Relay Bypass Pop At First Engage

[antonis]

Alternate solutions for glitches are RC snubbers across the coil.

Better for sure but overkill for DC..

[mickeybellinello]

OK, as an experiment, what if you connect a wire from the input jack directly to the input at Cin, leave all other wiring in place.    This isn't a solution but it might help narrow down the problem to the input or the output.

With a wire connected in this way no more pop...

What to do now?

Thanks

[Rob Strand]

What to do now?

Are you sure you added the 2M2 correctly before?  At this point the problem seems to be caused
by the input cap charging up.  The test you just did points to that also.

The way to add the input resistor is like this,



It that doesn't work try a smaller resistor say 1M or 100k.   Again this low value isn't a solution but more to find the true problem.   Under normal circumstances 2M2 should work fine.   If 100k reduces the problem then I'd start thinking the 10nF cap has a leakage problem.

[mickeybellinello]

What to do now?

Are you sure you added the 2M2 correctly before?  At this point the problem seems to be caused
by the input cap charging up.  The test you just did points to that also.

The way to add the input resistor is like this,



It that doesn't work try a smaller resistor say 1M or 100k.   Again this low value isn't a solution but more to find the true problem.   Under normal circumstances 2M2 should work fine.   If 100k reduces the problem then I'd start thinking the 10nF cap has a leakage problem.

Thanks so Rob for your help!
I apologize but i was sure that i specified that i have no input buffer.
The FX in cable goes directly to the 68k resistor (i used a 100k trimpot instead).
For the test i made i soldered the 2.2m resistor as you draw (except that the totale buffer part is missing.

This evening i got some free time so i added the 22pf (cin 2) and cin1 to my circuit.
Unfortunely didn't have chance to test it.
Does those mods has sense?

(Tomorrow if you think it could be useful i'ill try the 100k mod)

Last thing. Due to what I said (mainly the info about "no input buffer") have some new ideas?

Thanks really

[Rob Strand]

I apologize but i was sure that i specified that i have no input buffer.

Probably my fault.  You might have mentioned it somewhere in the thread and I've missed it.

The FX in cable goes directly to the 68k resistor (i used a 100k trimpot instead).
For the test i made i soldered the 2.2m resistor as you draw (except that the totale buffer part is missing.

No problem with the buffer missing.  It's a same idea.
Try the 100k just the same.

I have a feeling it's the 10n cap.  It wouldn't take long just to swap it and see.

This evening i got some free time so i added the 22pf (cin 2) and cin1 to my circuit.
Unfortunely didn't have chance to test it.
Does those mods has sense?

Sometimes the cap can help.  The reason why it might work is a bit obscure.  I don't think it's the problem but it's definitely worth trying (as something weird is going on).

Due to what I said (mainly the info about "no input buffer") have some new ideas?

I don't think the buffer being removed is a problem.

It's quite possible if you put the buffer in it could fix the problem but really it would be pot luck and doesn't really explain what is going on.  There's no reason why the circuit without the buffer should be more problematic than with the buffer.

At this point I wouldn't overlook the relay.   If you were really keen you could replace the switching with a DPDT toggle switch and see if that fixes it.   Another thing to try would be to try changing which contacts you are using on the relay.   You can swap contacts on the relay and still follow the same switching.   While the circuit is the same in each case the contacts being used are physically different.   It's a long shot but sometimes you have to do silly things to get to the bottom of tricky problems.

[willienillie]

Wish I'd seen this thread earlier.  I had the same issue with my DIY wah, switched popped first time only.  Ground input in bypass, you gotta run an additional wire from the switch to ground but it works and no circuit mod.

[Rob Strand]

Ground input in bypass,

So that could be because there's no "added" 2M2 to ground on the input side.  Most wah ckts don't have this.

You gotta run an additional wire from the switch to ground but it works and no circuit mod.

So maybe there's some oscillation occurring.  The 22pF cap discussed above can help this case.

[willienillie]

Ground input in bypass,

So that could be because there's no "added" 2M2 to ground on the input side.  Most wah ckts don't have this.

Right, mine had no pulldown added at the input.  And there's no need at the output, with or without a Foxrox output buffer.

You gotta run an additional wire from the switch to ground but it works and no circuit mod.

So maybe there's some oscillation occurring.  The 22pF cap discussed above can help this case.

I meant a wire to ground the input in bypass.  I think the pop is just DC in the input cap.

[Rob Strand]

Right, mine had no pulldown added at the input.
I meant a wire to ground the input in bypass.

Ah, that explains it then.

[mickeybellinello]

Thanks so Much for the support.
Are there any trick to connect the wire you're talkin about or i need a dpdt switch to do that?

[Rob Strand]

Are there any trick to connect the wire you're talkin about or i need a dpdt switch to do that?

Well, it's probably good enough just to keep the input and output wires separated.   The aim was to use your existing wiring to see if just changing the switch (ie. removing the relay board) fixes the problem.

However, if you really want to be paranoid you can run coax to the switch.  You ground the coax at one end only.   You can actually wire up your relay board like that.   For things like a wahs you usually don't have to go so far, a high gain distortion that keeps bursting  into oscillation then yes.    I don't think this is the cause of your problem.

I really think it is some sort of DC issue on the input.  The key piece of information is it only does it on the first switch over.  To me that type of thing says DC issue and possibly a cap charging up.   All the trickier issue like relay spikes getting into the audio would be expected to keep happening every time you switch over.

BTW, when you first power up the effect is the effect in bypass or effects mode? 
I'm thinking in bypass mode and so the click occurs the first time you switch to effect - yes?

[mickeybellinello]

BTW, when you first power up the effect is the effect in bypass or effects mode? 
I'm thinking in bypass mode and so the click occurs the first time you switch to effect - yes?

Yes You're right!

I just tried to swap the switch for a dpdt one momentary (the first switch is a spdt momentary).
One row is used for the relay control
The other row is for grounding the FX Input.

When the switch is depressed the fx connect to ground. when the switch is pressed the two relay wires are connected and the FX Input is not grounded.

With this configuration I completely eliminated the big "first time pop" but is present a little pop each time I engage the FX.

Update:  for the first cap after the first resistitor i used a 100n instead of the 10n reported in the schematic. Could be influence the issue?

[willienillie]

Right, mine had no pulldown added at the input.
I meant a wire to ground the input in bypass.

Ah, that explains it then.

Well, let me explain something else.  I'm a dumbass and skimmed right past the whole "relay" portion of the issue here.  My experience was with standard DPDT stomp switching, and probably has no relation to this thread.

[Rob Strand]

I just tried to swap the switch for a dpdt one momentary (the first switch is a spdt momentary).
One row is used for the relay control
The other row is for grounding the FX Input.

When the switch is depressed the fx connect to ground. when the switch is pressed the two relay wires are connected and the FX Input is not grounded.

With this configuration I completely eliminated the big "first time pop" but is present a little pop each time I engage the FX.

The idea of shorting the input *should* achieve the same purpose as the added 2M2 on the input.  The difference being the 2M2 frees up the switch for other purposes.

Update:  for the first cap after the first resistitor i used a 100n instead of the 10n reported in the schematic. Could be influence the issue?

If there's something weird going on it could make the pop larger but under normal circumstances it shouldn't make a difference.

It's sure looking like a DC issue.  Given the slight weirdness going on, perhaps it would be a good idea to replace that input cap and re-instate the 2M2 (or 1M0) at the input.   Anything between 10n and 100n would be fine.  You just need a to try a different cap as a sanity check.   If there's something wrong with the cap it would save a lot of grief.  To be honest I'm running out of ideas, mainly because there's something abnormal happening which is kicking us off the path.

[mickeybellinello]

I just tried to swap the switch for a dpdt one momentary (the first switch is a spdt momentary).
One row is used for the relay control
The other row is for grounding the FX Input.

When the switch is depressed the fx connect to ground. when the switch is pressed the two relay wires are connected and the FX Input is not grounded.

With this configuration I completely eliminated the big "first time pop" but is present a little pop each time I engage the FX.

The idea of shorting the input *should* achieve the same purpose as the added 2M2 on the input.  The difference being the 2M2 frees up the switch for other purposes.

Update:  for the first cap after the first resistitor i used a 100n instead of the 10n reported in the schematic. Could be influence the issue?

If there's something weird going on it could make the pop larger but under normal circumstances it shouldn't make a difference.

It's sure looking like a DC issue.  Given the slight weirdness going on, perhaps it would be a good idea to replace that input cap and re-instate the 2M2 (or 1M0) at the input.   Anything between 10n and 100n would be fine.  You just need a to try a different cap as a sanity check.   If there's something wrong with the cap it would save a lot of grief.  To be honest I'm running out of ideas, mainly because there's something abnormal happening which is kicking us off the path.

Thanks really for the support. Yesterday I got a gig and with the 2m2 resistor + input grounded the situation is definitively better. no audible pop. just a little bit when I try it at home with silence and high volume.
I just ordered a 10n cap...when it will be delivered I'll try it and post the results.

Thanks Thanks thanks!

[Rob Strand]

I just ordered a 10n cap...when it will be delivered I'll try it and post the results.

OK cool.

In case that doesn't fix the problem.  If you built it on vero board you might want to check you cut all the tracks, and all the ground connections are correct.  The way it is behaving is a little off there might be some obscure problem lurking in there.

[mickeybellinello]

As promised, Here I am!
I received the new 10n cap. Same situation but i noticed a big bass frequency lost using the 10n instead of 100n.
How is it possible?
Anyway i tried the pedal further and the little noise varies depending on the sweep cap that i use / inductor used.
As said the extra noise is acceptable and if i activate wah while playing it's un-noticeable so I'm pretty satisfied of the final result!
Thanks so so much for the support!