tri2sin

[Tony Allgood]

Hi folks,

My polysynth is getting revitalised. My first task was to rescale its VCOs..
what a task. Then I sorted out a simple triangle to sine converter for two
of the LFOs that drive the PWM. I wanted something simple that I could fit
without major surgery. So I tried the simplest of all. A resistor feeding
two diodes of opposite polarity in parallel and tied to ground. See
Formant's tri2sin. Worked well, I don't know how good in terms of THD. Then
I tried using four diodes. One 68K resistor feeds the output. This is
clamped by a network of two diodes and a 12k in parallel, joined in series
to another two diodes in parallel, which in turn is connected to ground.
Output load will affect performance, I was using a 10k pot. The input signal
was a 6v peak triangle, typical output from a integrator/comparator LFO run
off +/- 15V. The output was just 1v peak. A good quality output was
obtained. The resulting PWM was much more smoother and more musical somehow.
Non-uniform rates of change one wonders.

Regards,

Tony Allgood, Cumbria, UK

e-mail: oakley at enterprise.net

Rack mounted Moog VCF module. Details to be found at...

http://aupe.phys.andrews.edu/diy_archive/schematics/effects/filter.html