Different Ground references in schematics

[Little Muff]

Just for the sake of my own learning, does anyone know why there could be different GND references in the same schematics? I particularly got curious about this BYP_GND I found in the Power section of Aion Fx Xenotron schematics. Here you can find the whole documentation, but I attached a snip to show it.

https://aionfx.com/app/files/docs/xenotron_documentation.pdf

So I guess that BYP_GND might refer to the bypass pcb, the one where the footswitches and power wires are soldered. But in that same part of the circuit are those other ground points referenced just as GND.
I found that in other schematics from Aion Fx, like Neurotron or Theseus, where there's even 3 ground names: BYP_GND, GND and GND2.

So.. anyone could explain me why are they different? Thanks!

 

[giovanni]

My guess is that they are all the same and were named differently accidentally. I don’t see a meaningful reason to have multiple ground planes in a guitar pedal.

 

[Robert]

I don't know about that circuit or schematic specifically, but I separate the signal / LFO grounds and analog / digital / relay drive grounds in some circuits to help control current flow and noise.

It could be that a separate net symbol/name was used for BYP_GND so that particular ground branch could be manually routed and not absorbed into a generated copper ground pour. (Purely a guess. I don't know what software was used there or if it behaves in that way.)

Or, doesn't Kevin use star wiring? Maybe it's to accommodate a particular wiring pattern.

 

[Guardians of the analog]

I don't know about that circuit or schematic specifically, but I separate the signal / LFO grounds and analog / digital / relay drive grounds in some circuits to help control current flow and noise.

It could be that a separate net symbol/name was used for BYP_GND so that particular ground branch could be manually routed and not absorbed into a generated copper ground pour. (Purely a guess. I don't know what software was used there or if it behaves in that way.)

Or, doesn't Kevin use star wiring? Maybe it's to accommodate a particular wiring pattern.

kevin makes many design choices that leave all of us like

 

[Little Muff]

My guess is that they are all the same and were named differently accidentally. I don’t see a meaningful reason to have multiple ground planes in a guitar pedal.

That was being my main guess too, as they're both in the same bypass pcb.

I don't know about that circuit or schematic specifically, but I separate the signal / LFO grounds and analog / digital / relay drive grounds in some circuits to help control current flow and noise.

It could be that a separate net symbol/name was used for BYP_GND so that particular ground branch could be manually routed and not absorbed into a generated copper ground pour. (Purely a guess. I don't know what software was used there or if it behaves in that way.)

Or, doesn't Kevin use star wiring? Maybe it's to accommodate a particular wiring pattern.

Well, in this circuit the ground seems to be all connected. I'll have a look to the Theseus schematics to see if I get something clearer..
And I'm not familiar to star wiring. I've done some research but don't get how would this apply here.
Sorry for my newbie questions but, if ground goes to negative power, where are those other grounds suppose to go when isolating them in a pedal? IN and OUT grounds?
Also, a bit off topic, something I don't get yet: in eurorack is simple because power is giving positive and negative voltage besides ground, so powering with +12/-12v the rails of an opamp will keep the audio signal bipolar. But how does that go in a pedal?

 

[Robert]

Some pedals do run on bipolar power supplies, usually internally generated from the 9V input by a charge pump circuit.

Standard single-polarity 9V powered circuits typically shift the idle point of opamp stages to around 4.5V to allow for the positive and negative swing of the audio signal around the 4.5V "virtual ground" point without clipping.

 

[HamishR]

I noticed recently while experimenting with a Maxon OD-820 circuit that as Robert says the ICs run on a +9v/-9V arrangement via a charge pump. Only the ICs use the -9V as "ground", and the rest of the circuit used standard ground. I guess in this case ground is acting like VREF would in a standard 9V circuit.

 

[giovanni]

I noticed recently while experimenting with a Maxon OD-820 circuit that as Robert says the ICs run on a +9v/-9V arrangement via a charge pump. Only the ICs use the -9V as "ground", and the rest of the circuit used standard ground. I guess in this case ground is acting like VREF would in a standard 9V circuit.

That’s the textbook bipolar arrangement for ICs. VREF is designed to replicate the role of ground in the bipolar arrangement, not the other way around. The bipolar arrangement is actually a lot simpler to understand and analyze.

 

[HamishR]

Ha! That makes sense!

 

[Feral Feline]

Just for the sake of my own learning, does anyone know why there could be different GND references in the same schematics? I particularly got curious about this BYP_GND I found in the Power section of Aion Fx Xenotron schematics. Here you can find the whole documentation, but I attached a snip to show it.

https://aionfx.com/app/files/docs/xenotron_documentation.pdf

So I guess that BYP_GND might refer to the bypass pcb, the one where the footswitches and power wires are soldered. But in that same part of the circuit are those other ground points referenced just as GND.
I found that in other schematics from Aion Fx, like Neurotron or Theseus, where there's even 3 ground names: BYP_GND, GND and GND2.

So.. anyone could explain me why are they different? Thanks!
View attachment 80365

From an old post that has some now broken links to graphics about grounding, I found a few still work:

Notice the earth and chassis grounds above do not agree with those below.

Signal Common is like when you have a charge pump that swings the signal voltage +9v down to -9v, with Signal Common being at 0v — that's a swing of 18v so you have much higher headroom than if your signal is just swing from Power Ground to +9v, that's only a total swing of 9v, so nowhere near the headroom of +9v/-9v.

Here's another way to look at it:
The crap-low octane [EDIT: 87 octane] currently availabe that goes into today's daily-driver is NOT good for an ol' '60s/'70s muscle car that thirsts for 102-leaded-octane in its heyday with 98 octane being widely available — right now the highest octane I can find is 94, and only available at ABC Gas-Co, but NOT at all ABC Gas-Co's filling stations, only at a select FEW. Some cars are converted to running on LPG; go to the drag-strip and you might find racers running AvGas or serious racers running on nitro-methane... SO, there are various kinds of gas, but it's all gas. Right?

There are various types of ground, but it's all earth, ehr, ground.

Hope that helps a little.


Now seek out as many different graphic representations of variable-resistors, pots, potentiometers, rheostats, voltage-dividers you can find ...

Learning to read schematics is fun!

 

[Little Muff]

Some pedals do run on bipolar power supplies, usually internally generated from the 9V input by a charge pump circuit.

Standard single-polarity 9V powered circuits typically shift the idle point of opamp stages to around 4.5V to allow for the positive and negative swing of the audio signal around the 4.5V "virtual ground" point without clipping.

True! That part was tricky for me to deal with. I’m coming from eurorack DIY, built over 80 modules already, and even still rookie, the standard +12v / GND / -12v was easier to understand from the beginning.

Signal Common is like when you have a charge pump that swings the signal voltage +9v down to -9v, with Signal Common being at 0v — that's a swing of 18v so you have much higher headroom than if your signal is just swing from Power Ground to +9v, that's only a total swing of 9v, so nowhere near the headroom of +9v/-9v.

Oh, thoses graphics are interesting enough..
Well, Signal Common is called GND in eurorack schematics.

I noticed recently while experimenting with a Maxon OD-820 circuit that as Robert says the ICs run on a +9v/-9V arrangement via a charge pump. Only the ICs use the -9V as "ground", and the rest of the circuit used standard ground. I guess in this case ground is acting like VREF would in a standard 9V circuit.

Not in this one! Kevin uses something like VB and VC for those virtual grounds. Seems like..

I might’ve found out what’s going on here. From having a look to the Theseus schematics in which there are 3 grounds: BYP_GND, GND and GND2, I think they must be isolated in the PCB, although they’re all connected when PCBs are wired. But probably it’s a designer habit to help debugging and clarity.

In the case of the schematics of Xenotron I firstly mentioned, my guess is that, as @giovanni and @Robert pointed, those 2 GND C39 and C40 are connected to might have been left so accidentally, and they should be BYP_GND as they’re in the Bypass PCB.

Thanks all for your help!

 

[Robert]

I might’ve found out what’s going on here. From having a look to the Theseus schematics in which there are 3 grounds: BYP_GND, GND and GND2, I think they must be isolated in the PCB, although they’re all connected when PCBs are wired.

That's the star grounding I mentioned.

 

[HamishR]

I hope star grounding works in pedals because it sucks in amps! Grounding seems a lot easier in general in pedals than in amps, and I would guess that's because of the vastly lower currents involved.