Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 254

Circuits 32 and 33: The audio signal is rectified by D1 and delivered to the base of T1. If the threshold is
exceeded, T1 is electrically conductive, LED1 goes on or M1 shows deflection. Higher signal values result in
higher T1 collector current.
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Fig. 3.33: Circuit 33: Peak VU meter with coil-
moving instrument
Fig. 3.34: Circuit 34:
LM antenna amplifier
for antennas with
longer wires