Found in a 1980s American documentation, this circuit has a current consumption of only 1 mA. The crystal can be from 100 kHz up to a few megahertz.
Circuits like this one, using the LM386 audio amplifier, are available from other sources in this...
This bass and treble control only attenuates the corresponding signals, requiring further...
Using a large inductance, this circuit was found in a Popular Electronics from the 90s. The...