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Old 20th June 2013, 10:29 AM   #1
diyAudio Member
Join Date: Jun 2013
Location: Somewhere near Paris
Default Preamp Switch activated by 12V trigger


I'd like to build a switch to plug my HiFi preamp and HC Preamp to my power amplifier.

As my HC preamp has a 12V trigger out, I think that it should be possible to use a 12V relay activated with this trigger. Am I right ?
I'm not really skilled with an iron, so I'd rather purchase an assembled board

I've seen for example this board, do you think it could suit my project ?
eBay | DPDT Signal Relay Module, 12Vdc, TAKAMISAWA RY12W-K Relay. Has Assembled.

I don't really understand the power / control part though. I thought this relay power by 12V switch to NO, and when not powered stays on NC. So what is the control input on this board for ?

Thank you for your advices
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Old 20th June 2013, 11:10 AM   #2
DUG is offline DUG  Canada
diyAudio Member
Join Date: Jan 2003
Location: mississauga ontario canada
Good news and bad news.

Power Supply: 12V DC / 30mA (relay ON).

Input control signal voltage:
0V - 0.5V Low stage (relay is OFF),
0.5V – 2.5V (unknown state).
2.5V - 24V High state (relay is ON).
Input control signal high state current:
2.5V: 0.1mA
5V: 0.35mA
12V: 1.1mA
20V: 1.9mA

Good news:

Suggests that the relay will be on with an input of 2.5V to 24V and at 12V input will draw 1.1mA from the "signal" source and 30mA from the power supply to power the relay.

The relay has both NC and NO contacts. (DPDT or 2PDT or 2 form C)


Bad news:

The relay contacts are only rated for 0.5A at 120VAC resistive.

This means at most a 60W bulb per contact.

Probably not good enough for an amplifier.

Close but no cigar.

Keep looking.
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
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Old 20th June 2013, 11:25 AM   #3
diyAudio Member
Join Date: Jun 2013
Location: Somewhere near Paris
Thanks for your reply !

However I still have a few questions.

One basic to further my understanding of relays : what are the VCC (power signal) and INPUT (control signal) split in this board ? Can I use only the power signal ?
-> When my HC preamp is on (trigger send 12V) the relay switch on NO
-> WHen my HC peramp is off (trigger send 0V) the relay swith on NC

Second question : I don't want to power my amplifier, just send analog signal. Thus this will be low intensity signal right ? In this view won't the relay be enough ?

Last question : If not what do you think of the global schematic ? Can I use this board and plug another relay that would fit my needs ?

PS : Don't think it matters but I use 220V
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Old 21st June 2013, 11:37 AM   #4
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Join Date: Jun 2013
Location: Somewhere near Paris
Don't know if I posted in the good section.
If not could you tell me where could be most fitted ?
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Old 21st June 2013, 12:12 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
esp has given a few articles on remote starting and stopping.
Even triggered by the tiny audio signal.

I'm in the process of building a soft start with a power ON relay as well as the delay relay.
This suits a low voltage front panel (ON/OFF) switch rated for 12Vac/dc and also for a wire pair to remote equipment and through an overtemperature switch.
I am actually sending 12Vac around a switching circuit. If all are closed then the transformer secondary starts up the relays in sequence.
If any one switch goes open the amplifier relays both drop out, leaving just the 5VA with power (which has an F500mA fuse).
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 24th June 2013, 06:41 AM   #6
diyAudio Member
Join Date: Jun 2013
Location: Somewhere near Paris
Thank you for your answer.

Yet I think you've misunderstood my problem : I do not want to use the trigger to start or shut down anything
In fact I want to feed my amp with either the signal from my HiFi preamp, or from my HC preamp. To do that I need a switch which will choose which analog sinal to send to my amp.

The trigger is only my idea for choosing which signal to send. Usually, triggers are used to start amp, but here I thought of using it to choose HC signal over HiFi signal (which would be default position).

And my basic problem at this point is that I don't understand why a relay has to be powered and "signaled" (fed with a signal input). I thought powering it would make it switch positions.

If not I'll need to put a power in my switch, which would be a little overkill imo for what I want to do (prevent me from having to move my current switch manually ^_^)
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Old 24th June 2013, 07:23 AM   #7
diyAudio Member
Join Date: Jul 2003
Location: Dona paula, Goa
You will have to read esp site for understanding certain basics.

In your case, you want priority for one source over the other. This is easy if each of the units give out some DC voltage, which will never be the case.

For constructing it with the audio signal, it will be difficult for you unless some readymade design is available. I doubt there is any.

Gajanan Phadte
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Old 24th June 2013, 09:14 AM   #8
diyAudio Member
Join Date: Jun 2013
Location: Somewhere near Paris
Thanks for your answer.

I've read a website on relays (in french so giving you the link probably won't help), but I don't know esp. Do you have a link ?
I might not be able to do what I intend but at least I should learn more about relays

In fact here what I thought :
- relay when they are not powered, are on NC position
- when powered relays switch to NO position
- the relay doesn't contaminate the analog signal

Guess something isn't right there.

Yet this way would be perfect for me : the analog Hifi would be connected to NC and the HC to NO. For powering the switch I could use the 12V trigger out from my HC preamp (when the preamp is on it sends 12V).
I don't want to use the analog signal to control the switch.

It seems odd to me that nobody tought of this before. Mixing HiFi and HC is often an issue, and such a switch could be pretty handy.
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Old 25th June 2013, 04:41 AM   #9
diyAudio Member
Join Date: Jul 2003
Location: Dona paula, Goa
If there is a 12 VDC output, then you will have to find out what current it can drive. If it can drive a relay, then buy a relay with good contacts for audio (gold is prefered).

You will need minimum 2 change over contacts. Four will be needed if you want to switch the ground.

If the 12VDC has no drive capability, then you will have to construct a simple circuit.

Gajanan Phadte

ESP site

Last edited by gmphadte; 25th June 2013 at 04:42 AM. Reason: added link
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Old 25th June 2013, 10:14 AM   #10
diyAudio Member
Join Date: Jun 2013
Location: Somewhere near Paris
Thank you, the website seems great

I've already found something realy close to what I want :
A-B Box For Amplifier Comparisons
I guess k1 and k2 are in fact only one relay of you use a DPDT.
If I remove the manual switch, I have exactly what I'm looking for. Do you agree ?

You're right, I need to know now if the trigger is enough to power the relay. What would be the right way ? Mesure how many AMpere it delivers ?
If the trigger cannot drive a relay, I'm not sure I'll keep on this project.
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