[sdiy] lots of VCAs on one PCB

[Derek Holzer]

Thanks to everybody who replied so far! I'll try to run down the  
possibilities so far in this email:

1) Oscar Salas: "Tessera" quad VCA

I initially looked at Marc Bareille's Quad VCA, and I would have to  
pass on this VCA setup for the same reason. It needs too many PCBs. I  
use a fairly shallow case and mount all my boards parallel with the  
faceplate. There would not be room for four (or eight!) PCBs stacked  
up, especially considering the space needed for the joysticks, jacks  
and pots behind the board as well.

2) Kyle Stephens / Gergo Palatinszky / Andreas Wetterberg

Four seems to be a common number when dealing with groups of joysticks  
(see Tessera, Bareille's Quad etc etc. The THAT 2181 looks  
interesting, however I specifically mentioned using it for control  
voltage and this one is exponential.

3) Mark Verbos

4049 hex VCA looks great from the angle of low parts count and cheap.  
Heck, with SMD it would be almost microscopic!!!!! I just wonder how  
it sounds? I wouldn't be using it for audio rate modulation, however  
some of the gestural stuff with the joystick could get pretty fast.  
Anyone know how well this VCA design sounds?

4) Tim Parkhurst / John Mahoney

The SSM2164 was indeed the first chip I looked at, and yes it is  
exponential. My other joystick based project is in fact a quad  
spatializer, and nothing could be easier than to use 8 2164 ICs and be  
done with it. The fact that they must be doubled to get a linear  
response adds quite a bit of board real estate to the problem, and is  
basically the same as the Tessera that Oscar mentioned, and the same  
as Bareille's Quad VCA. If I could find a board layout small enough  
(my Eagle/Kicad skills are very poor) then I would certainly consider  
such an option. Ideally, I'd love it if someone with better PCB  
laypout skills than me wanted to take either the Tessera or the Quad  
VCA and SMD-ize them ;-)

5) Jason Proctor

I'm trying to avoid any digitization of the signal for the moment.  
Programming too. I got into analog synths to get away from digital  
music (Pure Data programming mostly). However I'll keep it in mind.

6) Kyle Stephens

The SSM2024 also looks interesting, however the first thing that the  
Bergfotron page you directed me to says is that the performance is  
quite poor. Too bad, a single IC with four linear VCAs would be a good  
solution!

7) Nathan Trites

Two boards of 8 would be just fine with me. I figure that I have room  
for two PCBs "under the hood", but not four. If you were interested to  
help with this project, let's talk!!

Best!
Derek

-- 
::: derek holzer ::: http://blog.myspace.com/macumbista :::  
http://www.vimeo.com/macumbista :::
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