[sdiy] LM13700 questions

[Tom Wiltshire]

On 17 Aug 2012, at 11:26, Stewart Pye wrote:

> On 8/17/2012 5:31 PM, David G Dixon wrote:
>>> The application I have in mind is voltage control of
>>> modulation amount.
>> This is a classic VCA application.  Why not just apply the voltage to one
>> OTA?  Why do you need two?
> 
> It's for a hand clap circuit. One half of the LM13700 will be the audio VCA, the other half will have a "velocity" input going to its Iabc pin, and the clap envelopes to its input. So I basically have and audio VCA with a voltage controlled amount for the envelope input. I'll be using another LM13700 package for the "reverb" section.

You *could* also do this with the two VCAs in series. The first one would shape the audio with the envelope, and the second one would alter the overall level according to velocity - or vice versa. I think Paul Maddox's Monowave works like this, IIRC.
I suppose the advantage of your way is that you only have one VCA in the audio path, so it should have lower noise/distortion.

HTH,
Tom