Bad audio quality through SCART from Genesis (using headphone out) – OSSC 1.6

[BuckoA51]

Thanks, I’ll give that a try as soon as possible.

[marqs]

@James-F there is no analog circuitry or load before PCM1862 audio ADC except a 100K pull-down to prevent floating.

@BuckoA51 so the mono output was no better? That somewhat contradicts with esp’s post, although in that case signal was tapped before buffer and op-amp. Is there some particular game where distortion is most apparent? The modified VA1 here should sound close to your VA5 but I have hard time hearing any notable distortion after pre-amp gain fix (Sample 4).

[James-F]

I think this 100k should have sufficed.

Page 56, PCM1862
The analog inputs also require coupling caps, does the OSSC has them?

[marqs]

@James-F Yes, it has them.

[James-F]

Very well then.
So it’s the CXA1034PM that is whacky, and using a simple headphone output splitter like you’ve suggested fixes the problem without modding the cable.
The only problem is noise from the headphones, might as well mod the cable if audio quality is top priority. 🙂

[James]

Anybody know if you still get this issue if you are mixing the audio from the headphone jack into a mega cd and then using the cd’s RCA connectors through a 1.6 OSSC?

Or does the mega cd apply the appropriate load to the CXA1034PM as it’s getting mixed with CD’s audio?

[marqs]

Good news!

I found a problem in PCM1862 initialization. The default ADC clock divider value appears to be different than specified in the datasheet, resulting to too high ADC clock. Setting the divider manually to correct value seems to fix the MD sound issue based on short testing.

[Damn-Deal-Done]

That’s awesome. So does this mean it can be done with firmware only?

[BuckoA51]

I was just going to pick up my modded RGB cable tomorrow too 🙂

[jonlad]

If it’s a firmware fix, then this has just made my Friday!

[Zoomer88]

Yay! Great news indeed!

[BuckoA51]

Just solder 1k resistor between pin 2 & 4, and pin 6 & 4.
Note that Pin 2 and 6 wired to the tip and ring of the 3.5mm plug, pin 4 is ground.

Ok so we tried that and it didn’t seem to make much difference, sound was still noticeably worse on 1.6 than 1.5 + Audio board.

Perhaps there’s two issues here that we’re running into, hopefully Markus’ fix will finally solve it.

[James-F]

Strange, for me a load of 1k has the effect as plugging headphones in parallel.
Anyway, great that this is solved by firmware.

[BuckoA51]

Beta testing firmware 0.80a here and now the audio from my VA5 Megadrive is identical through both 1.5 with audio board and 1.6.. so I think this one is solved…so in conclusion

If you have VA0 or VA1 console, solder 1k resistor between pin 2 & 4, and pin 6 & 4 on your SCART cable.

if you have a VA0 or VA1 or VA2 console, try the firmware update first and if you still have problems, see this thread:- http://www.sega-16.com/forum/showthread.php?27397-VA2-Preamp-fix

everyone else just needs to update to 0.80a which should be out very soon.

[jonlad]

This is great news – thank you

[Author]

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