help me design an analog gain reduction meter for a stompbox compressor

[tcobretti]

I am trying to figure this out.  What I'm thinking is that I split the signal at the input, phase reverse the clean part, split it again after the effect and combine the effected signal and phase reversed.  Send them thru a booster (mostly just to calibrate the meter) and then to the meter.  It seems like the sorta tricky part will be making sure the signals are the same voltage when they are combined to get an accurate reading.

Will that work?

Am I making this harder than it needs to be?

[Johan]

a little too tired to take in what you're thinking. but, a natural way of doing this is to tap the sidechain, so you get the same controllsignal at both meter and signalchain/gain reduction element. buffer it and driving either an old style needle meter or a LM3916, with a bias feeding the other end of the meter.
if you're thinking of a box being kicked around, I suggest using a LM3916 and LEDs over a neddle-meter
Johan

[aziltz]

needle meter = major mojo

[tcobretti]

It won't be a true stompbox, so the needle should be fine if I can figure out how to make it work.

Johan, I'm digesting what you suggested; I'm sorta tired and drunk.

[PRR]

> Am I making this harder than it needs to be?

Yes.

And probably not gonna get what you think you will get.

What is a compressor/limiter? Usually an electrically-controlled attenuator.

A) meter that electric control signal.

B) set up a parallel attenuator, feed it DC, meter the attenuated DC.


An example for B: many 9V limiters use a resistor-and-JFET attenuator. Get another resistor and JFET. Feed 1V DC into it. Strap the JFET gate to the gate of the audio control JFET. They both attenuate the same amount (+/- JFET matching, a trouble spot). But the extra one attenuates a steady 1V DC. Hang a 1V meter on its output. At no GR it reads 1V. At 6dB GR it reads 0.5V. At 20V GR it reads 0.1V. This is how some very high-class studio limiters do it.

This also works for photo-resistor limiters. Use a DC reference, another resistor, another photo-resistor.

An example for A: a tube limiter drives the gate of a tube negative to reduce current and thus reduce gain. Meter the control voltage you are putting on the grid. Even better: meter the tube current.

Thought for today: plagiarize, plagiarize, plagiarize! Dozens of limiters have been built over eight decades, and many of them have meters. Don't re-invent wheels you can steal... only please call it "research".

> sorta tired and drunk.

Don't drink and derive. (Math-heads call this humor.)

[tcobretti]

Hmm.  Thanks for the tips, I'll do some more research.

Paul, you have been a great asset here.  Thanks for all your help.