Audio problem with MegaFlashRom SCC+ and a Sanyo Wavy-70FD

By syn

Prophet (2061)

16-12-2015, 13:35

lol i corrected it for you

Daemos wrote:

Ill have a look at it. Give me a few minutes

Cool stuff keep us posted

By Daemos

Paragon (1951)

16-12-2015, 17:14

ok lets start easy. try changing R229 to 2K2 and see how the situation improves. Remember to stick the cart in slot 1

By Gustau Pérez-Querol

Resident (61)

16-12-2015, 21:06

Hi @Daemos,

would it be possible to put another resistor in parallel instead of replacing R229? I did the math and it would be around 4k1 resistor if I'm not mistaken.

By sd_snatcher

Prophet (3458)

16-12-2015, 21:22

@Guillian

Would you mind sharing the analog output schematic of the MFR SCC+ here so we can check if there's any conflict?

Just the analog circuit path, like we published for the PHC-70FD.

By sd_snatcher

Prophet (3458)

16-12-2015, 21:40

@Daemos

Comparing the PHC-70FD with the FS-A1WX schematics, it seems to be missing a pull-down resistor for each slot in the soundin pin. Could that be the cause of the problem?

By Daemos

Paragon (1951)

16-12-2015, 22:09

Quote:

would it be possible to put another resistor in parallel instead of replacing R229? I did the math and it would be around 4k1 resistor if I'm not mistaken.

no problem. Give it a try.

Quote:

Comparing the PHC-70FD with the FS-A1WX schematics, it seems to be missing a pull-down resistor for each slot in the soundin pin. Could that be the cause of the problem?

The pull down resistor I believe you speak off are to make a 0 point in the audio signal. This is allready done with R127.

Lets wait out the results for the quick fix.

By Guillian

Prophet (3449)

16-12-2015, 23:51

@sd-snatcher: there is no analog part in the cartridge.The sound output pin from the FPGA is connected to sound pin of the cartridge.

By Daemos

Paragon (1951)

17-12-2015, 07:32

Quote:

there is no analog part in the cartridge.The sound output pin from the FPGA is connected to sound pin of the cartridge.

That explains a few problems for some MSXes. I wonder if the FPGA's sound output is open collector as well.

By giangiacomo.zaffini

Champion (267)

17-12-2015, 12:30

Sorry to disturb You,
in my mind I thought many MSXs have sound problems when mixing sounds because each has different audio mixer circuit,
for instance Philips VG-8020 shunts AUDIO IN from both cartridge slots, so when both AUDIO IN are excited, one drain from the other, and audio mixer OP-AMP received lowered imputs.
It is sound mixing sources balancing, it should be preferred controlled but MSX hardware doesn't do this job.

By Daemos

Paragon (1951)

17-12-2015, 17:18

Quote:

Sorry to disturb You,
in my mind I thought many MSXs have sound problems when mixing sounds because each has different audio mixer circuit,
for instance Philips VG-8020 shunts AUDIO IN from both cartridge slots, so when both AUDIO IN are excited, one drain from the other, and audio mixer OP-AMP received lowered imputs.
It is sound mixing sources balancing, it should be preferred controlled but MSX hardware doesn't do this job.

correct