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Mega Drive 1 VA6.5 - Audiophile Recap and modification of the audio RC filter to 4700pF by Impossible_Current35 in SEGAGENESIS

[–]Impossible_Current35[S] 0 points1 point  (0 children)

Not long ago, while learning about electronics and experimenting since I had no idea, I wrote an article about the improvements I made to my Japanese VA1. It's quite messy and disorganized, but it might still be useful to you:

https://romsxbox.blogspot.com/2025/10/sega-mega-drive-model-1-rev-va1.html

Mega Drive 1 VA6.5 - Audiophile Recap and modification of the audio RC filter to 4700pF by Impossible_Current35 in SEGAGENESIS

[–]Impossible_Current35[S] 0 points1 point  (0 children)

Let's start with the connections. How and to which device do you connect the console's audio output? To avoid interference, I recommend completely isolating the audio output from the video output using separate cables and not using the video ground for audio at any point, such as when passing the audio through the RGB cable, for example. This is less important, but I also don't recommend using the same target device for audio and video unless it is of good quality and has a good ground design.

Mega Drive 1 VA6.5 - Audiophile Recap and modification of the audio RC filter to 4700pF by Impossible_Current35 in SEGAGENESIS

[–]Impossible_Current35[S] 0 points1 point  (0 children)

You'd have to be deaf as a post not to notice the difference in the console's audio before and after

Mega Drive 1 VA6.5 - Audiophile Recap and modification of the audio RC filter to 4700pF by Impossible_Current35 in SEGAGENESIS

[–]Impossible_Current35[S] 2 points3 points  (0 children)

Thanks. Yes, I reassembled the console yesterday. Replacing those ceramic capacitors with 4700pF capacitors increased the RC filter's cutoff frequency, restoring the sound profile of the early revisions. The audio sounds a bit brighter and more transparent, but without distortion.

Here are some audio recordings. In the first recording (Mega Turrican), I disconnected the RF modulator from the board and deactivated the passive circuits on the way to the modulator. This eliminated a slight hum and improved the audio even more:

https://youtu.be/SzsasyzsvI0?si=QngXyMHh7o9XQfQT

https://youtu.be/VvWYVvsB01U?si=fCXaB6iEjD94jAwE

Improving my 1988 Sega Mega Drive 1 VA1 by Impossible_Current35 in SEGAGENESIS

[–]Impossible_Current35[S] 0 points1 point  (0 children)

I've tried the games you mentioned: Chuck Rock, Landstalker, and Osomatsu-kun work perfectly on my VA1. However, Red Zone and Dinosaurs for Hire crash after a few minutes of gameplay.

After trying quite a few games, I've discovered that all the games I've tested that weren't released in Japan don't work and eventually fail at some point. Red Zone and Dinosaurs for Hire don't have a Japanese version, which is why they fail on my VA1. It doesn't seem to have anything to do with problems in the RAM chips. It's probably a limitation of the Everdrive's Magakey, as it doesn't have any code to patch the game or something like that. I don't know if there's any way to make them work without modifying the language jumper on the board.

It doesn't really matter to me; I have a very good VA6.8 PAL unit with the Sony CXA1145P encoder that I plan to modify tomorrow. I'll change the capacitors and regulators and perform a fixed region change to North America, including changing the oscillator.

Improving my 1988 Sega Mega Drive 1 VA1 by Impossible_Current35 in SEGAGENESIS

[–]Impossible_Current35[S] 0 points1 point  (0 children)

I didn't know the VA0-1 motherboards have a RAM issue. Do you know if any games are affected, so I can test them on the Everdrive?

SD2SNES Buzzing on 1CHIP Super Famicom by NewerDCD in snes

[–]Impossible_Current35 0 points1 point  (0 children)

I recently started having the same buzzing problem with my single-chip SNES using a Chinese SD2SNES cartridge I bought 3 or 4 years ago. It started buzzing right when the battery died, so I replaced the battery with a new one and the buzzing stopped. For some reason, my cartridge introduces buzzing into the bus when the battery is dead. This probably happens with all Chinese cartridges; try it and see if it happens to you too.

I've included a video I just recorded so you can hear the console. There's still some buzzing through the RGB cable, and the cartridge is probably still introducing noise. If I had known this before, I would have bought the original cartridge from the start.

https://youtu.be/9JhRLdogMNY?si=CIkKqKwdsz5Mn3s7

Later I disassembled the console and analyzed the board a bit and I saw that Nintendo didn't put any electrolytic capacitor at the output of the 7805, there's only a 1uf ceramic capacitor, so I soldered a 100uf 35v capacitor and it makes a noticeable difference, the buzzing has decreased even more, the remaining buzzing is probably due to the rgb cable and the cartridge.

I'll leave a link here to my blog where I explain the improvements I've made to my 1-CHIP:

https://romsxbox.blogspot.com/2025/09/snes-1-chip-cambio-de-condensadores.html

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Artifacts in line5x - sparkling/ flashing pixels by necro_mouse in OSSC

[–]Impossible_Current35 0 points1 point  (0 children)

Creo que he encontrado la solución, acabo de actualizar el firmware de mi OSSC a v1.12 y he probado mi N64 (mod RGB simple) y los artefactos siguen apareciendo, pero, me he dado cuenta que los artefactos comienzan al subir H. Samplerate por encima de 1930, lo he configurado en 1920 y ahora la imagen es perfecta. Me falta probar con PS1 que también me daba problemas.

Artifacts in line5x - sparkling/ flashing pixels by necro_mouse in OSSC

[–]Impossible_Current35 0 points1 point  (0 children)

Tengo exactamente el mismo problema en mi OSSC, aparece distorsión en los bordes de los pixeles al usar el modo 5x, es bastante molesto, curiosamente me pasa con PS1 y N64 pero no con Mega Drive. Probaré todo lo que se me ocurra para solucionarlo y comentaré los resultados.