This high input impedance circuit was found in American documentation from the 1980s. The power supply must be symmetrical. The circuit applies to modern operational.
We found this circuit in an 80's Radio Electronics. The circuit uses a PTC sensor and an LED...
In this circuit a 12 V lamp or LED blinks with the music signal applied to the input. R depends on...
Using a period sensor, this circuit was found in the February 1986 issue of Radio Electronics...