Sanyo MSX machines (even those made in OEM for Philips) are well known troublemakers in the sound department. This article is the first of a series of DIY recipes sd_snatcher is glad to share with you, on how to improve the sound of many MSX machines. This was the first machine to be tackled, because it also had one of the most challenging circuits to find a good solution for. This recipe fixes the following problems in this machine's sound circuitry:

  • Solves the problem where the SCC and some other external sound cartridges got muted. The impedance matching was all wrong. (note: some machines won't show this problem with the real SCC cartridges because Sanyo's customer service seem to have implemented a fix. But that was a poorly designed solution too and many other cartridges still got problems. The solution presented here is much better)
  • Fixes the mixer volumes to be standard, just like Panasonic MSX2+ and Sony MSX2+ machines (those beautiful Microcabin soundtracks will sound correctly now)
  • Boosts the OPLL bass frequencies
  • Fixes the recently discovered OPLL low-pass filter. Sanyo had done the best OPLL low-pass filter of all MSX2+ models (4.13KHz), but this fix enhances it way further, to 22KHz
  • Enhances the SNR of the sound output

High time to warm up our soldering iron and have a go at it. Have at you, Sanyo!

Relevant link: FRS's MSX Page - Hardware fixes and enchancements

Comments (21)

By Meits

Scribe (4460)

Meits's picture

11-08-2017, 12:21

I know how rotten a Philips NMS8250 (and up) sounds, but there are a couple to be performed fixes for that.
Very good to see that their makers, Sanyo, get their butts spanked as well now. And judging the amount of fixes, the spanking is serious.
It's ofcourse unforgivable that a modern SCC clone gets muted.
Great job sd_snatcher. It's very noticable that you're back in action. Very much appreciated, but please take care of yourself as well Wink

By syn

Paragon (1623)

syn's picture

11-08-2017, 13:53

Thanks sd_snatcher, i'll try to get someone to look at my sanyo in a few months when i got more time for this.

Meits wrote:

It's ofcourse unforgivable that a modern SCC clone gets muted.

No offense to existing FPGA clone makers, they are doing a great job supporting MSX, but I disagree with this remark. If a NORMAL scc sounds correct and the close SCC doesn't, isnt it obvious something is wrong or different compared to an actual SCC?

Besides, I dont think it is fair to blame sanyo at all for this, FPGA SCC's didn't exist back when these machines were build remember Big smile

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

11-08-2017, 14:54

The fix that their customer service did was such a lazy hack that it scares. They just soldered an extra resistor over each slot audio resistor and that's it. They even didn't take the motherboard out of the machine to do that, it was a very lazy soldering job.

And judging by the results, the value of the "patch resistors" was pretty much found out by tweaking until it worked with the original SCC. This has left potential for a lot of potential problems to occur, and the PGA SCC has just been caught by that trap.

That said, an opamp in the sound output path of the FPGA SCC would have been greatly advised too.

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

11-08-2017, 15:08

I'm glad you two liked it. You're welcome! Smile

Quote:

It's very noticable that you're back in action. Very much appreciated, but please take care of yourself as well Wink

Don't worry, I'm not overdoing it. I'm mostly releasing stuff I had finished before the surgery. I'll release more stuff soon, but I have to do it in small steps so I can have energy to answer all the questions that usually arise.

By Meits

Scribe (4460)

Meits's picture

11-08-2017, 15:36

syn wrote:

Thanks sd_snatcher, i'll try to get someone to look at my sanyo in a few months when i got more time for this.

Meits wrote:

It's ofcourse unforgivable that a modern SCC clone gets muted.

No offense to existing FPGA clone makers, they are doing a great job supporting MSX, but I disagree with this remark. If a NORMAL scc sounds correct and the close SCC doesn't, isnt it obvious something is wrong or different compared to an actual SCC?

Besides, I dont think it is fair to blame sanyo at all for this, FPGA SCC's didn't exist back when these machines were build remember Big smile

Agreed to a certain point. But seeing that Manuel Pazos' SCC works on every other system gives food for thought which isn't in favor of Sanyo.

By gdx

Paragon (1601)

gdx's picture

11-08-2017, 16:09

Thanks sd_snatcher

By PAC

Guardian (4373)

PAC's picture

11-08-2017, 19:20

Thank you for your great dedication Wink . Is it possible to know which other MSX models are awaiting for a sound fix?

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

12-08-2017, 03:56

Quote:

Is it possible to know which other MSX models are awaiting for a sound fix?

Yes. Here goes some teaser. Smile

The Panasonic Turbo-R machines are the next. Then (not necessarily in order):

- Sony HB-10 and HB-20P
- CIEL MSX-Music cartridge.
- Toshiba HX-MU900
- Gradiente Expert (gray models)
- Sharp Hotbit

If anyone is wondering why the NMS-8245 isn't on the list: because it's audio performance is passable. The PSG is a tad too high when compared to the slots, and it has this tendency to saturate the sound when strong bass notes are played together with some middle or high notes (*1), specially noticeable in MicroCabin songs. But in general, it's does the job. I think that there are worst offenders than this machine. I'm not convinced yet that it should be fixed. Maybe I can review this position someday.

*1: Probably it saturates because there's only a lone transistor as the output amplifier, and not a preamp. The Hotbit has the same design and the same symptom.

By Meits

Scribe (4460)

Meits's picture

12-08-2017, 22:57

Looking forward to the turbo R ST machine Smile

By Grauw

Enlighted (6159)

Grauw's picture

13-08-2017, 01:56

Me to the GT Big smile. Did you look at the NMS 8250? I think its audio is notoriously broken… Similar to the Sanyos?

Also some guidance about possibly modding various MSX-MUSIC extensions would be good.

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

13-08-2017, 03:45

Quote:

Me to the GT Big smile. Did you look at the NMS 8250? I think its audio is notoriously broken… Similar to the Sanyos?

This machine was made in OEM by Sanyo, you know? See any coincidences? Smile

Yes, I took a look at the NMS-825x service manual. This sound circuit is just unbelievably broken by design. It's the worst I have ever seen.

The circuit design seems to have been reused from an earlier cheap MSX1 machine, but then the engineer moved the amplifier section to the wrong place (only for the PSG line, that is usually louder than the other sources), and ruined for once what already wasn't exactly a great design.

IOW, the circuit only works properly for the internal PSG and you're lucky if anything else connected to the slot produces any sound. And I wouldn't recommend to connect two sound cartridges at the same time to these machines, because it short-circuits their sound outputs.

Sadly I don't have any machine of this series (8250/8255/8280), so I can't create a proper solution for them, sorry. If I tried to create something without the real machine to test, I would probably end up similar problem that the Turbo-R has: a very well designed circuit on theory, but terribly calibrated for the real world.

Some interesting background info: here's another thing that differentiates the MSX2+ from the MSX2: the MSX2+ and higher have more expensive/refined sound circuitry based on opamps, while the MSX1 and most of the MSX2 have a very basic sound circuitry with only one transistor as amplifier.

The FS-A1 seems to mark the transition. It features an opamp in its sound circuitry and its sound is indeed excellent for such a cheap price tag. Panasonic did such a wonderful job in that little machine in all aspects. No wonder the most of the competition gave up on the MSX standard in less than one year after the FS-A1 was released. They just couldn't compete with such a great design for such a low price. Only Sony and Sanyo accepted the challenge.

By Guillian

Prophet (3014)

Guillian's picture

13-08-2017, 12:47

sd_snatcher wrote:

Yes, I took a look at the NMS-825x service manual. This sound circuit is just unbelievably broken by design. It's the worst I have ever seen.

...

IOW, the circuit only works properly for the internal PSG and you're lucky if anything else connected to the slot produces any sound. And I wouldn't recommend to connect two sound cartridges at the same time to these machines, because it short-circuits their sound outputs.

Totally agree. And still some "users" keep blamig that if a cartridge does not work fine, the fault is in the cartridge.

Here is a tutorial (in Spanish) for fixing the 8250/8255/8280 sound mixer made by Aquijacks.

By syn

Paragon (1623)

syn's picture

13-08-2017, 17:25

Guillian wrote:

Totally agree. And still some "users" keep blamig that if a cartridge does not work fine, the fault is in the cartridge.

You probably mean me because I was saying that. indeed I'm not a user since I don't own a MFR. Perhaps I shouldn't have said "wrong" (since its still a good product that works well on other msx models) but don't you agree there is at least a difference if one works well on bad sound circuits and one doesn't?

Again I have nothing against you or your products. I only often discuss this topic because I was interested in buying a MFR+ but mostly because I try to stimulate improvements in the FPGA SCC(+) implementation(s) of future msx products and mfr revisions.

By Guillian

Prophet (3014)

Guillian's picture

13-08-2017, 18:11

@syn: No, I was not meaning you. Sorry for not being clear. I was meaning other "users" (probably banned from MRC) that just try to difamate MFR SD for whatever reasons they have. They argue that the cartridge must work fine on 8250/55/80. If it does not work, the problem is in the cartridge not in the computer.

Of course the FPGA implementation is different than other sound cartridges, but that does not mean that it is wrong. Can it be improved? Sure! Is it wrong? I don't think so.

I.e.: one user said all cartridges he tested worked fine on his computer, but MFR SD didn't. It turned out that the /CLK pin of his MSX computer was blended. Is it a fault of MFR SD? No. But all other cartridges he tested worked fine! Yep, those cartridges does not need the clock signal. But that does not mean that the problem is not in the computer.

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

13-08-2017, 20:17

Guillian wrote:

Here is a tutorial (in Spanish) for fixing the 8250/8255/8280 sound mixer made by Aquijacks.

This seems to be a good fix. While the mixing levels won't be optimal since it was copied from the NMS-8245, it will be good enough and reuse most of the existing circuit. And if I ever recalibrate the NMS-8245 mixer, the same recipe will apply for the NMS-8250/8255/8280 machines that were fixed with Aquijacks' tutorial.

I'll put a link to this document in my hardware fixes page. Thank you for sharing!

By raymond

Champion (293)

raymond's picture

13-08-2017, 20:31

I cannot wait for the Turbo R fix Big smile If the NMS-8250/55/80 fix was in English I could be upgrading my NMS-8250 in the meantime. Can somebody translate it into English?

By syn

Paragon (1623)

syn's picture

13-08-2017, 23:19

sd_snatcher: I just listened to some audio examples louthrax posted in that ym2413 manual thread: I hope you don't take the Sony msx2+ as target regarding the bass boost for this or your other projects, the bass there is too loud imho. Unmodified FM pac sounds perfect in his example.

To be honest I don't think I ever felt the bass was lacking on my sanyo, and I have recorded msx stuff on cassette tape many times back in the days, although i did not listen to music analytically back the.

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

14-08-2017, 00:38

raymond wrote:

I cannot wait for the Turbo R fix Big smile

Good news then: I have just submitted the news about this to the MRC. Let's wait for the processing pipeline to be flushed. Smile

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

14-08-2017, 00:45

syn wrote:

sd_snatcher: I just listened to some audio examples louthrax posted in that ym2413 manual thread: I hope you don't take the Sony msx2+ as target regarding the bass boost for this or your other projects, the bass there is too loud imho. Unmodified FM pac sounds perfect in his example.

The Sony MSX2+ machines have excellent bass levels. I don't think the fix will improve this aspect in these machines.

Quote:

To be honest I don't think I ever felt the bass was lacking on my sanyo, and I have recorded msx stuff on cassette tape many times back in the days, although i did not listen to music analytically back the.

Don't worry, neither the bass or treble are "boosted" by the sound fixes. In fact, they just stop being attenuated by exaggerated low-pass/high-pass filters respectively. The resulting sound is just the natural sound of the chips without any castration. Smile

By sd_snatcher

Prophet (2567)

sd_snatcher's picture

14-08-2017, 01:37

By "boost" I meant artificial boosting.

By Grauw

Enlighted (6159)

Grauw's picture

14-08-2017, 12:56

FM bass ❤

My MSX profile