via this auction
Pics of the inside below. You can find a demo of one here.
"Late 1960’s or early 1970’s Shin-Ei (Univox) 4 In The Floor Percussion Combo analog drum synthesizer pedal unit.
Works and is in good cosmetic condition (see photos). The four food pedals trigger kick, tom, clave and snare sounds. Rotary trim pots inside the unit (mounted off of circuit board) adjust the envelope of each sound, from very short duration to a nice decay to full-on self-oscillation. Four volume sliders (one knob is missing) control each sound’s level. A rotary “repeat’ control on the side adjusts the speed at which the snare sound repeats for ‘fills’. Runs on two 9-volt batteries or 9 volt power supplies (not included). One of the battery clips is a little flaky and may need additional attention if the unit is to be moved around a lot for gigging. A printout of the schematic is attached to the bottom plate. The screws attaching the bottom plate are not original to the unit but do the job, and one of the rubber bumpers on the bottom is also a replacement.
The sounds are classic analog drum machine, and the ability to adjust the envelopes for each of the voices allows for a lot of sound-tweaking possibilities. All four spring-loaded foot triggers work great. There’s a couple youtube videos demoing this unit that provide examples of the sounds this unit can make. I’ve noticed that if the batteries aren’t fully charged the snare sound is the first to drop down to a click, and in fact on the bottom of the unit it is printed “Replace both batteries if the snare effect become bad or the sustain of other effects become insufficient”. If you make sure to unplug the audio cable when not playing it the batteries won’t get drained (and there’s no power indicator light), but I’d recommend using a pair of plug-in 9 volt battery eliminator units as they will provide consistent power even if you leave an audio cable attached for days at a time."
