WMD - Synchrodyne

The Synchrodyne is an unusual module which contains parts of a classic synthesizer voice but it has to be seen as an experimental tool for generating and processing sound.

It contains an analog sawtooth wave oscillator with a waveshaper and a PLL circuit which drives the cutoff frequency of the "switched capacitor" filter.

The analog sawtooth-core VCO is built with very modern components providing the stability and speed needed for driving the Synchrodyne. CV inputs for 1V/oct, exponential and linear FM are available. Linear FM can be AC- or DC-coupled with a jumper. Besides a sawtooth output there´s a square wave output with a fixed 30%/70% cycle duty. This duty provides the best signal for the successive PLL circuit and it´s pre-patched to the PLL´s input.

PLL alias Phase Locked Loop is a circuit which follws a square wave and constantly tries to lock to it´s frequency. The faster the frequency, the more imperfect and slow the PLL will react to changes in frequency which will result in strange but interesting artefacts. Two controls with 8 positions each are there for setting the multiplication factor (8² = 64 factors) and one for setting the divider factor to modify the input frequency! The "Track Speed" potentiometer sets how fast the PLL tracks the incoming frequency. Fully CCW it will introduce lots of glissando in the filter reaction. Fully CW and it will over-track, causing the PLL to respond faster than the input frequency. Overtracking produces bursts of high frequency output and low frequency output. Damoing potentiometer dampens the overtracking and sltabilizes the behavior. Influence control and CV input affects both Track Speed and Damping and stabilizes the PLL construct even more

The Filter is a so-called "switched capacitor" filter whose cutoff frequency is solely dependent on a fast clock applied. In the case of the Synchrodyne this clock comes from the PLL circuit and can be fed into the filter clock input with a frequency ratio of 100:1 or 50:1. As you can guess the filter behavior is much dependent on the PLL behavior - the whole Synchrodyne is a construct of units which depend on and influence each other. the filter´s resonance can also be voltage controlled. At the audio input there´s a VCA and a four-stage wavefolder that adds much power to the sound. the filter characteristic can be switched between LP, BP and HP and there are two filter slopes available, 12dB and 24dB.  Per slope there are two outputs, one per and one post an one-stage wavefolder!