Need help with 100V ATT Switch

[ilia990]

Hi,

I have an amplifier that outputs 0-100V to speaker with a transformer and it is all ok.

What i need is to make a dry contact (close a relay) when the amp is on at output from 15V ?

any ideas.

View attachment 65244

I remind u that it is a 100V output !

Thanks in advance !

 

[Reloadron]

I am missing something as the audio out of the amp will be a varying waveform going above and below 0 at some frequency. Meaning it will not remain above 15 volts but be constantly changing.

Ron

 

[ilia990]

I am missing something as the audio out of the amp will be a varying waveform going above and below 0 at some frequency. Meaning it will not remain above 15 volts but be constantly changing.

Ron

yes i can use a full wave bridge rectifier so it won't go below 0

View attachment 65250

what next i

 

[Reloadron]

Attached is your circuit with and without the cap. The only way this will work with audio is maybe divide down the voltage and run it into a comparator that drives a retriggerable one shot with a time constant longer than the lowest frequency you expect to see. That would be my guess anyway.

Maybe someone else has a thought?

Ron

 

[ronv]

Do you really have 100 volts across your speakers? That's a lot of whats.

 

[ilia990]

Do you really have 100 volts across your speakers? That's a lot of whats.

yes, even more last time i measured at max volume it was 140V on a digital multimeter (unit) on ac 200 volt position !

so i might need it to be even more voltage restrain !

are u familiar with the public address system ?

 

[ChrisP58]

Public address systems usually use high voltages to distribute audio over distances of hundreds of feet. Transformers at each speaker drop the voltage down to voice coil level. The transformers usually have different primary taps to adjust the amount of power used by each speaker.

70 volt systems are very common. But 70 volts is the nominal voltage. Depending on the actual audio level, the measured voltage may be different. Also, unless the multimeter is of the true RMS variety, the measurement is likely accurate only if the signal is a sine wave.

 

[ilia990]

anybody has an idea of a comparator or something else with a pot so i can select sensitivity from which volt to close the relay ???

has anybody have an idea at all for this circuit ???

 

[Reloadron]

Read this link about comparators. Make a voltage divider circuit of about 10:1 off the bridge posted earlier. Then drive a retriggerable one shot off the comparator setting the time constant for about a second or anything as mentioned earlier. Longer than the lowest frequency you expect to see. I posted a sim of what your circuit outputs would look like with and without the capacitor.

Ron

 

[ronv]

are u familiar with the public address system ?

Ahh, missed the transformer part, just saw the cute little picture.

Yes I know 70 volt systems, used them in the football stadium.

Do you just want the relay to pulse everytime your signal goes over 15 volts, or stay on for a while or ??