Wanting to build Stereo A/B switch...need help.

[Hiwatt25]

I just finished my first project (a passive A/B amp selecter) and a buddy of mine (not a guitar player) asked me if I could build one for him but for two different sets of speakers (indoor and outdoor) he has running from one hi-fi amp.

Without hesitation, I said "sure" but then I realized it would be a different animal because it's stereo not mono.  So, I'm not sure how to switch two channels at once and had the following questions:

• Can I switch both channels at once using a single 3PDT switch?
• If he's just using bare speaker wire to connect his speakers, what kind of Jacks should I use?  Should I just use screw down terminals?  Where do you buy them?  How do I mount them to the enclosure?
• Has anyone made one of these?
• And finally, would it be simpler to just find a schematic of an existing stereo A/B switcher?  Does anyone have one?

Okay, that's it.  Thanks in advance.

[choklitlove]

this is almost as easy as the one you already built.  he's not going to want to stomp on his to switch it is he?  so, unless he wants LED indicators, or you want to go the extra mile to impress, you can get by with a simple non-stomp DPDT switch.  i like slide switches, but it's up to you.

as for the jacks, you should ask him what he uses for sure.  a lot of speakers use 1/4" or rca, and that would be better for you.  if i were you, and he's using bare speaker wire, i'd offer to put some plugs on the wires.  then, you could choose rca, banana, 1/4, whatever.

[choklitlove]

this will work:

[choklitlove]

one more thing:  if you're going to make one of these, go ahead and make two.  make one with 1/4" jacks and it is an effects looper.  score!

http://www.geocities.com/worthekik/loop.html

[Hiwatt25]

Very cool, thanks.  Does anything have to reference ground for this pedal.  God, I hope I'm saying that right.  I believe the A/B box I built connects one output to ground while the other is active to avoid noise.  Is that a problem here?

Thanks again.

[choklitlove]

depends on the enclosure you use.  if it's metal, none of the jacks need to have any other connections made to them besides the signal.  all of the grounds will make the connection through the enclosure.  having the metal enclosure will also provide shielding to minimize noise.

if you use a plastic enclosure, all jacks will have to be connected to ground.  i wouldn't worry about shielding, but if you do run into noise, you can line the inside of the box with aluminum foil or something, then connect it to ground as well.  i don't think you'll have any noise issues though.  just make sure you don't use bare wire (wire without a sleeve).

i don't understand what you mean by "the other is active to avoid noise".  please explain further, but i really don't think you'll need to (or needed to) do whatever you did.

[Hiwatt25]

Thanks for hanging in there with me I'm still learning much of this stuff.  The schematic I used was from fulltone and from what I understood, one of the two outputs was grounded while not being used and when the switch is activated the opposite output would be grounded and so on and so forth.  I think that is supposed to help with noise.

http://www.fulltone.com/PDfFiles/AB_switcher.pdf

But I'll take your word for it regarding noise in the Stereo switcher.  Lord knows I don't fully undersand the concept of ground yet...heck, I can barely keep from burning myself with my iron.

Thanks again! 

[Hiwatt25]

Okay, one other thing.  If there are two leads per speaker (red and black) wouldn't I only be able to switch one speaker at a time with the schematic above?  I may be over thinking this.   

[choklitlove]

Okay, one other thing.  If there are two leads per speaker (red and black) wouldn't I only be able to switch one speaker at a time with the schematic above?  I may be over thinking this.   

red is the signal.  black is the ground.  only the signal is represented in the drawing as the green wires.  the black will just connect to the case and the rest of the grounds in any way you choose.  i could answer more specifically if i knew what plugs you're going to use.

as for grounding the un-used outputs as in the fulltone layout: it's a good idea for the a/b box.  but, i don't think it would make any difference in this instance.  going through that in my head... i think you would need a 4pdt switch.  yeah, it would go like this:


it is possible to find them, but not as easily as a dpdt or 3pdt.  so, you can do that if you want, but i'm not sure how much of a difference it would make.

[Hiwatt25]

Choklitlove, again thank you.  I think I just had an "A-HA!" moment.

So, if I understand things correctly, I should be able to use the DPDT by just using red wires and making the chassis the ground.  Is that why ground is also sometimes called "common"?  It would seem that the chassis itself becomes a conductor.  Am I thinking of that correctly?

Planning on using RCA connectors for the input and Binding posts for the outputs (my friend insisted).  Is there a recommended way to connect the black ground wires to the chassis?  I'm guessing I could solder them to the enclosure (will be an aluminum hammond style) but if there is a neater/cleaner/longer lasting way, I'm all ears. 

Thanks again, I'm starting to owe lots of people beer...

[choklitlove]

Am I thinking of that correctly?

yup.

Planning on using RCA connectors for the input and Binding posts for the outputs (my friend insisted).  Is there a recommended way to connect the black ground wires to the chassis?  I'm guessing I could solder them to the enclosure (will be an aluminum hammond style) but if there is a neater/cleaner/longer lasting way, I'm all ears.

no solder with his speaker wires.  he might like to unplug them sometime.  whatever binding posts you use should have 2 contacts on the outside of the box, and 2 on the inside for soldering.  he will "bind" the speaker wire on the outside, and you will solder one to ground and one to the switch (signal) on the inside.  some panel or chassis-mount jacks (jacks that you screw or bolt to an enclosure) will have the ground automatically connected to the enclosure on the inside.  in which case (if you use a metal enclosure), you won't have to worry about ground.  either way, this may sound a little more complicated than it is.  so, to make it easier on yourself, don't ask too many questions before you have the parts and project in front of you.  the questions will answer themselves, trust me.  good luck!