12 volt trigger

[hams]

Has anyone ever implemented a circuit to turn on an Amp when you get a 12 volt signal from a reciever/processor?

I'm thinking of having a tri-state switch that has an "On" state which ignores the 12 volt signal, an "Off" state to turn off power completely and a "Standby" state that would switch the amp on when the 12 volt signal is detected.

Here's a conceptual drawing to help explain. I don't know how to draw a proper circuit diagram, this is just a high level idea....

[Nuuk]

Could you adapt this ?

[hams]

i was hoping for something already purpose built. i don't know too much about circuits, so i'm not sure that i could modify that plan...

[hotwaterwizard]

The switch Drawing has a big problem.
All of the outputs are tied together.

[dhenryp]

I've built a very simple circuit that has worked without a problem for 8 months now. I got a 12V DC 1 amp wall wart and plugged it into the switched AC outlet of my receiver. I used this 12V output to control a 12 V relay with a 30A (@>120 AC Volts) contacts. I use the relay contacts to switch the AC to several components, among them a 1200 Watt Crown Pro Amp. I bought the wall wart and relay from All Electronics for less than $10.

[Devil_H@ck]

This is how I plan to do it: in every amp/active crossover/whatever I create, I will put this circuit:


If the amp/... has a power button, it will be connected to one of the enable inputs. On the back I'll have 2 trigger connectors (probably a serial connector), one input and one output. The output pins are directly connected to the pins on the input connector.

The triggers (8 of them, 1 ground => serial connector) will be controlled by a relay driver in my preamp. The driver is capable of sourcing 200mA per trigger line.

In the amp/... one of the input pins is connected to one of the enable pins of the above circuit. If you have more than 8 things you want to remotely control, you can always use logic gates etc. to have more possible "control codes".

The only drawback I see to this is that you need an appropriate voltage in the amp/.... If you don't want to use the device's power supply for this, you'll have to add a small separate supply. A 78xx & a small transformer is pretty small, so that shouldn't be too much of a problem.

*Oh btw, if you want tri state with this circuit simple put a 240V switch in series with the AC input. You can then mount it on the back next to the AC connector. Then you'll have your: always off, always on (with another, simple switch on the front) & on on trigger signal.

[hotwaterwizard]

Why not put a short delay into the circuit as well. This will reduce popping in the speakers from the relay kicking in.

[hams]

Can some explain what the following parts from the suggested schematic:

1N4148
1N4004
BC547

Are the "En Signals" the trigger signals?

thanks.

[Devil_H@ck]

Originally posted by hams
Can some explain what the following parts from the suggested schematic:

1N4148
1N4004
BC547

Are the "En Signals" the trigger signals?

thanks.

The "En Signals" are indeed the trigger signals.

The 1N4148, 1N4004 & BC547 are about the most general available diodes & NPN transistor you can find, in Europe that is. If you can't find them replace as follows:
1N4148: general low current diode (can easily fit in 5mm footprint)
1N4004: general diode (1A 100V) (fits just into a 7.5mm spaced footprint)
BC547: general NPN transistor

If you're not sure with what to replace, here are the datasheet to give you a general idea. They are from OnSemi (Motorola). As these are general parts, the characteristics should be the same no matter what brand you have.
BC547: datasheet
1N4148: datasheet
1N4004: datasheet

Know that I haven't tested this circuit yet! I'll probably will do so today. Note that the BC547 can only source 100mA continuously. If you're going to use a low voltage relay (eg. 6V) you might need to use another transistor, one that can source more current.

[hotwaterwizard]

Here is another Schematic that does the same thing.