is using 2 dif bias voltages in a 2 effect pedal enough to cause switch click?

[west portion]

Should I be holding the circuit-in lug of the foot switch at the corresponding bias voltage before stomp activation?

I have a dual effect/2 foot switch build that uses a PT2399 and a TL074, with the PT generating its own 2.5V bias from the LM7805 supply and the TL being supplied 4.5V from a divider to the original 9V supply. The foot switches are wired in series, so that both could be on at the same time if desired, first the PT effect and then the TL effect.

I checked all of the signal pins on the TL074 with the effect off and they are all reading the 4.5V bias as they should.  The PT2399 however has a couple that are off from the 2.5V of the correct ones. I would suspect the use of electrolytic capacitors in the circuit to be the reason why, but the bias is internally generated, so i'm not sure if that would be the problem.

Even so, the issue is that both click when activated, the PT much less than the TL (the TL is running a high gain circuit). I'm pretty well versed in the anti-pop techniques, bleeder resistors, coupling caps, keeping the circuit input at ground before activation, current limiting and I've checked my caps for large DC bleed. The mild epiphany i had after typing the last line is at the top of this post now haha but if theres anything else I could try please let me know or chime in with whatever else you have. Thank you!

[GGBB]

Schematics would help - we don't know what voltages should be at various pins/lugs. Circuit inputs are normally tied to ground when bypassed, and are usually further isolated from DC by an input capacitor, so you would not want to tie that to Vbias.

[idy]

People will want to see a schematic. No, different bias voltages will not cause pops if you have proper decoupling caps...and pulldown Rs (I think that is what you mean by "bleeder resistors.")
The circuit in lug of the footswitch must/should be held at 0v. If there is DC, good luck on "matching" the levels... You say you tested. What DC (if any) did you find on the circuit in/outs?

There are a couple other possible sources you did not mention, including but not limited to:
"pedal ventriloquism," where another pedal, or amp, or active guitar, provides the voltage,

mechanical click of switch including microphonics (pencil tapping enclosures, swtiches, PCBs part of catching this.)

[antonis]

the issue is that both click when activated, the PT much less than the TL (the TL is running a high gain circuit).

Your issue might originate from power supply dip, possibly due to small reservoir capacitor in relation with current demand..

[west portion]

Respect for these replies! The TL074 is used in this https://dirtboxlayouts.blogspot.com/2019/06/keeley-rotten-apple.html and for the PT2399 I just used the Echo layout from the datasheet https://diyaudiocircuits.com/pt2399-digital-delay-analog-echo/. I swapped out the electrolytic 1uF output cap in the rotten apple to a 1uF film cap and it definitely helped. Same with the PT2399, except it was down from the original 10uF electrolytic. I've also added pull down resistors to both outputs.

I used this https://tagboardeffects.blogspot.com/2012/02/offboard-wiring.html two effect layout.

The DC voltage readings on the 3pdt foot switches were only a few mV at the circuit in/out, but were resting at 0V, only coming up after switching state and staying at say 4mV just for a couple seconds before descending back to 0.

I dont think this is the problem, as when i press the switch down slowly you can hear the stages of the contacts coming together and then locking in place. So is it microphonic then? I tapped the entire board and occasionally would hear some static but it didnt seem to be coming from a single spot/component. Repeat taps on a previously noisy place would be quiet. I know that ceramic caps can be bad for this, but even those I tapped directly to no response.

If there is a loose component on the board and that is the cause of this, would wire length cause it to worsen? I can definitely trim some of the pot wires to be shorter. Are there any other situations that would cause this? I've only managed to find loose components and ceramic caps to blame in my search.  Thank you!

[idy]

Good work so far on explaining things and choosing your sources.

Good work on adding pulldowns to the outputs. Missing from both schematic and layout..

Pops are usually worse on high gain circuits. Points to input.

Microphonics sometimes come from the switch itself (or so a crazy old man on the internet is telling you) so if you are tapping things, tap the switch itself. Trouble shooting often includes some clutching at straws.

[antonis]

Are there any other situations that would cause this?

Could you plz post a schematic of your particular power supply..??

In the mean time, implement following LED anti-pop configuration for both indicator LEDs....

[GGBB]

Be careful with that setup. When you switch the pedal on, a surge of current flows out of the 10µF cap through the LED by way of the CLR. At ~9-1/2V power or more through 330R there can be enough current to pop some LEDs, or at lease potentially shorten it's life span. Also the LED will briefly flash very bright. There's no point to that risk -go 1k minimum - or higher if you're running more than 9V - or better yet just split your total CLR resistance in half between the two resistors.

[antonis]

I can't get you, Gord.. 

When pedal is switched on, CLR (usually in the region of 4k7 for 1mA current) with 10μF cap form a sort of delay of about 1/5 - 1/4 sec till junction point sits at about 330mV higher than LED forward voltage drop..
In case you refer on fully charged cap when pedal switched on, "surge" current can't be higher than LED working current, set both by CLR and 330R 'cause cap's positive leg can't sit higher than LED forward voltage drop plus 330R X I_LED..

[GGBB]

In case you refer on fully charged cap when pedal switched on, "surge" current can't be higher than LED working current, set both by CLR and 330R 'cause cap's positive leg can't sit higher than LED forward voltage drop plus 330R X I_LED..

Try it and measure it. I use this anti-pop setup on all my designs. When bypassed, the lower CLR and LED are out of circuit - therefore the cap anode connected to the upper CLR rises to V+. When switched on, full V+ surge current momentarily flows out of the cap through the lower CLR only. You can SEE this happening.

You can of course modify the setup to eliminate this "problem" by connecting a resistor between cap anode and ground thereby forming a constant voltage divider with the upper CLR (which you can set to whatever voltage you want) - kind of like a dedicated "Vbias" for the LED. But that's an extra component and extra space on the PCB, plus a bit of extra current draw during bypass.

A more clever way is to connect the LED anode-lower CLR junction to the bypass switch - grounded when bypassed - and keep the LED cathode always grounded - effectively shorting the LED for bypass instead of disconnecting it. Then the lower CLR is always connected and therefore always providing a voltage divider to control the voltage at the cap anode. This requires a minor change to the switch wiring, and also draws a bit of extra current when bypassed:

[antonis]

When bypassed, the lower CLR and LED are out of circuit - therefore the cap anode connected to the upper CLR rises to V+.

Now it got you..
Upper CLR serves as "pull-up" one..

When switched on, full V+ surge current momentarily flows out of the cap through the lower CLR only.

Which surge current can't be greater than +9V minus LED forward voltage drop divided by 330R, resulting  into about 20mA for about 3ms..

[GGBB]

Which surge current can't be greater than +9V minus LED forward voltage drop divided by 330R, resulting  into about 20mA for about 3ms..

Yes - exactly. That CAN be a problem. As I said

be careful

I didn't say don't do it. It is not a one-size-fits-all solution. LED max current varies (10mA sometimes). LED Vf varies. PS/battery V+ varies (9.x? 12V? 15V? 18V?). There is no significant benefit of 330R over 1k. Be safe. Don't over stress your LED.

[west portion]

thank you for this continued support! i thought it could be the LED as well, but after removing the connection the click remains. linked here is a short video of the issue.
https://drive.google.com/file/d/1DcA2KnmTTUxVjJ9BI6ROBrlwJs5DMP2L/view?usp=sharing

in it i turned the volume of my guitar all the way down and attached my multimeter to various pins on the 3pdt while activating/deactivating the switch. the most DC voltage on any of the pins is 0.5mV, with the others reading 0VDC in reference to the common ground, but the activation of the effect clicks significantly louder. its hard to tell in the video, however i assure you that in-person the activation click is very noticeably amplified while the deactivation is not. the same loudness of the issue persists when i turn up the volume on the guitar and the click scales to the volume on the amp.

i tested all points of the shared ground to read 0mV. you can see that i disconnected the second circuit entirely, including its own foot switch, which was initially connected first in order to the input jack. now the 2nd switch, with the keeley rotten apple distortion, is connected solely to the input jack. i've also tried multiple foot switch types, including an opto-muting relay bypass pcb from MAS effects and multiple wiring configurations including this one https://www.madbeanpedals.com/forum/index.php?topic=27743.0 but they all click in the same way. how could the microcontroller relay muting bypass not fix the issue when used with proper anti-pop techniques (pulldown resistors on the outer side of in/out, coupling capacitors tested for DC bleed, holding the circuit-in at ground)? i even modified the Attiny85s code to allow for longer muting times.

so it has to be my wiring layout, right? i followed exactly the verified keeley rotten apple perf board layout https://dirtboxlayouts.blogspot.com/2019/06/keeley-rotten-apple.html and had originally added a pull down resistor at the output before the madbeanpedals 3pdt wiring suggested to remove all other pulldowns to work with the pulldown on the switch. my layout is a star ground to the input jack, the case is aluminum and there is continuity between the bare metal of the jacks/pots and the case. here is a drawing of the current pedal wiring https://drive.google.com/file/d/1De-dsdWeePK2gyPpUy866OWKVvpV4eQU/view?usp=sharing

i went over every solder point with fresh tin, allowing for complete melting, not noticing any visible cracks or shotty spots. tapped on the board and footswitch, discovering no microphonic components, and i've now swapped out both instrument jacks (and the different switches already discussed).

here are additional pictures of the build https://drive.google.com/drive/folders/1Dj42ZX9N0XbUP7raZhuJed7a_MUxl0xI?usp=sharing
if you notice loose wires they are from either the other disconnected effect circuit or from how i disconnected the one with the issue to better show the board. it also used to be a lot neater before starting this laborious endeavor.

wow this post is long winded, and i cant blame you if you dont want to touch it haha but if anyone responds, i will guaranteed have mad respect for you. thanks!

[GibsonGM]

It is OK west portion -- this discussion is normal   And fun.   

many are watching to see how this is resolved, and learning from it.