VCOs & Tempco

Fraser, Colin J Colin.Fraser at
Wed May 13 15:51:48 CEST 1998

> -----Original Message-----
> From: List, Christopher [mailto:Chris.List at]
> Sent: Wednesday, May 13, 1998 2:07 PM
> To: 'Paul Schreiber'; 'Tim Cockram'; 
> synth-diy at; 'Fraser,
> Colin J'
> Subject: RE: VCOs & Tempco
> The C-2AQ tempcos that I mentioned a couple of days ago from 
> KRL/Bantry
> are about $3.75 each for orders of only 25 pieces, and 
> cheaper when you
> buy more.
> How many VCO's are you going to build? Is the cost + effort 
> to build all
> the extra analog to digital circuitry worth $37 for 10 vcos?

I'm planning on building a poly synth with 3 vcos, 2 lfos, 3 egs,
transistor ladder lpf and ota-based hi-pass filter per voice. I want to
do this on a voice-cards-on-a-bus basis so that I can have a functioning
synth after only constructing one voice + the mainframe. 6 voices will
be the target 'full' system.
All cvs will be generated by a processor, so it seemed sensible to
dispense with the exponential convertors if it can be done in software.
I've thought about software envelopes etc. but decided against these on
the grounds that I've never heard a synth with them that I liked the
sound of (not to say it can't be done - I've just not heard one).
On the other hand, it might be more difficult to implement exponential
lfo and cross mod of the oscillators if they only have linear frequency
control. I'll need to look at some data sheets for 18bit dacs to see if
they can handle static cvs, consider what modulation routings I want
etc. before I decide what way to go.
The important thing is to get it right from the off, so I don't need to
pull the thing apart and start again...

Colin f


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