This amplifier, from Philips Databook is suitable for automotive applications. The input resistance is 60k ohms and the frequency range is 20 to 20 kHz.
In this circuit found in the December 1972 Radio Electronics magazine. R can be from 1k to 22k,...
This circuit can operate between frequencies from 1 to 15 MHz depending on the coil. For 3.5 MHz...
This metal detector circuit uses an AM radio as an indicator. The radio is placed off-station and tuned...