The schematic above depicts an addon for the FatMan which will add the
This circuit is actually 3 separate pieces as denoted by the colored
background. The LFO is in pink and the Triangle SubOctave is in blue.
The basic VCO and PWM is against white. The pink and blue parts are
optional, and all that is required to make the cicuit work without them
is simply to eliminate them. This means you can build as much of it
or as little as you like, and if you decide later to do more, the colors
make it clear what else to build.
- Sawtooth VCO with Voltage Controlled Pulse Width Modulation
- An LFO as one control voltage source to drive PWM
- A suboctave (subharmonic) that outputs either square and/or triangle
The whole circuit is tested, but there are some minor adjustments
required to the drawing.
The Triangle SubOctave will
output a more or less triangle wave, not perfect, because the sawtooth
that is driving it is not perfect. However, my mission was not to produce
a perfect triangle, rather just to get close; to change the timbre of the
suboctave to something more sine like than a square wave. I do not know
if this circuit is original.
Some part values have changed from René's original design due to changing
the power supply from a balanced +/- supply to the odd +8 -12 that the
FatMan uses. I am now doing all development and tests on a FatMan style
ICs required to build the whole unit:
Note that all of these parts are common and relatively inexpensive!
|2||...||4069 CMOS hex inverter|
|2||...||TL072 JFET input opamp, dual|
|1||...||4027 CMOS Dual J-K flipflop|
|1||...||4066 CMOS analog bidirectional switch|