The Flatline's rectifier questions

[midwayfair]

I like the way this rectifier behaves (no rippling and it stays "on" for a very long time), but I'm trying to understand it better.



1) What's the story with that 100uF cap? I think I remember from back when I first breadboarded this that a parallel resistor didn't seem to "work" right to set the decay here and it did all sorts of wacky things to the LED. Why might that have been?

2) Is the LED being lit by both halves of the op amp? Basically, is the input signal rectified *twice* and that's why we have two sets of diodes?

3) Can this arrangement be used profitably for things other than lighting LEDs? Or is there a major difference between what's going on here and other common envelope/rectifier circuits that create a voltage (and then, say, light an LED that's connected to ground).

[EATyourGuitar]

1)at lower voltages from the opamp, the cap is connected to the output while the opamp signal is disconnected. the cap only needs to have enough voltage to pass a 0.3vf + 0.3vf while the opamp needs to pass 0.3vf + 0.3vf + 2.0vf. then when the LED does switch on @ 2.6v (and off), any fast rise or fall in voltage is slewed by the cap.

2) yes it works on both sides. it does not rectify anything. it just blocks the small voltages and passes larger voltages.

3) it is a switching circuit, not a rectifier. other compressors need a control voltage the comes from a filtered rectified guitar signal. then that CV goes to a VCA. this has none of that. totally different. thanks for sharing the schematic, it is new to me.

[midwayfair]

1)at lower voltages from the opamp, the cap is connected to the output while the opamp signal is disconnected. the cap only needs to have enough voltage to pass a 0.3vf + 0.3vf while the opamp needs to pass 0.3vf + 0.3vf + 2.0vf. then when the LED does switch on @ 2.6v (and off), any fast rise or fall in voltage is slewed by the cap.

2) yes it works on both sides. it does not rectify anything. it just blocks the small voltages and passes larger voltages.

3) it is a switching circuit, not a rectifier. other compressors need a control voltage the comes from a filtered rectified guitar signal. then that CV goes to a VCA. this has none of that. totally different. thanks for sharing the schematic, it is new to me.

Thanks for the explanations! This was a big help.