GEM Drum15
(transistorized analogue drum machine)
This is a small analogue drum machine/ rhythm device. It is not programmable
like a modern drum computer, but by pressing multiple of the locking push
buttons simultaneously, a tremendous variety of additional rhythms can
be created. Very unusual is that this thing doesn't contain any ICs, i.e.
even the flip- flops of the digital counters/ control logics are entirely
made from germanium transistors.
main features:
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15 basic rhythms; a variety of additional ones can be created by pressing
multiple selection buttons simultaneously.
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volume and tempo control sliders. (The tempo range is somewhat limited.)
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"organ" jack for modulating the volume of 2 external signals by the rhythm.
I guess that this was intended to modulate the chords from an electronic
organ. The signal envelopes are modulated by LDRs of 2 light bulb based
opto- isolators.
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completely analogue, transistorized sound generator without ICs. (2 soft
droning drums, transistor noise hihats/snare, woodblock)
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integrated power supply with illuminated switch (which flashes slightly
dimmer during drums by the power drain of the opto- isolator light bulbs).
modifications:
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the transformer wasn't grounded and mains voltage wires almost touched
the metal case =>re-wired and properly insulated. Also the bulb in one
of the opto- isolators (tiny metal boxes with LDR) was burned out =>replaced.
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6.3mm output jack replaced with a common cinch one
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(more will likely follow later)
notes:
This thing has various trimmers to tweak the drum envelopes. Since it is
analogue, likely a lot of pots can be added to control the sounds. The
transistorized PCB looks interesting =>I might upgrade the case with an
acrylic top or similar to make it visible. The electronics uses somewhat
high voltages (18V?), which makes it questionable if sensor contacts can
safely be added. The rhythms are determined by the PCB trace wiring of
the switches, thus theoretically a matrix plug board could be added to
make them sort-of programmable.
| removal
of these screws voids warranty... |
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