Preamp with AGC

martin

nope IDRC

martin

Haven't looked closely but this schematic basically explains how it's done. You'll need low power opamps but there are plenty these days. One quad version would do. Keep in mind that for ham radio and especially SSB it is best to add a "fast attack - slow release" feature in the feedback. Otherwise your voice will sound like a circus announcer ;-)

This schematic is probably rather old. Schottky Diodes such as the BAT54 should work as well.

Ooops, forgot the link:

Thanks for your replies. The 'THAT' processor looks like it would do the job but is probably overkill for what I need (plus it's quite expensive).

I'll probably try the op-amp/jfet circuit. Interesting to see that the key to the agc is to use the resistive region of the jfet. I was thinking the variable gain would be done with a non-linear component.

Rob.

Has to be linear, else you'll end up with distorted audio. There are many other ways, for example Gilbert multipliers, dual-gate FETs and so on. The opamp/JFET combo is just one of the solutions and it works (I've used it).