DPDT to 3PDT switch transfer question

[mr_sooty]

Yay me! I have a Vox Wah that I modded for true bypass, but the mod used a DPDT switch. These switches seem to be totally unreliable, and I have had switching issues with every pedal I have had containing them. So I decided to change it to a 3PDT switch, which are supposed to be way more reliable. I managed to get hold of a switch, but I had to figure out how to translate the DPDT switch wiring to the 3PDT switch.

I'm no electroninc expert, I just follow my nose and do what ChrisK and Sumgai tell me, so I was happy to have been able to figure this one out, but I have a question about it.


Here's what I did:



Now the question is regarding the gray connection circled in orange on the 3PDT switch on the right. Originally I didn't put that connection in there, and it didn't work. I'm wondering why.

My understanding is that on the 3PDT switch, when orientated the way this one is, the middle vertical row throws to either the left or the right. Now the white wire is going to the bottom terminal, and then I have connected the bottom terminal to the middle terminal. I thought that because I had run that connection to the middle terminal, that when the middle row throws to the right, the white wire would be connected to the blue wire. But it didn't work.

So I made the connection circled in Orange, the little gray line from the bottom right terminal to the middle right one. Now it works.

Why did I need to do this? I only knew to do it because I had recently had another pedal's DPDT switches replaced with 3PDTs by the manufacturer of the pedal, and they had made these connections. I couldn't understand why they were needed, but I copied them anyway. They basically transfrered the bottom row of the DPDT to the bottom row of the 3PDT, and made upwards connections between all the bottom row terminals and all the middle row terminals. I see now that this is necessary, but I'm wondering why you can't just use a 3PDT switch the same as a DPDT switch but skip the middle (horizontal) row?

[mr_sooty]

Wait, I think i just figured it out. Because that circled connection doesn't move, right? OK, answered my own question. So it would have worked if the blue wire had've been connected to the bottom terminal instead of the middle one - right?

But I still don't get why the guys that did my other pedal needed to hook up all three bottom terminals to all three middle terminals, when they had no wires connected to the middle terminals.

Here's the bypass switch from the pedal that was modified by the manufacturer (it's an old pedal, they used to use DPDT's now they use 3PDT's, so they changed it for me):



Why do they need those grey connections to the middle (horizontal) row?

[JohnH]

Hi sooty

I know what you mean about those DPDT and 3PDT switches. The DPDTs I buy in Aus seem to be substantial robust units, but after a few weeks they get very unreliable and need hard stomping and frequent contact cleaner. Then I found a source of the 3PDTs, blue case with red bits around the lugs, that I've seen inside various high-end boutique boxes, and they seem much better. I've had one in for about 6 months with no problems.

With your circuit, it looks like it only needs two poles, so theres no real need to use one of the sets of three lugs at all. But by bridging the middle three to the lower three together, maybe it adds a modicum of further reliability, but not really necessary. The usual purpose of the three sets of lugs is one for input, one for output (these two connect together in the off mode, to give true bypass), and the third set to switch an LED.

John

[mr_sooty]

Cool, yeah I thought those connections weren't necessary, but I wonder why they bothered to do them.

You might be interested to know (unless you already do), that JayCar Electronics have started stocking those 3PDT switches. That's where I got the one for my Wah.

I had DPDTs in my Wah and two in my overdrive. All of them would occasionally not work properly, and you'd have to turn them off and on again, or the other way around. Nice to have them all sorted now (touch wood).

[JohnH]

Thanks, thats good to know about Jaycar - they were the people guilty of selling me the duff DPDT ones!

John

[mr_sooty]

Aug 2, 2008 4:01:29 GMT -5 JohnH said:

Jaycar - they were the people guilty of selling me the duff DPDT ones!

Same here! They have the good ones now though, but they're $11.50 NZD, probably about the same AUD.