This circuit allows the use of an electret microphone with a 1.5 V source. We found it in the Encyclopedia of Electronic Circuits volume 5 from 1995.
This circuit was obtained from a 1965 Radio Electronics. The semiconductors used admit modern...
In the bridged configuration the TDA2002 amplifier can supply 30 W of power at a load of 4 ohms...
This circuit converts a high voltage into a frequency using an optical coupler. The transistor can be 2N2646...