AV-Driver for Arcade RGB 'Supergun'

A device for connecting an JAMMA arcade game board to an TV is generally known as a Supergun. It contains a power supply, arcade controls (or other controller interface), and some electronics to adapt the audio/video signals to television standards. The video signal (usually) has the same timing as NTSC video, but the electrical properties are different to a standard TV/video monitor. It's an analog signal with TTL level amplitude (3-5 Vpp). This makes the video circuit simpler for both the game board and monitor. The Game board has an audio amplifier built in which can drive a speaker directly. The Supergun will either have a audio attenuator or just a speaker inside.

An RGB Supergun would typically have a audio/video attenuation circuit like this inside.

typical supergun wiring
This circuit has three separate potentiometers connected, one for each colour signal. This forms a voltage divider with the termination resistor inside the TV set. It usually works acceptably but there are some problems.

The audio part is a fairly ordinary speaker to line level attenuator. There is a stereo/mono switch for Neo Geo boards. For normal monaural JAMMA boards the speaker- pin is not connected (this isn't ground). The performance of an audio attenuator circuit like this is usually fine.

Here's another circuit for an RGB Supergun. This time using the AV-Driver and a 10k linear multi-gang potentiometer.

supergun with av-driver
Now there is just one control for all three colours together, making it easier to adjust. The purpose of R1 is only to protect the audio amplifier on the game PCB in case somebody changes the position of SW1 with the power on.

The load on the arcade game's video signal is very light, so it may be installed into an existing arcade machine to provide a standard 75 ohm RGB video output without having any impact on the internal monitor. The cable between the AV Driver and the TV set may be long if it's built from 75 ohm coax.

Multi-gang Potentiometer Calibration

It is an unfortunate fact that multi-gang potentiometers are usually not matched between each gang. If the gangs are chosen arbitrarily, it could lead to a gain error of up to 20% between colour channels which is unacceptable. The solution is to use a six gang potentiometer, test all six gangs, and pick the three which match the closest. This way it's possible to get a less than 5% error over the entire range.

Here's the test procedure. It requires a 5V power supply (doesn't have to be accurate, just stable) and a multimeter.

Start of test
Power supply voltage

1V 2V 3V 4V
Gang A (knob end)

Gang B

Gang C

Gang D

Gang E

Gang F

Test result example.

1V 2V 3V 4V
Gang A (knob end)
Gang B 1.09
Gang C 1.02
Gang D 0.94
Gang E 1.03
Gang F 1.00

AV-Driver Jumper Setting
Closed = 1
Open = 0

Gain value
43210 (jumpers)
1.0 00000

765 (jumpers)
no attenuation 001

Level for Sync Input (IT)
TTL level 1

Level for Sync Output (OT) 
TTL level 0
75 ohm (recommended) 1
The sync output type depends on your monitor.

Power On Audio Pop Suppression 
Enabled 0

Change Log
9/6/2016 - Page created.