[sdiy] Re: SV: Re: [sdiy] [SDIY] Faster Enveloppe Mod for Sixtrack ?

[Frédéric Bourgeais]

Hello,

David, Thanks for the explanation. I didn't know this CEM chip before, and
looking at datasheet and schemos, I was impressed by the possibilities of
the sixtrack ! (rather than my juno 106, who have also 6 oscillator).

The only change between the digitally controlled VCA input, and
Filtermod(Pin 5), is the addition a 1M resistor (R136), and 0.001
uf(C171), making a passive lowpass filter. The cutoff frenqency is about
15 hz.

For info (To know if I understand right the schemos for the first time ;-)
) Does it mean that attack signal, faster than 0,06 second are smooth (or
slowed ?) it's probably to prevent "Click" on attack, but my friend want a
more percussive enveloppe.

Why, there is no filtering on filtermod ?

-----

Tim, thanks too for the suggestion, It's also, what I suggest him, If caps
swapping was impossible. An External Log ADSR (7555 design) with a switch,
on only one voice. Sure preset should be lost, but it's not a problem.

I was thinking about gate signal problem to trig the enveloppe too. A very
low threshold level, on 4051 output, could do the trick. Does this trick
could introduce noticiable latency ? And yes, Pita is breed ;)

-----

Finally,
Karl, Is it possible ? is it not too dangerous ? I remember a long time
ago, a friend who succesfully overclocked a 486DX, simply swapping a 33
Mhz quartz on the mother board. Is it the same trick ? What's kind of
quartz is used on sixtrack and how many Mhz is it clocked ? which value to
replace with ?

Thanks all for your very interesting feedback !



> Try over clock the CPU! .-)
> Make shure the 68B50 uart has its 500khz
> maintained otherwhise your MIDI will go ape!.
> Z80 can usuall be over clocked a bit.
>
> KD
>
>
> --- Tim Parkhurst <tim.parkhurst at gmail.com> skrev:
>
>> 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
>>
>
>