The SA-21 is a typical Casio Tone Bank keyboard
from the last part of the 1980's, with a full serving of corny rhythms
and 'super accompaniments' and a 100 different PCM sounds, of which
a large part are more curious than musically usable. Half toy, half
musical instrument when new. Real cool retro-kitch today.
A small value potentiometer mounted on the positive lead from the
battery to the circuitbord enables you with some delicate
fine-trimming to choke the power supply just enough to make
the instrument function highly erratic without shutting it down.
The results are unpredictable and exciting. Ranging from "chaos-in-the-orchestra-pit"
and "run-amok-transitorradio" to endless drones or merely
a short click and then silence. At rare occasions rhythms or demo-tunes
can be brougt to repeatedly loop or glitch for a few beats before
One speaker can be switched to a alternative line-out, which is
usefull since the glitching/crashing acts differently than when
the build in line-out is used.