[sdiy] Opto-transistor question

[Erik Dower]

I recently built a VCA using an H11F1M as a variable resistor on the input to a buffer.  It worked but never fully turned off and I attributed this to the 300meg max resistance.  The datasheet has an AGC example that mentions 70db of stable gain control which is not enough for the modular synth levels I wanted it for so I gave up on it for a VCA.  I have had success using them instead of vactrols for various mods though.

epk

On Mar 14, 2012, at 12:57 PM, Harry Bissell wrote:

> we say "barking up the wrong tree"
> 
> Either the transistor or darlington type optocouplers are mostly specialized for switching applications.
> 
> There is a FET optocoupler H11 something (someone else will tell you the number) that has been used
> with some success, although like most FET VCAs it has a kind of limited signal input range.
> 
> You also want to look at Avago technologies, who make a large number of optocouplers that could easily be suitable for a VCA, although they
> are probably not either cheap or easily available.
> 
> I'd also check the list archives, look for optocoupler and that should get you there...
> 
> Good luck !
> 
> H^) harry
> 
> 
> 
> ----- Original Message -----
> From: Harlan Foster <harlan.foster at gmail.com>
> To: Synth-diy at dropmix.xs4all.nl
> Sent: Wed, 14 Mar 2012 15:50:06 -0400 (EDT)
> Subject: [sdiy] Opto-transistor question
> 
> Hello all, I've been diving into the SDIY thing for a few years now,
> but I'm still kind of wet-behind-the-ears. Recently I picked up some
> opto-transistors (4N32 & 4N36), I was thinking that they may come in
> handy. I've been breadboarding with them trying to cook up a simple
> VCA, but I've not had any success.
> 
> I'm shooting for something simple, I don't mind if the results are
> less than ideal. Am I barking up the wrong cheese? Can anybody point
> me  in the right direction? I have several transistor based VCA
> schematics that I have built in the past, but this has me stumped.
> 
> Thanks for the knowledge you all share in this forum, I really enjoy
> this mailing list!
>> Harlan
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> -- 
> Harry Bissell & Nora Abdullah 4eva
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