3pdt wiring

Adamo · January 27, 2015, 09:31:31 AM

I have a general question about 3pdt switches. Why are there so many different ways that they can be wired for pedal builds? I mostly use MBP boards and I follow Brian's wiring diagram. But just to learn a little I googled '3pdt layout' and got so many different ways that they can be wired. I just assumed there was a 'basic' way that the signal passes through the switch. Can anyone shed any light on this?

thx

GibsonGM · January 27, 2015, 09:36:25 AM

Hi Adamo - good question. I think the variety of switch schemes out there just has to do with the possible combinations that are available because you have 3 switches, 9 lugs! If you look closely, the same things are pretty much happening no matter how the thing is set up. There was no 'standardization' when these switches came out.

Yeah, there are a couple of designs that are actually DIFFERENT, but to the switch, doing the input > board / output jack > output is the same if it's on the L or R side of the switch. Or even the middle!

Adamo · January 27, 2015, 03:34:11 PM

Are there certain lugs on a 3pdt switch that are always used as a ground or does it vary from build to build? I'm trying to make sense out of these switches.

GibsonGM · January 27, 2015, 04:25:20 PM

It's not what lugs you use, it's how you use them! Here's a site with links to the "3 big sources" on this. I always use Tonepad's "offboard wiring" guide...it's consistent, and works very well: http://gaussmarkov.net/wordpress/thoughts/wiring-up-a-1590b/ He's nice enough to provide a tutorial on this with mint diagrams, so you probably need go no further...

As long as your switch arrangement makes the input go to output in bypass (that is what the jumper across the bottom does), and the in and out go to the proper board wires for those when engaged, you're all set. The ground you're referring to is for the indicator LED, which is the only reason we use a 3PDT over a 2PDT.

First thing ya do is make SURE you have the switch oriented the right way. Just look at the back....the blades should go left to right, not up down. When it's held the right way, your THREE switches are going to be center common, and switch to the blade above, and then below, this center lug.

It doesn't matter if you connect your in, out and LED on the left, center or right lug, altho if you go to the page I linked, you'll see a VERY nice way to do it so it never confuses you again - being consistent like this helps! Once you get it 1 or 2 times, you'll never really think about it again - save the diagram in your computer and refer to it, no problem

Very common to be confused by this when you're new

peterg · January 27, 2015, 04:30:05 PM

+1. Very straight forward arrangement.

Brisance · January 28, 2015, 05:24:36 AM

Is there any reason for connecting the ground to the third pole instead of positive? I have always connected the positive power to the third , which goes to the power led and the circuit.

Crowella · January 28, 2015, 06:09:23 AM

Connecting power to the third pole isn't an issue but there are *better* ways, better being a very subjective term to many.

The reason the extra connection is made to ground in both the gaussmarkov link and the one I picture below is that the 3PDT switch grounds the input when the effect is bypassed which can prevent some circuits from entering an unstable state with a floating input, which can cause noise/oscillation (in logic circuits, floating can cause significantly different outcomes to what you would want, even when off). I have found with high gain effects and some other pedals, grounding the board input significantly reduces switching pop.

Note that reduce does not mean remove. Popping can still occur in 3PDT switches due to things like switch de-bounce, the act of mechanically switching the circuit over. There are also some circuits/switches that can actually have and cause microphonic issues simply from mechanical and external vibrations but I'm not going to go into the tinfoil hat mode to discuss that because it's bordering "why bother discussing" territory... Basically, grounding the board input isn't a bad idea and for the extra few seconds it takes to connect, it might save a few headaches with a few pedals when you are at a gig and you get nervous to switch on your pedal in a quiet part*

*Actually happened to me with a "Hogs Foot" where I discovered it makes a very loud pop when engaged and didn't cure it until after a gig where that pop really is amplified.

EDIT: I will just stress this, the many different configurations fundamentally do the same thing. When engaged, connects in to board in and board out to out, when disengaged connects in to out. The LED is just a bonus you can add because of the 3PDT. There is just a few ways to do it for many reasons, some practical.

Brisance · January 28, 2015, 06:43:42 AM

but wouldn't that configuration leave the circuit powered, when on bypass? Could be a bonus on some circuits though

induction · January 28, 2015, 07:01:14 AM

All pedal circuits* should always be powered in bypass. Powering off in bypass causes enormous pops, and many circuits take several seconds to become usable after being powered up.

* Maybe there's an exception, but I've never** encountered one.

** Ok, I put a power switch on my univibe to save wear on the bulb, but the power has to be on before I start playing any song where I use it.

Crowella · January 28, 2015, 07:05:50 AM

Leaving the circuit powered is not really an issue, in fact, probably better to keep it plugged in as changing the current from switching can cause some parts to not function correctly until a few seconds in whilst components settle into a stable mode.

EDIT: Beaten. Pretty much what is said above me.

I understand why it makes sense though. That's why it is referred to bypass rather than on or off. A lot of electronics equipment doesn't necessarily switch off, it goes into standby which helps reduce the time between "off" and on.

GGBB · January 28, 2015, 01:01:17 PM

Quote from: Crowella on January 28, 2015, 06:09:23 AM

I have one major problem with this wiring which is the same as madbean's (and I've seen many other places) - the ground connection from left-middle to left-bottom and from left-bottom to center-bottom are redundant - just connect left-middle to center-bottom. Less soldering and less chances to damage the switch from overheating. If someone knows why this would make a difference please tell me!

GibsonGM · January 28, 2015, 04:50:13 PM

Probably just neater. But you are right, you increase the risk of heat damage when you solder it.

Crowella · January 28, 2015, 06:03:37 PM

Going through the bottom left isn't necessary and you don't need to solder it if you fear damaging it from heat. I usually just cut the lead off a resistor, poke it through that hole and bend it to the next one so it stays tidy and square and just solder the other two. Beats having a wire across connections if you have unsteady hands like me.

GGBB · January 29, 2015, 09:35:01 AM

Quote from: Crowella on January 28, 2015, 06:03:37 PM
Going through the bottom left isn't necessary and you don't need to solder it if you fear damaging it from heat. I usually just cut the lead off a resistor, poke it through that hole and bend it to the next one so it stays tidy and square and just solder the other two. Beats having a wire across connections if you have unsteady hands like me.

Leaving it unsoldered could make it susceptible to vibration causing it to connect and disconnect ever so slightly. Being ground, that's not a big deal, but it could make for some small noise I suppose. So why even bother when it has zero advantages and at least one disadvantage?

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3pdt wiring