SOLVED Pro 10 - Switch popping

[aj53202]

Hello everyone! I hope everyone is doing well.

I’m looking for some help with my Pro10 build. There is a loud pop when the Blue side is engaged & also sometimes when disengaged. Green side suffers from it too but very rarely.

Both the leds diffused type and are from Tayda. The blue led is very brighter than normal and the green is dimmer than normal.

Please advise how do I start with the troubleshooting. Should I try swapping out the leds? Would some sort of pull down resistors help at the output? If so, what could be the ideal resistance value?

Thanks,
-AJ

 

[spi]

I don't know about the popping, but regarding the LED brightness: I always choose the CLR for the LED on a breadboard beforehand, to ensure the brightness isn't blinding or too dim. Especially for pedals with 2 LEDS, I also try to match the brightness.

 

[chris.knudson]

Don't know if this will help, but it's something to try.

AMZ - LED Popping

How to stop the pops in audio from LED current surges when switched.

www.muzique.com

 

[JTEX]

You can try disconnecting the LED first as a troubleshooting step.

 

[Robert]

Both sides already have an output pulldown resistor. (Technically the blue side doesn't, but the level pot does the same job)

If the LEDs don't end up being the problem I'd suspect the output coupling capacitors, they're electrolytic on both sides and could be leaky.

C124 (Green) and C209 (Blue)

 

[aj53202]

Thanks all for the great inputs.Here are few things I have tried so far…

1) Disconnected the Blue led - Silent & no pop.

2) Changed the blue side led to ultra bright blue clear led from Tayda - still pops when engaged.

3 Changed the blue side CLR to 10K - still pops when engaged

Next, I’ll try to replace C209 and report back.

 

[JTEX]

If I had to troubleshoot this, at this point I would try disconnecting the LED negative from the switch and making it turn on and off without the switch (just ground/unground the cathode somewhere away from the switch, with a jumper wire). If the pops are gone, I'd now know why they are happening.

 

[aj53202]

Not sure if I understood it correctly but if I disconnect led cathode from the pad & ground it elsewhere, it stays lit up whenever the power is connected.

With this led set up, turning on the blue side with the footswitch does not cause any pop now.

 

[JTEX]

No, what I meant is to temporarily ground/unground the LED without going through the switch, as a test. Use the wire as a switch, don't solder it permanently. Just touch it to ground on and off and see if it causes pops.

 

[aj53202]

Understood. I did these…

Ground/unground the led cathode elsewhere without the footswitch on to turn on/off the led—> no pops, just some static noise.

Ground/unground the led cathode elsewhere with the footswitch on to turn on/off the led—> no pops, just some static noise.

 

[JTEX]

OK. Now we know what's going on. The switch contacts are fairly large bits of metal close together, resulting in some parasitic capacitance between them (a few pF). When the LED is grounded through the switch, the voltage step that occurs couples capacitively into the adjacent contact going to the sensitive, high impedance, high gain input. This is what you're hearing.

This is, BTW, the same mechanism through which you may get squealing in high gain circuits using a true bypass switch. In and out signals are brought too close together and the output couples back into ine input, making a nice oscillator. Same goes for many high gain circuits built on a breadboard. Too much capacitance between adjacent terminal strips can cause squeals.

 

[aj53202]

Should I try some other switch or am I just unlucky because it’s kind of expected sometimes & is accepted? There is not a lot of space available inside for anything complicated to try because the fit is very tight.

 

[JTEX]

See post #3 above, it looks like it should work.

 

[aj53202]

Thanks, I’ll try them & report back tomorrow.

 

[aj53202]

I tried the AMZ method #1 and 10uF was still not ok so went straight to 47uF because I didn’t have anything in between. There is still slight pop but a lot better, almost at par with the green side. I hope I did this right lol.

I didn’t have 390 Ohm for R1 and used 460 Ohm instead. R2 used was 20K Ohm to set the similar brightness to the green led.

I’ll take this is a win and probably try some other switch for future builds.This was the Tayda blue switch. I was ok with the switch pop for my use case but a friend wanted me to build him one and I didn’t want the switch pop to bother him.


Thanks a lot for all the help. Really love the fact that the community members here are very helpful.