[sdiy] Simple, single supply VCA

[Tom Wiltshire]

On 4 Feb 2010, at 18:55, Justin Owen wrote:

> Thanks all,
>
> I've read about people using the LM13700 with a single supply - but  
> I've never seen a schematic using it. Can I presume that I'd just  
> follow the same steps as I would for adapting a dual supply op amp  
> schematic to single supply - i.e. send the negative supply pin to  
> GND and bias any inputs to VCC/2 (or whatever)?

Justin,

I've got some relevant schematics in an old copy of R.A.Penfold's  
"More Advanced Electronic Music Projects", which is one of the Babani  
books (BP174). Lord only knows if you can still get it.
There's a shaped fuzz schematic in there using the 13700 as a VCA run  
off a 9V battery. All the "0V" connections are taken to a VCC/2 bias  
made with a couple of 5K6 resistors and a 470uF cap, exactly like you  
suggest. The same VCA turns up in a few other circuits in the same  
book (Split phase tremolo, envelope modifier). You can build VCFs the  
same way, and again Penfold has examples.

If you get stuck, give me a shout and I'll send you a picture. But it  
looks pretty straightforward.

Regards,
Tom