[sdiy] Multi Segment Envelope Generator

[Grant Richter]

For those with a Mini-Wave and Socket Rocket chip, the "MARF Discriminator"
bank is this type of window comparator with an adjustable threshold from
+/-40 millivolts to +/- 660 millivolts.

You can use other synth modules to "patch up" a multi-section envelope
generator from a sequencer.

The MARF part is actually a misnomer, the real Buchla MARF used a linear
ramp from the clock to control complementary PWM circuits. The linear ramp
sections were generated by averaging the output of the current and next
stage by PWM crossfading.

The basic circuit idea for a PWM crossfader can be seen at:

http://www.musicsynthesizer.com/Buchla/buchla_model_257.htm

and corresponds to the M and M not terms.

> From: patchell <patchell at silcom.com>
> Date: Fri, 29 Mar 2002 13:13:25 -0800
> To: Tim Ressel <madhun2001 at yahoo.com>
> Cc: "synth-diy at dropmix.xs4all.nl" <synth-diy at dropmix.xs4all.nl>
> Subject: Re: [sdiy] Multi Segment Envelope Generator
> 
> The heart of the circuit is actually just a "glide" (U2A,U3A).  The
> glide rate has an exponential control on it (Q1,Q2).  The reset of the
> circuit is more or less just an 8x2 sequencer.  One channel controls the
> glide rate, the other controls the level it glides to.  When the glide
> level is equal to the glide output, it goes to the next step.  All of
> this, is of course, controlled by the logic.
> 
> The logic could probably actually fit inside of a single 22v10.  The
> problem I have with doing this is I have found the newer pld's to be
> less than rugged.  The logic could also probably be done with a PIC or
> AVR...but, I am too lazy.
> 
> As far as the comparators oscilating...that is one reason I just
> used regular opamps as the comparators.  Less bandwidth.  I used a
> similar comparator on my 8x2 analog sequencer and it seemed to work
> pretty good.
> 
> Tim Ressel wrote:
> 
>> Jim,
>> 
>> This is an interesting circuit. It is similar to an
>> ADSR I tried to make. Basically a 4-segment version of
>> yours. From the schematic, it looks like this is an
>> exponential generator meant for a linear VCO. Yes? If
>> so, it looks pretty easy to make it linear.
>> 
>> I had a lot of trouble with the comparators on the
>> version I tried. They tended to oscillate from noise
>> when the inputs were near each other. This caused the
>> logic to go nuts. I never went back to see if I could
>> fix it.
>> 
>> Keep on truckin', and keep us informed!
>> 
>> --TR
>> 
> 
> --
> -Jim
> ------------------------------------------------
> * Visit:http://www.silcom.com/~patchell/
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> * -Yogi Yorgensen
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> 
>