• Front End Linear VCA
• Switchable Four Stage WaveFolder
• TempCo Sawcore VCO
• Linear (AC/DC) & Expo (DC) FM
• Bipolar Attenuators for FM
• Calibrated 1V/Oct Input
• Hard Sync Input
• VCO Range ~.02Hz – >=400kHz
• Phase Locked Loop
• PLL Frequency Multiplier/Divider
• Variable Slew & Damping in PLL
• Switched Capacitor Filter
• Multimode Filter Output
• -12 & -24 dB/oct Output Taps
• Stable Self-Oscillation at -24dB/oct
• Voltage Control of Filter Resonance
• Single Stage WaveFolder on Outs
• Expandable
• 14HP, ~60mA Power Draw
• 100% Analog/Discrete/CMOS

The Synchrodyne is designed as a way to implement a switched capacitor filter (SCF) chip without the use of a microcontroller to run the clock. We developed a fast analog VCO that can drive the SCF with a broad range of frequency control. The problem with this would be that the VCO is then dedicated to only running the filter. So we designed a frequency multiplier based around a Phase Locked Loop IC (PLL) to take the VCO and multiply its frequency up so that the VCO could be used as an audio source, while still controlling the filter. The SCF has a frequency ratio of 50:1 or 100:1 clock frequency to output cutoff frequency. The PLL allows for many ratios of input to output frequencies to be selected, making the VCO a simultaneous audio and control source. The PLL introduced its own challenges. Taming the PLL to stabilize at high multiplication ratios required us to develop a damping circuit. The Damping and Track Speed controls cause the PLL to have its own sound, sort of a slew limiter and self Frequency Modulation. We wanted the Synchrodyne to distort nicely with audio input, and also to self-oscillate. We added single stage rectifiers to the -12dB and -24dB filter outputs for a more aggressive sound. We opted to develop a VCA and wavefolder for the front end of the filter to further expand the palate of distortion and processing of the Synchrodyne. We had more features to add, but space was limited and we didn’t want to make an excessively expensive module, so we added two 14pin expansion headers for future development.