De Modules Notes

Malekko /Wiard/Richter Oscillator[modifier]

Grant Richter, from muffwiggler forum :

This is the "East Coast" oscillator for the system. It is a sawtooth core which is traditional for east coast synths versus triangle cores are more "West Coast".

In my humble opinion triangle cores produce a more musical results than sawtooth cores using linear FM, that is why the linear FM on the sawtooth oscillator is restricted to 0 to 360 degrees of modulation.

This is the classic sawtooth core developed by Terry Michaels and used by everybody and his uncle. The ancestor to it is in Electronotes #62.

That is where the difference ends. All the modern improvements are implemented, such as the use of Rossum rather than Franco high frequency compensation. This mean the sawtooth does not change shape with frequency which allows it to be coupled to a public domain 0 to 360 degree sawtooth phase shifter.

This produces identical but phase variable sawtooths which are are sent down parallel and identical waveshapers chains. Saw1, Tri1 and Sqr1 would correspond to the usual "inphase" or I outputs. Saw2, Tri2 and Sqr2 would correspond to the usual "quadrature" or Q outputs if they were only 90 degrees shifted. Since these three waveforms shift 0 to 360 degrees relative to the I outputs, we'll call them V for variable. A simple zener diode on the op-amp summer is used to try and restrict the sum of the fixed and external phase mod to the 0 to 360 degree range. Large modulations will produce glitchy results but won't hurt anything.

The "Fine" knob is a pull switch which will switch to the LFO mode. In this mode the "Coarse" control goes from approx. one cycle per 10 seconds to 40Hz. In the audio mode the "Coarse" control goes from around 10Hz to above 20KHz.

The external phase modulation will produce a nice vibrato with a small setting and 7 Hz or so sine input. Audio rate modulation will produce typical FM timbres but "cleaner" sounding somehow, because the phase vector is limited to within a single rotation.

Ambisonic Field Generation: When stereo was first introduced, many mono recordings were released with the original mono in one stereo channel and a 180 degree (inverted) version of the mono track in the other stereo channel. These were given all kinds of catchy names, but the one I remember was "ambisonic".

In fact it is surprising how little phase shift between left and right channels is needed to produce a 3D stereo field. The "width" of the field is variable between narrow and wide depending on the amount of phase shift. So the I and V outputs are designed to be used as the start of a true stereo patch.

Waveshaping: Adding and subtracting different waveforms with various phase shifts produces a large number of waveform variations. For example: Adding Saw1 and Saw2 goes to an octave shift at the 50% phase shift point, while subtracting the two produces traditional pulse width modulation.

Exponential Modulation: This is the typical input and fader you would use with an LFO, Sample and Hold, or unquantized sequencer.

Synch: This is the much beloved hard synch input typical of east coast synths. A square wave or waveform with a hard edge is needed, a triangle or sine will not work. For and interesting sound, try the "Mayhem" output of an Anti-Oscillator into the synch input of an Oscillator and vary the waveform control on the AO while monitoring Sqr1 of the Oscillator.

Phase Variable Synch: By taking the Sqr2 waveform of one oscillator to the synch input of a second, you can control the phase offset between the two VCOs.

Sine wave output: This is a special design for us by Terry Michaels. It has the lowest total harmonic distortion of any analog keyboard tracking VCO. For example the THD of an ARP2600 is around 10%. This sine generator produces typically less than 0.2% THD. The second and third harmonics are below -60dBv and can be better than -70dBv on some units. The use of such a pure sine wave will completely change your experience with a balanced modulator. Since balanced modulators produce two output frequencies for each input frequency, any harmonics in the carrier waveform fill up the frequency bins and produce the "muddy" sound your used to. The use of such a pure carrier allows even acoustic piano chords to remain pristine.

Wiard and Malekko would like to Thank Terry Michaels (Mikulic) for his decades of invaluable contribution to the development of electronic music circuitry which he generously published in Electronotes.