more popping questions

[Sensei Tim]

I did a search on popping and i still have more questions.

situation:

I've got a BJFE Blueberry OD and an AMZ MOSFET boost in a single pedal.

the boost is after the OD.

there is a 3PDT switch that will switch the boost in/out of the circuit. there is also a bi-coloured LED connected to the switch that allows the player to know if the boost is engaged or just the OD.

blueberry circuit:


Boost circuit (yes, i know that the transistor in the circuit is shown in the wrong orientation):


switch wiring:


when i toggle the switch either way i get popping.

First, I see that the AMZ doesn't have a pulldown resistor on the input. i added one (on the switch) but it still pops.  I read Keen's article this morning on pulldowns and he says that the pulldown should be put on the board, not on the switch. will this make a huge difference? why?

Second, would this switch wiring be better?  it grounds the boost input when it's not being used


Third, should i put  pulldowns on the outputs, also?

Thanks!

Tim

[Zanius]

I've done enough multi pedals lately, and very early on I decided to wire the leds with the anti-pop methods from muzique here. I use the one with the cap between two resistors. If any pop still occurs (I think it never did) it's time for pulldown bonanza!

Anyway, it is PITA enough to have one effect popping on its own, but when you have two or three it is best to take precautions instead of trying to fix things after they are boxed.

[induction]

I'd say a pulldown on the boost output is your best bet. If that doesn't solve it, I'd first disconnect the led's to see if the problem goes away. If it's not the led's, try replacing the switch.

[Sensei Tim]

the popping happens when the switch goes in either direction. would a pulldown only on the boost output help the popping when i switch the boost on/off?

[induction]

DC offset at the boost output would explain the symptoms. It will pop whether you engage or disengage the boost, and yes an output pulldown should fix it.

The pop could be caused by something else, but that's what I would try first.

Edit: I just noticed this:

Sensei Tim wrote

I see that the AMZ doesn't have a pulldown resistor on the input. i added one (on the switch) but it still pops.  I read Keen's article this morning on pulldowns and he says that the pulldown should be put on the board, not on the switch. will this make a huge difference? why?

It's possible to put the pulldown on the switch, but it's easy to do it wrong. To do it correctly, the pulldown has to be connected between the input cap and ground at all times. There is usually one lug on the switch that is permanently tied to the input cap (usually labelled 'circuit in' or something similar) and another that is tied to the input jack. If the pulldown is connected to the input jack rather than the circuit input, then it will be disconnected when the circuit is bypassed, and won't do anything to prevent pops. Likewise, some bypass schemes have lugs that are only grounded in one position of the switch. If the ground leg of the pulldown is not touching ground in bypass, the pulldown won't work. The same logic applies to output pulldowns.

If you put the pulldown on the board, it's easier to be sure that the pulldown is always connected. If you previously put the input pulldown on the switch and you weren't careful about how you did it, it's possible that it was disconnected when the boost was bypassed. In that case, it's also possible that the pop is coming at the input instead of the output.

Out of curiosity, does your boost function when the OD is bypassed? It's hard to tell because you've posted the boost bypass switch, but not the OD bypass switch. If the pulldowns don't solve the problem, show us a diagram of the entire switching scheme. We might spot a different problem we hadn't previously considered.

[Sensei Tim]

My signal path is:

input jack

1st 3PDT - this either goes to true bypass or to the OD

OD

2nd 3PDT - this selects if the OD output goes into the boost input or back to the 1st 3PDT.  if it goes to the boost, then the boost output goes back to this switch and then goes to the 1st 3PDT and on to the output jack. If the boost is bypassed, then the OD output goes thru this switch and then to the 1st 3PDT and then on to the output jack

[Sensei Tim]

So I tried disconnecting the led from +9v - still pops

Tried putting a 1meg on the same switch pin that the boost output goes to - still pops

Seems like it might be the switch?

[rocket88]

just read through everything and i think it's the switch. i had this happen to me on one of my builds for a customer and it worked fine when i first put it together and tested it, then when i went back to really mess with it to ensure it was all working got a switch pop. went through everything else, added a larger pulldown resistor and it was still there. i threw in a new switch and the pop was gone. tested it like hell and no pop.

[ξεναγος νεκροπολης]

hi there guys.
i've build mxr mc401 from the site.

it works as it should, but it pops like crazy.
here are the things i did.

up-ed the output pulldown resistor from 10k to 1M
reduced the output cap to 3.3μF and then to 1μF but nothing changed.
replaced the ic.
disconnected the LED
changed the 3pdt with an other one from a different manufacturer.
disconnected the hole board from the 3pdt and only then pop stopped.

so.....
my 3pdt is ok i guess. the LED is out, so the problem is not there ether.
what else should i do?

[Travis]

Changing the output resistor from 10K to 1M would be a downgrade in terms of discharging the output cap.

Are you able to measure a DC voltage at the output? Are you testing this with the pedal in question bring the only pedal in the chain?

My favorite amp is my 5e3 which doesn’t have an “input cap”. This means when you connect a guitar straight to the input, the guitar volume pots sound scratchy since there is a bit of DC on them from the grid. I could imagine this situation causing a stompbox switch to pop with a variety of tube amps and true bypass but that’s a guess

[ξεναγος νεκροπολης]

i meassure 0.6mV to 1.7mV on output jack every time i press the 3pdt.

i'll change back to 10k the output pulldown resistor and see what happens..