[sdiy] ? Modularizing prepatched analog synths.

[Scott Gravenhorst]

Hello to you.  I can't really comment on the exact synths you
are speaking of, but I am involved in modularizing 2 FatMan
synths.  You probably already know that a FatMan is a
prepatched small modular synth, so what I'm doing is very
much like what you intend.  My efforts began with identifying
where the invisible "patch cords" were inside the synth, that
is, identifying the electrical inputs and outputs of each module.

My approach to this was to first look at what is done in
standard modular setups.  For example, usually only inputs
have a pot as a level control to alter the signal level going
into them.  Outputs are simply a connection to a low
impedance point that presents a full scale output signal for
that module.  This is usually the output of an opamp, OTA, or
discrete transistor amplifier buffers.  In the FatMan, each
output is made from either an opamp or an OTA.

It is required that you obtain accurate schematics of the
synths you are converting to determine these points.  In the
FatMan, the VCOs, ADSR and ASR all have opamps as buffers. 
The VCF and VCA outputs are OTAs.

Inputs are slightly more troublesome to find, but usually an
output (OpAmp or OTA) has a wire (call it a patch cord) that
goes to an input, usually the top end of a pot which is
actually the next module's input.  In a FatMan, the only
place this isn't true is the VCF to VCA connection which is
AC coupled and amplitude reduced through a voltage divider
(think of it as a fixed pot with the level turned way down).

What you are trying to do is maintain outputs at a low
impedance and high signal level because this will be better
for noise control.

You'll also find that once you've modularized, you'll want to
add a few simple modules, like DC mixers to allow expansion
and connection of new modules.

We can be of more specific help if you identify points where
the module delineation is unclear or where unusual electronic
techniques were used.

Hoping this helps you.

Andalong Dudigual <andalongdudigual at yahoo.com> wrote:
>Hello all,
>The reason I have asked about how poly works, is that
>I recently purchased a Kawai SX-240, and a Crumar
>Orchestrator. (both of which need serious cleaning)
>and I wanted to know if anyone here has attempted to
>modularize such things or similar? I like the kawai
>but think that it can do alot more with added
>circuitry, (especially looking at those 8 SSM-2044's)
>The crumar is for pure parts since some goon dropped
>the beast and decided to put the side back on with
>duct tape and finnishing nails.for it I was thinking
>of taking it out of its massive box and adding
>patchability to it by interupting each section and
>adding jacks for each input/output/cv, ect. Any
>information on the two synths, and or modularizing
>similar synths would be greatly appreciated.
>PS. also I know its been on here before, but how does
>one go about cleaning pots and slide pots? all of
>these are really gunky, some to the point of not
>working.
>Thanks.
>
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>Yahoo! Mail SpamGuard - Read only the mail you want.
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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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