Author Topic: Switch pop  (Read 7701 times)

Kelby

Switch pop
« on: February 29, 2004, 12:36:26 PM »
I just built this box as my first project.  It came out great.  Thanks, Aron, for this site and for the detail on this project.

The only issue I have is that I get a pop when I click the switch on.  Any suggestions for a fix?

smoguzbenjamin

Switch pop
« Reply #1 on: February 29, 2004, 03:21:52 PM »
Use a pulldown resistor after the caps. It will allow the built up charge to flow away. I suggest 100k would be a good value :)
I don't like Holland. Nobody has the transistors I want.

Kelby

Switch pop
« Reply #2 on: February 29, 2004, 07:00:37 PM »
Thanks for the response.  But still being a tremendous newbie, where exactly in the circuit do I put this resistor?  (You mention between the caps, but I'm unclear on what that means.)

Thanks again for your help. :D

aron

Switch pop
« Reply #3 on: March 01, 2004, 01:43:36 AM »
It's pretty simple. Put a 1 MEG resistor before the input cap and another after the output cap.

In other words, outside the circuit input and output caps, but before the switches.

So lets say that you had a circuit all wired up and ready to go. Now connect a 1MEG resistor to the junction of the input wire signal (that goes to the switch) and input cap and connect the other end of the 1MEG resistor to ground.

For the output cap, connect a 1MEG resistor to the junction of the output cap and output signal wire (that goes to the switch) and connect the other end of the 1MEG resistor to ground.

Let me know if you have any other questions.

Kelby

Switch pop
« Reply #4 on: March 01, 2004, 10:56:49 AM »
Thanks Aron!  I'll wire that up tonight and see if it works.

Kelby

Switch pop
« Reply #5 on: March 02, 2004, 12:17:55 PM »
OK!

I pulled the box apart and put a 1M resistor going from the switch side of the input cap to ground.  I began to do the same on the output side, but noticed that there is already a 100K resistor going from the switch side of the ouput cap to ground.  I double checked the schematic Aron originally posted, and it definitely shows a resistor like this on the output side and not the input side, which is how I had it.  

Given there was already a resistor on the output side, I didn't put another resistor on the output side.  I hooked everything back up after making the modification on the input side, and everything works (no pop when I hit the switch :lol: )  Which leads me to a couple of questions.

First, was the 100K resistor on the output side in the original schematic a "pulldown resistor" or did it serve some other function?  If it was a pulldown resistor, was there some reason for not putting a similar pulldown resistor on the input side in the original schematic?

Second, I now have a 1M pulldown resistor on the input side and a 100K pulldown resistor (assuming that's what it was in the original design) on the output side.  Should I change one or the other to make them the same?

Third, on a totally unrelated topic, when I turn the pot there is a scratchy noise.  It doesn't interfere with the functionality of the pedal, as I won't turn the knob in the middle of a song anyway.  But is that a sign that I did something wrong?  Or that I have a bad pot?  (I got all my parts from Small Bear, so I'm guessing the problem isn't in the quality of the parts.)

Finally, one overall comment is that despite all my newbie errors, I am blown away at how great a little pedal this is.  The sound is what I hope for in a boost, and the hardware is very tank-like despite a relatively small investment in the box, switch and jacks.  I'm anxious to build another.  (Aron, just in case you haven't been asked enough times, when will you be doing the second one of these walk-throughs, which I think you mentioned would be a revised Shaka?  I'll be all over it!)  Thanks for all your help on this and for maintaining this great site.

aron

Switch pop
« Reply #6 on: March 02, 2004, 01:08:12 PM »
>Given there was already a resistor on the output side, I didn't put another resistor on the output side. I hooked everything back up after making the modification on the input side, and everything works (no pop when I hit the switch  ) Which leads me to a couple of questions.

Good point. I forgot you don't need it on the output. Good Call!

>First, was the 100K resistor on the output side in the original schematic a "pulldown resistor" or did it serve some other function?

It is a pull down and sets the impedance of the output.

>Second, I now have a 1M pulldown resistor on the input side and a 100K pulldown resistor (assuming that's what it was in the original design) on the output side. Should I change one or the other to make them the same?

Nope. It's fine.

Good job!

Kelby

Switch pop
« Reply #7 on: March 02, 2004, 02:13:03 PM »
Thanks Aron.  You da man!

smoguzbenjamin

Switch pop
« Reply #8 on: March 02, 2004, 02:19:27 PM »
Yes he is :) He got me started :) It's all your fault aron! With all the mess on my desk, it has become increasingly difficult to lead a normal life!! Nights of looking at datasheets, figuring out what on earth a semiconductor was, and generally debuggin my circuits into perfection! All your fault! Thanks! :D
I don't like Holland. Nobody has the transistors I want.

Triffid

Switch pop
« Reply #9 on: March 02, 2004, 08:14:21 PM »
I am not sure if I should create a new forum for this but...

I am having the same problem with a fuzz face that I recently built.  I put a 1meg resistor @ output and input and still am getting popping while switching.   I have a 50k pot (bias) before my cap/resistor, could that be the problem?   Also, the order of the resistor doesn't matter right... explainatin...  my input frmomy 50k pot goes into my perfboard, them my pull down resistor is on the right of it and my 2.2 cap is on the left... that should be ok right?

Thanks for your help

aron

Switch pop
« Reply #10 on: March 08, 2004, 02:40:36 PM »
Quote
them my pull down resistor is on the right of it and my 2.2 cap is on the left... that should be ok right?

Well, you want the pull down resistor to the "left" or BEFORE the input cap and it should connect with the input cap junction and then the other end should go to ground.

For the output, it's the opposite. The output pull down should be to the "right" or AFTER the output cap.

In addition there are other possiblities:

The input and/or output cap is leaky and there is DC on the input or output which you can check with your multimeter set to DC. Put the red probe on the output or input cap and the black to ground and look for DC.

Another pedal you have before or after is leaking DC and causing the pop.

It's possible that the switch could be popping.

Finally, for some weird reason, some amps will cause a pop. Maybe leakage from the grid to the pedal (if tube amp)

Triffid

Switch pop
« Reply #11 on: March 08, 2004, 02:47:11 PM »
I was referring to the physical layout of the resistor and capacitor, not in relation to the schematic.

Pretend the dashes are dots on my perfboard, r = resistor lead, i = input wire,  c = capacitor lead

Would it make a difference if it was like this....

- - - - - -
- r i c - -
- - - - - -

or this...

- - - - - -
- i r c - -
- - - - - -

I don't think it does... BTW... I fixed my original problem... it was due to a short around the output capacitor.

Thanks

smoguzbenjamin

Switch pop
« Reply #12 on: March 08, 2004, 03:39:38 PM »
It doesn't make a difference, the node is made and the actual physical layout doesn't make much difference. Do whatever suits your application best!
I don't like Holland. Nobody has the transistors I want.

aron

Switch pop
« Reply #13 on: March 08, 2004, 05:52:32 PM »
Correct, but if the R was to the right of the C, yes it would make a difference and that is what I was trying to explain. The placement of R is different if it's an input or output cap.

Triffid

Switch pop
« Reply #14 on: March 08, 2004, 09:20:08 PM »
Wait a minute... are you saying that this is different from the two above?

- - - - - -
- i c r - -
- - - - - -

If so, I really have to back to my electronics book because I always that that a node was a node... it doesn't matter which one physically comes first.

*edit*
and I don't know how any of my effects work because I rely on that fact all the time

aron

Switch pop
« Reply #15 on: March 09, 2004, 02:23:08 AM »
This is what I meant for the input pulldown resistor:

I could be wrong, but in one case, the resistor is "after" (to the right) of the input cap and does not allow the cap to discharge when the effects is disabled.

In the other case, the pulldown is to the "left" or before the cap and allows the circuit to discharge when the effect is disabled.


Triffid

Switch pop
« Reply #16 on: March 09, 2004, 08:40:48 AM »
Right, this is just a mis-communication on my part... I think you are talking about the schematic and I am talking about the actual physical layout.  All three of my attempts at showing my perfboard are supposed to match up with your top schematic.  

Thanks for the input aron.

smoguzbenjamin

Switch pop
« Reply #17 on: March 09, 2004, 08:47:32 AM »
As long as the three points meet at the right place it doesn't matter which one comes first.
I don't like Holland. Nobody has the transistors I want.

aron

Switch pop
« Reply #18 on: March 09, 2004, 02:27:36 PM »
Quote from: Triffid
Right, this is just a mis-communication on my part... I think you are talking about the schematic and I am talking about the actual physical layout.  


Cool! I just wanted to make sure.

Yes, when the components touch and make a junction, it doesn't matter which one is where for the most part. For oscillation sensitive circuits, the layout does seem to matter a lot and placement of a component can make a big difference - but not as it relates to a "node".