Why do some footswitches make a loud popping sound?

LionAquaLooper

I have a few pedals with "old school" footswitches that click (i.e not TC Electronic soft touch, or Boss type footswitches) and some of them are quiet when you press them on/off, and some make a loud popping sound. Just wondering if anyone knows what causes this and if it can be fixed?

I read somewhere that it could be due to caps discharging. I'm not convinced it's cables or power supply in my case because those are constant in my chain and some of my pedals are quiet. 

Danny1969

Often it's because some DC has built up and there's no discharge route for it to go ...could be a leaky output cap, often a pull down resistor will be fitted to prevent this but not always. 

A lot of pedals are biased at half the DC voltage (4.5V) and they swing either side of this. Capacitors are used to block this DC bias reaching the next stage / pedal / amp etc but the larger values needed for a low impedance output stage call for electrolytic caps and these all leak a little bit 

ICBM

It's caused by a DC voltage offset on the signal path in either the pedal circuit or - and this can be very confusing - the amp... the first stage in most valve amps is DC-coupled to the input jack, and if the valve leaks slightly from the grid (quite a lot do) a tiny voltage builds up on the signal cable. When you switch, the voltage is discharged which causes a loud pop. The same happens if the leak is in the pedal circuit.

Basically these are design faults - there's no reason for either amp inputs to be DC-coupled (a fairly large-value cap in line will fix it without affecting the sound at all) or pedals to do this, since you can have 'pull down' resistors which are a high enough value to not affect the sound, but low enough to allow any charge to drain faster than it can build up.

If it's only some of your pedals, it's probably not your amp. You can easily test if it's the amp with a particular pedal if you put another pedal after it between the suspect pedal and the amp, either a fully-buffered one like a Boss, or any other pedal that's turned on. If the suspect pedal footswitch now doesn't pop, chances are the leak is in the amp.

If you've identified the pedal as the culprit, you can fix it by adding the pull-down resistors - they need to be on the effect circuit side of the footswitch, from the signal path to ground. 1M ohm is a typical value which is high enough not to affect the tone, especially on the output. I would add that one first, and if it still hasn't fixed it, try a 10M on the input as well.

Or just do what I do and never again own any pedals which have mechanical bypass switching . (I know, that does limit my pedal choice a lot, but I'm not completely sure that's a bad thing!)

camelfish

As a minor pedal builder myself, I find the biggest culprit is LED popping, a sudden rush of current is to blame when the LED lights up.  There are fixes available (AMZFX site) that slows the current surge but I have not managed to get that system to work myself. It seems to be worse ie louder on boost pedals; the pop seems to get lost in fuzz/distortion pedals.

The only fix I have found, and I only found this out recently, is to ground the input and output when the effect is off. Some rewiring of the 3PDT footswitch required.

I should add that I always use pull down resistors and the LED problem is definitely a separate issue.

ScreamingDave

Interesting.  I have and EHX Small Clone and I occasionally get a loud poo, but just the first time I switch it of an evening.  After that it’s quiet

Yorkie

camelfish said:

I should add that I always use pull down resistors and the LED problem is definitely a separate issue

Sounds familiar. All my designs have pull down resistors, in and out, and I still get that boom whenever I turn the circuit on. I wanted to try using capacitors for a smooth on-off effect, but I got hilariously sidetracked. My biggest problem is that, while the boom can be annoying, the effects do work and sound OK. As they are for my own consumption, I usually prioritise working on new ideas. 

Sporky

camelfish said:

The only fix I have found, and I only found this out recently, is to ground the input and output when the effect is off. Some rewiring of the 3PDT footswitch required.

I'm not sure grounding the output is necessary, but the right way to wire true bypass does ground the input when in bypass - it's silly not to. The crap way to do 3PDT TB also requires the signal to go through two sets of contacts when in bypass which is not ideal for reliability.

octatonic

ScreamingDave said:

Interesting.  I have and EHX Small Clone and I occasionally get a loud poo, but just the first time I switch it of an evening.  After that it’s quiet

Probably the curry.

LionAquaLooper

Just to clarify - when you guys say "input" you don't mean the input jack do you? Do you mean the effect input of the footswitch? 

Jonathangus

ScreamingDave said:

I occasionally get a loud poo

Username checks out...

Sporky

LionAquaLooper said:

Just to clarify - when you guys say "input" you don't mean the input jack do you? Do you mean the effect input of the footswitch? 

Input to the circuit.

Think of the footswitch as wrapping around the effect itself.

camelfish

Yes ground the output too, I know it's not standard practise but grounding only the input didn't work for me. After all, the pop does come out of the output.

Sporky

camelfish said:

Yes ground the output too, I know it's not standard practise but grounding only the input didn't work for me. After all, the pop does come out of the output.

True - but that might not be where it's coming from. Still, if it works it works.

How are you wiring the footswitch to do that?

camelfish

it's a coming....negative ground setup.

Sporky

I can't tell whether that's cruel or funny!

camelfish

ScreamingDave

octatonic said:

ScreamingDave said:

Interesting.  I have and EHX Small Clone and I occasionally get a loud poo, but just the first time I switch it of an evening.  After that it’s quiet

Probably the curry.

OK. It’s a fair coo

LionAquaLooper

I saw this on YT and wondering if anyone can tell if it would work on any other pedal with a 3PDT switch? Are these switches wired the same way across different pedals?

Also he uses 2 resistors and I'm assuming both are acting as pull downs. I always thought you just need one. 

Sporky

camelfish said:

Cunning!