This is a pre-built version of my Twin-T notch filter/kick module.
The Twin-T is an interesting circuit - it consists of what amounts to a low and a high-pass filter in parallel, thus will filter out a narrow range of frequencies (hence 'notch' filter) but under certain circumstances it can also act as an oscillator, which gives rise to some interesting possibilities. I envisaged two possible use-cases for the module:
Firstly, as a notch filter - whilst not quite as exciting as their boring low/band/highpass siblings, depending on your input waveform you can get some pretty freaky effects out of it. However, it works best as a kick/percussion module, though - this was the original intention. For best results, use the output of an envelope generator as an input - my DV3 dual-AR module was designed for just this purpose but you can use an ADSR module if you prefer.
The ideal envelope will be short (almost trigger-ish) with a fast decay - use the level pot, in conjunction with the envelope attack, to reduce any click. Different effects can be obtained by judicious tweaking of the envelope.
Despite having a fully analogue signal path, not everyone digs the sound of the Twin-T - having said that, with some careful tweaking and maybe some post-filtering (try a resonant bandpass filter ...) it can sound pretty good.
Supplied fully built and tested; the finishing kit includes Alpha pots and Davies-style knobs - the panel is 3HP (~15mm) wide and fabricated from laser-cut perspex. A power cable and mounting hardware are included
You can get the lowdown on the circuit and whatnot here: https://bitbucket.org/yorkmodular/tt-kit/src/master/