Mega Amp Sega CD audio EXTREMELY quiet

[cr4zymanz0r]

So, I bought a pre-assembled Mega Amp board that Helder over at the assemblergames forums sells. Everything on his thread there shows version 1.2, but I received version 1.3. Overall it seems to be the same except smaller and no solder pad for mono audio, but no big deal there.

After installing in a VA1.8 model 2 Genesis, Genesis and 32X games sounded great with the limited testing I had time to do. When I tried Sega CD initially I thought its audio wasn't working at all. The drums in the Sega CD bios were not audible and I booted up Sol-Feace to silence on the CD audio intro. However, when I got close to the speakers I did hear that it was barely audible. The TV was set at a decent volume, but the Sega CD audio was more quiet than a whisper. Sega CD audio was working at normal volume levels before the mod.

I sent Helder a message and awaiting response for some troubleshooting ideas, but I don't know how long it'll take him to respond and I want to fix this as soon as I can so I can get to gaming and clean up my clutter . Has anyone else encountered similar issues when doing a Mega Amp mod or have any ideas?

[Voultar]

So, I bought a pre-assembled Mega Amp board that Helder over at the assemblergames forums sells. Everything on his thread there shows version 1.2, but I received version 1.3. Overall it seems to be the same except smaller and no solder pad for mono audio, but no big deal there.

After installing in a VA1.8 model 2 Genesis, Genesis and 32X games sounded great with the limited testing I had time to do. When I tried Sega CD initially I thought its audio wasn't working at all. The drums in the Sega CD bios were not audible and I booted up Sol-Feace to silence on the CD audio intro. However, when I got close to the speakers I did hear that it was barely audible. The TV was set at a decent volume, but the Sega CD audio was more quiet than a whisper. Sega CD audio was working at normal volume levels before the mod.

I sent Helder a message and awaiting response for some troubleshooting ideas, but I don't know how long it'll take him to respond and I want to fix this as soon as I can so I can get to gaming and clean up my clutter . Has anyone else encountered similar issues when doing a Mega Amp mod or have any ideas?

Pics of the installation always help.

[cr4zymanz0r]

Here's some pics of the install:

http://imgur.com/a/9ONbk

[cr4zymanz0r]

I've been corresponding with Helder trying to figure out what the issue is. I've got a related question that might help me figure something out.


If audio is traveling through the circuit above, does it:
a.) act as an input at point A and output at point B
b.) act as an input at point B and output at point A
c.) either/or depending on which end the input is hooked to

If you know, please provide the technical reason so I'll understand why.

[ApolloBoy]

It's very obvious that the answer is "A". You've got a signal that's being amplified, and then it goes through a cap and resistor to get the final output. Like I said, it's very obvious when you take a good look at the circuit.

[cr4zymanz0r]

Well, I was going down the wrong path thinking something was wrong with the Genesis routing/amping of the Sega CD audio before it goes to the Mega Amp.

It turns out there was some weird issue with the Mega Amp PCB. Some of the solder pads for the audio inputs on it were somehow getting connected to ground (slightly misaligned lacquer top layer maybe). Once I cleaned the solder off and used minimal amounts in the middle of the pad it fixed the issue. I figured it out because I knew the Sega CD audio inputs on the Mega Amp should be 75 ohm resistance to ground once connected, but they were getting 0 resistance.

Everything is good now