License: CERN-OHL-S-2.0

Original author and credits: Jaakko Oranen

https://codeberg.org/CBMretro/PC_Engine_RGB_and_Audio_Amp

https://cbmretro.fi/product/pc-engine-rgb-and-audio-amp/

Images and code made by Jaakko Oranen

This mod swaps out the RF modulator in the original white model PC Engine with a Mega Drive 2 style Mini-Din-9 RGB-video and audio out.

The project does consist of 3 boards. This is PCE_Amp PCB.

For the other two PCBs, please click on the two links below to view and order:

PCE_DIN_Adapter PCB: https://www.pcbway.com/project/shareproject/PCE_DIN_Adapter_PC_Engine_RGB_and_Audio_Amp_95ad74a1.html

PCE_Expansion_Adapter PCB: https://www.pcbway.com/project/shareproject/PCE_Expansion_Adapter_PC_Engine_RGB_and_Audio_Amp_11a3d79d.html

The amp board features Voultar's THS7374-based RGB amp circuit and Mobius' audio amp circuit, both integrated onto the same board.

Stereo audio from the HuC6280 chip is directly routed to the PCE expansion port without amplification, resulting in very low default volume. To address this, the amp board incorporates a simple LMV358 opamp amplification circuit designed by Mobius, boosting the audio to line level.

Included with the mod is an adapter board for installing the Mini-Din-9 connector onto the PC Engine, along with an adapter for the PC Engine expansion port, facilitating easy wiring of the amp.

Configuration:

The amp can be configured via solder jumpers to accommodate different types of Mini-Din-9 to RGB SCART cables.

Many inexpensive, unshielded Mega Drive 2 SCART cables available on platforms like eBay and Aliexpress come equipped with 75-ohm resistors and 220 uF capacitors on the RGB and Sync lines. The amp board can be set up to bypass its own onboard resistors and capacitors if the cable already includes them.

However, there's a caveat when using these cheap MD2 SCART cables: The 5V from the Mini-Din-9 is connected to SCART pin 8, which controls Status & Aspect Ratio. Voltage levels for this function are:

• 0-2V for off
• +5-8V for on/16:9
• +9.5-12V for on/4:3

It's crucial to set the LPF (Low Pass Filter) either to disabled or enabled; leaving it floating is not recommended. The THS7374 video amplifier includes a low pass filter designed to eliminate high-frequency noise from the output. For instance, my PC Engine displays some noise visible on flat dark areas on a few CRTs, which the LPF effectively removes, so I always keep it on.

If you notice jail bars on the image you should do a jail bar fix explained here https://wiki.console5.com/wiki/Hu6260#Jailbar_.2F_Vertical_Bar_Fix

This mod has been tested on PC-E Duo and Duo RX as well (an unique board with RGB video circuit installed, no need of AUDIO amp and spare boards).