Need schematic for passive 'pop free' A/B/Y box

[BDuguay]

I've been asked to build this for a friend and was wondering if anyone has a specific schematic that I can refer to.
Thanks all.
B.

[Mike Burgundy]

a passive AB is, well, passive. It won't introduce any DC offsets (which is cause #1 for pops) itself. So, if you're pedals are behaving nicely, you've got that covered.
Other things that can cause pos are bouncing switches (good switch will prevent that specific pop), and even offsets in the signal *when* you switch - if you switch on the zero-crossing (where the signal crosses through what it thinks is 0 - ground level) you're fine, but if you hit the switch inadvertently at the peak of the signal, things might sound slightly odd. Not very noticable, but there.
A passive AB will leave you open to ground loops though. Hummm...
That said, one DPDT for an AB, or two for an ABY is very doable. Check the fulltone website for a wiring diagram. A couple of active ones are at GEOfx.
hih

[BDuguay]

You're right Mike. Since it's a passive box, the only pops I should be concerned about are the ones that are produced 'mechanically'. I wasn't thinking too clearly about that one was I?
As for the potential of ground loop problems, that should be avoided if I use plastics output jacks right?
B.

[casey]

morley has a schematic of an a/b box.....on their website.

[TheBigMan]

Look at GEO or General Guitar Gadgets for iso'd ABs if ground loops are a problem.

[BDuguay]

To the BigMan from Hamilton, Scotland from Brian, the noodler from Burlington, Ontario (5 minutes from Hamilton, Ontario) Canada, Big thanks for the drawing.
And thanks to all who replied. The help is greatly appreciated.
B.

[Jayco]

Big Man,

Awesome... I've been looking for a schematic like this!

I had been talking to David over at loooper.com and he said his units (AB/Y) are completely passive and are noise free because they are grounded properly.

Do you know if this design is similar to how he does it?

He makes some very nice stuff for those who haven't seen it before.

Thanks,
Jim

[hershey]

I just built one from Bigman's layout (thanks!) , whilst hum free, I  get massive popping when switching from A-B but not when I switch to Y. any tips to improve this?
Thanks!

[R.G.]

I just built one from Bigman's layout (thanks!) , whilst hum free, I  get massive popping when switching from A-B but not when I switch to Y. any tips to improve this?

A "passive" ABY with LEDs is not passive. There is a battery there, and there are biggish currents flowing when you switch the LEDs. The circuit shown has the LED currents going through a jack to the battery, so there is a reasonable chance that the LED currents themselves cause a pop on the signal ground wire. And of course miswiring may make it look like it works OK, but still put DC on the signal lines.

There are a few ways out of this. One is to not use LEDs. Pull out the battery and see if it still pops. If not, you have one of the problems I mentioned. If so, then you may have other equipment putting DC on the signal line.

[hershey]

Thanks R.G yeah Initially I tested it without the battery and was getting the popping. I'm using it to change channels on my amp head (there are individaul inputs for each channel). I've only got my guitar going straight into the aby box into the amp.

[Phorhas]

Well, that's another story.

You can't use a passive A/B (LEDs or not) box to switch betwwen amps. The differant amps see differant input potentials and when switching between them you get that big pop.

You should build yourseld an active (and isolated is even better) A/B box such as the one found on R.G.'s geofex.cpm site.

[hershey]

Thanks phorhas.
It's actually only one amp head but with two inputs, on input for clean one for dirty but like you mentioned the principle I figure would be the same.
Thing is it seems to not pop sometimes and other times it does. Also I tried a old dod ab box with not popping issues. Dunno if that is passive or not...