Sir Sull ATARI Comp Mod

The Sir Sull ATARI Comp Mod is a small through-hole board that gives your Atari a clean composite video output and a separate audio output, so you can skip the noisy RF modulator and plug straight into the composite input on a TV or upscaler.

Credit to the original: this mod is based on the simple DIY composite video mod by simon.plata, first posted on the AtariAge forums in November 2017: https://forums.atariage.com/topic/271678-simple-diy-composite-video-mod/#comments

The circuit is the two-stage transistor amplifier from that thread.

All credit for the original circuit goes to simon.plata and the AtariAge community.

How it works

A 2N3904 and 2N3906 form a two-stage video amplifier that boosts the console’s weak video signal to a proper composite level. A 5kΩ trimmer sets the brightness to suit your display. Audio runs through its own 10kΩ resistor to a separate output, so you get video and sound on separate wires ready for RCA jacks.

What’s new in this version

Compact 21 × 29.8 mm board so it fits easily inside the case

Inputs (V, G, 5V, A) at one end and outputs (VIDEO, GND, AUDIO) at the other, labelled on both sides

A ground pad sits between the video and 5V inputs, no 5V trace crosses the video path, and ground fill covers both sides for a cleaner picture

Every part value is printed on the board (18Ω, 3.3kΩ, 47pF…), so you can build it without the BOM

Transistor legs spaced 2.54 mm apart for easier soldering, with outlines showing which way each one faces

Wide 5.08 mm output pads for soldering the AV cable if desired

Parts

8 resistors, a 5kΩ trimmer, a 47pF capacitor, a 2N3904 and a 2N3906, plus an optional 4-pin header. The full BOM is included.

Build tips (from the original thread)

Disconnect or remove the RF modulator.

The circuit is DC-coupled, so tight-tolerance resistors work best, and testing your transistors for good gain helps.

Adjust the 5kΩ trimmer with the console running until brightness and colour look right.

The design targets NTSC. It has also been reported working on a PAL 2600A.

I have yet to test this on Atari 5200 and 7800 but i have used a 1 transiter set up on both and had amazing results with the correct install on both and when I get around to testing this mod I will update and add if it is compatible

This is a DIY hobby project, shared free for personal and educational use. It is provided “as is”, without warranty of any kind. Building and fitting this mod involves opening your console, soldering, and permanently modifying original hardware. That carries real risks, including damage to your console, TV or other equipment, voided warranties, and personal injury from soldering or electrical work.

By building or installing this mod, you accept full responsibility for your own work and any results. I (Sir Sull) am not responsible for any damage, loss or injury from using, building or installing this design, including damage from mistakes, faulty parts, or errors in these files or instructions.

Please check the board and your wiring before applying power, work carefully, and always unplug your console before working on it. If you’re not confident with soldering or electronics, ask someone experienced for help.