3PDT Footswitch Popping Sound

[meltunes]

Hi All -

I just built my first stompbox using GGG Stratoblaster Boost Kit (SBB), and am having an issue with the 3PDT footswitch making an audible pop sound when the pedal is turned on and off. I have the same issue whether using the 9v DC power supply (pedal power ISO 5), or a 9v battery.

Seems like my build is successful except for this issue, meaning that the pedal boosts my cleans, after its on doesn't make any sounds or buzzing noises (same as when off too and connected in pedal chain)...

Sorry to start a new thread on this issue... I searched this forum and found a couple other posts about this issue, but as a newbie to stompbox building, I wasn't certain if the fix that was recommended in those posts would apply to my situation (LED was promoted as source of popping sound)...

I followed the GGG kit build instructions exactly and doubled checked that all my wiring connections to the 3PDT footswitch were per the kit's documentation.

What can I do to eliminate the popping sound, or how to troubleshoot the issue?

Thanks, Mel

[GibsonGM]

Hi Mel,  welcome )
Yes, LED popping is pretty common.  To see if it's the LED, why don't you disconnect one end of the LED wiring (whichever is convenient).  If that makes the switch quiet, then go here and follow the advice on LED popping.  Save the site, there is a TON of great info on there! And a link at the top of our forum page, too:

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

Sometimes the switch popping isn't the LED, but DC charging up input/output caps - in which case pulldown resistors can help.   But try the above first, it's the more likely culprit.  Let us know how it turns out!! 

~Mike

[zombiwoof]

Did you use the wiring scheme that grounds the circuit input in bypass?.  That's supposed to help with popping, but LED problems are also possible.

Al

[amptramp]

This can come up for another reason that depends on whether the input switch section activates before or after the output switch section.  The three sections of the switch do not all switch at the same time because of differences in the travel of the switch plunger before each section changes state.  If the output goes from effect to bypass before the input switches, you will have an open circuit regardless of pulldown resistors and the effect will depend on the input pulldown resistor of the next pedal or if it is the final pedal, on the amplifier.  This difference in switching times will likely fall into the audio region.  A number of pedals use switching based on an internal flip-flop and discrete analog FET switches which can have their gate signals slowed down by R-C networks.  With this, you can get a gradual transition from effect to buffer and vice versa.  True bypass is good if you do not need to switch anything during a piece of music, but if you do, it will probably cause trouble.  Ignoring the LED switch section for this consideration, note that there are four possibilities with a true bypass stompswitch:

1. When switching from bypass to effect, the inpuit switches first
2. When switching from bypass to effect, the output switches first
3. When switching from effect to bypass, the input switches first
4. When switching from effect to bypass, the output switches first

The first two events are independent of the last two, so there are four possibilities:

1. Input switches first in both cases
2. Input switches last in both cases
3. Input switches first going from effect to bypass but last from bypass to effect
4. Input switches first going from bypass to effect but last from effect to bypass

If you test one sample of a stompbox, you will not be able to guarantee what you will hear from another example.  It would pay to test by using separate input and output switches so you could simulate all four conditions.  Without knowing what comes ahead of or after the stompbox, you cannot determine in general what will happen, but look at the system: if you have three pedals and you switch the second one from effect to bypass, you will get an output that depends partly on the characteristics of the first and third pedals.

True bypass has a number of fans who don't like the cumulative effect of buffers.  I would venture to say that none of them play music where an effect is switched on or off during a song.

If you have an oscilloscope, you can test the switch sequencing.  If you determine that it is unsatisfactory, it may be possible to swap input and output switching sections to get something more satisfactory.  Good luck and good hunting!

[meltunes]

Hi Guys -

I disconnected the negative side of the LED which was connected to the footswitch, connected a 9v battery, and just used this pedal by itself in front of the amp.

Unfortunately, the popping sound was still there.

I don't have a scope, as I also new to electronics, and pretty much have just the basic tools (soldering iron, pliers, cutters etc), and even less knowledge about how things work.

Would it help if I posted images of the kit's build diagram and the schematic? ... I can do that tomorrow after I scan the docs.

Thanks, Mel

[GibsonGM]

It may help, Mel, or it may not.  But go ahead, and we'll have a look!
Like the others have mentioned, there could be several causes.  Sometimes you can fix it, sometimes not. I feel your pain, having done a good build, you want it perfect...

It really depends on how much the pop is bugging you!  A 'pricier' 3PDT switch might do the trick....re-wiring it and "reversing" how input and output are wired up could help too, like Amptramp suggests.

In virtually all cases of pop, there are 2 different DC voltage levels sitting there. 1 "outside' the circuit, and 1 inside.  When you hit the switch, they equalize with a "POP".  So the key is to get the voltages the same both in and out.  This is done with pulldown resistors, generally.  There could be a fix, so taking a look at what you have may be good.

Additional questions are:
- Does it pop when you only have guitar>pedal>amp?
-Does it pop if using a different amp?
-Does it pop if you put another pedal in front of it (esp. a Boss pedal)?
-"                                                  " after it?
-"                " if you ground the input? (by jumpering tip to ground)
- "                " if you ground the output?

See, the DC is coming from somewhere. Could be 'bleeding' out of your amp and back into the pedal (ok, that's worse case).  Sometimes you can measure where it is located w/a DMM (try that).   Might find a few volts after the input cap, and then BEFORE it, indicating a leaking cap which needs to be exchanged, etc etc.  You can measure these DC voltages right off the patch cords, 1 at a time.   All info you can collect might find the cure!  That's the beauty of troubleshooting.   Keep trying.
)

[meltunes]

...working on posting the images ... finally figured it out (thanks to poster who said use photobucket.com) !!

[meltunes]

Below are the kit's documents... perhaps you guys will see something here that will help...

I really appreciate the comments, I can tell you guys know yer stuff!

I gotta ask a really sophomoric question... when its said to reverse the input/output, what you guys are saying is switching around where the wires from the jacks connect to the footswitch pins? If so, a specific direction such as "move the orange wire from pin#8 to pin#__" and move the "xyz color wire from pin#a to pin#b" etc., would be extremely helpful.

Thanks, Mel

[GibsonGM]

Yeah, I meant to reverse all the wiring if you "switch it around".   Like, you would remove the wires on the switch and reattach them in the mirror image of how it's wired now.   No guarantee, though - I would most likely just replace the switch! If I'm going to do the work anyway, I'd like a new part.

As for the schematic: you have a pulldown resistor, the 1.5Meg at the input.   They even say it's for "switch pop reduction".   The way I see it, you could reattach the LED, add the cap to ground like from the AMZ site.  If it continues, I would add an input cap after the 1.5M resistor, and before the 100R input resistor, maybe 10uF.   Call me high, but that might help....

[amptramp]

Yeah, I meant to reverse all the wiring if you "switch it around".   Like, you would remove the wires on the switch and reattach them in the mirror image of how it's wired now.   No guarantee, though - I would most likely just replace the switch! If I'm going to do the work anyway, I'd like a new part.

As for the schematic: you have a pulldown resistor, the 1.5Meg at the input.   They even say it's for "switch pop reduction".   The way I see it, you could reattach the LED, add the cap to ground like from the AMZ site.  If it continues, I would add an input cap after the 1.5M resistor, and before the 100R input resistor, maybe 10uF.   Call me high, but that might help....

Agree with the first paragraph.  But adding a capacitor to the gate lead in series with the 100R resistor would let the gate float.  It would go to an indeterminate voltage due to lack of a DC return path.  The 1.5M resistor is needed to establish the gate bias voltage.  It does reduce switch pop, but it must be there anyway.

[GibsonGM]

Like I said, call me high.....I don't design with FETs   :wink:  seems like bias could be established another way?  Or a 1M resistor could be added after an input cap?   If this is a design flaw, it's worth exploring.  Does it need an input buffer maybe?  But we're not at that point yet; we need more info.

At any rate, the OP needs to determine where the DC is located that is causing the 'pop'.  Or perhaps it is something that can be lived with (most of my high gain pedals will pop a LITTLE when turning them on - which usually occurs on the "1" of the song I am coming into, and nobody can ever hear it....).   

[meltunes]

Last night after work I used my multi meter to test the resistance of 1.5M resistor and I found it really difficult to get a consistent, solid reading from it... when I first touched the probes to it, the DMM would read out ~ 1500 +/- go to zero, then some negative numbers, back to zero etc.... if I pulled one lead off then the screen would read a value like ~ 1400 or ~1800 for a brief moment then go to 1.

I tested 4 other resistors on the board and got solid steady readings from them as per the schematic values indicated...

Do I have a bad 1.5M resistor?

Can I piggy back another resistor on this one? If so, what value would you recommend to try? I don't know how resistor values are added together... is there a formula?

If there is a solution that doesn't involve removing the circuit board I'd like to try that first, as I'd probably damage other components trying to remove it out of the box etc...

Would this avenue be a first thing to try before rewiring the switch?

I appreciate everyone's help and guidance!!

Thanks, Mel

[KazooMan]

It sounds like you are trying to measure the resistor in place on the board.  You can't really do that.  You are measuring not only the resistor itself, but all of the other components connected to it.  To get a valid reading you need to "lift" (unsolder) one end of the resistor and take the  reading.

[amptramp]

I have had plenty of trouble in the past trying to measure resistors when they still had soldering flux on them or the leads were tarnished.  In this circuit, depending on which way the probe leads are arranged, you could get the 1.5 Meg value or you could get it in parallel with R1 + R3 + the diode drop between the gate and source.  But quite often, I have trouble even touching the multimeter leads together and trying to get an indication of a short.  To get a true measurement, ground should go to the lead on your multimeter that is positive during the ohms test and the top of R6 should go to the lead that is negative during the ohms test.  If you do it that way, you should get the 1.5 Meg value.

[meltunes]

Thank you for the clarification Ron!

Proceeding with the thought that the 1.5M was suspect, I bought some additional (being a total newbie builder I don't have any stock of any parts on hand at home...)

Used alligator clips to run a known good 1.5M parallel, ran the pedal by itself on a 9v battery, to remove any possible complicating issues with pedal power unit, thru front end of amp (guitar --> pedal --> amp)

...as luck would have it, my amp decided to go on a vacation last night, and I could hardly get any sound out of it. The previous night it worked perfectly fine and it had just been sitting in my house all day while I was at work... hmmm

Powered everything off, reseated all connections, powered back on and got a wee bit volume out of it, but clearly my amp wasn't back 100%.

Anyway, while I could get some sound out of it, I turned the pedal off and on several times and the pop was gone. When the pedal turned on, I could definitely hear the volume get louder, so I know the pedal was working.

Tested my amp (guitar --> amp) this morning before I had to get to work and the amp was back to normal.

I'll rerun my pedal test again tonight...  I'll have an update tomorrow.

Mel

[meltunes]

Re-ran testing last night with two 1.5M ohm resistors in parallel and the popping sound was there big as ever. With the two in parallel I got a DMM reading of 750, so I know the on-board resistor is working fine (when removing the alligator clipped in second resistor, I got a reading of 1500 from the on-board resistor).

Seems like looking at the wiring scheme on the footswitch is the next step...

What is confusing to me is that when I look at other sites, geofex and beavisaudio for instance, I see by their wiring diagrams that they have the wires going to different lugs.

So to help both myself and any of you guys who can point me in the direction of the most logic next thing to try is, maybe this image will help...



Do these different schemes make any difference?

Other guys trying to help me out in this thread (really appreciate your advice!!), have described the physical aspect of the footswitch as being "like a plunger " will connect internally with some points before others... With this in mind, are there specific wires that I should move from one lug to another?

The BeavisAudio wiring scheme doesn't use all nine lugs, does that matter?

Any advice is greatly appreciated!

Thanks, Mel

[Steve Mavronis]

There are many ways to wire a 3PDT as long as you keep the poles separate. I really like how this guy wires a 3PDT switch because it ends up being so symmetrical and organized. It it easy to understand what is going on looking at it; inputs on one side, outputs on the other, grounds in the middle, bypass at the bottom, etc:

Wiring Up a 1590B by gaussmarkov:
http://gaussmarkov.net/wordpress/thoughts/wiring-up-a-1590b/



I think it's brilliant!

Personally I would label the 3PDT switch like a spreadsheet has columns and rows, which help out drawing a schematic representation too:

A1 B1 C1
A2 B2 C2
A3 B3 C3

[meltunes]

Thanks Steve!

That is the best explanation of how to wire up a 3PDT switch I've seen so far, and as a novice builder, I understood it to boot!

Now I feel like I can re-wire the switch and have a good idea of what I'm doing and why... (keeping my fingers crossed that this re-wiring solves the popping sound I get when "stomping on the switch")...

-Mel

[Steve Mavronis]

I've decided to do that same wiring myself. But as far as popping sound the switch wiring alone may not totally fix that, although it does ground the PCB input when switched to bypass mode. But I'm also adding a 2.2M resistor in between the 3PDT switch input lug (A2) and the PCB circuit board's input pad. It should help a little especially noise from plugging in the jack but I'm far from an expert since I'm new to this too. Otherwise we would need some advanced PCB circuitry to filter out the switching noise.

Anyway, here's a schematic I whipped up in ExpressSCH detailing Gaussmarkov's 3PDT wiring:



I hope this helps.

[amptramp]

I do things a little differently from the schematic above.

The main difference is the input jack goes to pin 1of SW1A and the board input goes to pin 2 of SW1A.  Pin 3 of SW1C (the bypass output) goes directly to the input jack on pin 1 of SW1A.  The input bypass ground goes from pin 3 of SW2A to the board input.  This leaves pin 3 of SW1A open.  The other connections are the same.  This means that the bypass connection only goes through one switch contact and the ground input to the board when bypassed only goes through one ground contact.  This seems to do the equivalent job but with the robustness of having only one switch contact from input to output and only one contact from board input to ground during bypass.  This leaves SW1A pin 3 open.