silent disco deck switch

7-32 — elektor July/august 1981 K. Kirk silent disco deck switch amounts to a few me transformer. The transformer output voltage needs to be symmetrical about ground and can be anywhere in the region between ± 12 V to ± 24 V. If this is not available then a small separate transformer can be used. Two anti phase 50 Hz signals are derived from the transformer output which are then rectified by- diodes D1 and D2 to produce a series of negative going pulses (100 Hz) across resistor R1. These pulses are then shaped by the Schmitt trigger formed by gates Ni and N2 to produce a series of short spikes. These spikes are synchronised to the the zero-crossing point of the mains waveform andos of mea width of the spikes can be adjusted by This circuit is primarily intended to eliminate the distinct "click" or "thump" which occurs in many disco systems when the record decks are switched on or off. This unwanted effect is produced by back-emf from the motor, which causes a large "spike" to ...