Audio Signal to Gate Convertor

Ray Wilson authored this content while he was actively running MFOS as the founder and resident genius.
We retain the content because it reflects a valuable point of view representing that time and place.

Article by Ray Wilson
This project is an older design and has most likely been superceded by a newer one. However, it is still a viable design and useful for your home-brew synth. Sorry but most of these do not have circuit descriptions, parts lists or PC board layouts (They really put the 'Y' in DIY). The designs are here for individual and educational use only and no permission is given for large scale production for sale.

This is an intermediate to advanced project and I do not recommend it as a first project if you are just getting started in synths or electronics. Only the circuit and some explanation are shown here. A lot of project building, troubleshooting and electronics experience is assumed. Additionally, electronic equipment ownership (scope, meters, etc.) is taken for granted. If you are interested in building this project please read the entire page before ordering PC boards to ensure that the information provided is thorough enough for you to complete the project successfully.

Introduction

This circuit simply amplifies the signal fed into its input, rectifies it, feeds the resulting high-gain signal into a pulse stretcher and feeds the resulting logic signal to the output via a 1K current limiting resistor. You can feed in a guitar signal for example and create a gate signal everytime you hit a note. The signal is also fed out (with some gain) so you can input it into synth modules (like VCFs or VCAs).

Audio Signal to Gate Convertor Schematic