Buffered/Transformer Isolated Splitter

[Nacht]

Theoretically, there is only one ground. In practice though, we have different circuits in our home wiring, which means that if two different grounds from different circuits end up getting connected, they may actually be at slightly different voltages, which will cause interference (noise) because the voltage difference will create a current (this is commonly referred to as ground loop). This is pretty significant if two amps end up sharing the grounds. So when using an ABY splitter, you are lifting the ground of one of the outputs just to break the connection of the ground of the outputs, in order to avoid the grounds on the amps to be connected and thus creating a ground loop and consequently interference (noise). The input ground won’t matter as much, comparatively (although I know ground lift is often use by itself so it must have an effect). That’s why you only need one isolated output. If you have two, you may reduce noise a tiny bit more.

Please take all this with a grain of salt since my knowledge is a bit rusty.

Ah thanks, actualy i did not know the ground loop term meant that 2 different grounds were not at the exact same voltage and creating a current between them = ground loop noise. So that's good to know but... I'm still confused how the isolated ground of out B can work, like where does out B and amp B get's it's ground to make it work? Also when we isolate via a transformer, is that called ground isolation or we really must lift the ground at the output stocket of the aby pedal out B ? Transformer isolation of ground is isolation and lifting (disconnecting the ground at the output stocket) is ground lift?

 

[jwin615]

I somewhat misread/understood the intent of the first question.
I wonder now if ground was switched via jack incorrectly and there was an issue with ground plane on the pcb.
BUT, the isolated out should have its ground established from the amp/next device. Outputs (in pedal world) generally don't have/need to be grounded because the input of the next device should be. We don't typically get ground loops on pedalboarss due to the short runs we have and the fact that it's all serial in connection and on one circuit. But, once you start splitting and potentially running to other circuits, (amp and FOH for instance), it can become a big problem.
So, if you are using a transformer as an isolation device, utilizing the following inputs ground is advisable or at minimum implementing a ground lift.

 

[giovanni]

Ah thanks, actualy i did not know the ground loop term meant that 2 different grounds were not at the exact same voltage and creating a current between them = ground loop noise. So that's good to know but... I'm still confused how the isolated ground of out B can work, like where does out B and amp B get's it's ground to make it work? Also when we isolate via a transformer, is that called ground isolation or we really must lift the ground at the output stocket of the aby pedal out B ? Transformer isolation of ground is isolation and lifting (disconnecting the ground at the output stocket) is ground lift?

Ah sorry I shouldn’t have said ground lift. Transformer isolation is not ground lift. I conflated the two things unintentionally. As @jwin615 said, output B’s ground will connect to the amp input ground. So it will find its path to ground through the power circuit that the amp is connected to.

 

[Nacht]

Ah sorry I shouldn’t have said ground lift. Transformer isolation is not ground lift. I conflated the two things unintentionally. As @jwin615 said, output B’s ground will connect to the amp input ground. So it will find its path to ground through the power circuit that the amp is connected to.

i see, so when we lift ground on out B of an ABY pedal, signal goes out the ABY pedal into the amp B input and that amp B gets it's ground through the power cord ?

What if i make a ABY pedal where there is a transformer and ground lift switch on out A, then out B is identical: also has transformer and ground lift switch. In this case lifting both grounds on out A and B on that ABY pedal going into 2 amps would not work at all? Or would both amps still be able to use the ground through their power cords and thata ground also connected back to the power cord that powers the pedalboard?

 

[jwin615]

i see, so when we lift ground on out B of an ABY pedal, signal goes out the ABY pedal into the amp B input and that amp B gets it's ground through the power cord ?

What if i make a ABY pedal where there is a transformer and ground lift switch on out A, then out B is identical: also has transformer and ground lift switch. In this case lifting both grounds on out A and B on that ABY pedal going into 2 amps would not work at all? Or would both amps still be able to use the ground through their power cords and thata ground also connected back to the power cord that powers the pedalboard?

You can do that. It's not absolutely necessary but it can be done.
The OP schematic does this.
But just using one is sufficient and possibly better as you aren't coloring one side of the signal with the transformer.
The one transformer setup can be an issue if for some reason the input Z of the unisolated side is changing, IIRC. This could cause a change in volume on the transformer out.
I'm pulling deep into the long term storage bucket on this, so I may be off a bit. But I think that's correct.

 

[Nacht]

You can do that. It's not absolutely necessary but it can be done.
The OP schematic does this.
But just using one is sufficient and possibly better as you aren't coloring one side of the signal with the transformer.
The one transformer setup can be an issue if for some reason the input Z of the unisolated side is changing, IIRC. This could cause a change in volume on the transformer out.
I'm pulling deep into the long term storage bucket on this, so I may be off a bit. But I think that's correct.

Yeah ok i see.
Now another thing...
I see the polarity switch after the transformer on the schematic, it's connected directly to the output socket.
I tried something quick here, i have a pedal that can accept mono in and stereo outs.
I soldered 2 TS sockets together with inverted tip and sleeve tabs between them:
Socket 1 tip goes to socket 2 gnd and socket 1 gnd goes to socket 2 tip.
Out A of my stereo pedal goes to amp A.
Out B of that same stereo pedal goes to my "inverted quick soldering socket job" then into amp B.
I was thinking it would flip the phase but...
Problem is It completely shuts down the signal when i try it with my 2 amps... why is that?
It's like it shorts the signal to ground on both out A and B of that stereo pedal, both amps are muted as soon as i connect my "inverted socket job"...
Why is it working on the aby schematic posted here but not when i try the same concept with 2 sockets here?

 

[jwin615]

That concept works in DC world.
Audio is AC.

In the aby, the current is alternating(AC) between terminal 6 and 4 of the transformer.
On your jack, it's riding on one wire.
Once you ground that wire on the jack, you are sending your signal to ground and ground to your amp.

(Below is an oversimplification)
Once you ground one terminal/side of the transformer in the aby schematic, all potential is above ground(as ground has zero potential).
The phase is determined by which side is grounded.
Now, if you ground the center tap(5), you can alternate above and below ground. But that's a topic for another day.
This can be done electronically as well but you loose the isolation afforded by the transformer.
I would recommend doing some more research on grounding, transformer and phase, beyond forum questions, before designing your own ABY. Or sticking with a known good schematic.
It's been a couple decades almost but IIRC the Yamaha sound reinforcement handbook has pretty good and not overly technical explanations of a lot of this.
I don't say this to deter your inquiries, more so to hopefully save you some time expense and frustration.

 

[Nacht]

That concept works in DC world.
Audio is AC.

In the aby, the current is alternating(AC) between terminal 6 and 4 of the transformer.
On your jack, it's riding on one wire.
Once you ground that wire on the jack, you are sending your signal to ground and ground to your amp.

(Below is an oversimplification)
Once you ground one terminal/side of the transformer in the aby schematic, all potential is above ground(as ground has zero potential).
The phase is determined by which side is grounded.
Now, if you ground the center tap(5), you can alternate above and below ground. But that's a topic for another day.
This can be done electronically as well but you loose the isolation afforded by the transformer.
I would recommend doing some more research on grounding, transformer and phase, beyond forum questions, before designing your own ABY. Or sticking with a known good schematic.
It's been a couple decades almost but IIRC the Yamaha sound reinforcement handbook has pretty good and not overly technical explanations of a lot of this.
I don't say this to deter your inquiries, more so to hopefully save you some time expense and frustration.

What you mean DC world ? I was refereing to this thread schematic... why does it work in this schematic from this thread but not when i try it with reversing the tip and gnd from a socket and guitar cable? What makes it different between what i tried and the schematic here?