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Aug 12, 2019
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I'm messing around with some different circuit options for line level conversion and was wondering if someone had good examples of common boards that don't have shared GND tied to Audio GND, meaning that audio GND has some amount of Bias.

I know some Mahjong games of mine does (Taisen Hot Gimimck games is one example), but must be some other common non-jong ones?

If I understand things correctly, certain Amp circuits (like Bridge Amplifiers) does this, but dont have a good list of example hardware doing it.
By audio ground, do you mean the speaker- connection?
Do you plan to tap signals from say the JAMMA edge?
In that case many games have the SPK- pin not connected to ground. I actually thought it was the norm for it NOT to be connected to ground but rather the audio- output of the amplifier.
Examples of games I played recently: Gunbird, Pit Fighter, Wrestlefest, etc.
if I had to guess there are VASTLY more games with Audio ground being Speaker - and NOT tied to PSU ground than there are games where it is tied to PSU ground.*

Tatio platforms like F3, G-Net, FX-1A, and FX-1B actually use Speaker - to produce stereo sound on their E29 (and possibly other) cabs
on that hardware Speaker+ is Left channel + and Speaker - is Right Channel -, and then the speakers tie Left - and Right + to ground, allowing the boards to produce Mono sound on normal JAMMA cabs and stereo Sound on the E29.

The Psikyo SH2 is one of the few platforms that has a strict adherence to the JAMMA standard in that it has speaker - and speaker + on the correct pins while also producing mono line-level audio on the designated JAMMA pins (which nearly all other boards leave empty)

Midway Y and T units have a really clean connector output directly from the audio board for speaker + and speaker - if you're looking for an easy platform to play around with, without having to tap the JAMMA Edge.

*I say this because of the E29 configuration I mentioned above, there is a jumper in the harness to convert from this stereo mode to normal mono speaker mode for PCBs that have speaker - tied to PSU ground (because otherwise audio will only come out of half the speakers). I can count on one hand the number of games where I've had to swap this jumper and most of them were bootlegs.
The most common one for using gnd as speaker - has got to be multi slot MVS boards. Pin 10 is R+, pin L is L+, and gnd is used for both speaker -. Pin 11 is listed as mono audio with no accompanying -, so that must use gnd for - too.