yet, another true bypass pop (differential) diagnostic...

[Gainmonger]

Hi friends.
As lately I'm bumping with switching pop problems despite my carefully built circuits or high grade soft action 3pdt (and in order to achieve a more systematic quiet switching from a pedal to another), I decided to experiment a little to (possibly) diagnose what's the culprit:

I've built two identical high gain mosfet distortion pedals.

Both have the same part values, same part type and have the same 3pdt with grounded input.
Both have also a 1M pulldown resistor at the input and a 1uF electrolytic cap at the output, the dc path to ground being provided by the a1M volume pot.
One is loudly popping, the other is quiet.
i've checked/verified every single detail (by the book) that could show a difference with no results.
-diff dc voltage
-led current draw
-bounce is quite hard to detect
-mechanical noise (both are soft action and have the same "spring" to it)

From there and according to your experience and knowledge, what would be the right angle to investigate?

[PRR]

What is the DC voltage after the output cap?

[Gainmonger]

PRR, there's no detectable voltage after the output cap, pointing on either a mechanical noise or switch lever bounce. The circuit being (really) high gain, any of these noise would be heard.

In order to have a method when searching, I've drilled an identical enclosure with jacks and a simple 2pdt footswitch for simplicity,  ready to be grafted with the circuit.
Right away, the loud pop is not heard anymore which clearly points to the 3pdt's themselves.
I've tested all 8 3pdt's I have for noise, especially the throws combination (left-center, left-right, center-right)
-All expensive soft action ones are loudly popping,regardless of the throw combinations.
-cheap and stiff alpha ones are noiseless on at least one throw combo.

Quick guess is that soft action switches have more of a lever bounce, maybe not suitable for high gain stuff.They previously worked on 2 transistors fuzzes without a hitch so far though.
However, stiff ones have a more direct and frank connection reducing the bounce and  making them (maybe) more suitable for high gain (five gain stages in this case)
Obviously I can't confirm any of this but it seems to be the most likely explanation...

[amptramp]

You have a problem with 3PDT switches: the switching is break-before-make meaning the connection is left hanging in the breeze for a short time but that is the amount of time that produces an audio pulse.  There is no way to determine whether the input or output switch section breaks first or makes first and you can build a stompbox, test it and approve it for production than find the 3PDT switches have random switching order and some of the production units have a pronounced pop.

[Gainmonger]

Indeed. I think that's why the stiffest switches are so far the most reliable.
Now, I'll be testing 3pdt's along with each circuit I make and pair them accordingly

[thermionix]

Large amounts of gain downstream of whatever's switching will exaggerate the noise too.

[amptramp]

I have shamelessly bumped my own thread from March of this year to show people there are alternatives to the 3PDT as well as to add the pictures that PostImage obliterated:

https://www.diystompboxes.com/smfforum/index.php?topic=120006.0

The big manufacturers have given up on the 3PDT due to cost and reliability issues and it so happens that their circuits do not have a switch pop problem.  Their circuits based on JFET switching (usually using 2SK30 devices) are not the only ones that are imaginable.