This circuit is placed between the instrument pickup and the amplifier input. The same version can be found from other sources in this section. This is from an English magazine from the 80s.
Found in old National Semiconductor documentation, this indicator uses an integrated circuit from...
Other amplifiers of the series like the MC3301, MC3401 and LM2900 can be used in this circuit. We found...
The microwave sensor of this circuit is a common ceramic capacitor. The circuit is from an 80's...