Announcement

Collapse
No announcement yet.

12V Trigger Hum - Receiver (pre-out)-->Power Amp

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • 12V Trigger Hum - Receiver (pre-out)-->Power Amp

    I'm seeing a 60Hz hum when connecting my receiver pre-out to amplifiers (have tested 2). I suspect there's some sort of issue in the receiver, but in lieu of sending it in for service, is there some sort of "cheat"? Could I throw some kind of optical isolator on the line to decouple? Is there such a thing as a blocking inductor to pass DC but not AC?

  • #2
    Sounds like a ground loop and either the receiver or amps have a two wire power cord. Try hooking up a wire between the chassis ground connection on the receiver, probably near the antennae input and the ground connection on the amp.

    Comment


    • #3
      Would you expect that there is an external ground screw or similar on the outside of the cases? The receiver does have a 2 prong plug (and corresponding IEC socket) so that seems likely. I'm sure I can find the ground inside the case of the amp, but there's nothing external on it regarding grounding:
      https://www.nordacoustics.co.uk/prod...nnel-amplifier

      Comment


      • #4
        I just checked the amp out - definitely no ground screw or connection on the back of it. There's not a super clean way to connect a wire to the amp ground.

        Comment


        • #5
          What are you using to provide the trigger DC signal? The ground loop might be between the trigger (-) and the RCA grounds. Sent from my SM-G960U using Tapatalk
          Electronics engineer, woofer enthusiast, and musician.
          Wogg Music
          Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

          Comment


          • #6
            The receiver (Marantz SR6011) is sending the trigger. If the trigger cable is plugged in, the hum is very clearly audible. If I pull the trigger, the hum goes away for all intents and purposes. Its there and audible with my ear a few inches from the woofer cone, but inaudible at the seating position. It completely goes away if I disconnect the input cables (RCA).

            Comment


            • #7
              Trying running a wire from the GND on the receiver, under HDMI 1, to a GND on the AMP touching it to the outer conductor of one of the RCA inputs. Try from RCVR GND to the center screw on the outlet it's plugged into.

              I hate equipment that floats,

              Comment


              • #8
                Are they both plugged into the same wall outlet?

                Comment


                • #9
                  Originally posted by Adam_M View Post
                  The receiver (Marantz SR6011) is sending the trigger. If the trigger cable is plugged in, the hum is very clearly audible. If I pull the trigger, the hum goes away for all intents and purposes. Its there and audible with my ear a few inches from the woofer cone, but inaudible at the seating position. It completely goes away if I disconnect the input cables (RCA).
                  There's your ground loop.

                  Is the RCA signal coming from that same Marantz receiver, or do you have other processing gear in the chain?

                  Two options I can think of:
                  The easy method: get a transformer isolator on that RCA input to the amplifier.
                  The complex but nothing in your signal chain method: use a relay and a separate 12V isolated power supply. Connect the receiver's 12V trigger to that relay, then use the relay to switch the separate 12V supply to the amplifier.
                  Electronics engineer, woofer enthusiast, and musician.
                  Wogg Music
                  Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

                  Comment


                  • #10
                    No other processing gear in the chain, just separate sources upstream of the receiver, which I've tried to isolate and they don't seem to be related - the hum exists from all sources.

                    Regarding the complex solution - could the 12VDC power supply be something as simple as a low-current wall wart, or would that be too noisy and the DC not rectified enough?

                    EDIT:
                    Could I isolate the other end of the loop with something like this:
                    https://www.parts-express.com/ground...utput--320-365
                    and still achieve the goal of nothing in the signal path?

                    Comment


                    • #11
                      A wall wart would work fine. Have you tried disconnecting everything from RCVR? The reason I ask is because I've seen ground loops/hum caused by a coax antenna cable hooked up.

                      Comment


                      • #12
                        Good news about the wall wart - I think I have a 12V one laying around and setting up a relay isn't terribly hard. Yep, I've tried disconnecting everything and connecting back in one-by-one to see if I could isolate the upstream issue.

                        Comment


                        • #13
                          Any chance the isolator in my edited post would work?
                          https://www.parts-express.com/ground...utput--320-365
                          I'm not sure if that's just a 1:1 transformer that would only pass AC or if its something more elaborate. If it is just a 1:1 transofrmer, would the reference implementation of a chip like this:
                          https://www.digikey.com/product-deta...212P-ND/307874
                          do the job?

                          Comment


                          • #14
                            Originally posted by Adam_M View Post
                            Any chance the isolator in my edited post would work?
                            https://www.parts-express.com/ground...utput--320-365
                            I'm not sure if that's just a 1:1 transformer that would only pass AC or if its something more elaborate. If it is just a 1:1 transofrmer, would the reference implementation of a chip like this:
                            https://www.digikey.com/product-deta...212P-ND/307874
                            do the job?
                            The one you linked is essentially the same thing that I linked, a 1:1 audio transformer for the input signal. It's just built with 3.5mm connections for convenience in the car, but the RCA's would probably be easier in your case.

                            That TI device is neat, not sure how much current draw your amp needs for the trigger signal but it it's very small that may do the trick and be much smaller than a relay setup. Lots more info and example implementations on the Data Sheet.
                            Electronics engineer, woofer enthusiast, and musician.
                            Wogg Music
                            Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

                            Comment


                            • #15
                              Originally posted by wogg View Post

                              The one you linked is essentially the same thing that I linked, a 1:1 audio transformer for the input signal. It's just built with 3.5mm connections for convenience in the car, but the RCA's would probably be easier in your case.

                              That TI device is neat, not sure how much current draw your amp needs for the trigger signal but it it's very small that may do the trick and be much smaller than a relay setup. Lots more info and example implementations on the Data Sheet.
                              Sorry - I should have been clearer. I was intending to use the PE isolator on the trigger cable, not the RCA. Would that device work on the trigger, not input cable?

                              I'm a little concerned about the current capacity of the TI chip as well - but the data sheet did note it can be paralleled for increased capacity. I may do a search and see if there's a higher wattage device (within reason, of course.

                              Comment

                              Working...
                              X