[sdiy] Simple compressor, agc, ?

[Scott Juskiw]

At 12:10 PM +0000 2004/09/30, Toby Paddock wrote:
>Howdy,
>I'd like to build a very simple AGC type thing
>for a "tuning display". Room mic (or whatever
>tuning standard) gets compressed like 100% and
>drives the horizontal of an o-scope. Whatever
>you're playing gets compressed some and drives
>the vertical. Then look for lissigu...
>lissajue... lissijou...   some of those patterns.
>
>Need:
>Pretty high compression.
>Cheap and easy.
>A few volts output. Either +/- or 0-V.
>
>Don't care too much about:
>Distortion, noise, speed, freq response.
>
>Thanks,
>Toby Paddock

Many years ago I built the one from Craig Anderton's Electronic 
Porkchops for Musicians book and it worked great (I still have two of 
them). Very simple design, only 3 op amps, uses a vactrol in the 
feedback loop. Project #8 in the book.