[sdiy] Roland TB-303 "square" wave variation

[Richie Burnett]

How the shape of the 303's square waveform changes over the pitch range from 
10Hz up to 1kHz:

http://www.richieburnett.co.uk/temp/303sqr.gif

The broad rounded waveform is at the lowest frequency (about 10Hz,) and the 
tall narrow pulse is at the maximum frequency (about 1kHz.)

There's only a small region around 85Hz on my TB-303 where the duty ratio is 
50% and the shape is practically square.  All this funkiness is a result of 
using an over-driven common-emitter amplifier to clip the VCO's sawtooth 
waveform into something that is approximately square in shape.  No wonder it 
has a unique sound.

-Richie,