Audio to Gate detector/convertor?

[frequencycentral]

Any suggestions for a simple opamp circuit to derive a fixed voltage from a (guitar) audio signal out there? I guess I'm thinking a window comparator maybe, am I on the right lines?

[StephenGiles]

Look at the EH Microsynth circuit, I'm it has a signal present detector - far too difficult  for fuzz boxers

[frequencycentral]

Look at the EH Microsynth circuit, I'm it has a signal present detector - far too difficult  for fuzz boxers

Thanks Stephen! Hey -I ain't no fuzzboxer!

[StephenGiles]

Look at the EH Microsynth circuit, I'm it has a signal present detector - far too difficult  for fuzz boxers

Thanks Stephen! Hey -I ain't no fuzzboxer!

I know you're not! Look on p1 of the mk1 Microsynth circuits - everything you need, but I don't think you can do it efficiently with one opamp.

[frequencycentral]

What I want is a LED to fades in as the guitar note fades out. So I think I'm looking at a detector followed by a decay circuit followed by an inverter, the output of the inverter driving the LED, which is hooked up to an LDR. Seems so simple when you say it fast. I've looked at the Micro Synth circuit, I'm also looking at the Korg MS20 External Signal Processor and the Roland 100m Gate Delay. The Roland uses an opamp and a 555, I have to figure out if I want to use a vref or a MAX1044 for bipolar power. A simple idea soon becomes a big parts count!

MS20: http://dl.getdropbox.com/u/967492/circ2.gif

100m: http://dl.getdropbox.com/u/967492/s100m10b.jpg

The Roland schematic sheet is also of interest for it's voltage controlled phaser and voltage controlled BBD delay.