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Gaber 30th January 2002 07:36 PM

Remote trigger circuit for amp
I have just finished building a 5 x 100W amplifier based on the OMP MF100 amplifier module from BK Electronics. I would like to add a circuit to power up the amp from a remote 12V trigger from my preamp. Is this something that is easily done? Has anyone designed a circuit to accomplish this?


R. McAnally 30th January 2002 10:40 PM

Use a 12V relay that makes/breaks the mains power. You might want to parallel the relay with the power switch so it can be manually turned on with the switch if necessary.

Jamie F 30th January 2002 11:12 PM

See Rod's soft start circuit at but ignore the load resistors.

I posted a veroboard layout for a dual version of this a while back.


ftorres 30th January 2002 11:30 PM

2 Attachment(s)
Depends if the 12 V are only a pulse or a constant level as long as the preamp is powered on. But in both cases, you should use a D flip flop to drive a relay.

The little schematic I attached shows you an ubiquitous circuit. The main switch is a tactile one, it just relies on the relay to power any load, as heavy as you want. The remote assumes you have a constant level when preamp is on, thus a little differenciator performs the switch on/off work.

If you have a 12V pulse instead, when preamp goes on and when it goes down, just remove the differentiator and drive directly the OR input with the pulse.

Hope this helps

R. McAnally 31st January 2002 03:43 AM

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Since a 12V source is unlikely to exist inside the power amp, the circuit seems a little overkill. Assuming the 12V will be high when the preamp is on, low when off, direct coupling to the relay would be a much easier and less time consuming option.

If the relay needs too much current, a simple BJT or MOSFET follower can be installed in the pre-amp, so 12V power is not needed in the power amp.

Lisandro_P 31st January 2002 04:25 AM

I did exactly this on my amp.... i took Rod's project 38 ( as a basis and modified it a bit; my design uses a small 9v 1A transformer that's constantly feeding the circuit and it's driven by an external signal (or a switch that connects the 12v to the input to turn it on); that and a couple of indicator leds did the trick wonderfully. If you do need the schematics i'll draw them up for you.

paulb 31st January 2002 04:54 AM

If you're using a relay, also check out Rod's idea (well, he may have copied it from somewhere else) of reducing power consumption in the relay by using an R/C in series. Relays require a lot less current to just hold them closed than they need to initially kick on.

Gaber 1st February 2002 05:25 PM

Thanks for the replies everyone. I think I have a good idea on how to proceed now. I figured someone had to have done this before. Will report back with results.


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