12 Volt trigger for Krell KSA amplifier.....

I have a Krell KSA 250 amplifier in my system and it is the only amp in my system with which does not have 12 volt trigger to turn it on. Does anyone know if it would be possible to convert the power switch to have a 12 volt trigger attached somehow to it? And yes I am that lazy that I don’t feel like turning it on every time I want to listen to it…. :-) Let me know your thoughts on this and thanks in advance!

How good are your DIY skills ? I have a couple of solutions for you, but they involve some amount of DIY. The simplest is a relay with 12VDC coil and contacts rated 20-30A @ 120V. The relay coil can be driven by a 12V wall wart, plugged into a switched outlet.

You will need an RC snubber across the relay contacts to suppress arcing each time they switch current. This arcing, if not suppressed, will eventually destroy the contacts.

You will also need a reverse-biased diode across the coil, to suppress back EMF that occurs each time the controlling voltage is cut. This EMF can be damaging to any sold state device in the wall wart, such as a voltage regulator.

The other option is the same type relay, controlled by an IR receiver chip like the TinyIR2 kit by Tauntek.com (URL below). The TinyIR2 can be taught any IR remote code. It cannot drive a relay by itself, so you will need a relay driver circuit in-between. You will also need a 12VDC source for the TinyIR2 and relay driver circuit. A 12V wall wart with enough current rating to operate the TinyIR2 and relay coil (probably 100-300mA) should be adequate.

I have DIYed these options and they work fine. Paste the following URL into your browser to see a recent post on the same topic.


First of all Thank you for your reply Gbart!!! And I am all about DYI projects but am having some troubles finding some of the parts described above? I think I may have found something that will work for the relays but would like to run it past you to double check my findings...

Here is the 12VDC coils I found:



As far as the RC snubber or reverse-biased diode I could not seem to find a single site that had anything describing these parts. The wall wart which I'm sure I already have one that will work. Please let me know where I might look for the RC snubber or reverse-biased diode and if the listed above relays will work? Thanks again for your help!

All of the parts you need can be obtained from Digi-Key. YMake sure that you connect the diode properly -- i.e., cathode to the positive output side of the wall wart.

30A 120V DPDT relay:

0.1uf 275V X rated cap:

100 ohm 1/2 watt resistor:

1N4007 diode:
On second thought, you really don't need a DPDT relay. SPST will work as you only need to switch the hot line. If you go with a DPDT relay, you will need to put a cap and resistor across each set of contacts.

SPST relay:
Wow thanks a ton Gbart!! I really appreciate your help with this one! But I have one more question that I would like to double check, this assembly that I put together will replace the power switch that is currently on the amplifier or does this connect in elsewhere? Thanks again!

You will need to wire the assembly to a 20A single outlet with the relay on the hot line and plug the amp into that outlet. It occurred to me that before you go buying the parts for this project, the type of power switch on the amp will determine whether or not it can work. Is the power switch a maintained or momentary pushbutton type ? If it is momentary, then you're wasting your time, since to turn the amp on remotely, the power switch will need to be in the on position at all times.
The switch on the front of the amp is some type of relay switch. ( not sure what type exactly it is so I will explain it's behavior) As it sits right now, I currently have it on a switched outlet and when I turn on the switch to give the outlet power you still have to push the power button on the amplifier for it to come on. Then if I turn the outlet off with the switch it then obviously looses power and turns the amp off and if turned back on you will still have to hit the power button to get the amp to turn on. (sorry for the long explanation) So I am thinking that this is a normally open momentary switch that actuates a relay of some kink? Let me know your thoughts? Also I will be running a dedicated circuit for this amp in the near future that will not have a switch so the wall switch will not be an issue in the future. Thanks again man!!!
From your explanation, what you have is a momentary contact switch that when pressed, activates a power relay -- same as my Classé amp. I'm sorry but you will have to abandon your idea of turning the amp on remotely. Of course its not impossible for a skilled person to mod the amp so that it could be triggered remotely, but many people would consider that to be an act of heresy. You would certainly be lowering the resale value. I've done a good share of mods and thought they actually enhanced the equipment, but not everyone would share that view.

Here's my mod of a vintage Phase Linear 400 series 2 where I upgraded the connectors, power cord, and added DC protection circuitry which these amps lacked:


Very nice work my friend! I am very impressed! Looks very professional! Being that I am not an electronics major, my profession is in electronics (computer networking) I think that this one, at least at this time, might have to wait however I would like to know your thoughts on how this could be done hypothetically given that I do one day conjure up the confidence to give this a shot? I also have a friend that has a degree in this type of electronics so I might run it past him to see if he could potentially do this for me?

Just off the top of my head (have not done any research on this as of yet) would it be possible to use some sort of solenoid to actuate the push button switch? I think that if I could find a solenoid that would fit this application I would potentially not have to modify the amp what so ever. Let me know your thoughts and thanks a ton man for all of your help on this!! Wish there was a way that I could leave feedback for you as much of help you have been for me…

An IR receiver (like the Tauntek TinyIR2) could be installed in the amp along with a relay driver circuit and relay. The relay contacts could be connected in parallel with the amp's front panel pushbutton. The TinyIR2 or substitute should be programmed for momentary pulsed output. Closure of the relay contacts will duplicate the action of pressing the front panel pushbutton.

I have tried such a switching arrangement with my Classé amp which lacks a standard 12V trigger and it worked just fine. The one difference is that the Classé amp has an RJ12 jack on the rear panel that provides a breakout of the internal connections for switching, ground and 12V supply, so any triggering solution can be employed externally.

You could either drill a tiny hole for the IR sensor in the amp's front panel or, alternately, it could be placed outside the amp on a pigtail. Power for the IR receiver and relay driver could be tapped from the amp's auxiliary power supply or a small 12V supply employing a 100mA-300mA transformer could be built and mounted inside.