very strange bypass and popping problem

[beatnik]

Hi Gurner,

The overdrive circuit is wired to a standard 3pdt true bypass switching, with fx input grounded when in bypass status. nothing fancy, just the usual wiring i've used in the past pedals i've done.

I tried to remove the led, as if using a dpdt switch, but nothing changed, so the popping is not coming from the led.

As I said before, I previously tried to wire the overdrive with two millenium bypass circuit, but both of them didn't work, so I guess something is wrong apart from the switching circuit.

Again, thanks everybody for giving help, I really hope somebody could help me finding a solution. Please keep going

[Gurner]

Whilst what you say is probably bread and butter for those who use bypass switches on all their builds...I come at this from a slightly different angle, I don't build stompboxes (but design other audio related stuff), so have no massive familiarity with what you say...that's why I asked for a schem re how it all fits together - I know how to read one of those!

Now of course I could head off & try & reference what you've done & try & map it all out in my head wrt how it interfaces with your circuit  ...but a picture paints a thousand words (and when you're asking for help, goodwill & other's keeness to delve only extends so far!).

Things you could try....

1. short to ground your IN1 input (temporarily) - does it still pop?

if so, leave the link inplace &

2. short to ground your OUT1 input (temporarily) - does it still pop?

if it does then your popping is not related to sudden DC shifts...and therefore  likely to a current transient colocated close to your signal ground etc.

You mentioned an LED, but your schem shows no LED... I presume it's wired to the bypass switch ...whilst you say it still pops with the led removed, that area is worthy of investigation if you are still getting popping with the IN1 & out1 shorted to ground.

The thing is with a problem like this, it's just about peeling away all the possibilies...eventually you'll switch & there'll be no pop....just a case then of retracing your steps and adding bit by bit back in.

[beatnik]

You are right is definitely better putting all the useful info in this thread as i'm asking for help.

Here you have the schematic I used for the switching of the circuit.



I try right now to do the things you suggested and report back. stay tuned and thanks as always

[beatnik]

1. short to ground your IN1 input (temporarily) - does it still pop?

still pops in both directions (bypassed --> on  /  on --> bypass)

2. short to ground your OUT1 input (temporarily) - does it still pop?

still pops, but only in one direction, bypassed --> on

I tried with the led out of the circuit.  I am almost sure the problem is not the led, but more probably to the current signal leaking into ground as you mentioned.

Something more to check?

Thanks as always

[beatnik]

I still haven't figured anything out yet. Please help

[Gurner]

Ok, if you've still got popping with the circuit output shorted to ground, it's likely to be a current spike getting into your signal or ground path from somewhere or other....just a matter of continuing the process of elimination.

IMHO that led current path still seems the most likely suspect.

What happens if you remove the 9V or the ground from the led path (in other words no current will flow through the led when you switch), check this with the output of the circuit still shorted to ground as you've done above.

[beatnik]

I have previosuly taken away the led path from the switching circuit. 9V is only going from DC jack to pcb.

I suppose this isn't led dependant but somewhere else in the circuit. What would you say?

Thanks a lot mate

[Gurner]

Then this remains a matter of just methodically lifting various points of your circuit to see where the spike is getting into your signal.

For example....have you tried desoldering the  point on your switch that is connected to fx out? (this will illustrate whether you popping is getting into your signal hot wire, or the signal ground)

You could try running a dedicated wire from your battery -ve to your incoming & outgoing signal ground ....star-esque (so that this is the only point where the signal grounds connects to the battery negative reference)..... if your signal grounds happen to reside in the overall battery return path for your circuit they are going to pickup some switching transients)

Not wanting to belittle your problem (as I'm all too  aware how pesky these things can be to troubleshoot), but really is just a matter of a 'disconnection frenzy' to isolate where the problem is eminating from ...once you've got the localised area, then we can focus on the specifics.

[beatnik]

Good point, I'm understanding better what's going on. Really learning something, thanks a lot!

I've tried to disconnect the "fx out" from the footswitch, and no popping happens anymore. So does it mean that the popping comes from the signal hot?

About the star grounding thing.. I don't know if I've understood correctly (sorry, english is not my first language).

I've joined all the grounds to the input jack ground point, ie star grounded. You mean I have to take out the battery ground from the star ground point?

[Gurner]

I've tried to disconnect the "fx out" from the footswitch, and no popping happens anymore. So does it mean that the popping comes from the signal hot?

It means this is where to focus our attention.

Probably time to revisit the 'short the output to ground' test I mentioned earlier....are you certain that you shorted the fx output in such a way that it was at total ground potential?  This is important, as if you are certain that was the case, then your problem is likely grounding arrangements/current related ...so probably worth double checking where you shorted it to ground. Once you've double checked, then consider running a single ground connection wire from your output signal ground socket back to the battery -ve connection (ie remove your jack socket so that there's no possibility of it being grounded by anything else ...eg chassis etc.....and run it's ground lug back to the battery -ve where it joins the board) ...the rationale for suggesting this is to ensure your signal output ground is not in any significant current return path within your circuit.





[/quote]

[ORK]

You are right is definitely better putting all the useful info in this thread as i'm asking for help.

Here you have the schematic I used for the switching of the circuit.



I try right now to do the things you suggested and report back. stay tuned and thanks as always

Your "FXIN" doesn`t go to ground directly, but rather from "SW1A-2" to "SWB-2", which is only grounded when the switch turns over. This never happens at exactly the same time for both (or all three of the poles of that switch). there you get your blip. Route a (hard) wire from "SW1A-2" to signalground. Route the centercontact of SWB to a point of ground as close as possible to the powersupply`s largest electrolytic cap.

[beatnik]

Probably time to revisit the 'short the output to ground' test I mentioned earlier....are you certain that you shorted the fx output in such a way that it was at total ground potential?  This is important, as if you are certain that was the case, then your problem is likely grounding arrangements/current related ...so probably worth double checking where you shorted it to ground.

You are right. I have now grounded the out fx to the star grounding point and no popping anymore. The first time I have probably been mistaken.

Once you've double checked, then consider running a single ground connection wire from your output signal ground socket back to the battery -ve connection (ie remove your jack socket so that there's no possibility of it being grounded by anything else ...eg chassis etc.....and run it's ground lug back to the battery -ve where it joins the board) ...the rationale for suggesting this is to ensure your signal output ground is not in any significant current return path within your circuit.

I'm not sure I'm getting this right. Sorry if I'm stressing your patience too much, but I am really trying to learn and solve this.

I've taken the output jack out of the chassis. grounded it's tab to the star ground point (which is on the input jack ground tab, where the battery ground goes, too).

In such a way, and if the fx out is not grounded, I still got popping.

Your "FXIN" doesn`t go to ground directly, but rather from "SW1A-2" to "SWB-2", which is only grounded when the switch turns over. This never happens at exactly the same time for both (or all three of the poles of that switch). there you get your blip. Route a (hard) wire from "SW1A-2" to signalground. Route the centercontact of SWB to a point of ground as close as possible to the powersupply`s largest electrolytic cap.

I've tried to put the ground points on the switch directly to the star ground point, but nothing changed. I got your point though, thanks a lot

[Gurner]

The whole thing I said about running star grounding was if your popping was to do with current spikes, but you've just gone and changed the results of one of your tests, so I don't think it is current related anymore.

If you are saying no popping when you ground fx out, but popping when it's not grounded, then this is DC related on your fx out (& not current related).

I'm snatching these replies in between visits to the beach (I'm on holiday!)...I'll try & revisit your schem a little more when I get back....but this is now fairly standard drill to ensure there's no DC present (however small) on your fx out pin when you switch out of bypass mode.

Edit: Those final two resistors, don't know if it's the low bandwidth link that I'm on here on hols, but they're hard to read....what value is R25?

That final cap should be blocking dc...so you may want to check this area ...if you've a dvm, check for the presence of dc on the right hand (output facing) pin....make sure r25 does have a good connection to ground.

(I'm assuming your schematic out1 goes to your fx out pin on your switch?)

[beatnik]

A final update!

Man, I've been so silly. I had a very little short to ground on the output buffer stage. I checked the solderings and then everything solved.

Once again I will repeat 100 times.. "checking is never enough"

Anyway, the whole progress has been very instructive and I've definitely learned something.

So, thanks a lot guys for sharing knowledge and patience!

Cheers!