Sony RGB Encoder
S-Video Buffer Circuit (2SC1815 Based)
This is the classic, simple circuit that can be used to obtain a Y/C component signal from the CXA1145. Build this circuit twice: once for the Luma signal and once for the Chroma signal.
I've changed out the 75/33Ω resistors in the original design for potentiometers. A pot range of 500-2kΩ is typically sufficient. This will allow you to better adjust the signal for your monitor and reduce the vertical bar effect created by an excessively strong chroma.
- Parts List (Build twice - once for luma, once for chroma):
- R1: 10k
- R2: 10k
- R3: 110k
- R4: 110k
- C1: 100uF, 6.3v (or higher) electrolytic
- C2: .1uf ceramic
- T1: 2SC1815*
- VR1: 500Ω - 2kΩ Potentiometer
*An NTE85 is frequently cited as the transistor for this circuit. NTE typically makes substitute parts, not original parts. NTE85 is the replacement for the 2SC1815, except the NTE part is about 20 times the cost.
S-Video & Composite A/V Circuit (C945 Based)
This newer circuit reduces the component count of the 1815 circuit and is reported to have better compatibility with modern HDTVs.
- Parts List:
- C1: 220uF, 6.3v electrolytic (chroma)
- C2: 220uF, 6.3v electrolytic (composite video)
- C3: 10uF, 6.3v electrolytic (mono audio)
- T1: C945 (2SC945, KSC945, etc)
- VR1: 500Ω - 2kΩ Potentiometer (luma)
- VR2: 500Ω - 2kΩ Potentiometer (chroma)
- VR3: 500Ω - 2kΩ Potentiometer (composite)
Try to connect your +5 and GND as closely as possible to the CXA1145 to avoid ground loops.
In the provided schematic, analog ground (Pin 1 & 24) as well as +5 (Pin 12) are shown.
- For the variable resistors, common starting values are:
- VR1: 33Ω
- VR2: 75Ω
- VR3: 75Ω
By using potentiometers instead of fixed resistors, you can tune the device to look best on your display.
The connection for monaural audio is shown. Stereo audio is system dependent.