Finally I have good news to report on the all-in-one OPL Studio! 

This design is like a night and day difference compared to previous prototypes. The audio is clear, the line out has a higher output level and the speaker out has a much, much lower noise floor. There is no more noise on the line out and on the speaker out there is only very slight noise from the LCD if you're listening through headphones and the OPLs are silent.

There is light at the end of this very long tunnel now!

Mistakes With The LCD

Is it all good? No! Of course I did find more mistakes. The biggest one being the LCD connector. At one point during the design I had rotated the footprint, but I fell into 'a trap for young players' and I forgot to also reverse the order of the pins! So the LCD was dead. After realizing this I was a bit hesitant about fixing it, because it was tricky enough to solder the connector the first time and desoldering it and soldering it back after rotating was a good challenge! Also because there was no room. I had to solder the connector back at an angle and let it rest on some resistors and capacitors. To my surprise I managed to do it! 

The LCD showed some signs of life, but still no clear image. It only showed a garbled mess of gray pixels. So I was sure that I messed up when soldering the connector. But to my surprise, when I added a connector for one of the old LCD modules, it was showing the same mess of pixels. This confused me and took me a while to figure out. It turned out to be the reset signal. On the kit design I had not used it, but for the all-in-ones I intended to use it. Turns out that I had not given the LCD controller enough time to properly reset. Problem solved after a simple software fix. Even the touch screen worked on the first try.

The brightness is still a bit of an issue, because it doesn't work as it did on the old design. The screen is very dim, so that's still something I need to fix.

Other Small and Easy Fixes

There are other small things that need fixing. Transistor footprints that are not quite right, the MIDI status LED being too bright, the 3D printed LCD mount that needs some tweaking.

All small thing that I will be working on in the next two weeks and get another few PCB prototypes made to check what should be the production version of OPL Studio.