On Wed, 3 Sep 2003 Martin.Buehler@KEYMILE.COM wrote:

> Does anyone know of a simple circuit for automatic gain control in audio
> range?
>
> I would like to automatically equalize the audio level, when switching
> playback source.
>
> I think this should be really simple, als even lowest cost tape recorders
> have such circuits to adjust record level.


I don't know about tape recorders, but you can implement simple gain
control with with a diode, a couple of resistors, a capacitor, and a
"variable" resistor. The diode can half-wave rectify the analog signal and
the R's and C filter the high-frequency ripples. This provides some
estimate of the short-term averaged peak signal. The filtered signal
controls the gain. Without knowing your circuit, there's not much I can
offer beyond this point. But if you have a simple opamp configuration
it's possible to either attenuate the incoming signal or lower the gain
with a transistor (and a couple more resistors).

Scott

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