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True-bypass switch "pop?'

Discussion in 'Effects, Pedals, Strings & Things' started by DaveG, Sep 20, 2006.

  1. DaveG

    DaveG Gold Supporting Member

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    Recently, I've been helping a friend with a short weekly gig; it's a small room, and I'm trying to travel light. I've been taking one guitar, my Fender Champ, and a couple of pedals; the Champ is mic'd, and I'm running the pedals on batteries. So far, it's been sounding great, but...

    My pedals (Strobostomp, PowerScreamer, Small Fry) are true bypass, and they make a loud POP through the amp when switched; what's causing this? Is it because all three pedals are true bypass? I've never noticed this with my main pedalboard, maybe because I have a DigiDelay at the end of my chain (buffer)? Any easy fix for this, with my setup? Thanks!
     
  2. TieDyedDevil

    TieDyedDevil Member

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    The popping happens because there's some DC leaking into your signal chain from somewhere. Could be the amp, could be one of the pedals. Can't be the guitar unless you have active pickups. Use a process of elimination to figure out where it's coming from... First try one pedal at a time. If you find just one that pops, then it probably has a leaky capacitor or a missing resistor; a tech should be able to figure this out. If the pedals are all OK, try changing V1 in the Champ.
     
  3. DaveG

    DaveG Gold Supporting Member

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    Thanks, I'll try that out tomorrow morning.
     
  4. StompBoxBlues

    StompBoxBlues Member

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    A lot of pedal makers that make TB pedals advise the user to "turn it on, let everything warm up, then turn the pedal on and off a few times, after that it won't pop"....

    Is it happening even after turning on and off a few times? I think it mostly has to do with capacitors building up a charge, and when you turn off the pedal, the charge sits there...has no where to go because both positive AND ground are isolate, when you turn it on again it goes into action, but first discharges the caps. I think turning it on and off a few times is supposed to help (and I experience this to be the case on my TB that pop...not ALL TB pedals pop, and some can be fixed by turning on and off a few times, and still others maybe it can happen any time or not) in a lot of cases.
     
  5. TheGigPig

    TheGigPig Member

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    Actualy the 'pop' could be caused by a couple of things. With the most commonly used True Bypass circuit the effect circuit is in fact FLOATING when it's bypassed. It has no reference to ground so it can float way above ground. The 'POP' is caused by this circuit being shunted back down to earth....BANG!
    There is also a very common problem that alot of guys miss becaus it doesn't affect your tone called a D.C. input offset. What does that mean?
    It's basically when your amplifier input which should be sitting at 0 volts has drifted to a different level. When your guitar is plugged in and playing normally, the input is given a ground reference and everything works great, but when you break the circuit, even for a fraction of a second like selecting pickups, or with true bypass switching, that voltage drifts back up to a different level. The pop sound is when the circuit is reconnected and the voltage comes back down to ground…with a THUD!

    Often this can be as simple as a faulty input valve (or tube as you might call it) in your amp.
    You can measure this offset easily with a multi meter. Just plug your guitar cable in and with your voltage selector on D.C. volts take a reading between the tip and the shield of your lead. Get a reading other than 0? There's your problem.

    I have a 1962 VOX AC10, which I have a barely legal relationship with. The D.C. input offset on this amp is 3.2 volts! That's huge, but it sounds amazing. (A bad D.C. offset won't affect your tone, which is why most people miss this as a problem.) It has the original Mullard EF86 valve in it. With a new valve the popping goes away, but the old Mullard just sounds too good so I live with the popping.
     
  6. mild

    mild Member

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    Great writeup Daniel! That is something to commit to memory, right there...
     
  7. autopilot

    autopilot Member

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    yes having a good buffer or using a clean boost at the end of your chain will take away the pop.
     
  8. theelectic

    theelectic Guest

    I presume you mean the effect INPUT is left floating. Even so that's usually not the case, 99.9% of TB FX have a pull-down resistor on the input to send the DC leakage to ground. If that resistor is not present the designer really doesn't know what they're doing.

    Pops can still occur even with a pull-down resistor - could be switch bouncing, LED on-rush current, or any other number of little gremlins.
     
  9. theelectic

    theelectic Guest

    If the amp is leaking, yes. If the popping effect is before, and the cause of the popping is that effect leaking (or a bad switch, or whatever) the pop will still be there.
     
  10. DaveG

    DaveG Gold Supporting Member

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    Thanks for all the input, guys. I tried each pedal by itself, and each one popped when switched. I switched out the pre amp tube in the Champ, as it was the only one I had in the drawer; I've got a set on order, so I'll install them over the weekend. For tonight, I'll run my Digidelay and see if that takes care of it.

    Geez, it would probably be less trouble to just take my pedalboard... :jo
     
  11. Holy Falance

    Holy Falance Member

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    Bad switch jangling as it is connected, Bad patch cable caping up some signal or its DC from the caps in the effect.

    You could try and new cable, a pull down resistor to ground from the efefcts input and output caps or replace the switches.

    Have fun!
     

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