Understanding different 3PDT connection concepts

[rectifier]

So after building a couple of pedalpcb boards I'm asking myself why some 3PDT configurations are chosen over others. Might be a noob question, but I just want to understand it.



For example, let's look at this board: There are 4 pins In, GND, SW (which acts as a GND for the LED) and Out. The Input and Output jacks are connected with cables. So far so good. With bypass, the input is grounded.

This leads to my first question:

Why is the input grounded, and the output doesn't ? I've seen some 3PDT wirings with both inputs and outputs being grounded. Any benefits to this design over both input and output being grounded?



Now with this board the connections are a little bit different. The 3PDT connects with 6 Pins. The Input and Output Jacks are directly connected to the pcb. Input is grounded like in the example before.

Now my questions would be:

- Is this 6 pin design somehow better than the 4 pin design that is basically used on 90% of all the other boards ?
- Ain't the wires from the input and output jacks get some kind of hum or interference with the components on the board? Is this why all the other boards only have 4 pins and rout external cables from the input and output jacks ? Or is this more a matter of taste? I mean with this 6 pin connection and the 3PDT adapter boards the build is much cleaner with no wires floating around.

Thank You
Happy New 2022

 

[Robert]

The input is grounded in bypass to reduce any noise generated by the circuit with no input signal. It also prevents pop when switching by discharging the input capacitor to ground when the pedal is bypassed.

Some circuits (Fuzz Foundry, among others) will oscillate and squeal when the guitar isn't connected (eg: bypass). In some extreme cases this signal makes it's way to your amp by way of the outer sleeve of the cable even though the pedal is bypassed.

We don't ground the output because that puts a low impedance path to ground on the output stages. In most cases this isn't a huge issue because there is usually some series resistance between the output stage and the output pad of the PCB, but occasionally the resistance is low enough that it could cause damage to an output transistor or opamp.

Your first example is exactly the same as the second example, the only difference is the two orange wires are incorporated into the PCB layout itself. This isn't possible (or practical) in every single design, but I do it whenever possible to simplify and clean up the offboard wiring... especially with dual footswitch builds.

It doesn't always work out with extremely high gain circuits or circuits with LFOs because the input trace can only be routed so far away from the active signal path.

There are lots of other wiring configurations that significantly different from these two, it just depends on what the circuit requires for the footswitches function.

 

[phi1]

Here’s a cool article that breaks it down with visuals. I think pedalpcb already answered all your specific questions. There’s some different connection patterns that accomplish basically the same thing. I like pedalpcbs pattern so I use that in most of my builds.

https://www.madbeanpedals.com/tutorials/downloads/MBP_FootswitchWiring.pdf