NMS-8250 - alternatives to MFRSCC+SD?

Page 2/4
1 | | 3 | 4

By Bastiaan

Champion (333)

Bastiaan's picture

04-04-2016, 20:30

Can the mod to the mfrscc+sd be done by the use aswell? I thought I did not need the mod on my 8280, but I do....
Can mfrscc+sd add the /p1 option automatically? ☺
Can sofarun add the /p1 option automatically? ☺

By marcoo

Expert (110)

marcoo's picture

04-04-2016, 21:33

@Bastiaan
I have a NMS 8280 too with the mod but it also does not work I still have no PSG
if you download the RECOVERY Rom like GUILLIAN said (opfxsd recovery.rom /i34) and you start your MSX with the cursor up
you can select the clone PSG that works for me
The only thing is if you reset your MSX you have to select it again
Maybe it's possible that the PSG is allways on when you start your MSX

By mfeingol

Champion (291)

mfeingol's picture

04-04-2016, 22:51

I need to play with the latest MFRSCC+SD recovery rom. But it sounds like there are two problems with that approach:

1. It needs to be enabled on every boot.
2. FM-PAC audio will still be muted, if you have an FM-PAC in slot 2.

@Guillian, what does the MFRSCC+SD Philips mod actually do? And does it solve these two issues?

By Guillian

Prophet (3457)

Guillian's picture

05-04-2016, 16:24

Bastiaan wrote:

Can the mod to the mfrscc+sd be done by the use aswell?

If you have soldering skills you can try to add a capacitor (100nF) + resistor (1.2K) to the sound output of the cartridge.

Quote:

Can mfrscc+sd add the /p1 option automatically? ☺

Yes, you can modify Multimente (MMRET.DAT file) to add that option automatically.
Also, if you have the latest ROM disk you can press GRAPH and then select "P" to load the ROM and clone the PSG.

mfeingol wrote:

@Guillian, what does the MFRSCC+SD Philips mod actually do? And does it solve these two issues?

The mod adds resistance to the sound output, so you can hear the PSG when using MFR SCC+ SD. But that will not fix the problems with other sound cartridges.

Daemo's explanation:

Quote:

Lets try to explain why the sound does wierd things on the NMS8250/55/80 series. Pin 49 of the cartridge is being connected at the output of the PSG buffer without any resistance. Lucky for us the output of the buffer is decoupled with a capacitor so what happens is, that when something is being connected to PIN 49 of the cartridge slot you pull down the exit plate of the capacitor to a near zero. You actually cause a safe shortcircuit of the PSG versus external SOUND signal. Now most SCC cartridges have some resistance to their output pins so the volume just gets attenuated or the PSG signal gets pulled really low. Each cartridge has some difference in its output resistance so you get different mixdown levels. We are talking about extreme low resistance here. The output resistance of, for example the megaflashrom is practicly zero thus the PSG volume is being pulled to nothing.

By mfeingol

Champion (291)

mfeingol's picture

05-04-2016, 17:56

Makes sense, thanks. But why is the sound from an FM-PAC affected as well?

By Manuel

Ascended (18247)

Manuel's picture

05-04-2016, 20:31

mfeingol: because it is connected to ping 49 of the cartridge slot?

By Bastiaan

Champion (333)

Bastiaan's picture

05-04-2016, 20:34

So I guess with a 8250/55/80 there are a few hardware options and a few software options. Since I usually have a fm-pak in slot 2 and mfrscc+sd in slot 1, (and some other scc carts) I guess modding the msx makes most sense.

I know there is a mod to the mainboard, but if I read the above posts I think there is also the possibility to modify pin 49 of the cartridge connector?

By mfeingol

Champion (291)

mfeingol's picture

05-04-2016, 20:46

Manuel wrote:

because it is connected to pin 49 of the cartridge slot?

I'm probably not understanding the problem, in terms of how the audio signals flow... Without the MFRSCC+SD installed, FM-PAC audio in the second cartridge slot works fine. Shouldn't it continue to work fine when a "fixed" MFRSCC+SD is used in the first slot?

By Grauw

Ascended (10159)

Grauw's picture

05-04-2016, 21:22

If I understand it correctly, due to the Philips/Sanyo hardware design, the cartridge slots are directly connected in parallel, so the resistances combine resulting in an even lower total resistance, and affects both slots.

By Wild_Penguin

Hero (641)

Wild_Penguin's picture

06-04-2016, 17:20

I've been folllowing at this thread, and somehow feel oblidged to mention (again!) one more alternative: the OPAMP mod.

In this mod (by Daemos and Luppie!), the pin 49 is decoupled completely from PSG (but only for one cart slot!) and mixed on the addon board. The board is doable on a stripboard (I've done it myself), and can easily be modified to include the other slot, too. YMMV.

Page 2/4
1 | | 3 | 4