Simplest LED "overload" indicator circuit?

I'm trying to find the most simple circuit to light up a LED when the input level hits a certain level, around 16dBu.

Need:

Very high input impedance. (Or certainly high enough to not bother the "CUT"; circuit under test.
Full wave rectifying (would precision rectifying be needed?)
Find a way to power the circuit from a +30vdc power supply. (Would a simple resistor railsplitter virtual ground be sufficient?
Have a RC circuit to have some crude control over the lenght the LED will be lit after the peak has passed.

Any ideas?

A comparator (dual LM393) should be fine. Or if you really wanted to cheap out, you could probably even get away with a single transistor (i'm thinking MOSFET, since it wouldn't need any input bias current).

supersonic said:

I'm trying to find the most simple circuit to light up a LED when the input level hits a certain level, around 16dBu.

Need:

Very high input impedance. (Or certainly high enough to not bother the "CUT"; circuit under test.
Full wave rectifying (would precision rectifying be needed?)
Find a way to power the circuit from a +30vdc power supply. (Would a simple resistor railsplitter virtual ground be sufficient?
Have a RC circuit to have some crude control over the lenght the LED will be lit after the peak has passed.

Any ideas?

Click to expand...

I think I already cut a pasted (in response to a previous question) a one op amp circuit I designed for a console (last century).

My one op amp circuit used a bi-color LED. Green for signal present, and red (with hold) for near clipping. As I recall my circuit supported input diode sampling, so could look at multiple circuit nodes in a channel strip.  Unfortunately my circuit was half wave rectified (to support the diode input sampling).

In my experience the peak hold is very important because just lighting red for brief peaks is not very noticeable.

There are many ways to skin this cat, and over the decades I have done most of them...  ;D

JR

Hi,
Like John,
please find  attachment

or other

plimousse:  Read my post:

Find a way to power the circuit from a +30vdc power supply.

Click to expand...

Unless you were aware, opamps and comparators, in most cases, will run on 30V easy - that's 30V between the V+ and V- terminal. Not sure you've noticed, but opamps don't have a "ground" pin

Either one of the circuits shown above will work. The "-15" will be the ground rail in your case (the most "negative" rail), the "+15" will be your 30V rail, and with a pair of 10k resistors, you can get a virtual ground, for biasing.

Hello Khron,
+1

This is a very simple circuit, used by a manufacturer of budget mixers.
And yes, they just feed audio into the circuit!