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True Bypass and POP when switching

Discussion in 'Effects [BG]' started by Nu11nV01D, Aug 22, 2012.

  1. Nu11nV01D


    Jul 8, 2011
    Howdy. I've got a DHA overdrive/distortion pedal that pops very loudly when I turn the true bypass on and off. From what I can gather, true bypass just...does that.

    What I want to know is if the pop can do any damage to house speakers or anything like that? Of if there's any way (compression, resistors, etc) that I can fix the popping. The pedal itself sounds good, but I can't deal with this popping to the point where I'm considering selling it.

    Note: I'm in college studing Electrical Engineering, so I know a thing or two about how these things work, but only a little. I'd love to be able to plug in a resistor somewhere to fix it.
  2. I am having trouble with a true bypass switch on an effect looper pedal popping. I always cycle it 20 times after powering up the board and connecting my bass, but before powering up my amp or connecting to the PA to dissipate any built up static electric charge. It seems to be helping.
  3. DannDubblewe

    DannDubblewe Knob Wrangler

    Apr 3, 2009
    Pulldown resistors should be incorporated into the circuit to prevent this...right?

    I guess a good temporary solution would be isolating it in a true bypass loop, so you could just turn it on and use the loop to engage/ disengage. The loops I've used never pop, so that SHOULD work. Maybe? :ninja:
  4. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    The pop is caused by charge building up on one side of the switch, which is released all at once when the switch opens. This only happens with mechanical true bypass, like the common 3PDT switch.

    Pulldown resistors can help, but are not a 100% always cure. Definitely if the switch doesn't have a pulldown, it's a good idea to add one. The idea is to create a connection between the signal path and ground; when the switch is off (open), the path of least resistance is to ground, and when the switch is on (closed), the path of least resistance for the signal is through the switch. The resistor (high value, like 2 meg) prevents feedback or noise from leaking into the signal path from that connection.

    Here's one example:


    From here (useful info in thread): http://www.diystompboxes.com/smffor...22be19bc4b67698ab9d591f1fbeb08a&topic=75778.0

    Clicking the footswitch several times, with your amp muted, is a good way to dissipate the charge.
  5. Nu11nV01D


    Jul 8, 2011
    Thanks for the replies! I will probably try to click it on and off a bunch of times before I use it, and if that doesn't work swipe a resistor from school and fiddle the the innards.
  6. EskimoBassist


    Nov 2, 2007
    Leeds, UK
    This is one of many reasons why i don't believe the TB TB hype (see what I did there, ey?).
  7. I see what you did there! I like it.

    Yes, true bypass implemented via mechanical 3PDT switches is not a great solution. Actual relay based bypass is the way to go, I hope more effects manufacturers start to use the better solution.
  8. NeroJazz


    May 2, 2011
    Putting a buffered pedal or dedicated buffer before the troublesome pedal can sometimes fix problems with popping switches.

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