AGC circuit virtual ground

Thread Starter


Joined Aug 12, 2009
I'm trying to build the circuit found here, for use with an audio signal.

It says use +-15V but I want to use just +5 volts. I have a virtual ground at 2.5 volts for the circuit too. How can I substitute in my power source

How should I try connecting the circuit?
Should I make the ground shown the virtual ground and connect the real ground to the opamp power terminals
Or do you know of a better automatic gain / volume control circuit?



Joined Jun 19, 2012
The FET is the heart of the circuit, it needs to be considered first.

The main issue I see is that running on only 5 volts you might not have enough voltage range available to get the FET to cut off properly. From the MPF102 data sheet- gate cutoff voltage = -8 volts.


Joined May 11, 2009
I was thinking the same. You will probably get a very narrow gain range.The circuit will not work very good as AGC circuit, if at all. You should simulate this circuit using +/- 15 and +/-volt 2.5 volt before you start to build


Joined Aug 7, 2008
Might consider an analog optical coupler as the gain control element, available with incadescent lamp or LED. 5V should be enough for a 1 V RMS output.


Joined Dec 20, 2007
AGC circuits used by most TV stations sound awful. A background noise like a little SNAP causes voices to disappear for a few seconds!
Loud voices are clamped like they are hit down with a hammer!
If a low level sound follows a loud sound then the low level sound is not heard for a few seconds.
Compressed sounds usually have high distortion.