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Loud Popping from True Bypass Pedals - why?

Discussion in 'The Stomp Box' started by SMurphy28, Jul 6, 2010.

  1. SMurphy28

    SMurphy28 Tele-Meister

    Sep 23, 2003
    Madison, NJ
    I'm getting a loud popping noise when engaging the two true bypass pedals on my board - Analog Man King of Tone and a MXR Phase 90.

    Any ideas why?

    The board is powered by a Voodoo Lab Pedal Power 2 and is connected with George L's and Mogami Cables. The Pedal Power is plugged into a Furman power conditioner when on stage.

    Is this just the nature of the beast? It does this in my house, at rehearsal and in all the rooms we play in so it's has nothing to do with the location that I can tell.
  2. mikeyd990

    mikeyd990 Tele-Meister

    Oct 24, 2008
    Lansing, Michigan
    Im interested in this too, as i get a popping from my Rat 2, and Digitech Chorus... both which are true bypass...
  3. yonie

    yonie Tele-Meister

    Oct 10, 2009
    I can imagine the circuits physically disconnecting and reconnecting causes some noise - just as pulling a plug does. But i might be wrong.
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  5. JesterR

    JesterR Tele-Afflicted

    Jul 8, 2009
    Russia, St.-Petersburg
    I think, that there is some process with capacitor, when you turn on and off pedal circuit.
  6. mlove3

    mlove3 Tele-Afflicted

    Apr 15, 2008
    Phoenix Az
    "I can imagine the circuits physically disconnecting and reconnecting causes some noise - just as pulling a plug does. But i might be wrong. "

    You would be right though. The pop is likely due to a DC charge disipating, or just the physical action of the footswitch. One way to eliminate that is to modify the pedal with a couple of capacitors on the switch, but that changes the circuit of course, and possibly the tone.
  7. fndtele24

    fndtele24 Tele-Meister

    Oct 16, 2005
    New Haven, CT
    It can also be caused by an impedance mismatch. Example, My Fuchs Pure Gain is a true bypass pedal. However when engaged it changes the 1 meg input impedance to a 1K output impedance. And since it is after and before other pedals which usually have a 1 meg input, it causes a pop. Not all the time, but sometimes. I just leave the pure gain on all the time. That cures that problem.
  8. stlthinkin

    stlthinkin Tele-Meister

    Jul 20, 2009
    Richmond, VA
    Nature of the beast: pop comes from a DC voltage difference to ground when the effect is on/off. Better said here by geofex:

    almost all effects are powered by a single 9V battery, and this means that for DC biasing reasons they have both an input and an output DC blocking capacitor to carry the signal into and out of the circuit. No capacitor is perfect, and whenever the outermost end of either capacitor is open-circuited by a hard (mechanical) bypass switch, the leakage will allow some of the voltage to bleed into the outer terminal. When the capacitor is again connected, it no longer perfectly matches the average ground level of the signal, and this voltage is coupled into the signal path as a pop, the loudness of which depends on the size of the capacitor and the amount of the voltage change.

    A lot of makers will add a 1M or higher pull down resistor to always connect the caps to ground. Fulltone does this for all their true bypass circuits, other builders leave them out to be more vintage correct.

    So to fix the pops you can add a resistor to bleed the DC offset to ground, or live with the problem. After you plug up sometimes a click or two on each TB pedal can get rid of any static buildup and help make the pops quieter.

    I had a fuzzface that made a pop louder than turning on a PA in the wrong order (I had to mod that...). My old Rat has the loudest click of my current TB pedals.
  9. Kevin Wilson

    Kevin Wilson TDPRI Member

    Jul 4, 2010
    You have to be sure to do it on the board before the first cap in the circuit. You can't just do it from the input jack to ground. Even with the resistor you may notice the pop when first powering the pedal up but it should go away after you engage it the first time. Another cause of this could possibly be the LED popping. This is also fixable but requires a little more work. I would email the manufacturer first to see what they would suggest.
  10. Jeff B.

    Jeff B. Tele-Meister

    Oct 25, 2008
    Nova Scotia, Canada
  11. schenkadere

    schenkadere Friend of Leo's

    May 13, 2009
    Funny...I never get that popping.
  12. Telegazer

    Telegazer Tele-Holic

    May 6, 2008
    Republic of Korea
    Sounds quite familiar, my Prescription Electronics Depth Charge bass fuzz nearly blew a speaker cone (or two) on the Trace Elliot I use from such an explosive pop. Clicking it at least 10 times with my end-of-chain passive volume pedal heel-down before letting the signal pass through seems to take care of most of the mess, but it'll still engage with rage during a set and can be a little unnerving just the same.
  13. 11 Gauge

    11 Gauge Doctor of Teleocity

    Mar 21, 2003
    Near BWI Int'l
    But the KoT in particular already has that "pulldown" resistor.

    There are some designs that are quiet even without pulldowns, so they aren't a cure-all.

    Some causes of switch pop that are a little less obvious:

    - Status LED noise - many pedals with TB have the LED crudely wired with nothing more than a series resistor. Sometimes it's sufficient. Other times, it adds noise. The solution is a secondary series resistor with a capacitor tapped into the junction.

    - Not wired for mute on bypass. While many pedals have this (in bypass, the effect input is dumped to ground), some don't. And they don't all need it. And - sometimes it can actually make the pop louder.

    - Overall gain. And I don't mean amount of distortion. Sometimes it's just the output level.

    - Mechanical switch noise. Some switches are simply noisier than others. Roll down the volume on your guitar, and engage the pedal. Now play with the switch mechanism with your fingers, and see if you get any noises, particularly while switching it on and off. Some pedals (like the KoT) have the footswitches mounted directly on the circuitboard, which can actually make the noise worse. The terminals on those switches were not designed to be soldered directly to a circuitboard, so it's required a bit of "kludgery" to make them work. IMO.

    - Other pedals in chain. Sometimes parking something with a buffer in front of the noisy popper is sufficient to nuke all sorts of noises. But sometimes removing a buffered pedal from the tail end (or in between) can remove the popping as well.

    There are yet other potential causes, but the above are some that I have experienced more than rarely.
  14. Jack Deville

    Jack Deville TDPRI Member

    May 3, 2010
    Portland, OR
    Don't forget DC leaking from the amplifier's input!

    And yes, I've gotta second 11's notion: mechanical switches make lots of noise as they debounce. There are techniques to minimize the noise injected into the signal path, but you gotta be "clever," pull-down resistors won't cut it.
  15. Jayson

    Jayson Tele-Meister

    Mar 25, 2009
    Houston, TX
    All of my pedals are true bypass, and I don't pop.
  16. Radspin

    Radspin Friend of Leo's

    Mar 7, 2008
    Long Island, NY
    Great thread--you learn something every day. I have a couple of pedals that pop when I first use them, but if I click them on and off a few times they stop popping. I never had any idea why, until now.
  17. Ronsonic

    Ronsonic Tele-Afflicted

    Other pedals and some amps can leak DC onto the signal path and that will cause noise. Do your guitar's controls become noisy under these conditions? I would expect that if this was the cause.
  18. scottrollick

    scottrollick TDPRI Member

    Nov 29, 2011
    Northwest, Louisiana
    I'm bumping this because I want to add that it is also related to the amplifier and sometimes related to the wiring of the room as well.

    I have two true by-pass pedals: a boutique 73 rams head clone and a new production way huge aqua puss. Both of these pop louder than hell on my 2011 Fender PRRI -- though not always at my band mates house. I say "not always" because curiously enough, sometimes they do -- but rarely. They do it EVERY SINGLE TIME at my house and no amount of pressing the switch bleeds off the DC and lessens the pop.

    However, on my peavey classic 50 212, both pedals pop, but you have to have your ear pressed to the speaker to hear it. The pop is not noticeable in a band setting on this amp at all. I should add that this amp was made in the early '90s.

    I am going to try to add the pull-down resistors, first to the rams head and see if it makes a difference. But it's annoying as all get out and definitely happens on some amps more than others. Other than the resistor modification, I don't see much by way of a fix on the internet and "true bypass" seems only to gain marketing momentum.
  19. 1955

    1955 Poster Extraordinaire

    Apr 10, 2010
    I put those kind before a TU2, then mute before stepping on them. Helps some. To me it gets old after a while. Nobody ever wrote a review of a pedal saying they love a popper.
  20. Dave_O

    Dave_O Friend of Leo's

    Jul 27, 2006
    offline and IRL
    My somewhat cloudy memory of 60s and 70s pedals that I owned was they all popped (listen to when Keef kicks in his fuzz in "Satisfaction"). I had a Roland phaser, a CryBaby wah and a Coloursound Tonebender that always popped when you turned them on. It was just the nature of the beast. If I got an old pedal like those to gig with today the first thing I'd do after setting up a 9v power input would be to get rid of the old-style switch and put in a silent one.
    The Ibanez pedals of the late 70s were the first I remember with the FET "silent" switches. I had an Ibanez Overdriver (precursor to the Tubescreamer). The smaller Boss pedals were also good to use because of their silent switching. It was a great bonus to not have to deal with that damn noise.

    But now everyone's been partaking of the "True-Bypass" Koolaid.
  21. czech-one-2

    czech-one-2 Friend of Leo's

    Oct 3, 2008
    I had this problem with an arion sch-z chorus. It was leaking some dc on the input so any true bypass pedal hooked up before it would 'pop'. Took me awhile to isolate this problem.
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