multistage rate level env generators

[Grant Richter]

You don't really need a microprocessor for this. Some CD4000 logic and 
op-amps would do the job cheaply.

Lets say you make a regular 8 stage sequencer out of a CD4051, a counter
chip and output buffer. You could have 8 10K pots to set 8 voltage levels.

If you put a 1 meg pot on the wiper of each 10K pot and a cap on the 4051
output before the buffer you could have adjustable portamento (slope or slew
time) for each stage. (Gabe Catanzaro showed me this one) If you want linear
segments, use a voltage to current converter before the cap.

This could be the start of a multi-ramp envelope, but you need to make the
circuit self clocking. You need a circuit that decides when the slew of the
previous stage is close enough to the target voltage to step the counter to
the next "segment".

Use a second CD4051 connected directly to the pot wipers before the
portamento pots, and address it from the same counter as the first. Use this
output as one input to a standard differential amp, and the slewed output as
the second input. This will give you a voltage proportional to how "close'
you are to the target voltage, or how much of the ramp time is completed.
(It will get closer to zero as the ramp approaches the target).

That voltage could be positive or negative depending on if you are slewing
up or down. So a window comparator could be used to derive a "close enough"
signal. That signal could be used to advance the counter to the next
segment.

A Set-Reset flip-flop starts the process and the last stage resets the
flip-flop and puts everything back to start up again. Additional logic could
be used to make one stage a "sustain" stage and the pots could be powered
from +/- to make bipolar envelopes. The circuit that decides when the
ramp is close enough and generates an advance pulse is the key.

----------
>From: patchell <patchell at silcom.com>
>To: "M.Ruberto" <indridcold at usa.net>
>Cc: synth-diy at node12b53.a2000.nl
>Subject: Re: multistage rate level env generators
>Date: Sun, Oct 22, 2000, 10:08 AM
>

>     Although I never actually completed it...I did something like that, but it
> was hybrid.  The core was analog, used an OTA to make the standard voltage
> controlled RC network, it had two inputs, one to control the rate, one to
> control the level it would ramp to.  And there was a window comparator to tell
> when the output was settled to the level voltage.  The other half was a micro
> controller.  The parameters were stored in memory.  In theory, I could have as
> many stages as I wanted....but, I will never know, I abandoned the project
long
> ago.  I keep thinking I will get back to it sometime....maybe.
>
> "M.Ruberto" wrote:
>
>> hi,
>>
>> lately i've been thinking about designing a multi-stage rate/level envelope
>> generator. i think i had this idea once before but never moved on it. i have
>> some interesting thoughts about how to make it work but before i start
>> protoboarding i thought i'd ask if any of you folks have seen this done in
>> analog before. if there are designs out there i would like to see them.
>>
>> thanx
>>
>> -<mike>-
>>
>> ____________________________________________________________________
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>
> --
>  -Jim
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