Fading switch pop w/LED

[sixstringphil]

My appologies in advance if I've missed this while searching the wiki and forum, but I'm having a switch pop issue (I'm using aron's 3pdt switches) that I haven't found addressed. I built an Orange Squeezer from the Tonepad pcb layout. Everything works nicely except when first powering up.  (using voodoo labs pedal power 2+) I'm having an intermitten switch pop that I'm trying to eliminate. Here's what I've found...

-the pop only occurs when the power supply is first turned on and the O.S. is switched from "off" to "on"
-if I switch back and forth a few times, the pop lessens and then goes away for good.
-If I turn on the power supply with the O.S. switched "on," there will be no popping when I switch "off".

I'm very new at this, so it's very possible that I'm misunderstanding some basics here. More than just knowing "how to fix," I'd appreciate someone pointing me to a resource of understanding what's possibly going on in this situation. I'm willing to read and experiment.

(I did not post the tonepad layout, but here is the link to the project on his site) http://www.tonepad.com/getFile.asp?id=88

[John Lyons]

There are a few reasons for a popping switch but this layout has the bases covered so it shouldn't pop.
See if you can read DV voltage fron ground to the input of output pins on the switch.
Usually this is the cause of popping. When the effect is off (foot switch in bypass) the DC voltage builds up in the input or output caps.
WHen the switch in taken out of bypass (effect turned on) then the DC is sent to the inpout of the effect and you hear the POP!
If you switch on and off a couple times the DC is discharged and the POP isn't heard until the DC voltage is allowed to build up again.
There are times when a switch will be funky and pop as well.
See what you can measure at the switch.

John

[spudulike]

Sounds like a leaky decoupling cap ...

[sixstringphil]

With power connected and the switch "off", I am getting <1 mV at both the Input and Output posts on the switch. It's zero at the effect input and output. With the switch "on", there is 0 V. So what exactly would this mean, and how might it be corrected? Here's my switch layout...

X         X-led   X-gnd     

X-in     X-out   X-fx out
   \ ________
X         X       \X-(in)
gnd     fx in

If that's too confusing, I'll draw a pic later. Thanks for the help so far. Maybe we're on to something!

[sixstringphil]

Which cap in that circuit is the decoupling cap? Thanks.

[sixstringphil]

Here's a better pic of the switch...


(I guess it's actually sideways)

So...if I see a small voltage at the IN post on the switch, does that mean there's a leaking input cap? Is that the "decoupling" cap spudulike referred to?
And in this circuit, would it be the 4u7 cap at the gate of Q2?

Thanks for your help!!

[sixstringphil]

Anyone able to help follow up on this?

[sixstringphil]

Ok. I completely started over. Built a new Tonepad OSC. I wired the switch like Analogman suggested in another thread. Exact same problem! Is it possible that this is common to that circuit? Again, I use a VL Pedal Power 2. Only happens when the pedal is "off" when power is connected. Pops the first 2-3 times, then no more. Anybody?

[sixstringphil]

Has anyone built the Tonepad O.S. that can confirm their pedal does not pop when switched on? Thanks for any help you can offer.

[analogmike]

that is normal, Mike Fuller even puts a note on his boxes about that. The larger the caps you use, the longer it takes them to charge to equilibrium.

[sixstringphil]

Thanks for the reply.  Is this a separate issue from pop introduced by the LED? If not, would it be worth adding the circuit shown here: http://www.muzique.com/lab/led.htm to try and eliminate this? Thanks again.

(BTW, Analogmike, I am a very satisfied customer of yours. My modded TS9 is the envy of all my studio friends here in Muscle Shoals!)

[petemoore]

  Might not be the LED, pull the LED from the circuit, try it out 'till you know, that kind of 'input pops but only for the first few times' seems humidity altered or something. seems like quite often enough after the caps cycle about 30 times the voltage holds still better...IRC about pedals that started off as poppers, haven't heard a good pop lately now that you mention it.
  I had a FF and a phaser...both popped good enough, enough times, back when, for me to now remember my  'prestomp' routine as being quite popular among spectators...[lol]["what's that dance all about, pete?"] Micro Vibe did that for a little while when recently trying it out for the first times [it's 'nearly new now, I haven't noticed any recent popping].
  Maybe there's something about new metals and plastics and.. being placed in recent proximity with one another charges up the inside of the box somehow..that gets into the cap as a stored charge, maybe after all the various items acclimate under same conditions and the effect is reduced?
  *Maybe whacky theory but [try an ionizer..lol] it just seems that newly constructed pedals definitely popped more.
  I used to get nasty pops sometimes, maybe weather related...pre-cycling the DC blocking caps most often, not always, immediately lessened the amplitude of the subsequent charges released.

[sixstringphil]

Removing the LED has no effect on the popping.  I have never used the Millenium bypass; would there be any advantage to that instead of the 3pdt method?

[Fp-www.Tonepad.com]

True bypass can be a tough problem to solve, as all of us DIYers know by now.

Here are some thoughts about it:

Using a mechanical switch means that some mechanical noise is bound to get across.

Ideal capacitors block all DC current... "ideal" doesn't happen in the real world, which means that 'real world' capacitors don't perform so well and let some DC flow across them.

That DC that 'leaks' across the cap needs to go somewhere and that's why we have the infamous 'bypass pop' stopping resistors.

Sometimes the caps are so leaky that the recommended 1Mohm and higher resistors are not sufficient to keep the leaked voltage from building up.

It all gets worse when the circuit being bypassed amplifies that little leaked voltage. (in the case of a compressor, you can see how it's all even worse!)

Then, there's the 'ground the input' bypass switching scheme... but what if the pedal before or after (heck it could even be the amp), has a couple of millivolts built up when in bypass?

And that's without adding an LED to the equation. With an LED, pop can also come from the led turning on drawing the current from a grounding bus which can bleed into the signal path (this is the reason for my proposed grounding scheme using the input jack ground and not multiple grounds on a pcb, as you can see in the offboard wiring diagrams at tonepad), it kind of keeps the grounds separated in a pseudo star ground scheme...

But that's not the only reason for LED turning on and adding pop to the signal path, as most of you have stated in this thread, the pop can bleed into the audio path at the bypass switch!

In conclusion, bypass pop troubleshooting seems simple, and it might well be in some cases, but in my experience, it has so many variables that it can be a real nightmare. Mother Nature at it's finest!

[sixstringphil]

I finally went back to this problem and seem to have found the answer. I used a different type/brand of input cap, and now the popping is gone. Thanks to everyone for the advice. However, I still have a couple of questions related to this...

1. The tonepad Orange Squeezer layout uses a 4M7 pulldown resistor. Why use this value instead of the standard 1M?
2. I'm troubleshooting another issue on the beginner project and noticed very small voltage on the in's and out's. With a DMM, should I read an absolute ZERO volts, or is it normal to have small M-Volt readings?

Thanks again!

[ambulancevoice]

I finally went back to this problem and seem to have found the answer. I used a different type/brand of input cap, and now the popping is gone. Thanks to everyone for the advice. However, I still have a couple of questions related to this...

1. The tonepad Orange Squeezer layout uses a 4M7 pulldown resistor. Why use this value instead of the standard 1M?
2. I'm troubleshooting another issue on the beginner project and noticed very small voltage on the in's and out's. With a DMM, should I read an absolute ZERO volts, or is it normal to have small M-Volt readings?

Thanks again!

1. 1M and and higher can be used, it doesnt have to be just 1M, i think in this case, 4.7M works better