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

Page 2/6
1 | | 3 | 4 | 5 | 6

By sd_snatcher

Prophet (3458)

sd_snatcher's picture

09-07-2015, 23:32

If we remember that Philips NMS-825x & 8280 are in fact the Sanyo MPC-25FS in a different color (just an OEM with the Philips brand screen printed over), it doesn't come as a surprise that other Sanyo machines had issues with the SCC sound, be it the real SCC or the ones in FPGA chips.

By Gustau Pérez-Querol

Resident (61)

Gustau Pérez-Querol's picture

10-07-2015, 11:57

sd_snatcher wrote:

If we remember that Philips NMS-825x & 8280 are in fact the Sanyo MPC-25FS in a different color (just an OEM with the Philips brand screen printed over), it doesn't come as a surprise that other Sanyo machines had issues with the SCC sound, be it the real SCC or the ones in FPGA chips.

Thank you for pointing that out, I wasn't aware the NMS-82[5|8]0 were in fact oem versions from Sanyo. Knowing that, I'd also have said we should have expected sound problems with the FPGA SCC sound.

There are a few things that puzzle me:

  1. An original SCC cartridge sounds just fine. No mixing problems between the internal PSG and the SCC chip
  2. With the MFR-SCC the SCC audio level is lower than the internal PSG level of the Wavy
  3. Placing a capacitor (100nF for example) and a resistance (1,2kohm) in the cartridge leverages the problem (scc audio level is closer to the internal psg audio level). This should make little sense (at least for me because of what because @Daemos and @ roadfighter previously said in this same thread) because doing attenuation in the cartridge should make the SCC even lower.

I'm not sure, but I'd say it makes little sense to modify the internal PSG circuitry, given the fact that a regular SCC cartridge does work fine with the internal PSG. If we modify the internal PSG on the wavy to have PSG and FPGA SCC levels equal, wouldn't that give problems using a regular SCC the internal PSG? If so, then I think the proper way to fix would be to modify the cartridge.

Any idea how to proceed any further?

Best

By msxholder

Champion (382)

msxholder's picture

11-07-2015, 11:51

Any of you ever seen the inside of an mpc-25fk ? I did.
It is sure an mess like a hitachi.
I really do ask myself are the nms 8250 and up made by Sanyo.
It is more like NEC produced And i am pretty sure Philips made there own designs for electronics
Only the case and keyboard are similar .

By syn

Prophet (2061)

syn's picture

11-07-2015, 12:55

Would it be possible to disable the internal SCC from the megaflashrom and just use a real konami scc (game) cartridge instead?

By sd_snatcher

Prophet (3458)

sd_snatcher's picture

11-07-2015, 20:03

Quote:

Any of you ever seen the inside of an mpc-25fk ? I did.
It is sure an mess like a hitachi.

They may have different versions of the board, but we can't be sure that there weren't any MPC-25FS with the newer version of the board, as it was usual back then. Just like the Sony HB-101 has different board versions for the very same machine: see here and here

Quote:

I really do ask myself are the nms 8250 and up made by Sanyo.

I guess these pictures leave no doubt about who made the machine:

By Gustau Pérez-Querol

Resident (61)

Gustau Pérez-Querol's picture

11-07-2015, 20:31

IIRC there's no way to disable the SCC in the cartridge.

Yesterday I found out that the software the MegaFlashRom ships to flash the eprom with rom's allows to patch those roms to use the PSG contained in the MegaFlashRom (yes, I did not know it also has a PSG).

Tried this and the result seems to be both scc and psg are equal (I think this is no big surprise). However now both levels are quite low and thus I need to raise the volume level on my TV. With a regular SCC cartridge (and the internal PSG) both audio levels are correct.

To summarize:

  • Without patching the cartridge [1] levels are incorrect. Even by patching the ROM to use the internal FPGA
  • Patching the cartridge, if I don't patch the ROM to use the internal PSG the SCC gets closer to the internal PSG (but fairly noticable). If I patch the ROM to use the cartridge PSG, then both SCC and PSG levels are equal, but I have to raise a lot the audio on the TV

So my conclusion (like @Daemos already suggested IIRC) would be that the sound coming from the cartridge is is lower than the PSG audio level. The only solution I can think of is that the audio path in the cartridge needs some kind of amplification.

Any idea?

[1] Suggested by @Gullian: a 22nF capacitor and a 1,2kohm resistance between the output pin of the cartridge and the FPGA

By Guillian

Prophet (3449)

Guillian's picture

11-07-2015, 21:45

I suggested a 100nF capacitor and a 1.2K resistor, that is what fixes the problen in the 8250/55/80.
Since it does not work on the Wavy, I suggested to try different values to check if there is any improvement.
I'm not a hardware guy, so I don't really know where the problem is. But my bet is that the sound mixer has some fault, similar to the one in the Philips.
The volume of the cartridge seems right in the other MSX machines.

By Daemos

Paragon (1951)

Daemos's picture

12-07-2015, 00:02

Schematics. Just get me schematics of that machine and I can figure it out. Photo's are not enough. It really needs a active module + PSU input for that and I need to know where we can get a positive and negative voltage from + where the sound can be cut, tapped etc.

By Gustau Pérez-Querol

Resident (61)

Gustau Pérez-Querol's picture

12-07-2015, 01:40

Guillian wrote:

I suggested a 100nF capacitor and a 1.2K resistor, that is what fixes the problen in the 8250/55/80.

Hi @Guillian,

I'm very happy the cartridge! and I'm also pretty sure your suggestion was based on the behavior of the 82[5|8]0 family and with the best of the intentions. I just mentioned you because I'm also not a hardware guy Smile

Guillian wrote:

The volume of the cartridge seems right in the other MSX machines.

I does pretty well with my nms8245 (and I'm pretty happy with the mfrs and the nms). But with the wavy it has some problems with its mixer; however a regular Konami SCC with the internal PSG does fine, but the FPGA SCC + FPGA PSG sounds lower, that makes me think that the cartridge needs some active amplification with the wavy.

By Gustau Pérez-Querol

Resident (61)

Gustau Pérez-Querol's picture

12-07-2015, 02:28

Daemos wrote:

Schematics. Just get me schematics of that machine and I can figure it out. Photo's are not enough. It really needs a active module + PSU input for that and I need to know where we can get a positive and negative voltage from + where the sound can be cut, tapped etc.

Thank you @Daemos. I'll try to find that. However a first search gave me nothing; I hope anyone else has the schematics or can provide a bit on help on this.

Page 2/6
1 | | 3 | 4 | 5 | 6