Minimizing switch pop in boost section

[mdcmdcmdc]

I've been plagued recently by popping switches, and this latest build is no different.
The design is a pretty straightforward boosted overdrive with a couple of switching options.

Here's the block diagram, hopefully it makes the signal path pretty clear:


Here's the schematic (there may be some mistakes, I haven't gone back to double check it super closely... pretty sure the tone pot lugs are backwards, etc):
https://imgur.com/7YKgPCH
LINK TO FULL SIZE: https://i.imgur.com/7YKgPCH.png

And here's the layout with wiring:
https://imgur.com/iMAtB4u
LINK TO FULL SIZE: https://i.imgur.com/iMAtB4u.png

I built the circuit up as a series of small vero boards rather than as one large board with lots of crisscrossing to make the wiring a little easier to manage and to minimize any chance of error laying it out and building the individual blocks. Every block has been tested individually and seems to be working a-ok.

Per a suggestion in a previous thread about switch pop, every circuit block is star-ground to the dc ground. Similar for the 9V supply.

So, the issues are a VERY noticeable switch pop when the BOOST is engaged via the footswitch, and a very slight but noticeable delay between hitting the switch and the boost circuit engaging.

The on/off switch has a very minor pop when the box is turned off, but it seems pretty normal and is quieter than the hum from single coils. 2 of the 3 toggle pop, but that's honestly not surprising and since they're set-and-forget switches, I honestly don't care.

NOTE: The boost footswitch was initially wired for true bypass. I started troubleshooting like that, and tried the following:
- disconnect both LEDs. No change.
- 1M pulldown resistor on the BOOST footswitch from the centre lug (ie, the wire headed to the cap selection switch) to ground. No change
- replace 3pdt switch and rewire so signal is always going to the boost circuit (this is what's shown in the layout posted above). SOME IMPROVEMENT!

There's still a pretty substantial pop, and I'm at a loss as to what to try next. Any suggestions on where to go with this would be much obliged.

I'm happy to post shots of the board, etc, but there don't seem to be any issues with the circuit blocks themselves. It seems more like a more general design issue, or something with how I've wired it.

Thanks in advance, all!

[PRR]

You need a LOT more DC blocking. R-C networks. Notice how many of those switch terminals have DC on them, DC which changes with switching.

[PRR]

[mdcmdcmdc]

TYSM! That's incredibly helpful.

[mdcmdcmdc]

That absolutely did the trick - thanks again!

[mdcmdcmdc]

...and just so I have a better idea of what's going on for next time; when it comes to a circuit like this with some mechanical switching involved, is it best practice to treat the switch like a 'stage' of sorts that needs the same kind of coupling cap/DC blocking/RC network that you'd put between gain stages etc?

[ElectricDruid]

Yeah, that's perhaps not a bad way to think about it. The switches certainly need to be "outside" the DC-biased part of the circuit, and if there's several stages with switches between like in your schematic, then that means you have to go from DC-biased to not biased to the switch and then back to biased again - so yes, it's going to be surrounded by DC blocking caps and biasing resistors as if it was a separate stage of the circuit.