No announcement yet.

Need Help Building a Relay Circuit

  • Filter
  • Time
  • Show
Clear All
new posts

  • Need Help Building a Relay Circuit

    I am putting the finishing touches on integrating my Mac Mini to my VW Monsoon Amp.

    I have the amp working thanks to the FAQ posts.

    I would like to install a relay that uses the presence of audio current to switch on the 5v needed to turn on the Monsoon Amp. If you are unfamiliar the 5v is injected into the negative leads going to the amp.

    The purpose of this circuit is to turn the amp on/off based on the presence of an audio current. When the current is present the audio sounds great. If I close the MAC applications or browser providing audio output then I get a buzz from the 5v being applied. So, the relay circuit would ensure that the amp is only powered when there is current on the audio output.

    Mac Mini --------Analog out 3.5mm to L/R RCA------Ground Loop Isolator---------Circuit box (splits the RCA to 4 channels, adds 5v to the negative terminals)------Monsoon Amp

    The relay would connect in the Circuit Box

    RCA positive lead ------ Relay Magnet--------RCA positive lead out to amp

    5v PSU ----------------Relay Switch-----------5V applied to negative leads

    What relay should I purchase?

    What is the current across the Analog audio signal which will be used to activate the relay?



  • #2
    well there are some car audio pieces that can do low voltage senseing without building a relay . u can use something called a TR-4 its made by pac audio ,its designed for that kinda of thing . TR-4 link

    amazon link tr-4


    • #3
      I was going to say a circuit that drives a relay since audio is not a constant DC voltage etc.

      But Michae's suggested TR-4 is a commercial version of that otherwise DIY solution which at $16 IMO is quite acceptable.

      As to Amazon's ~$8 --- Bargain! (I'm tempted to by a few even though I have no need... but just in case...)

      Thanks Michae for your reply and links.
      Last edited by OldSpark; 07-29-2012, 04:07 AM.


      • #4
        Originally posted by Michae View Post
        well there are some car audio pieces that can do low voltage senseing without building a relay . u can use something called a TR-4 its made by pac audio ,its designed for that kinda of thing . TR-4 link

        amazon link tr-4
        Cool Thanks!

        I can use a voltage regulator with a 5v output to power the amp on.

        My only question is, does the TR-4 12v output switch off when there is not audio current present?

        I sent an email to Pac-Audio to find out if the switch is on and off.
        Last edited by cazzz; 07-29-2012, 07:50 AM.


        • #5
          the part is designed to go on when audio or any kind of voltage , it will work from voltages .08v-12 the specs are on the site and it work quite well for aftermarket amp integration. but the thing is what buzzing are you getting on the system? u mean the noise in the system buzz? also since this is a voltage sensing piece it says a 1 sec delay so i dunno if it will help u out in what ur looking for .cause if not mistaken ur using low level out-puts (rca-level) i dont think that would be enough to trigger the relay.heres some low voltage relays, u cant use bosh type they need 12volts to trigger

          5v relay

          ebay relay


          • #6
            The buzz is from the 5v on the negative audio lines going to the amp when there is no audio signal.

            From what I read on Pac-Audio the TR-4 should work. The only question is will it also turn off the signal when no current is sensed on the audio output.

            There is also the T-7 and T-7 pro which are programmable.


            • #7
              I have the tr7 im not impressed an the programming is quite frustrating if u havent done it a few times . The tr7 pro literly just came out like 2 weeks ago so i havent had time to play with it so i cant tell u on the sensitivity of it. But its nice since programable from either android or pc .im using 2 of these for automation of van doors opening and closing on a morticians van . They want to open it from the viper remote


              • #8
                Do you have a TR-4 that you can test to see if when you remove the signal the 12v output cuts off?


                • #9
                  no i dont have any around ,i havent had the need for quite a bit .im sure the voltage cuts off but if u think about it . when ur computer is idleing the audio will shut off and then it will take a second or 2 to come back on . im sure something like that would get annoying after some time .but im thinking that the tr7 pro would be better since it's very customizable .