noob question : pop when effect is switched on.

[poppyman]

Hello,

I never really have any problem with pop before when I clicked the foot swtich.

I build the throb tremolo on a PCB from Poodle fuzz....I did one before and it didn't pop.

I had a pull down resistor as described on the build document (on the switch itself). I tried to move it on the input jack itself, it's the same problem.

Now, I realised that the "pop" is louder sometimes: when I switch the pedal on and off several times, it gets quieter.

Is it the symptom of a capacitor "discharging" or something else?
Does it affect only the polarized caps?
Can I identify the faulty cap or should I just change them all?

Thank in advance.   

[brianq]

What's the value of pull down resistor? 1M? Have you tried 2.2M?

[poppyman]

The one on the build document was 1M (the one that you had to solder on the footsdwitch itself), the one I tried on the input jack was 2M...same thing: this quiter pop after a few on/off clickings.

[R.G.]

I build the throb tremolo on a PCB from Poodle fuzz....I did one before and it didn't pop.

So what - in great detail! - is different between the two? The answer is there. Go compare them.

Now, I realised that the "pop" is louder sometimes: when I switch the pedal on and off several times, it gets quieter.
Is it the symptom of a capacitor "discharging" or something else?

Yes, it's a capacitor charging up.

Does it affect only the polarized caps?

No. All caps.

Can I identify the faulty cap or should I just change them all?

It is most unlikely that changing them all would help. It is also most likely that any of the caps are faulty. Experience with many, many - many! - new constructors says that in the vast majority of cases, the problem is with PCB or board construction, soldering issues, or wrong pinout connections.

[poppyman]

Cheers.

I don't have the 1st trem anymore, it was given to a friend. It was built on the updated board (so  a more recent one than the one I used for the pedal I have problem with).

The pulldown resistor is now "on board" on the newer PCB. I don't really have a clue if there was such a problem with it but when I tested it , I don't remind hearing a pop and I didn't have any complaints about it from my friend.

Does moving the pulldown resistor somewhere else (like at the input on the PCB) would change anything?
Changing the caps won't be an ordeal so I might give it a go but your post made me wonder if it's a good idea at all.

[R.G.]

Frankly, the right thing to do is for you to read and follow the sticky note: "Debugging: what to do when it doesn't work".

[induction]

A link to a schematic would be very helpful here. Is it this one? If so, there's some misleading info in that build doc. Looking at the schematic, no input pulldown is required as that job is handled by R2 (and the input is grounded in bypass anyway). The more likely cause of the pop is at the output. C4 is the output cap, and there is no output pulldown in the schematic or build doc. Try removing your 1M input cap from wherever it is now and putting it at the output. You can put it on the switch from lug 9 (board out) to lug 5 (board gnd). You can try it with alligator clips first, to see if it works without making it permanent.

A bit of more general advice:
An input or output pulldown placed on the jack will potentially add tone-suck (even when the pedal is bypassed), while accomplishing absolutely nothing to prevent pops since it's not connected to the circuit board in bypass. The type of pops that pulldowns prevent are caused by DC voltage leaking through the input/output cap causing a sudden DC shift when the pedal is engaged. The pulldown resistor bleeds this DC voltage to ground, keeping the switched leg of the cap at 0V in bypass. If the pulldown isn't connected to the input/output cap in bypass, it won't be able to do it's job. Putting the pulldowns on the switch is ok as long as 1) one side is connected to the input or output from the board, not the jack (ie. input: lug 2 not lug 3, output: lug 9 not lug , and 2) the other side is connected to a permanent ground, not a switched one (ie. lug 5, not lug 1 or 4).

Edit: 'lug 8' not lug

[snarblinge]

Also disconnect the led, does it still pop? If so keep looking, if not, there is your problem, implement a solution there.

This has so far solved every one of my problems......to do with popping

http://www.muzique.com/lab/led.htm

[poppyman]

Yes, it's the build guide with the schematic.

So I put the pull down resistor at the output as described (ground and board out on the switch)...At bedroom level, it sounds like it tamed things a little bit but it's still there.

I try to disconnect the LED and didn't make any difference. But it's good to know that it could come from that and that there's a solution for it, thank you both, I learned lots 

RG is right it's time to read the debugging thread again
cheers guys!