[sdiy] LM13600/13700 VCA circuit recommendations

[Scott Gravenhorst]

Dave Kendall <davekendall at ntlworld.com> wrote:
>Hi All.
>
>I recently scored a couple of tubes of these ICs cheap from Evilbay, and am
>looking for simple VCA designs. Found a couple so far;
>Scott Bernadi's one for routing CVs,
>http://home.comcast.net/~sbernardi/elec/og2/og2_dual_linear_vca.html
>or maybe LM13600 VCA *2 from Jorgen Bergfor's VCA shootout
>http://hem.bredband.net/bersyn/VCA/lm13600%20vca%202.htm
> - doesn't say if it's Linear or expo response to CV though, and I can't
>work it out from the schemo....

Looks expo to me.

>Has anyone built these or got any comments on these designs? I'm looking for
>simple designs, one linear for CV, 

See the datasheet, I think there's actually more than one.  One thing to watch with the
datasheet tho, they call running a stiff voltage through a resistor "linear", which isn't
totally right.  A real linear current driver will usually be an opamp current source
where there's either a Darlington pair or a MOSFET in the feedback loop.  The FatMan VCA
is done this way (Darlington).

>and one expo for audio, that don't have
>to be *mega* quiet or feature rich. They'll be part of a routing matrix in a
>fixed architecture synth that (one day) will see the light of day.....
>
>Any comments on these or other designs would be most welcome.
>
>cheers,
>
>Dave 
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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