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Pedal popping noise is intermittent... cause?

Hollow Man

Hollow Man

Supporting Member
Apr 28, 2003
4,062
111
Springfield, VA
#1
I've been getting into effects lately, and I've indulged and purchased several different effects by different manufacturers in a relatively short amount of time. I've noticed that some of them, when switching the effect on and off, put a very loud pop through the speaker, which is obviously very undesirable for both performance/recording integrity as well as potential damage to the speaker. However, the problem isn't always there... sometimes it's loud as hell, and sometimes it's as quiet as I'd expect it to be.

So... do any of you have experience with this on-again/off-again popping? What causes it? Is it more inherent in certain types of effects, certain manufacturers, or certain pedal models? For what it's worth, the most recent offender has been a BJFE Blueberry, although I've noticed this on a few different pedals too. What do you guys think would cause a loud pop on one toggle and no pop on another?
 
#3
I have a couple pedals that do that. I use them live and it doesn't really bother me. It's not really noticeable in a band mix. I think, the more highs you have dialed in, the more it pops.

Maybe a noise suppressor, like the Boss NS-2 would help.
 
#4
A noise suppressor wouldn't help, they are just noise gates that only open up to let sound through once it reaches a certain volume. The pops would go through straight through.

The loudest popping I ever heard came from a WMD Fatman I was playing with, but then all of a sudden the next day it stopped happening. The DHA tube pedals also pop but only when the boost circuitry is engaged. I've also heard complaints about the Carbon Copy popping excessively but mine's quiet as can be. I'd also like to know what causes it and why it's only intermittent!
 
#8
It is my belief that the pop is caused mainly by leaky DC blocking capacitors. The construction/operation of the switch also contributes.

I doesn't have anything to do with static electricity. The switch body is already well grounded by virtue of it being attached to a metal enclosure which is earthed via the signal cable shield to your amplifier.


FX boxes need to pull some tricks in order to work from a single voltage source - the battery. The entire circuit is 'biased' to half the supply voltage, meaning the signals all throughout the circuit are actually sitting on top of a DC voltage of around 4 volts. To isolate this DC voltage from the outside world, large-ish electrolytic capacitors are placed at the input and the output of the circuit, effectively blocking the DC voltage while allowing the signal to pass through.

Capacitors are not ideal devices - they have many faults, one of which is leakage resistance. This leakage resistance allows some of the DC literally to 'leak' through the capacitor where it can create a DC offset voltage where there should ideally be 0VDC.

When you stomp a TB switch from bypassed to engaged, these DC voltages are suddenly connected into the circuit causing a momentary blip in the signal path. Result = WHUMMP!


There have been many attempts to deal with this problem, but as far as I am aware none of them are 100% effective.
 
#10
This is a result of true bypass. I have a true bypass looper I use to create channels of effects combos. I find that if i turn the effects in the loop on, and then click the switches off and on a few times it happens once and then not again, or not at all and its not a problem.

I have heard about using pull down resistors, but I know nothing about electronics so I don't know how to do that modification
 
#11
The pull down resistor is there to allow the input or output capacitor to release it's charge to ground so the pop doesn't happen when the pedal is switched on. It's a matter of voltage differences. If the pedal design doesn't have a pull down resistor adding one can get rid of the pop. If it does and the pedal still pops it's possible that input or output capacitor is leaky and replacing it can get rid of the pop. Failing that it's possible the stomp switch sucks.
 
#12
i had a bunch of TBP pedals that popped.... only on the first engage after being powered up. all i had to do was turn on my power supply, engage all the pedals once, and i wouldn't have to worry about the pop

i have absolutely no electronics knowledge so i don't know WHY what i did worked. but i guess a little bit of smarts gets around problems sometimes :)

it also depends on HOW the TBP switching was designed, as i believe that there is no 'standard' method of implementing TBP in a pedal
 
#14
The pull-down resistor things doesn't always work. The ideal value of the resistor depends on many factors which are virtually impossible to predict. Basically, some people get lucky and it works. Others aren't so lucky and it does nothing.

If you had a bunch of pedals in a TB loop you should only need pull-down resistors on the loop switch itself. But, if you change the pedals in the loop, even altering their order, you might find that what worked before the change doesn't work after the change.
 
#15
When I'm building pedals I always put a 47UF cap from +9V to ground and a 2.2M pulldown resistor on the input signal to stop this happenning.

It works in the vast majority of cases. Depending on circuit topology you can do a few different other things to stop it. In some designs it's not possible to stop.
 

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