envelope follower question

[Harry Bissell]

Hi Michael

The term "envelope follower" means a circuit that converts the amplitude
"envelope" of an AC signal to a DC level following the overall shape of the
original "envelope" , so...
envelope follower. It has an AC (audio) input, and a DC (envelope) output.
Usually these are some kind of precision rectifier, or peak detector circuit.
They can be simple or very complex depending on the type of signal you want
to put in, vs. the accuracy you want to get out.  The trade is usually "fast
tracking with lots of ripple (ac feedthrough)" or "slow tracking with litle
ripple". Its hard to make a circuit that does both.

Ask anytime...

H^)   harry

michael wrote:

> hi all!
>
> i'm trying to figure out Tom's preamp/envelope follower schematic
>
> http://www.geocities.com/efm_gc/cbook/pics/apm1a_sd.gif
>
> i only see one input and output from the envelope follower. where does it
> take the envelope from? unless i understand wrong, shouldn't there be an
> input signal and an envelope input?
>
> could someone straighten me out on this?   :)
>
> michael