Auto Switching Relay Between Two Input

Thread Starter

Abhishek1909

Joined Apr 12, 2021
4
Can Someone help me to to understand How this problem will be resolved.

I have 2 Amplifiers having audio Signal Input, 100V Speaker Output & 24 V DC Output. Now I need One relay box between 2 Amplifiers. All the Input and Output from both the Amplifier will come to this relay box and Speaker will be connected to this relay box (not directly to amplifier). The purpose of this relay box is to provide hot standby between both the amplifiers. First all the speakers will get signal from the 1st amplifier through that relay box, If my 1st amplifier goes fail or power off, the relay will switch output signal from 2nd amplifier and loudspeaker will get signal from 2nd amplifier.


Hope you understand the requirement?
 

Yaakov

Joined Jan 27, 2019
3,579
Could you explain how these amplifiers are being used, that is, what are they doing? It will help understand your problem.
 

Thread Starter

Abhishek1909

Joined Apr 12, 2021
4
Really I am not technical person but i have prepared a diagram for you to better understand.
The Amplifier can be failure because of Power Fail, or Any Inside PCB Fail.

Please see the attached diagram to understand better.
 

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Ian0

Joined Aug 7, 2020
3,473
On a 100V-line amplifier the 24V DC terminals are generally power input from a battery, in case the mains fails.
(How could an audio amplifier have a DC voltage output?)
 

Alec_t

Joined Sep 17, 2013
12,249
The Amplifier can be failure because of Power Fail, or Any Inside PCB Fail.
There are a thousand and one ways an amplifier and its components can fail, so for practical and economic reasons you would have to limit failure detection to just a few ways. Monitoring all the power rails in the amp would be a start, but detecting things like excessive audio distortion would be much harder.
Switching over instantly from one amp to the other would likely cause unwanted thumps/clicks from the speakers, so you'd need a soft-start arrangement.
 

Ian0

Joined Aug 7, 2020
3,473
If you first monitor the power rails, then detecting whether the long term average DC voltage was close to zero would be a good indication that the amplifier was working.
On a system which spends most of its life doing nothing (except when someone makes an announcement) it is tricky to prove that the output is producing a signal!
One way would be to add a high-frequency signal at the preamp (say 21kHz) then detect it at the amplifier output. As 100V line is transformer coupled, generally with not great quality transformers, 21kHz would not make it to the speakers (which probably have an upper limit of 5kHz, so no-one would hear it if it did)
Clicks and thumps from the switchover could be avoided if both main and backup amplifier were both kept running.
 

LesJones

Joined Jan 8, 2017
3,510
The only way I can see to detect a fault in the amplifiers functionality is to inject a low level signal above the audio range but still within the amplifier's bandwidth (Say 25 Khz) and have a detector on the output to detect that frequency. If that signal was absent on the output then it was not working so it could cause a switch to the other amplifier.
Edit. I see that Ian has beat me to that idea. (I started the post then broke off when my wife arrived home with the shopping. We than had a coffee. I then finished the post.)
Les.
 
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