Raiden DX New Version V33 Audio Enhancement - Thoughts?

[billd420]

Hi everyone-

I got a Raiden DX "New Version" V33 PCB in the mail yesterday, and immediately noticed the sound was very poor quality. I initially thought I had some bad caps in the audio section, and went ahead and replaced them. I jumped the gun a bit on the repair. I realized AFTER I did the cap-out its been documented here over the years how bad the sound is. Since the caps didn't improve anything, I decided I should go for a different approach.

I recently did a NeoGeo MV-1B stereo mod which is what inspired this. In the NeoGeo mod, you tap the quad op.amp. for the left and right audio signals, then combine with the synthesised audio to form line-level stereo. Well, since the Raiden DX PCB ONLY has digital audio, its safe to assume there are no signals to combine. So after poking around in some datasheets and looking at the PCB with my multimeter, I've come up with a preliminary (simple) "stereo" circuit.



I think this will work fine, however I'm confused about the audio going into the dual op amp on the raiden DX pcb. There are IN1(+) and IN2(+) pins on the 4560D op amp. From what I can tell, only IN1(+) gets an actual audio signal. IN1(+) traces back to Pin36 on the M6295 (voice synthesiser chip), which is voice synthesized output. IN2(+) goes through a resistor, which is tied to two caps. One cap is tied to GND, the other is looped back to the 4560D's OUT2. So, unless I'm interperting this wrong, IN2(+) is merely a ground signal, and IN1(+) is the ONLY audio being processed in the equation.

Anyways, I think my "stereo" circuit will work, however since the source is mono, it will just be mono split over two channels. What I'm hoping to accomplish here is slightly better audio quality, in hopes the amplifier circuit is contributing to a lot of the high bass levels and "muffled" sounds.

Can anybody confirm that Raiden DX New Version sounds terrible strictly because the digital sampling was done incorrectly? Or is it possible it degrades even more when it enters the (low quality) audio amp circuit? Since I'm playing this on a Blast City, line-level mono split over channels will work just fine. I'm HOPING the blast's stereo amp will handle the audio a bit better.

Thoughts on all this plz...

[dpful]

I'm interested in this, too. I could imagine that a crappy amp could be making the sound worse, but I'd guess that It's much more likely that the sounds themselves are just horrible-- I've never heard an amp chip make something sound that way unless it was just about to explode or turn to dust. I'd forget the stereo, just tap the sound, and run it through you're hi fi for the test. Again, probably 100% bad samples.

[dpful]

If it was 100% bad samples, then some kind of eq circuit WOULD make some difference- thin the sound out and reduce some of the offending frequencies.