Atari ST OPL3 cart development prototype update

I’ve received alot of great feedback and I’ve introduced more changes to OPL3 cart prototype. So, this is the latest pcb design I will use for further development. It’s little smaller than last one. Bad news are that whole DAC->audio out circuit needs to be revised and rebuild (probably).

What have changed:

• Separated analog part from digital part of circuit.
• PCB has four layers now.
• All small SMD components are on one side.
• Reworked decoupling capacitor sections.
• Signals from digital domain to analog domain aren’t crossing with any other analog / digital signals.
• Replaced previously used op-amps with TL084 (as in 8-bit cartridge Yamari), to basically have something working and because previous design wasn’t suitable for +5V – 0V input.
• Fixed some issues with connection of YAC-512M and clock generator.
• Added pins to enable / disable analog circuit (DAC to mini jack output) and ease prototyping analog part e.g. have possiblity to plug in different DAC->audio circuit.
• Removed “Line in” for now. Can be solved later.
• TL084 use / integration will be temporal solution, because at this moment it can distort / cut input signal on output (case still needs to be more thoroughly investigated).
• Skipped splitting power / ground planes for now. Turns out that topic is quite controversial and hard to tell who is right or wrong without actually doing different pcb versions, which means more work and is more expensive and comparing them against each other. Working on it right now doesn’t make sense, because I don’t know if OPL3 interface with ST works at all. Current solution might be good enough for now.
• Added mounting holes, but they aren’t very relevant at this stage.
• Added missing GND fill ins on top and bottom layers
• Split TL084 into two TL082 ICs.
• Removed Line In (for now).
• Replaced all blind vias with normal through-hole vias. PCB manufacturers will either refuse to produce it (JIL PCB) or will significantly increase the price (PCB Way).
• Debug header changed to horizontal, vertical was obscured by computer case, when cartridge was connected.

Very likely this version will be sent to manufacturer (~5pcs).

When I confirm that cartridge<->opl3 interface works as intended I will be able to focus more on next things like: redesigning DAC->audio output circuit, make final pcb version (smaller, with SMD / SMT / SOP parts and without debug inputs), create case and labels.

When waiting for pcb’s, there will be plenty of time to write / finish drivers, so I will be able to test assembled cartridge rather quickly.