[sdiy] Cheapest, simplest but still reliable VCO & VCA for polyphonic project

[Neil Johnson]

Hi,

Paul Maddox wrote:
>> Next question is in regards to the fact that since i'm doing a  
>> poly synth where one set of knobs controls all the voices, i'll  
>> have to make *every* parameter voltage-controlled, so i'll need a  
>> hell of a lot of VCAs. Any suggestions on good, cheap and very low  
>> parts-count VCAs? I'm guessing a LM13700-design.. ?
>
> SSM2164 gives you 4 vca's in a single 16 pin package, BUT, they're  
> AC only (IIRC).

No - DC coupled, so you could use then for CV mixing, as long as you  
want logarithmic mixing.

> Also, consider if you really need lots of VCAs, look at stuff like  
> the prophet 5 and memory moog, the modulation sections of both are  
> pretty complete, but also quite simple and require very few VCAs.

Indeed.  Another example, the Siel Opera 6 I'm playing with at the  
moment uses one SSM2024 quad VCA per voice and some clever CV  
switching to give some useful modulation routings.

As to George's point about SSM2164 VCOs, I would go the other way -  
use something else for the VCO (perhaps even, dare I say it, a DCO),  
then a single SSM2164 would give you a 2-pole state variable VCF with  
CV-controllable resonance (2 VCAs for the filter, 1 VCA for the Q),  
and a VCA.

Neil
--
http://www.njohnson.co.uk