Master system AV mod - quiet sound

[trimbonz]

After following several threads and tutorials on modding Sega consoles, I decided to mod my Mega Drive 2 and Master System 2 for S-Video and line-level audio. The results for the Mega Drive were great, but I'm struggling to get good sound from the Master System.

My MS2 comes with just an RF output by default, so pretty much any av mod is a good mod
It has a CXA1145P chip, from which I can get the Y and C signals (required for S-Video) and the audio if desired.

I found the Y signal needs a voltage follower amplifier as mentioned <a href="http://gamesx.com/wiki/doku.php?id=av:g ... d">here</a>, but the C signal works well with just a 75ohm resistor and a 220uF capacitor.

The problem is getting sound at a decent volume. When using the RF module, sound comes through nice and loud if not clear. So far all points on the board where I can get audio result in a clear but very quiet signal. I've followed it from inside the RF modulator right back to the source (pin 15 of the 315-5246 processor), and everywhere seems to have the same quiet sound level relative to ground.

Just wondering if anyone has managed to overcome this? Is there another reference I should be taking it instead of ground for example? Do I just need to put up with turning up the receiver to full volume to play Alex Kidd?

thanks,

[NotBlaine]

My first real suggestion is... you should post this on the gamesx forums. I'm gonna start guessing just because - I wanna see if I can guess. But, seriously, you should take this thread over there.

I have two questions, which are, where are you pulling audio from? And, are you checking the stereo or the mono mix?

You mentioned you went all the way back to the processor (so there's no amp circuit there at all) but did you test the audio from the 9 pin connector after you modded the system?

If it's weak even from the 9 pin then, yeah, you might have done something during the mod. If it works from the 9 pin, you can always pull audio from there. I'm imagining you added an s-video port, so you can just have your audio from one and your video from another.

If it's still weak from the 9 pin, and you never find out why, you could amplify the signal with an LM386N IC (costs about $1 at radio shack) - I'm pretty sure it has a modest increase if you leave the gain pins open. It might beef up the signal past line level though.

Again, don't take my advise on this one - at all, I ask the experts. I'm just guessing at lotto numbers here.

[trimbonz]

Hi NotBlaine,

Thanks for the suggestion to take it to gamesx. I'm fairly new to the retro modding scene and am still discovering where the right places are for this sort of thing.

My Master System 2 has no 9-pin connector, unfortunately - just a single RF output. There's also no stereo mix as it's mono all the way. It seems they took a lot out when designing the second revision of this console.

Thanks