Big Fat Mamma - DIY Cheap Modular

[Christopher_List at Sonymusic.Com]

  > 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.
  > OK, that's it. What do you think?
  >
  >  - Chris Thorpe, cheapskate would-be synth builder.

  Couple of quick things to keep in mind -
  1. The cost difference between a v/Hz VCO and a v/oct VCO is negledgable
  UNLESS you want it temperature stable. If you don't care about the temp
  sensitivity, the parts count can differ by as little as 1 transistor, one
  op-amp and a handful of resistors. Since MIDI-> CV converters that output
  v/Hz are often more expensive than those that output v/oct you might want
  to think about the cost trade-off. You've got to generate an exponential
  scale <<somewhere>> in the system. The Fatman does it via sneaky use of
  the uProc and table look-ups. If you really don't care about mapping your
  notes to a keyboard (ie you just want to make cool synth noises) then you
  shouldn't care about temp. stability - so make a cheap expo. converter
  for in the VCO (i.e. normal transistors and no temp-compensating
  resistors)

  2. The cost of the case and knobs is very often more expensive than the
  electronics. You'll probably save more money by putting the whole thing
  in a big plastic box and not getting FracRack panels than you ever
  possibly could by simplifying the circuits. Your basic non-voltage
  controlled ADSR is a perfect example.

  3. Along the same lines, super-simplifying your modules can save cost,
  but will lead to more patching. For instance, you could take the "depth"
  knobs for FM and PWM off of all of your VCOs and just have a couple of
  separate "stand alone" attenuators. Do this with all of your modules and
  you'll save a lot parts - but you have to do a lot more patch cord
  routing - if that's no big deal to you, it's something you should keep in
  mind. You may still, however, want to show the attenuators on the schems
  for each module - just as a reference for the builder - to say "this is
  an input (or output) you might want to scale".

  Just some food for thought. While I tend to be a proponent of fancy parts
  (just because higher tolerances help cover up my lack of EE skills :) - I
  think a lot of the circuits discussed here are simple and economical.
  Most of them come from Electronotes and they were definitely striving for
  simple low-cost designs. I think the Electronotes Preferred Circuit
  Collection is exactly the sort of collection you're asking for - provided
  you don't follow every circuit to the letter and make some of the
  adjustments and substitutions I described above.

  - CList