Exponential Converter

Version 0.1 from February 2021

Exponential Converter that I built for my modular synth drum machine project. I wanted a snappy release based on the linear one from the Envelope Generator (EG). This will make the snare drum sound natural.

It’s based on a design by Robin Mitchell in “DIY Synth Series Part 1 — The Exponential VCO”.

Details

To find transistors with the same HFE, you have to match them. I used the instructions described in “Transistor matching” by Kassutronics 👍

For the calibration I build a testing circuit with different voltage inputs (set by trimpots) and checked the output with a multimeter. You can see a photo of that and the resulting chart below. With the trimmers I set it to peak at ~10 volts input because this is where the CV of my envelope generators peak.

Links

• Video Demo
• Schematic (PDF)
• Stripboard Layout (PDF)
• Front Panel (PDF)

Improvement Potential

See the comments on Instagram and Reddit.