Big Fat Mamma - DIY Cheap Modular

[Chris Thorpe]

This is my first contribution to this list - sorry if it seems to run 
somewhat against the prevailing philosophy but bear with me...
Looking at the postings to this list and other stuff elsewhere on the 
net, analogue modular enthusiasts seem to want one of two things - 
EITHER  - the best possible giant system 
OR  - anything at all just so long as it's cheap, fun to build and quick 
from first solder smoke to first musical results.
All power to the first group for keeping the standards high but I'm of 
the latter persuasion.
One milestone event for those who think like me was the appearance of 
the PAIA FATMAN, John Simonton's masterpiece of simple, effective and 
economical engineering. It sparked a whole wave of mods & tweaks ranging 
from adding a switch to phase locked loop trackers and complex sound 
generators (Scott Gravenhurst and others - keep 'em coming).
Looking at all these parts, I kept seeing the germ of a collection of 
circuits for an ECONOMICAL modular synth.
Then I thought I'd share my thinking so far and see what other feel 
about this subject.

PHILOSOPHY
What's needed is a set of design guidelines so that anyone who feels 
like building or designing a cheap modular synth has confidence that all 
their modules will work together. Publishing the spec online taps into 
the whole community of analogue-synthists - the design of the synth 
becomes a collaboration with people contributing whatever they can add 
to the pool. The target of this spec is probably -
 - impecunious
 - impatient
 - doesn't own a scope!
Therefor -
 - no module should cost more than an arbitrary cash limit to build 
   ($50?)
   (one could break this rule by, say, splitting oscillators & wave
    shapers into separate modules)
 - modules would follow a standard, FATMAN compatible, set of levels
   (8v pp, 1v/1kHz, etc.?)
 - no module would be thought too wacky for inclusion
   (voltage controlled shortwave radio?)
The FATMAN is the godfather of this idea so the name ought to reflect 
this - Big Fat Mama?

WHY VOLTS/Hz
 - it's cheaper (modules can use standard components)
 - easier to set up & stabilize
 - as long as one can get musical results out, who cares?

HARDWARE
With any modular, the bugbear is always the hardware.
CASING - I suggest either PAIA's FracRack or standard 1u rack panels 
(possibly turned sideways). Unless anybody can come up with something 
cheaper....
PSU - Use surplus PC power supplies? These offer beefy stabilised +12, 
-12v & +5v. And who really enjoys building power supplies?
CONNECTORS - Molex for power (keep within that PC standard). Banana 
plugs for signal & control (no multiple panel sockets needed - keep 
those per module costs down!).

SUGGESTED MODULES
The usual plus
Wide range vc-clock generator to drive
 - bucket brigade delays
 - shift register type noise generators & complex wave generators
 - switched capacitor filters (I've seen one of these chips with 
   80db/8ve cutoff!)
Spring reverb (with feedback!)

COPYRIGHT
Note that the PAIA FATMAN and all the published mods are the copyright 
of their respective authors. It's entirely up to them if they feel like 
either adapting or allowing their efforts to be adapted for this 
purpose. Designers of new modules need to keep the laws of copyright in 
mind if their efforts are not wholly original.

OK, that's it. What do you think?

 - Chris Thorpe, cheapskate would-be synth builder.