Remote turn-on for power amp

[jwb]

I'd like to put a 12VDC trigger input on my new amps, to allow the preamp to turn them on. The obvious way is to install a relay with a 12V coil in the power amp, but your standard 12V relay coil is going to draw 25mA or more. I checked some datasheets of commercial preamps and the limit of the 12V trigger output is 30mA, not enough to turn on two or four or more 25mA loads. Since I'm using a DIY preamp, I can make the trigger output drive as much current as I please, but I'm wondering if there are any more clever designs for this sort of thing. I'd rather not have a second supply in the power amp just to drive the relay, so all the power needs to come from the trigger source.

Maybe I could daisy-chain the trigger so every component turns on the next one?

In the absence of cleverness, I think I'll just make a 500mA trigger output with something more substantial than those sissy 1/8" phono jacks.

[Jason Hubbard]

Don't know if that will egt you around your problem - they have no coil so should only require a few ma to trigger - quite tolerant on trigger voltage as well...

[pinkmouse]

Originally posted by jwb
Maybe I could daisy-chain the trigger so every component turns on the next one?

From an asthetic point of view I like that, and it will also spread out any surge currents on start up, rather than all the relays banging in at once

[JensRasmussen]

Hello,

I made this module that both has slowstart DC protection and mutedelay on start.

I use it to start 2 500VA transformers and 320000µF @ 55V

It needs a "stand by" transformer, but has an on board 12V regulator.

\Jens

[tpenguin]

Originally posted by JensRasmussen
Hello,

I made this module that both has slowstart DC protection and mutedelay on start.

I use it to start 2 500VA transformers and 320000µF @ 55V

It needs a "stand by" transformer, but has an on board 12V regulator.

\Jens

Jens, can you post a schematic for it, please? Does it require a ±12V supply, or will a single supply work?

[JensRasmussen]

I'll see what I can do for schematics.... I have to dig it out from a backup disk, since I have changed computer since I made this board.

It only needs an AC of say 15V. There is an onboard 12V DC supply on it, this powers the relays and control cricuit.

\Jens

[maylar]

An alternative is to have the remote relay and its power source in the power amp chassis. Run the coil with a transistor driver, so all you need to supply from your preamp is a couple mills of base current.

Or.. you can use a multipole power switch for the preamp, and have as much current switching as you want.

Or.. mount an AC mains recepticle on the preamp and simply switch the AC power to it with the preamp power switch. A lot of commercial preamps have that feature for powering a turntable.

[jwb]

Thanks for the ideas. I wasn't planning to ever kill the mains on the amp, they will be powered all the time. The relay will switch the DC power from the power supply to the main part of the amp. So I suppose I will have plenty of power laying about to drive the transistor, to drive the relay.

Nice looking board Jens. I like the idea but I don't have room for a second transformer.

[grataku]

A solid state relay, a thermistor for surge (when needed) and an auxiliary transformer in the preamp PS box. In my case the apox IR board controls the whole thing via remote. Since PassLabs amps and preamps need no protections or mute relays one can get away without adopting mute relays.

[sam9]

Regarding the question of daisy-chaining the 12V voltage:

I've noticed that many commercial (home and pro) units that have a trigger input also have an output. I don't know what is going on inside but it would make more sense to me the the current for the output is provided by the unit with the output and not the original source. This sems to indicate that that daisy chaining is more the standard practice than trying to trigger all "slave" units from a single "master". It also seems a much better approach - partly for the reasons stated by Pinkmouse and also because it eliminates the need to provide enough current from the "master" to turn on all the "slaves". If each "slave" unit taps off a few mA to turn on the next unit, there is no limit to the number os slaves that can be supported.

I've wondered about this in regard to some future system plans. This thread clarrifies the issue (to me anyway) and is thus quite beneficial.