Detailed mode of operation

Inputs

All input is via a single HD15-F connector, labeled “RGB INPUT”.  It defaults to the “Arcade RGB” channel and the “TTL Sync” channel.   This is the setting to use for Jamma games.

The 75-Ohm and Scart sync channel can be selected by editing the .ini file that will be created when you start the scaler with a micro-sd card inserted.  Be aware that if your ‘scart system’ is modded, it may already output a sync signal that is compatible with the TTL channel, so try that first.

The TTL sync channel has an additional anti-jitter stage that is not present on the Scart sync channel.

Sync is forwarded to the sync processor which cleans the incoming sync, and separates it into H/V if the input signal is C-sync. 

For RGB, the signal is terminated with either 75-ohm or 900-ohm depending on which channel is active, the Arcade channel also attenuates the signal.

From input to output

The system goes through different stages before it can output an image, the different stages are described below.

Stage 1

The system will be in stage 1 when no sync activity is detected.  In stage 1, most of the circuitry is either off or in stand-by and the system consumes very little power.  Once sync activity is detected, the FPGA is activated. 

The scaler will illuminate the red LED while in stage 1.

Stage 1.5

If the sync is higher than about 24 kHz,  the bypass function will be activated – this can be overridden in the .ini file.  If sync is lost or goes below threshold, it will go back to stage 1.

Stage 2

The FPGA analyzes the signals from the sync processor, and once stable, move on to stage 3.  If it fails to make sense of the incoming sync, it goes back to stage 1.

The scaler will blink the green LED while in stage 2.

Stage 3

ADC is powered up, and the FPGA analyses both sync and RGB from ADC.  Individual analog gain for R,G & B will be adjusted to achieve maximum use of the ADC’s headroom while also ensuring proper white balance (RGB gain match). 

If the output from the ADC is unstable, it will fall back to stage 2.

The scaler will blink the blue LED while in stage 3.  

Stage 4

Analog pre-ADC gain is re-adjustet after 8 seconds, this interval can be changed in the .ini file.  Video is line doubled, and the output section of the scaler is powered up.  

To protect the ADC, gain will be re-adjusted in case there is clipping – i.e overload on the ADC input.

If sync is lost, it will revert back to stage 2.

If sync goes above scaling range, e.g. to 31kHz, it will quickly jump to stage 1.

The scaler will have red, green and blue LEDs illuminated while in stage 4.

 

Connect a source

By default, the Retro Scaler A1 is configured for arcade games.  If you use it for something else, you need to make sure that RGB and SYNC is configured correctly.  You can change this by editing the [input] section of the ‘scalera1.ini’ file that will be created if you have an sd card inserted when powering up the scaler:

[input]
rgb=arcade
sync=TTL

One important distinction to make is that the Retro Scaler only accepts negative sync – which is the norm for pretty much everything relevant, except retro x86 PC’s where it’s a bit of a mix.

RGB input level

This one is easy, set to arcade for arcade boards and 75-ohm for everything else.

System	Setting	Note
Arcade PCB’s	arcade	0 – 4Vpp video level, 1000 Ohm impedance
Everything else	75-ohm	0 – 1Vpp video level, 75 Ohm impedance

Warning: feeding the scaler arcade level RGB signals while configured for 75-ohm will trigger constant brightness adjustments at best, and may at worst damage the scaler.

SYNC input level

This one is a little more tricky.  For ‘plain’ sync, set it to TTL, this is your basic digital sync that goes between 0 and 5V.  If you have no luck with TTL you can try the ‘scart’ setting – this will take most forms of sync that is not plain TTL.  If your system is ‘RGB modded’, there is a fair chance it outputs sync that works with the TTL setting, even if it’s designed to work with scart, so try TTL first.

System	Setting
Arcade PCB’s and most other systems	TTL
SCART sync*	scart

The TTL setting has additional jitter-reducing circuitry, but does not work with odd sync signals.  

Warning: feeding the scaler TTL level sync while configured for scart sync for a prolonged time may damage the scaler

A note for HAS users

If you’re using the excellent super-gun HAS, https://homearcadesystem.wordpress.com/, configure the A1 to use:

[input]
rgb=75-ohm
sync=TTL

The HAS always attenuate and re-amplify the RGB to 75-ohm, so you may experience a dark image if you use the A1’s default rgb=arcade setting.

On the HAS, verify that sync level is set to TTL with no processing if possible.   The capabilities in this respect varies a bit between the different HAS versions.  In order of preference, use either:

• Unprocessed, or
• Buffered

The “Regenerated” mode on the HAS will work in most cases, but can potentially cause issues with some games when used with the A1.

Making an input cable for the Retro Scaler A1

To make life a little easier, I highly recommend getting one of these off ebay, search for ‘vga male breakout shell’.

You don’t need to connect all the GND pins, but connect the ones you have in your cable.

The pinout of the caler is:

1. Red
2. Green
3. Blue
4. not connected
5. GND
6. GND
7. GND
8. GND
9. not connected
10. GND
11. not connected
12. not connected
13. HSYNC and/or CSYNC
14. VSYNC
15. not connected

The shield of the input port of the scaler is by default not connected, as there is some debate if this is smart/safe or not.  There is a solder jumper on the bottom side of the PCB you can close if you know what you’re doing and feel this is necessary.

Introduction

The Retro Scaler A1 will upscale the RGB video signals from your

• Arcade Games
• Retro Consoles
• Retro computers

AFAIK, it’s the first and only purpose built Arcade scaler.

What it does

It line-doubles the input signal, effectively transforming a 15kHz signal found in Arcade Games and older systems into a 31kHz VGA signal.  It’s perfect for playing arcade games on a 31kHz VGA (or higher) CRT monitor like the European Sega Naomi Universal.  It’s also great if you want to build a ‘super-gun’, or user older consoles/computers with a a PC VGA CRT.  PC VGA monitors generally have a fantastic picture, but doesn’t do 15kHz – until now.

Lastly, while not specifically built for it, it’s a great alternative to get Jamma in your Vewlix cabinet.  Taito used to make a scaler similar to the Retro Scaler A1.  Subjectively, the Retro Scaler A1 has better image quality and is objectively easier to use – no need to dial in sync settings for different games.

Features 

• Console/Computer AND Arcade/Jamma level RGB input
• Scart type sync input
• TTL/Jamma/Computer sync input
• c-sync and h/v sync, only negative – most systems use negative sync.
• 5 levels of scan-lines, from none to heavy.
• Interlaced NTSC 480i and PAL 576i support
• Automatic analog bypass of RGB – it does not touch the video signals from 31K sources
• Dedicated sync stage to deal with tricky systems
• Sync Analytics with automatic configuration, no user settings needed
• Analog pre-adc gain stage with 512 steps to accommodate non-standard signal strength
• 30 bit high quality ADC video input, 30 bit high quality DAC video output

Disclaimer/Warning

A lot of effort has gone into making the Retro Scaler A1 easy to use and compatible with older systems – with it’s sync analyzing features it is likely best-in-class.  However, it is impossible to test all systems ever made and some systems may have quirks or oddities that will not play nice with the Retro Scaler A1.  I will do my best to fix any issues, but sometimes the nature of the quirk will make a fix impossible. Please have a look at the list of tested sources.  If you have problems with a particular system and it’s not listed, please let me know!

Additional note on using with LCD monitors

LCD monitors are less forgiving when it comes to vertical refresh rates, which the Retro Scaler does not alter.  It can also be less predictable how certain monitor will deal with arcade resolutions with low vertical refresh and more vertical lines than ‘normal’, e.g. games like R-Type and Mortal Kombat.  The Retro Scaler will not crop lines, but your LCD may not display them.