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DIY | VCO | Multi phase | Ian Fritz

VC Multiphase Oscillator by Ian Fritz presented in this thread : http://electro-music.com/forum/topic-19841-0.html&postdays=0&postorder=asc&highlight= from Ian himself on this circuit :

This multiphase oscillator may be switched between 6-phase and 8-phase operation. Of course by using appropriate subsets of the six or eight signals, 2-phase, 3-phase or 4-phase operation is easily achieved.

The circuit is illustrated below. At first glance this looks like a four-pole filter with feedback. But look again -- it is really quite different and more subtle than that. The difference? This circuit has negative feedback around each individual stage. The feedback resistors are carefully chosen so that the linear part of the system (small signals) oscillates, but just barely. On startup the oscillations build up slowly over dozens of cycles.

At large signal amplitudes the zener diodes begin to conduct, adding additional negative feedback that prevents further growth in amplitude. In other words, large amplitude signals decay over time. The delicate balance between these opposing forces cause the system to perform stable, high-purity sinusoidal oscillations at a finite amplitude. The amplitudes are adjusted by the two "Level" trimmers, which vary the strength of the nonlinear feedback.

The six-pole switch (Sa-Sf) allows a choice between six phase and eight phase operation. Using alternating outputs give three and four phase operation.

visit Ian's homepage for more info on this circuit and demo : http://ijfritz.byethost4.com/sy_cir11_68phase.htm