==== Atari 2600 S-video / Audio Mod ====

This page contains the same mod as the Atari 2600 Faq. With the exception of the CD4050 buffer. As you can see at this [[http://www.cheeptech.com/2600mods/2600mods.html|mod comparison site]], the mod actually looks a bit better without the chip.

== Luma Decoder ==

The TIA chip outputs the Luma signal in digital form and you have to perform a simple digital to analog conversion with the circuit below. As the sync appears on the luma line in s-video, the synch signal is mixed in here as well.

{{av:2600_luma_decoder_t.gif}}

== Luma Impedance Matching Amp ==

A [[http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/npncc.html#c2|common-collector amplifier]] is used to drop the output to the correct 75 ohm impedance. 

{{av:luma_amp_final.gif}}

== Chroma Impedance Matching Amp ==

{{av:2600_chroma_amp.gif}}

== Audio ==

{{av:2600_audio.gif}}

=== Where To Find the Signals ===

{{av:2600_tia_sources.jpg}}


The 2600 FAQ specifies the Chroma and Audio sources differently. You can find the audio at the junction of R206/C208, but this point is wired directly to pins 12 and 13 on the TIA chip.

The Chroma is a bit more complicated. The FAQ says to pull the Chroma signal at the junction of C210 and R210. In this case there is some circuitry between pin 9 (TIA Chroma) and C210/R210.

{{av:2600_chroma_extra_corrected.gif}}

So you can get chroma at C210/R210 or connect directly to TIA pin 9 and add a capacitor and pullup resistor to the Chroma circuit above.

== Parts ==

  * 100uF Capacitor
  * 10uF Capacitor
  * 10 ohm
  * 75 ohm (4)
  * 750 ohm
  * 1.6 kohm
  * 4.7 kohm
  * 9.1 kohm
  * 18  kohm
  * 1N4148 low power silicon diode (CR1)
  * 2N3904 or equivalent transistor (2)
  * S-Video Jack
  * RCA Jack
  * If connecting directly to pin 9
    * 47pF Capacitor (diagram shows 27pF)
    * 6.8 kohm resistor (diagram shows 1K)