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

[Karl Ekdahl]

Hi guys, thanks for all the response.

I was considering using the SSM2164 at first but they are way overpriced for my budget.

As many have said, common practice is to use switching instead of VCAs, and perhaps this is indeed the way to go. The specific scenario i was thinking of is waveform-selection in the VCOs, normally i use a crossfader inbetween square and saw instead of switches and it didn't even really cross my mind to break this tradition. What occurred to me is that by having this (necessarily) voltage-controlled one could probably create some pretty neat pwm-like effects. BUT perhaps this is wasteful, seeing i'm putting patchable separate outs for each waveform in conjunction with a mix out..

So let's take another scenario then instead; remote LFO and ADSR output attenuation at PWM, Pitch, Cutoff etc. inputs. I thought about the simple resistor-transistor idea that JH talked about but i couldn't find any good references to this (and i'm gonna guess it's a little tricky seeing we're talking DC here)..

Thanks!

Karl


--- Den tors 2009-01-08 skrev George Hearn <georgehearn at btinternet.com>:

> Från: George Hearn <georgehearn at btinternet.com>
> Ämne: RE: [sdiy] Cheapest, simplest but still reliable VCO & VCA for polyphonic project
> Till: synth-diy at dropmix.xs4all.nl
> Datum: torsdag 8 januari 2009 20.15
> Minimal JH, I like it.  Another option for a VCA is a single
> FET in the
> linear mode Vds<(Vgs-Vt) as one half of a potential
> divider.  For a VCO it
> is possible to make four exponential VCOs from a single
> SSM2164, I never
> tried it so I don't know what they'd be like but if
> you have autotune on
> your polyphonic synth the scale errors wouldn't matter
> too much.  George
> 
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
> JH.
> Sent: 08 January 2009 19:07
> To: elektrodwarf at yahoo.se; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Cheapest, simplest but still reliable
> VCO & VCA for
> polyphonic project
> 
> > Any suggestions on good, cheap and very low
> parts-count VCAs?
> 
> Yes - a single diode + one resistor.
> Terrible CV feedthru, limited range, but good enough to
> control the filter 
> resonance in a Korg PS3200.
> For a slightly "better" VCA, a single NPN
> transitor + a resistor.
> 
> JH. 
> 
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