Switch pop

[Rpschultz13]

This reverb pops when engaged. I suspect I’m doing the ground wrong. Thoughts?

 

[Nostradoomus]

If it’s quiet otherwise it’s not the grounding. What board is that? Link a schematic if you have it!

 

[music6000]

GitHub - brianthornock/T60: A PT2399-Based Reverb Pedal

A PT2399-Based Reverb Pedal. Contribute to brianthornock/T60 development by creating an account on GitHub.

github.com

 

[Rpschultz13]

Here’s the power section.

 

[Rpschultz13]

There are 2 LFO sections like this.

 

[music6000]

Switch popping is usally caused by no pulldown resistors.
Do you have a 1M resistor going to to Ground on the Input of this circuit?
Does it pop when you switch it off?

 

[Rpschultz13]

Yes 1M. No it doesn’t pop when I turn it off.

 

[music6000]

Is the On/Off LED soldered to the main board?
Are we talking a minor pop or thud!?

 

[Rpschultz13]

Yes LED soldered to main board. It’s a reverb, so I get a thud and then a splatter of reverb.

 

[music6000]

I have to ask what is going on with the resistor leg sticking out of the pad below the 9v power pad?

 

[Nostradoomus]

Measure for DC on the output jack

 

[Rpschultz13]

I have to ask what is going on with the resistor leg sticking out of the pad below the 9v power pad

That’s a bit of an optical illusion. There is a resistor there that I left out on purpose - R66? Is if one of the pots are left out, R67 on the other side (under yellow wire) is similar. But the resistor you see is soldered in parallel with the one to the left. To reduce it from 22k to 7k I think, to give more gain at the mix stage.

 

[music6000]

If you are getting a thud then nothing coming from the pedal, I suspect you have a cold solder joint in there somewhere.
You may have to pull it out & inspect & show a Picture of the back of the PCB, there is a lot of solder joints & it needs to be clean of any debri so you can inspect the joints.

 

[Rpschultz13]

No the pedal works fine. When I switch it on, It thuds, gives a little reverb and then is fine.

 

[music6000]

No the pedal works fine. When I switch it on, It thuds, gives a little reverb and then is fine.

If it thuds, there is a bad joint!

 

[Rpschultz13]

I took it apart, checked the 1M pull down, measured, reflowed, etc. I also reflowed about 1/2 the other joints. None looked back though. Still pops. Any other ideas? A larger pull down value?

 

[Nostradoomus]

Did you check for DC on the output? Can also try removing the LED and see if that kills it.

 

[Rpschultz13]

Did you check for DC on the output? Can also try removing the LED and see if that kills it.

There is 0.5-0.6 mV on the output. I have no idea if that is acceptable or not.

 

[Nostradoomus]

If the output cap (1uf) is electrolytic try replacing it with a film cap (even of a lower value just to see if it helps). I’ve solved lots of my switch pop problems replacing electro output caps, they’re prone to leaking DC.

(I can’t open the build docs on my phone, I’ll check on my laptop later)

 

[Rpschultz13]

If the output cap (1uf) is electrolytic try replacing it with a film cap (even of a lower value just to see if it helps). I’ve solved lots of my switch pop problems replacing electro output caps, they’re prone to leaking DC.

(I can’t open the build docs on my phone, I’ll check on my laptop later)

No, the output cap and all 1uF's are MLCC. There are 9 electrolytic caps total: a 47u on each PT2399, a 10u on each LFO; and 2 100u's and a 47u in the PS section. There are eleven 1u's, all MLCC. All the other caps are film.

Picture at the top is still correct, except I did replace the 2 resistors in parallel with a single 6k8 (see post #12).