The go-to phaser builds for DIY’ers are:
Phase 45 – Intermediate build. 2 stages. FET matching required. No regen. Very subtle.
Phase 90 – Advanced build. 4 stages. FET matching required.
Ross Ropez – Advanced build. 4 stages. OTA design.
Small Stone – Advanced build. 4 stages. OTA design.
The design concept for “Causality 4” was to achieve a musically useful intermediate build 4 stage phaser with regen, using easily available parts, and requiring no matching of components. It has two swept stages using a dual OTA, and two fixed stages using opamps. The LFO utilises a dual opamp and is based on the MXR phasers, much simpler than the LFOs in either the Small Stone or Ross Ropez. The fixed stages came from an idea suggested by Mark Hammer in this thread: http://www.diystompboxes.com/smfforum/index.php?topic=80111.0
Having four stages, even if two are fixed, allows for the addition of regen, which for me is a phaser essential. The Regen control goes from zero to just short of self oscillation - some great sounds available here. The Depth control is particularly interesting and useful, specifying where in the spectrum the phasing occurs.
Your critiques are welcome!
Soundclips, perf and PCB layouts to follow - it's on the breadboard ATM, I want to build it first.