Re: VK3YE AGC pcb.
Paul Galburt - K2AYZ
Nice feedforward audio limiter/compressor. Back in the day, when I designed professional audio gear, I sometimes used packages like this
for such applications. The main limitiations were transfer curve repeatability from unit to unit, limited overall dynamic range, and somewhat slow attack time for some applications.
Ultimately designs based on log characteristics of semiconductors worked better (like THAT 2180 part).
LED/LDR work fine here, except that sharp spikes will sneak throught the attack delay.
I have a batch of about 50 odd 2180's left from the old days that I hope to press into this service. These were kicked out of production THD tests on audio consoles where the limit was 0.005% THD.