amputator - stereo tube filter

optical stereo compressor
reading in those keyboard and production magazines i found an article about legendary optical compressors - very expensive, very few knobs. i remembered about a very simple schematic i got some years ago. Because i had an empty metal-case over i started to build this one. it took about 10 hours. the worst step was to get these holes for the sliders in the aluminium.
the compression is archived by a lightsensitive resistor (LDR) adjusting the amplification of the input signal. the LDR is mounted next to a LED, which lights up in dependance of the input-level. the brighter it gets, the more is the inputsignal regulated down. you could also feed the led with an external LFO to make an optical tremolo out of this. or you can use your hands under a tablelamp to steer the out-level. interesting device ... with only two op-amps (4 if you need stereo) you have a real, optical compressor.
click the small image to the right to take a closer look. on the upper edge you can see the red LED directly lighting the LDR. the LED for the other channel is in the middle of the board. to the left there are 2 additional LEDs to indicate the compression amount on the front-panel.
i also added some attack/release possibilities. i am not an electronic-master. they surely can be implemented much more intelligent. but it works. the whole thing costs about 20 EUR (without power-supply). if you like to build one for yourself, here is the schematics