Rectifies an AC signal and filters out high frequencies
Ideal for monitoring audio signals on a meter or LED display.
CIRCUIT DETAILS
Input
An AC signal from 1 to 12v
Output
A DC voltage matching the peak of the higher frequency input signals.
DEMODULATOR RectifierLow Pass Filter
Explanation
The circuit works in 2 parts:
First the negative siganls are removed by the rectifier D1 & D2
Then the higher frequencies are removed by C2 & R1 acting as a low pass filter - so the output follows only slow changes in the input signal
Circuit Simulation
To change the response of the output, adjust R1 & C2.
Increasing R1/C2 slows down the output response
Decreasing R1/C2 speeds up the output.
Blue Trace = Input Red Trace = Output
APPLICATION
This circuit is useful for monitoring peak audio signals from a music source and driving a meter or dot/bar display driver. The circuit bricks for an audio meter are shown below.
Note the diodes used are germanium types which have a voltage drop of around 0.1-0.2 volts rather than 0.7 volts for a silicon diode. This reduces the loss in signal. Take care not to overheat these when soldering them.
