Teensy reading SPDIF and triggering 12V to activate amp

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Bolduque

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Hi there,

I'm new to this forum and new to programming microcontrollers in general. I have a question for a little project I'd like to attempt, but have zero experience with whatsoever. I have a preamp that outputs a signal on SPDIF and XLR/RCA at the same time. The XLR signal goes to my two monoblocks (amps) which drive my speakers. My amps have 12V trigger in to switch them on/off depending on the signal but my preamp does not have a trigger out. I was thinking to connect a teensy board to the spdif out of my preamp and on ANY signal it sends a signal over 12V to both my amps to switch them on. If no sound is being played for 60s or whatnot the 12V signal is cut off again and my amps will switch off. Is this doable with teensy and where would I begin (as in, next to the teensy board it self, what components should I get?). Thanks in advance and open to any suggestions!

edit: Initially I thought I would have to trigger both amps at the same time, but this is actually not needed as the amps have 12V in/out, so one amp can trigger the other.
edit2: On some other forums you read that amps can sometimes already be trigger at a 5V signal, I could check this with the maker of my amplifier as this might reduce the components required?
 
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Is it coaxial S/PDIF or optical?
Is the setup automotive 12V or mains powered?

Actually you would not need a Teensy or any other microcontroller for this task. If signal is present, the 12V signal becomes active, so this could be done with a few electronic components. The contents of the S/PDIF stream may be of no interest at all. It could be reasonable to add a timeout so the amps do not switch off immediately after playback is stopped. Constant switching would surely wear them off earlier. If they are switched on only if a signal is present, wou'll lose a few seconds of playback, if the amps have sort of speaker protection etc.

What about the following idea:

The playback device or preamp take their power from a so called master-slave socket as a master. On the slave side is a simple 12V brick that gets powered as soon as the preamp is switched on and off as soon as the preamp is switched off. The components are all availabe ready-made.
The monoblocks get their power directly from mains, not from the master-slave, in order to keep protection circuits functional and not overload the master-slave socket.
In the automotive setting, almost every playback device has a 12V trigger output to activate power amps, so look for that.
 
Your plan is sound. I'd buy a toslink input module and a relay module (to send the 12V amp on signal). Then it's just software.
 
Hey there, thanks for the reply! Its coaxial S/PDIF. You're right that the contents of the signal is not important to me, i just need a 12V signal to the amps once any output is measured on the pre-amp. The master-slave socket is a good idea, be it not for the fact that the preamp is basically always on (no standby or power-off, so that's another 10W idle I cannot get rid of :)). This is the reason I wanted to use the free S/PDIF out's on the back (that provide a signal together with analog out which goes towards to amp) to provide a 12V trigger to the amplifier.

I agree adding ad elay would be a good idea, 10 or 30 minutes or so. In general once we are playing music or watching TV we do it for a longer stretch of time, not on and off the whole day.

Do you still think I do not need a teensy to do this? What alternative would you have to the master-slave socket? again, thanks for your time!
 
If the preamp has no power switch, you might connect it to the slave side as well and use the TV or whatever signal source on the master side. The master-slave sockets usually have a potentiometer to adjust the threshold when to activate the slave, so low standby would not, while full power would activate the slave devices.

Anyway, not knowing the setup or the devices involved, I'll stop watching my crystal ball now.
 
Hey Deleted User, you make a good point, so let me specify a bit more:

The preamp (miniDSP SHD) also includes a network streamer so at any time someone can start streaming spotify, so while I was complaining about the 10W, it's fine as this is pretty much what I wanted I guess! The amplifiers are 2x Red Dragon Audio S500 (overkill for whatever speakers I have, I know) which include a 12V in and out via 3.5mm ports.

The miniDSP (preamp) works such that whenever I provide some output (say spotify, or whatever else) to output 1 and 2 (left/right), a signal will be provided over S/PDIF 1+2, XLR 1+2 and RCA 1+2 at the same time.

The amplifiers are connected via XLR, so RCA 1+2 and S/PDIF 1+2 are providing a signal that is not being used anywhere. Capturing that and triggering a relay to provide a 12V signal which I send to my amplifier would basically solve my solution I think. If for whatever reason doing this with analog audio is easier than with digital, I could also use the signal from RCA 1 and 2.

As usually I only program high level code, could you guys help me with 1 more thing. How would I provide power to both the teensy and the relay? Are they powered separately or can I use one power source for both at the same time (due to the difference in voltage requirements). This is probably very basic to have to explain, but maybe you guys can point me in the right direction. My physics was never too bad, I just have not applied it in years!

edit: Someone on the MiniDSP forums has pointed me to this which is pretty much exactly what I am looking for, but it would cost me $100 to get this to Europe, I think that this can be solved for much less with a few parts.
 
A 12V voice activated corridor switch relay could be a simple and easy solution for this.
It has an adjustable timer and a microphone input that you could just connect to an audio out, either by coupling an earbud to the microphone, which gives electrical insulation as well, or by capacitors. Earbud can be even overpowered by the line out, but who cares for quality here.
Just beware and check not to inject voltage to the audio output of the DSP.
Power the relay by a 12V brick and switch the 12V to the amps as well over the relay.
You should find these relay in every good brico or DIY store.
 
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