough to be used for pitch - it was for VCF cutoff 
Another example was to get wider more usable range from low resolution 
control voltage in VC ADSR. Here I've used just 2 stages of Zener with 
resistor: 3V9 || 68k in series with 5V6 || 360k.


W dniu 2022-03-19 o 13:40, Sean Ellis via Synth-diy pisze:
> Based on a suggestion on Modwiggler I tried a cheap way to get rough 
> linear response from a 2164 using diodes to compress the CV, then scale 
> it. So far it looks good in Spice but comes (I think) at the cost of 
> S/N. Haven't tested this yet but if it works, I'm sure it could be improved.
> (I'll try to attach the pics here but if not check the link.)
> https://modwiggler.com/forum/viewtopic.php?p=3719506#p3719506 
> <https://modwiggler.com/forum/viewtopic.php?p=3719506#p3719506>
> Ignore high resistor values in the signal path, had some trouble 
> figuring out the 2164 model. The circuit is a polarizing VCA using an 
> inverted part cancelling. With the exponential response this crossover 
> is not really useable even from a large panel pot, it's so sharp. Dont 
> need any precision here but a softer front panel experience (I just want 
> to save a chip 😉 )
> When I took these captures I had made the expo section lopsided in 
> error, but the shape is the same when spaced out more. Any thoughts? I 
> think it could be trimmed better down to 0 volts but that was where I 
> started to lose the shape, rather trade some attenuation for the shape.
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