[sdiy] CMOS Synth

[Osamu (Sam) HOSHUYAMA]

Hello List,

Finally, my CMOS modular synth (MOSular ;-) began to work as a system!

    http://www5b.biglobe.ne.jp/~houshu/synth/MOSular01.JPG


Frankly, it's a toy project, but not so bad as a toy.  I know that 
plastic lunch boxes can't last so long.  However, they are extremely 
cheap (1 CDN each), and drilling and lettering panels are very easy. 
(Drilling a box took less than 1 hr.  I used 4 sheets of inkjet-
printed paper for the panels.)  The boxes are not robust, but much 
better than bare boards.  I think this is the best choice for my 
limited tools and time in Canada.  I first planned wall-mount modular, 
however, the panel is too weak to support so many plugs unfortunately.


Most of the schematics including block diagram are available here:

   http://www5b.biglobe.ne.jp/~houshu/synth/index.html


Features (that I'm proud of):
  * All the audio signal paths including VCF consist of CMOS 4000 
    series.  No OTA is used.
  * Very compact including Midi to CV converter (Synhouse MidiJack: 
    http://www5b.biglobe.ne.jp/~houshu/synth/MOSular02.JPG)
  * VCOs are temperature compensated using NTC resistors.  Their 
    stability is comparable or better than my PAIA 9700 synth.
  * Almost every module uses just one chip except for VCOs and VCF.
    Very simple in the schematics.


Problems (a little shame):
  * Too many modules are packed in small boxes.  Complex patching is 
    not easy.
  * Power consumption is large because all the amplifiers (inverters)
    are operated in class A.  (Heatsinks are needed for regulators.
    I used 2 sets of 3 terminal regulators to distribute the heat, and
    to reduce noise with VCF and soft sync with VCOs.)
  * VCF and VCA are a little noisy and have some thump with fast attack.
  * S&H's performance is very poor.
  * LFO can't generate real sawteeth waveform (0:100).
  * A lot of resistors need trimming, which depends on the chips.
    I don't want to change the chips. ;-)


Anyway, my absurd but challenging project has been almost completed.
Thank you very much.

Special thanks to Rene Schmitz and Scott Gravenhorst for their
inspiring schematics, and to Harry Bissell, Mike Irwin, and Peter Snow
(and Mark Hammer and Gilles Caron) for their encouragement on the 
packaging.


My deepest sorrow to Columbia's accident.


Sam Hoshuyama
-- - ---  - -- ------ - -------- -- - ---- -
Osamu (Sam) HOSHUYAMA      houshu at rogers.com
                              Ottawa, CANADA
--------------------------------------------