About the Sinulator
The Sinulator is a Eurorack module based on our SineCore Modulator, built in collaboration with West Oakland Music Systems (WOMS). It is an improved version of the SineCore Modulator with +/-1080 degrees of modulation before distortion. There is also an integrated VCA and offset/gain knobs for both the VCA and modulator. The Sinulator can be used as a sine wave shaper, converting either a triangle wave or sawtooth wave into an extremely low distortion sine wave. It can also be used as a wavefolder with up to 6 folds in either polarity, controllable by the VCA CV. Finally, it can be used as a phase modulator (PM) with through-zero capability.
How to use the Sinulator
The Sinulator performs the following mathematical function:
AUDIO OUT = sin(A*(n*B+j)+(m*D+k)),
where A is "AUDIO IN", B is "VCA CV", D is "MOD IN", and the pot settings are m for "MOD AMOUNT", k for "MOD OFFSET", n for "VCA MOD AMOUNT", and j for "VCA MOD OFFSET". So, the only difference between "AUDIO IN" and "MOD IN" is that "AUDIO IN" goes through a VCA, whereas "MOD IN" is pot controlled. The amplitude of the VCA is controlled by the sum of the "VCA MOD OFFSET" pot and the "VCA CV" attenuated by the "VCA MOD AMOUNT".
For linearly increasing input signals (ramp and sawtooth waves), the output is a pure sine tone. To use the Sinulator as a sine waveshaper, insert the oscillator into either the "AUDIO IN" or "MOD IN", and adjust the amplitude with their respective controls until you have a low distortion output. Next, adjust "MOD OFFSET" to exactly zero the input. You might have to go back and forth between the offset and gain to get the lowest distortion. To make higher harmonic sinewaves, simply increase the gain to the next harmonic.
To implement phase modulation (PM), insert a sawtooth wave into the "AUDIO IN" and adjust for a pure tone. Next, insert you modulation signal into "MOD IN", and adjust "MOD AMOUNT" to the desired modulation depth. You can also reverse your inputs, which gives you a VCA for your modulation. A sinewave as the modulation source and an envelope as the VCA CV works quite well.
To implement wavefolding, apply your oscillator to "AUDIO IN", and your modulation source to "VCA CV". The output will pass through harmonically rich tones between each pure tone at integer multiples of the fundamental.
As with all Open Music Labs projects, we encourage tinkering with electronics. The Sinulator has a few patch points that can be used to extend its range.
- Linear output VCA - The final output of the Sinulator can be amplitude modulated with an external CV. This can be done either linearly or exponentially. For linear control, cut the trace between the 2 pads of J2, and apply a 0V to 5V signal to pin2 of J2 (the round pad). if you want 0V to 10V control, add a 36k resistor in series with your input CV. Use an input jack that is normalled to +5V, so that the output is enabled when no signal is present.
- Exponential output VCA - For exponential CV control, cut the trace between the 2 pads of J7, and place a 1k resistor between those 2 pads. Next, connect a 47k resistor from pin1 of J7 (the square pad) to your CV input. Finally, cut the trace between the 2 pads of J2 and place a 1M resistor between these 2 pads. This will allow a -5V to +5V signal to set the output from -60dB to full open.
- Wider offset range - the phase offset knob controls the output over +/-180 degrees. To increase this range over the full +/-1080 degrees, and into the distortion region, place a blob of solder on J8 such that both pads are now connected.
C14 moved from ground to negative voltage rail to improve noise immunity on the LM13700 current source.