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BOSS TR-2 Tremolo with audible oscillator ticking in bypass mode

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  • BOSS TR-2 Tremolo with audible oscillator ticking in bypass mode

    Greetings to you all. My current conundrum is a Boss TR-2 Tremolo pedal that I rescued after someone did some very crude modding to it. I opened it up to find all of the mechanical mods done with solid thick gauge wire and electrical tape. It's the old 4 IC version and the following mods were done:

    C7 - cut from board (I've since replaced it)
    R31 - removed from board and wired into a switch with a 250k potentiometer
    R19 - replaced with a 6.8k resistor

    Even in bypass mode you can hear the ticking of the oscillator, which I've confirmed by changing its speed with the rate knob. I Googled my brains out on this topic and found a few pages worth of good info, but in regards to this particular issue I only found a page that suggests swapping out the op amps or adding a resistor/capacitor to IC4. I know the TR-2 has a history of being noisy, but even in bypass mode? Seems odd. Whether it's related to the mods done to it, I can't be sure...

    Thanks for any and all help, as always. I missed you guys!
    Hope this finds everyone well.

  • #2
    Just as an experiment bridge the battery terminals with an electrolytic - 100uf or so - and see if it kills the noise.


    • #3
      And try to post the schematic

      I know C4 is an explosive (I watch all dem' Action Movies) but not so sure about C7
      Juan Manuel Fahey


      • #4
        Schematic & parts info: Boss TR-2 Tremolo Pedal Schematic Diagram


        • #5
          Sorry about forgetting to post the schematic. Thank you, Jazz P Bass. I cleaned up the board and popped a 100uf cap on the power supply, and ticking sound is still there whether the pedal is engaged or not. Should I start poking around the transistors and getting some readings?


          • #6
            I poked around with a multimeter in diode test mode and got the following readings for Q1 and Q3, which are both 2SK118Y N-Channel FETs.

            Pin 1 Pos, Pin 2 Neg: OL
            Pin 1 Pos, Pin 3 Neg: .220
            Pin 2 Pos, Pin 1 Neg: .694
            Pin 2 Pos, Pin 3 Neg: .694
            Pin 3 Pos, Pin 1 Neg: OL
            Pin 3 Pos, Pin 2 Neg: .205

            Pin 1 Pos, Pin 2 Neg: OL
            Pin 1 Pos, Pin 3 Neg: .200
            Pin 2 Pos, Pin 1 Neg: .693
            Pin 2 Pos, Pin 3 Neg: .693
            Pin 3 Pos, Pin 1 Neg: .219
            Pin 3 Pos, Pin 2 Neg: OL

            Weird discrepancies between the last two measurements for each, yeah?
            I also checked all the diodes and D4 is giving the same measurement with the leads reversed, but I'm not sure if that's the cause of the audible LFO ticking.

            Thanks for any and all help, as always.


            • #7
              Boss TR-2 Schematic

              I would remove Q1 to isolate the issue.
              Attached Files
              Last edited by Jazz P Bass; 03-27-2015, 01:56 AM.


              • #8
                my notes on this say "changed out R9 with a 4k7 to fix the volume drop" ( i know, this has nothing to do with the problem at hand)

                If we hear ticking when in bypass, its either ground loop voltages interfering (unlikely), or maybe the 4.5V supply has ticking noise.
                If you remove Q1 and you still have the noise, look for ticking voltage on the 4.5V supply, maybe add 100u in parallel with C10 to see if that fixes it.

                It may be worth while replacing all the low value electrolytics, especially all the 1uF 50V ones C1, C5, C20, C21 in case these are leaky, or dried out.....


                • #9
                  I forgot to mention that when I first opened the pedal, there was NO ground connection on the output jack at all. It didn't look like it had ever been connected, no signs of previous solder on the tabs. Very strange. I went ahead and connected the ground. Not sure if any of that is important, but there it is.

                  I'll remove Q1 and see what happens, and I was planning on replacing all the electrolytics. So should I not bother with the higher value ones?

                  Thanks guys. I'll get back with the results.


                  • #10
                    Alright, so with Q1 out of circuit the sound is much more faint. I know that with a lot of these pedals a little noise is to be expected.
                    What should I do now? Replace the low value electrolytic caps? What about that diode I was getting a funny reading on?


                    • #11
                      With Q1 out of circuit, the pedal is 'bypassed'.

                      It sounds to me like the ticking is getting injected into the power supply.

                      Bottom left of the schematic: I would check all of those nodes for any ripple.

                      Also, someone may have botched up the grounding scheme.
                      Pay special attention to the two ground symbols.


                      • #12
                        Being that whoever worked on this before me made some very odd choices, the grounding scheme may likely be an issue. In a previous response I noted that there was no ground connection to the output jack. I wired it to the ground of the input jack. Bad idea? Either way, I'll go through and check all the nodes for ripple. Should I continue these tests with Q1 still out of circuit?

                        I should also add that I have almost no formal training. I started circuit bending a few years ago and just recently got into small repairs, so dealing with a circuit with digital/analog ground is fairly new to me.


                        • #13
                          And I just saw that I made the exact mistake you mentioned. After checking the schematic again, I got the output jack wired to the correct ground. With Q1 out of circuit, this made the noise even less-noticeable.


                          • #14
                            did you try 100u in parallel with C10 ? that will help filter any "noise" on the 4.5V supply


                            • #15
                              I popped a 100uf on C10 and it knocked the noise level WAY down. I put Q1 back in place and I think it's probably about as good as it's gonna get. Should I still go ahead and swap out the lower value EL caps?