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"Obtruta stands for: One Button To Rule Them All.
This device is an analogue synthesizer and sound machine with simplified controls, however the complexity of the sounds it can synthesize still remain vast.
It is constructed from old and recycled parts- oak, mahogany, copper, brass, glass and bakelite.
The sound synthesis circuitry is of my own design, the modules it consist of are:
Two VCOs
Two Envelope generators (AHR and AR / Attack-Hold-Release and Attack-Release)
VCF (low pass with resonance and super-overload-resonance)
Modulator / Weird LFO
Internal signal heterodyner
Light sensor control voltage (CV) level controls
Explanation of operation:
The knife switch is the main power switch. When the button is pressed it activates both the envelopes and the modulator. One envelope controls both the VCOs and the second envelope controls the VCF, the far left switch mixes the modulator with either the VCO envelope or the VCF envelope control voltage. The modulator only cycles when the button is pressed and the frequency of VCO2 is lower than VCO1. Additionally the modulator speed is controlled by the frequency of the two VCOs so strange feedback loops happen when it is directed back to the VCOs.
The level of control voltage applied to the VCOs and VCF is controlled by the light sensors; The center light sensor is for VCO2, VCO1 via the left sensor and the VCF via the right sensor.
The center switch and right switch change the envelope shapes between HR and AHR, the two dials on the front control both attack and release time for each envelope.
The round dial with an arrow controls the filter resonance and can also be driven into super-overload-resonance when turned beyond the half way point.
The meter indicates the modulator level and frequency, the glowing crystals and glass tube show the control voltage level of both the envelopes and modulator, depending to which module it is directed.
Lights can be used as control elements for the light sensors however be aware that they can introduce mains hum through the very light beam itself if they are powered by AC mains electricity! This means that you could modulate the VCF or VCO at audio frequencies using a light source controlled by an audio signal. Modulation by using flashy lights has not yet been explored, I implore you to experiment! The sonic possibilities are vast and unknown!
The output socket can be found behind the small door in the back of the device, closed by a copper latch. The socket is a little bit stiff but I have had no problems using it, it accepts a mono quarter inch jack plug."
"original R.A. Moog Melodia Theremin by Bob Moog probably produced in the early 1960ies.
