This circuit was found I a 1965 Radio Schack documentation. The transistors are from that time, admitting equivalents. The transformer has 500 ohm primary and secondary depending on the speaker.
This very high input impedance circuit is suggested by Texas Instruments. The circuit can be...
We found this circuit in the August 1994 issue of Electronics Now magazine. The circuit is based on...
This bargraph circuit using LM3914 was found in the October 1980 Radio Electronics magazine. Note...