Noob help: A/B audio switchbox w/ 3PDT + 3.5mm stereo jacks

Armchair Bronco · Post by **Armchair Bronco** » 30 Dec 2009, 11:49

Hi, first post here...and it's an easy noob question for y'all.

I want to build a simple A/B audio switchbox that has two 3.5mm stereo inputs and a single 3.5mm stereo output. I want to build something that lets me use one set of Boston Acoustics PC speakers + sub-woffer with separate inputs from my Windows 7 PC and the headphone out jack on my small 19" HDTV. Obviously, for my needs I'll be using *either* A or B but never both at the same time.

I want to use a small enclosure and 3PDT switch from Small Bear and use three 3.5mm stereo jacks from Mouser.com

Here are the parts I plan to use:

3PDT toggle switch:

Hammond 1590A enclosure:

3.5mm Stereo connector (three of 'em):

So: how do I wire this up? Let's say that the 3PDT switch has the following contacts:

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1 --- 2 --- 3  
4 --- 5 --- 6  
7 --- 8 --- 9

And let's say that the three 3.5mm stereo jacks each have contacts labeled:

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G (for ground)
R (for ring)
T (for tip)

Finally, let's say that two input jacks are labeled "1" and "2", respectively, and the output jack is labeled "X".

So, we have:

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1G, 1R, 1T
2G, 2R, 2T
XG, XR, XT

Can someone please tell me how each of the jacks should be connected to the switch? Thanks!

Armchair Bronco · Post by **Armchair Bronco** » 30 Dec 2009, 20:31

Anyone? I'm just looking for a mapping like this:

1: 1R
2: 1T
3: 1G

etc.

Dr Tony Balls · Post by **Dr Tony Balls** » 30 Dec 2009, 20:39

I dont know why you'd use a 3PDT. All you need is a SPDT. Wire the SPDT like so:

1: Input #1 tip

2: Output tip

3: Input #2 tip

then ground all of the sleeve connectors together, or if you're suing a metal enclosure they should ground together anyway.

If you MUST use a 3PDT, then just use one pole (column of three terminals) on it and wire it the same.

Armchair Bronco · Post by **Armchair Bronco** » 30 Dec 2009, 20:56

Dr Tony Balls wrote:I dont know why you'd use a 3PDT. All you need is a SPDT. Wire the SPDT like so:

1: Input #1 tip

2: Output tip

3: Input #2 tip

then ground all of the sleeve connectors together, or if you're suing a metal enclosure they should ground together anyway.

If you MUST use a 3PDT, then just use one pole (column of three terminals) on it and wire it the same.

On another site, someone said that I would risk popping sounds when switching between the two sources if I didn't use a 3PDT switch. I was originally planning to use a 2PDT switch as both of the build plans I found on the web for similar projects used 2PDT switches.

Dr Tony Balls · Post by **Dr Tony Balls** » 30 Dec 2009, 21:34

i dont see why any other switch would cause popping, or even why you'd need a 2pdt.

rocklander · Post by **rocklander** » 30 Dec 2009, 21:42

even if it pops.. it's not like you're on stage in front of a crowd.. big deal, no?

Armchair Bronco · Post by **Armchair Bronco** » 30 Dec 2009, 21:51

So even with stereo audio jacks, I only need to use the connectors for the tip and the ground? You're saying I can just ignore the ring?

Dr Tony Balls · Post by **Dr Tony Balls** » 30 Dec 2009, 21:57

OH shit....you're right, i forgot about stereo.

yeah, you'll need at least a DPDT like so:

1 - 4

2 - 5

3 - 6

where:

1. Tip of Input 1
2. Tip of Output
3. Tip of Input 2
4. Ring of Input 1
5. Ring of Output
6. Ring of Input 2

Armchair Bronco · Post by **Armchair Bronco** » 30 Dec 2009, 21:59

Cool. Someone over at OffsetGuitar.com just posted this schematic for me.

Looks like a DPDT is the way to go. Thanks for the input!