Neo Geo:Audio Bypass Mod (AES)

Unfortunately, motherboard revisions 3-3 and 3-4 had flaws in their audio circuits causing audio buzz through the headphone jack, requiring a mod to bring it back up to full quality. Luckily, FirebrandX made a detailed guide to fix the audio issues, which was used as the basis for this page.

All other revision AES consoles have good quality audio and only require that you use the front audio jack to get high-quality stereo audio. RGB cables generally have separate audio cables to address this issue.

Required Items

DigiKey list of the following items

• Five ceramic 0.1uF 50V capacitors.
• One aluminum 470uF 35V capacitors.
• Two ceramic 1000pF 50V capacitors.

Fixing the Issue

Once you get the parts from Digi-key, you'll want to solder the ceramic-dipped caps EXACTLY as shown on the underside of the mainboard in the image below:

Electrolytic Capacitor Installation:

Now all that is left is to install the missing 470uF electrolyctic cap found in the MVS arcade hardware version of the Neo Geo. For this, turn the mainboard back over to the top side. What you'll want to do is bend the legs of the cap to a 90-degree angle and then pull them just enough apart to slide snugly over pins 8 and 9 of the JRC 2066D chip. Then it's just a simple matter of tack-soldering them to the legs. Your results should look like this:

Left Channel Polyester Capacitor Swap (optional):

Lastly, the 3-3 and 3-4 have another error from other revisions in that the polyester caps for the left channel are swapped by mistake compared to the right channel. If you're absolutely obsessive about symmetrical component arrangement, you can desolder and swap these caps. Highlighted below in yellow outline are the two caps in question (photo by MKL):

For posterity, Ste Kulov of HD Retrovision simulated in SPICE the result of the caps being incorrectly placed on the left channel. The net effect is it slightly changes the low pass filtering slope just a hair from the right channel's slope. See Ste's graph below, where the green slope is the left channel and the red slope is the right channel:

Well that's all there is to it! Note however, I discovered recently the Super NES controller adapters sold by a French person on ebay make use of Arduino Nano boards that pull power to the point of re-introducing 60-cycle buzz into the audio output. As such, I do not recommend using those adapters. Sound will be crystal clear with original SNK sticks. If you'd like to hear the end result after this mod, click the link below for a track I recorded from "Art of Fighting":