Passive ABY Ground loop swich schematic?

I'm building a passive ABY and was hoping to eliminate some of the buzz I get when connectiong my amps in Stereo (DRRI and Vox AC4).

Anyone have a schematic for how to do this without a buffer (if possible). I could always add an ouput buffer I guess, I have some extra opamps sitting around.

Simply do not connect the shield on one of the outputs, and you'll be fine. The shield will still be grounded through the amp on that side, and the rest of the box will be grounded through the other output.

It's really not that complicated.

The issues that require more elaborate solutions when it comes to ABY switches are polarity of the amps (easy switch solution) and the loading down of the signal when split to two amps, which is what would require the buffer.

By "lift the shield" do you mean that I should not ground one of the output jacks to the casing of the pedal?

I will be using this with 2 amps in stereo, should I be considering adding a buffer stage? I'd really prefer not to use transfo's but if it's the only way, I guess it's the only way.

Using resistors, like 47K, from the input to each output is the classic method for passive mixing and splitting. The resistors offer isolation between each path. Any pasive solution will result in a slight volume drop, so your tolerance to that drop will determine if you want a buffer. Since your 'Y' in this case is actually dual mono, the drop may be covered up having two amps blaring rather than one at a time. Resistors are cheap - try that first.

Yes, if you can isolate the ground of one of the jacks form the enclosure, that will be necessary as well, but you should also not connect the shield conductor on that jack to anything. You're essentially just breaking the ground connection between the two amps, but everything remains grounded.

I agree with Mr. Lover that the need for a buffer is really based on your personal impression of both amps running. Personally, I've plugged in passively to two 50w Marshalls, and didn't mind at all - plus, I hate batteries.

A word of caution!Always lift the ground in the signalpath(if it is necessary)as Ben and Fenderlover suggest.Never ever lift it in the power cord.The hum will disappear but you won`t have a safety ground on that amp and if you`re unlucky it may be the last thing you`ll do in this life.There are always safe ways to get rid of the buzz!

Using resistors, like 47K, from the input to each output is the classic method for passive mixing and splitting. The resistors offer isolation between each path. Any pasive solution will result in a slight volume drop, so your tolerance to that drop will determine if you want a buffer. Since your 'Y' in this case is actually dual mono, the drop may be covered up having two amps blaring rather than one at a time. Resistors are cheap - try that first.

So put a 47k resistor in the signal path from each switch to the output? Sounds good.

Yes, if you can isolate the ground of one of the jacks form the enclosure, that will be necessary as well, but you should also not connect the shield conductor on that jack to anything. You're essentially just breaking the ground connection between the two amps, but everything remains grounded.

I agree with Mr. Lover that the need for a buffer is really based on your personal impression of both amps running. Personally, I've plugged in passively to two 50w Marshalls, and didn't mind at all - plus, I hate batteries.

So one jack will be isolated from the enclosure and will also have no negative wire going to it? Just positive? How does that work (or maybe I'm misunderstanding what you mean by "shield conductor").

A word of caution!Always lift the ground in the signalpath(if it is necessary)as Ben and Fenderlover suggest.Never ever lift it in the power cord.The hum will disappear but you won`t have a safety ground on that amp and if you`re unlucky it may be the last thing you`ll do in this life.There are always safe ways to get rid of the buzz!

Yeah, that's goes without saying. I wouldn't even think of lifting the ground on the amp itself, I like being alive :lol:

Go here and download the pdf file. It's got all you need.

http://www.singlecoil.com/docs/aby.pdf

The warning wasn´t intended for you but I´ve seen enough people who´ve lifted the ground on the powercord without realising what they´ve done.

A guitar cable actually has no negative conductor. The signal from the guitar is AC, traveling down a single wire. The other wire in the cable is simply a shield which connects to ground in order to conduct interference away from the signal path. It is this shield that creates a loop when it's grounded in more than one place. What you want to do is create a break in that path between the two grounds. Not connecting the shield to one of the jacks will do that. The shields of both cables will still be grounded on the amp side, so noise will not be a problem.

If the jacks are not isolated from the metal enclosure, then they could have a ground connection between them, which will negate your effort, so at least the jack that does not have the shield connected should be isolated from the enclosure - if the enclosure is metal.

Go here and download the pdf file. It's got all you need.

http://www.singlecoil.com/docs/aby.pdf

Nope. Doesn't have ground lift. Also uses 3pdt switches, I'm going to be using DPDT because they're way cheaper.

A guitar cable actually has no negative conductor. The signal from the guitar is AC, traveling down a single wire. The other wire in the cable is simply a shield which connects to ground in order to conduct interference away from the signal path. It is this shield that creates a loop when it's grounded in more than one place. What you want to do is create a break in that path between the two grounds. Not connecting the shield to one of the jacks will do that. The shields of both cables will still be grounded on the amp side, so noise will not be a problem.

If the jacks are not isolated from the metal enclosure, then they could have a ground connection between them, which will negate your effort, so at least the jack that does not have the shield connected should be isolated from the enclosure - if the enclosure is metal.

Awesome info man, thanks for the help.

Ok, so I tried lifting the ground on one of my cables (I admit this might not of been the correct way to do it), but I ended up with even more noise when running stereo from my Stereo Memory Man w/ Hazarai.

bump