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

[David Moylan]

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
>
>
>
>  
>