Remote trigger circuit for amp

[Gaber]

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?

Gabe

[R. McAnally]

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]

See Rod's soft start circuit at www.sound.au.com but ignore the load resistors.

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

Jamie

[ftorres]

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]

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]

I did exactly this on my amp.... i took Rod's project 38 (http://sound.westhost.com/project38.htm) 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]

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]

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.

Gabe