GND, GND2, BY-GND?

[matopotato]

I saw in the schematics of two dual drive pedals that there were 2 or even 3 references to ground. I thought one fundamental aspect was to avoid ground loops by having them all meet in a single point.
In these examples from Aion FX:
Gladiator
https://aionfx.com/app/files/docs/gladiator_documentation.pdf there are 2 grounds GND a d GND2
and Theseus https://aionfx.com/app/files/docs/theseus_documentation.pdf there are 3 grounds: GND, GND2, BY-GND.

This is a bit confusing. Tried to read up a bit but felt more driven towards single ground. And I am quite convinced Aion FX know what they are doing.

[Aph]

One example: If I have a circuit with an LFO, I always isolate the LFO circuitry ground from the audio ground and tie both directly to the negative connection on the DC input jack.

[GibsonGM]

I'd suspect it's just their way of establishing what are called "Stars" in a "star grounding" plan. You can look up star grounding w/search engine.  That way you can have the real tech explanation since mine tend to be a bit layman and less about theory, more about practicality.

Basically, you separate discrete sections of a complete circuit based on their power requirements.  Each section then has its own ground point.  These multiple gnd points all connect back to 'home ground', if you will...like Aph said.  In the end there is only ONE.  You separate the LFO from audio ground points because you'll have pulses of current flowing on the LFO ground, which may 'get into' the audio path and cause thumps and so on.   Same is true for keeping grounds of input sections of high gain circuits from later ones, because the low level input signal is susceptible to coupling noise.

It's a good practice, and not hard to do at all once you identify where you may need to do so, and have built a few circuits that have good star grounding.  Sometimes it's overkill, but when you need it, you'll be glad you did it (or may never know it's what's making your circuit successful, ha ha).

[matopotato]

Thanks both @Aph and @GibsonGM. Will study some more.

[GibsonGM]

Merlin B from this forum put together what I feel is a concise and appropriate 'talk' on this issue, here:  http://www.valvewizard.co.uk/Grounding.html
Figure 15.14 seems to clearly show 'the idea' here.

I took a look at some info that comes up in a search engine, and it's mostly for PCB design, little about offboard stuff as we are always doing, so Merlin's article is a great intro to the concepts involved.  Basically, it's just keeping those grounds 'clean' and trying to separate/mitigate those that may have appreciable currents flowing on them from circuits that don't.   His page is about amplifiers, but same ideas apply to stomps.

[ElectricDruid]

My way of describing this would be to say that it's a side effect of the way that PCB packages work.

On the package I use (and others will be similar) any tracks that are joined together become...well, all part of one thing! So it's very difficult to say to the PCB package "Yeah, but I only want these joined back at the power input" or "back at the input jack" or whatever. Consequently, the way to deal with this is to set up different ground paths within the schematic as actual different grounds (hence with different *names*) and then manually connect them either off-board or at the input jack or whatever.

I was forced to do this on the DigiDelay pedal I designed, where I wanted separate ground planes for the digital and analog areas. If I told the PCB package that these two areas were eventually to be connected together, it would simply have flooded the whole area with one ground plane and completely screwed up what I was trying to achieve, so I had two different ground planes, and then added a jumper to connect them on the PCB, close to where the power ground came in.

This page of the schematic shows the details:

https://electricdruid.net/wp-content/uploads/2016/10/DigiDelay-Schematic-Pg3.jpg

There's both Gnd and GndDigital on the schematic, and J11 and J12 which were the jumper points to link the two. I did it on the PCB close to where the power ground came in, but it could easily have been off board too.

(If you want/need to see the rest of it, it's here: https://electricdruid.net/diy-digital-delay/ )

[matopotato]

Thanks! Quite comprehensive. On much more than grounding strategies.