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A VERY usefull circuit , but how...

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I was on a studio , and i saw a 32 channels console for recording.
I noticed on EACH channel 3 leds

A yellow , that showed PRESENT of signal (guess -20dB)
A green that showed 0 dB signal
A red (non adjustable !?) that showed distorsion , clipping

So , i think , if this console has 32 circuits like this , they must not be very complicated

Imagine how usefull circuit can it be , on the car amp , on the home amp , on everething !!!
For us who construct usefull projects , i think this is a MUST HAVE

I think even only red and yellow leds are fine , forget the green led !!

But there must me some adjustment because each one will use this project on diferent purposes (amps with diferent amps , etc)

the clipping means present of dc , negative or positive , so that time the led flashes
the yellow led should have some transistor that can find low signals
for the green led i can not imagine the circuit

the whole circuit its impossible for me to find (i am a newbee in advanced electronics,IC's etc), but a electronic i think can make it !!

So i say lets start building this , and put it on every audio source we have (calm down :P)
More than that we make it even better if forum's readers have anything else to suggest

Go GO GO electronic maniacs!
i am dying to see a diagram ;D

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Hi Nano,
I agree that clipping indicators are important on power amplifiers.
Detecting when the output of a power amplifier clips is complex, due to the amplifier's power supply voltage constantly changing with power output and mains voltage variations.
GPG's LM3915 post will not work if connected to an amplifier's output, because:
1) When a power amplifier clips under load, then its output voltage actually [b}decreases. So the "clipping" LED won't light.
2) The LM3915 lights LEDs in 3dB steps, which is very coarse, the 2nd one down is half-power. An LM3914 would be better since the 2nd one down is 90 percent of the voltage.
3) You would need to connect the clipping detector to the amplifier's input, and never change its volume control, and guess that its output is clipping with a particular input voltage.

A very good explanation and rather complicated clipping indicator project is here:

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Thank you for replying
as for the project i cant understand the diference between a project for an power amp and a project for a mixing console

as you say they are not the same

well , i set the gains for my amp with an osciloscope , so the inputs are not clipping for sure
but what about the output of the final amp?
That is what i want to monitor , the outputs

I think GPG is right , a mixing console is not an power amp
But i think that audioguru is also right for the problems with the output of an power amp

so what can we do?
the project audioguru posted is very nice , but complicated , i think i will try it :) . i know the sound.westhost , and the projects are very good , and the explanations are too :)

my idea was not to use an IC , but i think this cant be done , i dont know , you know !

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thank you for replying

actualy i think tha t you both are right

GPG is right cause what i saw was on a mixing deck , and not a power amp

Audioguru is right too for the problems he said that tis project has

anyway , what can we do to make the project?
i think the solution of the 3 leds was pretty good

maybe i will try the project from westhost , ive seen many projects from there and they are all good

what about the LM? wich should i use?
i am interested on a output indicator for the ffinal amp
the inputs to the final amp are beeing set by an osciloscope , so they do not clip .They outpts maybe will clip

i am waiting for a new reply !

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Hi Nano,
A mixing console has many outputs (one for each microphone), each having its own volume control and a lot of gain. It would be easy to turn down the "master" output control to get the desired output level, but have some input controls turned up too high and clipping.
Your home system probably doesn't have this problem because its sources (CD player, tuner etc.) are designed with fixed gain and do not clip. So the only things that will clip are your power amplifiers.

The output stage of a power amplifier clips when it runs out of supply voltage (which constantly changes because it probably isn't regulated), or current limits to protect itself from supplying too much current into a load whose impedance is too low.
If your power amplifier doesn't have much phase-shift, then a simple way to indicate that it is clipping is to compare its attenuated output to its input. Normally they would be the same, but are very much different during clipping since the input would go positive (or negative) but the output won't follow it. The comparator's output should be full-wave rectified then fed to a monostable "pulse duration stretcher" that drives your indicator LED. Each channel needs this circuit and the outputs can be combined to drive a single LED. Fairly complicated.

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