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Need help interpretting the schematic for an EMG PA2 boost circuit

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  • Need help interpretting the schematic for an EMG PA2 boost circuit

    The product page on the EMG site for the PA2 boost circuit ( https://www.emgpickups.com/pa2.html) has a downloadable wiring instruction sheet. Within that sheet, is a schematic for the circuit of the PA2 - see attached pic. Can anyone tell me what the two triangle symbols with the plus sign inside them represent? I have not found a reference online for that exact symbol. I have found descriptions for triangle symbols that are slightly different - none exactly like these two.

    Edit: I suspect they represent the boost itself, but then that makes me confused about the circuit, because you are supposed to be able to turn the boost on or off. Yet this seems to show the input signal going through the boost in either case (?)

    Click image for larger version

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    Last edited by Jack_TriPpEr; 06-01-2020, 03:58 PM.
    Sanford: "The hardest part about tone chasing is losing the expectations associated with the hardware."

  • #2
    Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    I’m assuming a very simple inverting OpAmp schematic, omitting a decent amount. The bottom one being a unity gain amplifier and the top one having variable gain set by the pot.
    Oh no.....


    Oh Yeah!

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    • #3
      Re: Need help interpretting the schematic for an EMG PA2 boost circuit

      thats a block diagram, not a schematic and i suspect darkside is correct that one is just a unity gain amp while the other is a boost

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      • #4
        Re: Need help interpretting the schematic for an EMG PA2 boost circuit

        Originally posted by PFDarkside View Post
        I’m assuming a very simple inverting OpAmp schematic, omitting a decent amount. The bottom one being a unity gain amplifier and the top one having variable gain set by the pot.
        Ah, the 2nd amp being unity gain - that makes sense. Thanks!
        Sanford: "The hardest part about tone chasing is losing the expectations associated with the hardware."

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        • #5
          Re: Need help interpretting the schematic for an EMG PA2 boost circuit

          Originally posted by jeremy View Post
          thats a block diagram, not a schematic and i suspect darkside is correct that one is just a unity gain amp while the other is a boost
          Ahh, thanks for the clueing me in that not everything that looks like a schematic, is actually a schematic. And for corroborating Darkside's theory.
          Sanford: "The hardest part about tone chasing is losing the expectations associated with the hardware."

          Comment


          • #6
            Re: Need help interpretting the schematic for an EMG PA2 boost circuit

            Originally posted by PFDarkside View Post
            I’m assuming a very simple inverting OpAmp schematic, omitting a decent amount. The bottom one being a unity gain amplifier and the top one having variable gain set by the pot.
            Yup. Can't add to that. Although, without +/- input labels, there's no way to know if its inverting, without watching the output on a scope.

            Edit: I take that back. You could temporarily connect the booster to just one pup. If it went OOP after activation with another pup, it would be inverting. If not, then it isn't inverting.
            Last edited by ArtieToo; 06-01-2020, 04:22 PM.

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            • #7
              Re: Need help interpretting the schematic for an EMG PA2 boost circuit

              ive used it only on one pup and it wasnt inverting

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              • #8
                Re: Need help interpretting the schematic for an EMG PA2 boost circuit

                Yeah, I was thinking inverting due to the layout and how there were two amplifiers it is being switched between (to keep phase the same whether engaged or not). Non-inverting makes more sense so you could use it on a single pickup and not cause additional phase issues.

                It’s an interesting layout though, rather than simply bypassing the boost entirely or switching from fixed unity resistor to potentiometer.
                Oh no.....


                Oh Yeah!

                Comment


                • #9
                  Re: Need help interpretting the schematic for an EMG PA2 boost circuit

                  Originally posted by jeremy View Post
                  ive used it only on one pup and it wasnt inverting
                  Originally posted by PFDarkside View Post
                  Yeah, I was thinking inverting due to the layout and how there were two amplifiers it is being switched between (to keep phase the same whether engaged or not). Non-inverting makes more sense so you could use it on a single pickup and not cause additional phase issues.

                  It’s an interesting layout though, rather than simply bypassing the boost entirely or switching from fixed unity resistor to potentiometer.
                  Great insights, thanks again to you both
                  Sanford: "The hardest part about tone chasing is losing the expectations associated with the hardware."

                  Comment

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