[sdiy] CA3280 VCA Design

[Simon Brouwer]

Hi Rob,

At 18:20 20-11-2005, Rob Keeble wrote:
>Hi,
>I have a tube of CA3280's which I plan to turn into dual VCA's, however I
>can't find a circuit design on the web...so I have cobbled one together -
>which is here (37k GIF) - mainly using ideas from the SCI Prophet 5..
>
>www.emulatorarchive.com/assets/vca.gif
>
>Before I put this on the breadboard, any changes I should make?
>Audio and CV ins are 0 to +10V standard. VCA is linear, unity gain, and
>should't invert signals. Only one VCA shown...

The amplitude control will not remain linear at low control voltage, i.e. 
when the voltage across R11 becomes small in comparison to the Vbe of T1.
Better to make a voltage to current converter like that around ic13c in the 
Paia fatman (http://www.paia.com/fatmwork.pdf)


Vriendelijke groet,
Simon Brouwer.

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