Sunday, August 27, 2017

DIY RGB Adapter for Sony CRTs with a 34-Pin Multi Input

RGB from the Genesis on the KV-25XBR via RGB Multi Input

While SCART inputs never showed up on CRTs on American soil, there are still a handful of sets out there that natively support 15kHz analog RGB. Sony in particular released several models in the 80s that sport a 34-pin RGB Multi Input connector. Models that feature the connector include:

  • KV-1311CR
  • KX-1901A / KX-2501A
  • KV-20XBR / KV-25XBR
  • KX-27PS1

The rear panel of the Sony KV-25XBR with an RGB Multi Input

While finding the OEM cable is now pretty much impossible (Sony Part Number PX-34), the port is actually the same size and shape as a standard IDC floppy connector. With just a little knowledge of the pinout of the port we can easily wire up an adapter that will convert from a standard SCART cable into the 34-pin input.

The back of the manual for these sets contains all the needed information about the pins, except for how they're numbered on the connector. Luckily, DanAdamKOF from the Neo-Geo forums was able to figure it out, and I've added it to the image above. There's still one problem left though - Sony's pin numbering isn't the same as standard IDC cables like the floppy! In order to match our SCART lines to the floppy, we'll have to translate it.

Start by cutting your floppy cable in half, and then use the diagram above to figure out which side is pin 1. To find the appropriate wire, just start at the side with pin 1 and count down the wires. I found it easiest to separate the wires using a hobby knife, and then used a lighter to strip the ends. Once you've identified all the wires and prepped them, you're ready to solder it up.

  • Sync - Floppy 9 to SCART 20
  • Sync (Ground) - Floppy 10 to SCART 18
  • Blue - Floppy 15 to SCART 7
  • Blue (Ground) - Floppy 16 to SCART 5
  • Green - Floppy 17 to SCART 11 
  • Green (Ground) - Floppy 18 to SCART 9
  • Red - Floppy 19 to SCART 15
  • Red (Ground) - Floppy 20 to SCART 13
  • Audio Left - Floppy 21 to SCART 6
  • Audio Left (Ground) - Floppy 22 to SCART 4
  • Audio Right - Floppy 29 to SCART 2
  • Audio Right (Ground) - Floppy 30 to SCART 4
  • Audio Select - Floppy 34 to Floppy 1

I've seen people recommending caps, sync strippers and all kinds of other things online, but please know you don't need any of that. The sync input on the KV-25XBR will take anything you throw at it: Composite Video, Csync, and Sync on Luma. Even my GroovyMAME machine with a custom sync circuit works great on it. The one special thing to note is that if you want audio, you will need to connect pin 34 (5V) of your floppy to pin 1 (Audio Select). Other than that, everything just works in my experience.

It's not the most elegant looking adapter, but it works!

A huge thanks again to DanAdamKOF for the help getting this working. I would probably still be scratching my head to this day if it weren't for him. Hopefully this small guide has helped dispell the myths about these ports and shows just how easy it is to wire up something for them. Happy gaming!

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Wednesday, March 22, 2017

Wavebeam NES Palette

The many different colors of Super Mario Bros. (NTSC Hardware, FCEUX, Nestopia, Wavebeam)
If you grew up playing the NES as much as I did, then you probably have the 50 some colors of the system forever burned into your memory. The interesting thing though is that the colors you experienced probably weren't the same as someone else. Many have run into this problem after loading up their favorite games on an emulator or the NESRGB and realizing how different the games look from their memory. So what exactly is going on?

While hue and chroma aren't tracked by NTSC and can cause TV sets to look different if not properly calibrated, it seems the TV's NTSC decoder is the main culprit for why no one can agree on what the colors are supposed to look like. TV manufacturers wanted their sets to stand out in the showroom from the competition, so they started sweetening and tweaking the NTSC signal when decoding it to make it more colorful and vibrant. Every manufacturer used different chips with different formulas, and to make things worse, not even all TVs from the same manufacturer treat the signal the same. (Note: see the Sony CXA2025AS palette in the comparison images at the bottom. It was reverse engineered from a consumer Sony IC and shows what this processing can do to the image) So because of this it seems impossible to ever come up with a single NES palette that everyone can agree on.

For me, this all started after getting an NESRGB. I wasn't happy with the colors on its stock palettes so I started researching more about it. I began to learn of the great work people like FirebrandX were doing to create very accurate palettes based off the raw composite signal coming out of the system. My hope was that if I fed their raw capture palettes into my RGB CRTs I'd have something identical to how an original NES displayed on it. Unfortunately, it looked the same as the raw capture since RGB inputs skip the TV's NTSC decoder.

I decided then to create my own palette that looked great on CRTs and brought back my nostalgic memories. I do not claim that it's accurate in any way to a single CRT or mathematical formula or even Nintendo's intentions. It's only based off my preference and the many CRTs I've owned. The palette was created on a calibrated IPS screen and then tested on several CRTs. I went through dozens and dozens of games, cross-checking eight different palettes for consistency and tweaking the colors to hit the sweet spot between authentic and vibrant. While the palette is meant for display on a CRT, I think it works great on digital displays as well.

View the full comparison

Download the .pal

Download the NESRGB Firmware Pack

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