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

[Paul Maddox]

Karl,

> Hi list, so i wanna make a poly synth and as usual i'm looking for  
> the cheapest possible VCOs and VCAs that'll still cut it. Note; i'm  
> not after absolutely perfect pitch or anything, in fact i'm going  
> analog to avoid this.

You need to speak to George Hearn ;-
http://diy.synth.net/gallery/main.php?g2_itemId=1662

That board, IIRC, has two VCOs, two VCADSRs, VCF and dual VCA.

> 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).

The other thing, if you're planning on controlling them from a micro  
(front panel with memory/rotary encoders perhaps) you could use a  
multiplying DAC. Analogue devices do some octal DACs each with their  
own Vref input and output. I think they're a 20pin package and use SPI  
to control them.

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.

I mean, for the output of the LFO do you need loads of VCAs? one for  
every routing?
I'm planning on using a single VCA for the output of my LFO and FETs  
to control destination on/off. Simple, lower cost, and a simpler  
panel :-)

Just some ideas
Paul