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.

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?

 

[Nacht]

There's something probably obvious i'm not understanding here about how both output terminals of the transformer works with the output socket.
I have a hard time making a clear difference in my mind between the transformer pin 4 and the output socket sleeve pin.
What you mean "on your jack its riding on one wire" ?

 

[jwin615]

There's something probably obvious i'm not understanding here about how both output terminals of the transformer works with the output socket.
I have a hard time making a clear difference in my mind between the transformer pin 4 and the output socket sleeve pin.
What you mean "on your jack its riding on one wire" ?

I'm not the best at explaining things but I'll give this a shot. I highly recommend the book I linked before.

In a non-transformer isolated output(most petals), the out is on 1 wire. It's potential/energy is in reference to ground.
Think of this like a single phase (110/117v) AC outlet.
Signal. Ground. That's it.

Now, the transformer outputs potential/energy has nothing to reference except it's two poles.
Just like an amplifier speaker output.
There's no ground, it's current alternating between two points.
This is also comparable, somewhat, to a 2 phase mains panel(220/240v US residential).
A transformer with a high voltage primary and a low voltage 3 tap secondary(again, over simplification, wye delta etc) feed the residential panel. The middle tap, or center tap is the neutral.
On each side of the neutral, there should be ~110V potential. But across the phases there's 220V.

Audio on a non grounded center tap transformer is alternating between the two outer taps. Similar to a breaker panel.
Audio on a 1 wire +ground(out jack) is signal potential vs ground, like a US single phase outlet.

Bestest most practical example I can put together.
Read the pdt I posted. It's all there in the first chapter with pictures and diagrams, written by people who can spell and everything.
It's written as an intro for audio engineers, not electrical engineers. Very digestible.

 

[Nacht]

OH i see, thanks, yes i will read it this weekend
I'll try to understand where exactly it changes from being the transformer signal to a normal pedal cable signal... there must be a point where it converts to normal guitar signal "riding on one wire" + ground.
I think what confused me is it's all audio, and people say audio is ac but it seems its not the same concept in a transformer VS a guitar cable.

 

[Nacht]

So basicly with that transformer output connected to the socket out of the aby pedal, we are connecting this signal from the transformer that has no ground reference, directly in the guitar amp input and then the amp converts it to a normal signal (signal on the TIP and ground on sleeve) ?

 

[Nacht]

I think what happens with my test using my stereo pedal is the way that pedal works, i was shorting the signal to ground instead of reversing polarity because the pedal output jacks are grounded the same way with the sleeve to ground. One of the output in my quick reverse polarity adapter was just throwing the signal to ground via the pedal case ground connected to both of it,s output sockets...

 

[giovanni]

Exactly. In a non transformer isolated signal processing, you have a “fixed” ground, because the entire circuit and the input signal use the same ground point. So if you try to flip output signal and ground, you end up sending ground to your amp, that is zero voltage (silence).

The secondary of the transformer in isolated ABY boxes is not grounded at all, by design: the ground connection happens only when the output is connected. So you can flip the phase before that connection by flipping the leads. That works because you are starting from a non grounded circuit.

I hope this clarifies things!

 

[jwin615]

You must use an isolated jack for this reason. Otherwise, the whole thing doesn't work.

 

[giovanni]

You must use an isolated jack for this reason. Otherwise, the whole thing doesn't work.

Ah yes, very very critical detail!

 

[Nacht]

Thanks!
Yes i'll use the plastic isolated sockets for ins and outs

So i came up with this, 3 switches:
switch 1 does transformer bypass or engage
switch 2 lifts the ground or not
switch 3 flips the phase
Does it look correct?

I think i got the transformer poles wrong when i made that custom component pattern in diptrace... or i guess it's common to flip the phase when looking at the datasheet and the actual transformer itself, to keep the output in the same phase as it's in i have to reverse the leads at the secondary.

 

[jwin615]

Don't get why you would bypass the transformer.
Also:
1)you need to lift the ground at the out jack
2)bypassing the transformer as wired will send signal to ground in 1/2 of the phase invert option.

 

[Nacht]

Don't get why you would bypass the transformer.
Also:
1)you need to lift the ground at the out jack
2)bypassing the transformer as wired will send signal to ground in 1/2 of the phase invert option.

Because transformer in this low price range color the sound compared to the original direct signal, it's not always needed to use transformer isolation.

Ok i changed the ground lift switch to be at the output, does it looks good now?
I was thinking it's the same using it before or after the phase flip, but i'm not sure how to wire properly the phase flip so ...

 

[Nacht]

ah nope it's about the same problem, i'm trying something else