ASR Envelope

My first envelope was a traditional ADSR envelope, adapted from Yusynth's design which uses a (7)555 timer as the core logic element. That design works great, but I originally made it only on prototyping board. Recently, in need of more envelopes, I decided to make a proper PCB layout, and revisit the envelope design in the process.

I realized that in typical uses of an ADSR envelope, I tend to set the Decay and Release controls to roughly the same value. This gives the decay and release portion of the sound the same time constant, which often sounds natural to me. I decided that it would be handy to have some envelope generators where the Decay and Release time combined in a single knob, and the result is this module which I called ASR envelope.

Transistor ladder filter

When I started with synth DIY, I knew little about how transistors work, and the famous Moog transistor ladder filter just looked like magic. Intrigued, I stared long at the schematics posted by Yusynth, and worked my way to the very detailed and mathematical analysis by Tim Stinchcombe.

Avalance VCO

Thanks to Look Mum No Computer, a super simple oscillator circuit has been popular lately based on the reverse avalance breakdown effect in normal transistors. I decided to experiment with this idea myself, and in particular see if I can add basic V/Oct control to it.

VCO 3340

The CEM3340 VCO chip is one of the legendary chips designed by Doug Curtis that played an important role in the analog polysynths of the 1980s. By integrating a complete analog VCO on a chip, it made more compact and cost-effective synth designs possible.

Together with the classic analog polysynths themselves, the Curtis chips have long been out of production. In 2018 however, thanks to the new boom in analog synthesis, the 3340 VCO chip is once again available, from no less than three sources. Curtis' own company OnChip Systems re-issued the CEM3340 Rev. G, and cloned/compatible devices are available from CoolAudio (v3340) and from the Latvian company Alfa (AS3340).

Precision attenuverter / mixer

The word attenuverter, a combination of attenuator and inverter, has become pretty standard in the modular synth world.  The attenuverter does exactly what it's name suggests: it is a single control that can be used to attenuate and optionally invert a signal. Turn the control clockwise to get an attenuated version of the input signal, and counter-clockwise to get the inverted version. With the control at center position, the output is simply off.