3PDT Wiring Question

[seten]

A lot of 3PDT wiring diagrams I have seen, like the one I linked below, make it so the pcb input is connected to ground when the pedal is switched off. What is the reason for this?

https://photobucket.com/gallery/user/putzdaddy/media/bWVkaWFJZDo3MDQ2MzQ2NQ==/?ref=

[GGBB]

The short answer is noise reduction.

It 'mutes' the circuit input, which can help with switching noise, oscillation, and other problems. Not all pedal designs need it, but generally it doesn't cause any problems so it is a fairly standard practice.

[seten]

The short answer is noise reduction.

It 'mutes' the circuit input, which can help with switching noise, oscillation, and other problems. Not all pedal designs need it, but generally it doesn't cause any problems so it is a fairly standard practice.

Thanks! could you explain in detail how it mutes the input?

[antonis]

Because input is grounded..!!
GND is the easiest path for signal flow (practically zero resistance path) so no part of signal (plus any interference) comes into input..

Another reason for grounding Input is for prevent "pop" when effect engaged..

Almost all effects have an Input DC blocking capacitor..
That capacitor is "floating" (one of its legs stays unconnected) when effect disengaged (by pass mode) and exibits leakage due to some factors (you can consider it as a self-discharging battery..)
The above results in possible voltage level difference (in the mean of opposition) between input cap and instantly incoming signal, which voiltage difference results in an audible sound (pop).
When grounding input, you effectively pull cap's floating leg down to zero volts so any signal voltage level hasn't to "fight" for overcoming any potential difference..
(oversimplified of course but I think you get into the point..)

Same stands for output cap but it's usually pernanently grounded via out volume pot..

[GGBB]

Another reason for grounding Input is for prevent "pop" when effect engaged..

Also known as noise reduction, switching noise.

Almost all effects have an Input DC blocking capacitor..
That capacitor is "floating" (one of its legs stays unconnected) when effect disengaged (by pass mode) and exibits leakage due to some factors (you can consider it as a self-discharging battery..)

Pedals with input caps typically include an input pull-down resistor - a large value resistor (typically 1M) between the cap (input side) and ground - which allows the cap to quickly discharge in bypass mode so the cap is not floating.

[antonis]

Of course Gord but I (and some other people too..) exhibit popping even with moderate value pull-down resistors..
(in the range of some hundred kilo-ohms..)

So, I prefer to wire 3PDT switches with IN & OUT grounded as a standard procedure (and sleep in peace, when LED anti-pop circuitry is also wired..)

[bean]

Of course Gord but I (and some other people too..) exhibit popping even with moderate value pull-down resistors..
(in the range of some hundred kilo-ohms..)

So, I prefer to wire 3PDT switches with IN & OUT grounded as a standard procedure (and sleep in peace, when LED anti-pop circuitry is also wired..)

I've done a few builds using a transistor with a small R-CR attached to do soft on and off with LEDs. Not sure how much it helps but I feel smarter when I do it.

[antonis]

I feel smarter when I do it.

Tha's the point, Brian.. 

Any "improvement", like passing from a passive delay system to an active one, should make us feel smarter..
(or dumpest, on the other hand..) 

[GGBB]

Of course Gord but I (and some other people too..) exhibit popping even with moderate value pull-down resistors..

That sounds like a medical problem.

There's no guarantee that bypass grounding or a pull down resistor gets rid of switch pop. If the pull down doesn't take care of it, bypass grounding probably won't either (it's not a floating input problem). But it can't hurt, can it? I sometimes think the extra switching can actually add to switching noise.

[antonis]

I sometimes think the extra switching can actually add to switching noise.

Your thought is absolutely True & Correct...!!! 

(but let's not turn OP thread to a "BBM" or "MBB" switch query..) 

[seten]

I sometimes think the extra switching can actually add to switching noise.

Your thought is absolutely True & Correct...!!! 

(but let's not turn OP thread to a "BBM" or "MBB" switch query..) 

I'd love to hear about it! What's the difference?

[antonis]

The brute difference is the way poles are switched..

In "brake before make" poles are instantly "open"  where in "make before brake" poles are instantly "shorted"..

For a BBM SPDT switch with 1, 2 & 3 lugs, lug 2 (middle) stays "on air" for a while traveling for lug 1 to lug 3 where for a MBB SPDT switch, lug 2 makes contact with lug 1 AND lug 3 for a while..

[duck_arse]

you'll need to release the brakes on those make-before-break switches, tho.

[antonis]

But you have to admit "brake" sounds muuuuuuuuuuuuuuuuch better than "break", doesn't it Stephen..?? 

[zombiwoof]

I was under the impression that board input grounding in TB wiring was to avoid "tone suck" in bypass?.  It takes the board completely out of the signal path, reducing that tone suck.
Al

[digi2t]

I was under the impression that board input grounding in TB wiring was to avoid "tone suck" in bypass?.  It takes the board completely out of the signal path, reducing that tone suck.
Al

I would hazard to say that "tone suck" would only refer to bufferd bypass effects. If you are in true bypass, you're eliminating that factor, whether the board input is grounded or not. As mentioned above, input grounding is to help mute some noisy circuits but not letting the input float in bypass. In some extreme cases (Schumann Two Face is a good example), the circuit can be so noisy in some settings that grounding the output might be necessary as well. The LED antipop portion is a bonus;