[sdiy] linearizing an exponential CV

David G Dixon dixon at mail.ubc.ca
Tue Jan 12 23:14:07 CET 2021

Hi Neil,

What you need is a logarithmic amplifier.

This is exactly what "linearizing" the 2164 VCA achieves.  I suggest that
you read Mike Irwin's article in EDN about that. 

Dave Dixon

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Neil
Sent: Tuesday, January 12, 2021 2:07 PM
To: synth-diy at synth-diy.org
Subject: [sdiy] linearizing an exponential CV

hey everyone,

i'd like to linearize a control voltage that rises exponentially. i'm
familiar with how to do the opposite, taking a linear voltage and making it
exponential (transistor pair expo converter or 2164), but I have no clue how
to do the opposite.

on paper I think I can take the exponential rising voltage, invert and
offset it to get a falling log curve and then feed that thru an expo
converter to get a falling linear curve. then I can invert and offset that
linear curve to make it rising 0-5V. but that definitely doesn't sound like
the most efficient way.

/// Neil Harper
/// Every Wave is New Until it Breaks

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