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design of a circuit to detect an audio signal from audio amplifier???

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tarekegypt

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HI ALL;
kindly help me to design a circuit to detect(supervise)the output of audio amplifier.

the case is :there is for example 10 speakers concocted to the output of audio amplifier and i need to monitor this line for open circuit or short circuit or amplifier power off .

what i need is when the signal is active(music on or volume high or low or mute) a certain relay will activated on this circuit and when there is open circuit or short circuit or amp power off the relay will deactivate .

the main problem is ,the output of the amplifier is varying with the amplitude of sound ,i.e when volume increase the relay activate and when volume decrease the relay dectivated although there is a signal already exists ???

Thanksss.
 

You must have some sort of delay with the switch as music is not continous. In broadcast transmitters a high frequency tone is added right at the input of the site and is detected at the output of the transmitters (22.5 KHZ @ -20dbm). If this tone goes all the way through so will the programme. We used a 10 second delay on our programme detectors and even then they used to alarm on some sort of programme material.
Frank
 
Hi Tarekegypt
You can easily get sample from out put voltage , with two resistors and then rectify and filter it , thus you will have a DC voltage as sample , it means when you have audio at your out put , you will have a DC signal , that can be as command of an op amp and then .....
Best Wishes
Goldsmith

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By the way for increasing sensitivity , you can do : don't use resistors ( voltage divider ) just use a resistor and zener diode ( to prevent damages ( to limit voltage at maximum modes )) then a precision rectifier with opamp , and then .....
 
A peak detector is similar to the replies already given. It will store the presence of a signal for a time.

Sample schematic:



Values can be adjusted for desired operation.

The output can be amplified, if you want it to be recognized as high or low by a logic device.
 
Thanks for your interest.
but I dont want to use extra poer supplies or DC for VCC for opamp,is it possible??

- - - Updated - - -

A peak detector is similar to the replies already given. It will store the presence of a signal for a time.

Sample schematic:



Values can be adjusted for desired operation.

The output can be amplified, if you want it to be recognized as high or low by a logic device.

Dear BraidTheRad
if the output of the amplifier 100 volts ,what will be the out of this circuit ,and can i get a free contact signal from it without using any extra dc source??

- - - Updated - - -

You must have some sort of delay with the switch as music is not continous. In broadcast transmitters a high frequency tone is added right at the input of the site and is detected at the output of the transmitters (22.5 KHZ @ -20dbm). If this tone goes all the way through so will the programme. We used a 10 second delay on our programme detectors and even then they used to alarm on some sort of programme material.
Frank

how to detect 22.5 KHZ ?
 

Dear BraidTheRad
if the output of the amplifier 100 volts ,what will be the out of this circuit ,and can i get a free contact signal from it without using any extra dc source??

If the output is 100 VAC, then its peaks are at 140 V. My simple circuit will produce about 135 V with no additional power source.

Your relay might be activated by signals at that level, or by a lower level if you add the proper value resistor inline.
 
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