[sdiy] [SDIY] Faster Enveloppe Mod for Sixtrack ?

[Tim Parkhurst]

On 9/17/05, David Moylan <dave at westphila.net> wrote: 
> 
> I believe those are Sample/Hold caps. The 4051 is an analog multiplexer
> which is routing DAC generated CVs to the caps where they are stored.
> If I recall the 3394 datasheet mentions that all the CV inputs are
> buffered hi impedance so there is no additional need for S/H buffers.
> You don't want to change those caps.
> 
> I don't think there's much hope in speeding up the envelopes as they are
> CPU generated then just routed to the chip. Plus any cap that might
> theoretically slow the envelope down is likely necessary to smooth
> quantization of the envelope.
> 
> I was very interested in the 3394 for a while and stared at the
> datasheet a lot. Who doesn't like a synth on a chip?
> 
> Dave Moylan
> 
> Frédéric Bourgeais wrote:
> 
> >Hi all,
> >
> >A friend who own a SCI sixTrack, wish faster Attack to control the output
> >VCA.
> >
> >I took a look to schematics available here:
> >http://www.geocities.com/SoHo/2163/ST_schem/
> >
> >And CEM 3394 datasheet here :
> >http://www.synthtech.com/cem/c3394pdf.pdf
> >
> >3394's Pin 18 is used to control the Final Gain CV, but unfortunalty
> >Enveloppes are CPU generated, so it's not easiest as swapping a capacitor
> >to a smaller one with good old analogue synths...
> >
> >Is there a last chance for faster CV, simply playing on caps or resistor
> >values on the input of the 6 sixtrack's 3394 (such C171,R136,C169 on U131
> >pin 18 here: http://www.geocities.com/SoHo/2163/ST_schem/st_b1.gif )
> >
> >Does these componants are used to smooth the Enveloppe CV ( a bit like a
> >glide ? )
> >
> >Thanks for your help
> >Fred
> >
> >
> >
> >
> >
> 
>  You might have better luck by building simple hardware EGs and adding 
their outputs to the VCF and VCA CV inputs on the 3394 (yes, a nifty little 
chip). There are however, two major drawbacks to this approach: First, 
getting the right 'gate' signal to trigger the EGs would be a PITA (perhaps 
from decoding the right address on the 4051s). Second, these EGs would not 
be programmable, and even if they were voltage-controlled, there would be 
little hope of adding these settings to the existing program (unless you 
felt like doing a major rewrite of the Six's operating system). 

Tim (and I thought PITA was a type of bread) Servo
-- 
"Imagination is more important than knowledge." - Albert Einstein
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