Boss TR-2 Ticking Sound In Bypass Mode

Discussion in 'General Electronics Chat' started by IowanChef, Mar 25, 2015.

  1. IowanChef

    Thread Starter Active Member

    Mar 6, 2010
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    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. Sinus23

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    Sep 7, 2013
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  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    An LTspice simulation of the circuit section around Q1 suggests that any leakage path (e.g. from dust, flux residue or other contamination) of <~ 2megOhms from Q1 gate to either its drain or source, could result in waveform distortion and/or DC shifts which might be heard as ticking. I'd suggest cleaning the pcb in that area to see if it makes any difference.
     
  4. IowanChef

    Thread Starter Active Member

    Mar 6, 2010
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    Cleaned up the board and double-checked solder connections, but the ticking sound is still quite present whether the pedal is engaged or not. I even attempted putting a 100uf cap on the power supply, but that did nothing.
     
  5. Alec_t

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    Sep 17, 2013
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    That's a horrible schematic; component numbering is all over the place and there are two caps labelled C1 !
    One possible cause for clicks getting through is poor power-supply decoupling. With age, electrolytic caps can lose capacitance or develop high ESR. Might be worth replacing at least C9, C24, C19, C10, C4.
     
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  6. Kermit2

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    Feb 5, 2010
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    you beat me to it. I would also suggest ruling out the power supply by substituting with another one.
     
  7. Sinus23

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    Oops didn't notice that :( But after some searching for a better schematic I found that even though one of the C1 turns into a C3 in some of the schematics, there are two R25s and the numbering is still all over the place :confused:

    I think it would be best if OP would post the schematic he was referring to in his post#1. That is if changing the caps doesn't fix it.
     
  8. Alec_t

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    Sep 17, 2013
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    A further opportunity for clicks to be picked up is the way the JFETs Q1,Q3 are used. I don't like the Boss arrangement whereby when the diodes D2,D3 are reverse-biased the gates are left in a floating high-impedance state, making them vulnerable to noise pick-up.
     
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  9. #12

    Expert

    Nov 30, 2010
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    I tried everything except peanut butter on a Fender Super Showman that clicked.
    It ended up being humidity in the circuit board.
     
  10. Alec_t

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    Perhaps peanut butter would have kept the moisture out :D.
     
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  11. Alec_t

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    Does using a fresh 9V battery, or using the AC adapter, make any difference to the clicks?
     
  12. IowanChef

    Thread Starter Active Member

    Mar 6, 2010
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    I've removed Q1 and the ticking is much less noticeable. Here's the schematic I am working from. The noise is present with both the 9v battery and AC adapter with no audible difference between the two. I lucked out and ended up picking up an old oscilloscope at a flea market (just needed a fuse). Now to see if I can figure out how to use it to my advantage in this situation...
     
  13. Alec_t

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    Scope the 9V, 5.5V and 4.5V rails, looking for spikes coinciding with the ticks.
     
  14. IowanChef

    Thread Starter Active Member

    Mar 6, 2010
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    I see the points in the schematic for the different voltage supplies, and when I hook up the scope probes to ground and those points, I can't get it dialed in fine enough to really tell. I think a lot of the noise was due to the person who modded it (again, quite crudely) didn't wire the grounds up properly. After rewiring them with the schematic as a guide, I eliminated most of the noise and put Q1 back on the board. There's still faint ticking, but I'm guessing that the level it's at is likely common with many tremolos, yeah? I'll still try to get the power supplies dialed in on the scope and swap out the lower level EL caps.
     
  15. Alec_t

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    Poor grounding could explain at least part of it.
    Can't say. I've never used a tremolo circuit; but some other members here may have?
     
  16. Mike33

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    Feb 4, 2005
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    My bet is that if you add a 100R resistor where you power enters the board, with a nice big decoupling cap (1 or a couple 470u's from that resistor to ground - could get away with smaller ones if you can't fit 470s), you'll notice that tick go away. It's worked for me on a lot of LFO builds....the LFO is creating spikes on the power supply that manifest as audible ticks in the output. Only hard part is trying to make the cap fit in the enclosure, if you haven't put it in a new one.
     
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