VOGONS


First post, by Eep386

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...And it works 😀

I have a dead CT1740 and a healthy CT2910. I rather like the CT2910 a lot as its YMF289 OPL3 FM chip sounds exactly as I remember the FM synthesis on my first sound card, an Addonics YMF719E-based card, had sounded. But one thing that was off-putting was that notorious bugged v4.13 DSP with its clicks and stutters, so I've been sticking to a CT1770 SB16 SCSI up to this point.

Today I worked up the courage and swapped the DSP chip on my CT2910 with the v4.05 from the dead CT1740, and much to my surprise everything works fine (so far). I haven't tested specifically for the single-cycle DMA clicking problems and the like, but for now I am happy to have a YMF289 OPL3 SB16 with a 'non-bugged' DSP. Earlier on the CT2910 I had changed the MC3403 quad op-amps out for TL074's, and that had cut the hiss roughly in half. I also changed the op-amps on the CT1770, and got a similar (albeit somewhat less pronounced) improvement. The CT2910 already has a good CT1703-A DAC so that does not need to be changed.

Further testing (and pictures) is pending.

Last edited by Eep386 on 2019-03-15, 07:25. Edited 1 time in total.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 2 of 15, by Eep386

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Here's the card:

IMG_0879.JPG
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The star of the show, the v4.05 DSP:

IMG_0880.JPG
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And now a view of the TL074 op-amps:

IMG_0881.JPG
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Unfortunately the only way I can think of to get v4.05 DSP chips, is from busted old SB16's. At least the one broken CT1740 I had wasn't going to go to total waste.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 4 of 15, by appiah4

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The obvious question is - did this completely fix all MIDI interface bugs? Can we once and for all confirm it's DSP related and not a silicon bug in the other ICs?

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Reply 6 of 15, by Eep386

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appiah4 wrote:

The obvious question is - did this completely fix all MIDI interface bugs? Can we once and for all confirm it's DSP related and not a silicon bug in the other ICs?

Unfortunately I don't have a single MIDI device to my name to test it with, not even a Wave Blaster-compatible rompler. Guess that will be the next thing on my agenda, next paycheck.

https://www.ebay.com/itm/Dreamblaster-Synth-S … vUAAOSw0rdb3cOL
Would this be good? Or is it too expensive?

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 7 of 15, by appiah4

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That auction leads me to a gibberish listing from China I would not trust. Dreamblaster is a fellow Vogoner who makes and sella these MIDI devices, his Dreamblaster S2 wavetable board can be had for around 20 EUR on his wesite http://www.serdashop.com; he also sells other fantastic midi gear.

Last edited by appiah4 on 2019-03-15, 20:49. Edited 1 time in total.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 8 of 15, by keropi

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^ that Chinese seller is legit and he gets his stock from Serdaco in bulk - no issues buying from there if necessary
"source" shop is here: https://www.serdashop.com/

🎵 🎧 PCMIDI MPU , Orpheus , Action Rewind , Megacard and MK8330 soundcard website

Reply 9 of 15, by MrSmiley381

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Well, this is a rad mod that quickly went quiet. I'm totally interested to learn if this fixed all the issues common to SB16's. I finally got around to testing my CT3900 (listing said CT3900-S, so a second revision?) and it's a nice card, though I'd like to stress test it a bit. According to James-F and Cloudschatze here the illegitimate hanging note bug is more than likely an issue with sound drivers and CPU hiccups.

I spend my days fighting with clunky software so I can afford to spend my evenings fighting with clunky hardware.

Reply 10 of 15, by Jo22

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Interesting., Congratulations! 😄

Btw, does anybody know what the SB16 DSP actually is ? I apologize if that sounds ignorant, but I just don't know.
- The original Sound Blasters used an 8051 series microcontroller (8751 to be precise), so maybe the SB16 uses a related one ?

If so, that would be cool. It would make it possible to make replicas of the v4.05 DSP, maybe adding some features (Thunder Board modes) or emulate SB Pro mixer etc.
There are controllers with an 8052 compatible instructions set that can run up to ~100MHz by now..

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Reply 11 of 15, by SirNickity

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As I understand it: Nobody has successfully dumped the ROM image of the later SB cards. Doing so is likely to require decapsulation, or hacking the chip's IP protection via power glitching (etc.)

Reply 12 of 15, by SaxxonPike

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I know this is an older topic but I don't want this to fizzle out. Got a friend to swap a 4.05 onto a CT2290. Going to see how that goes. The trades are generally on cards that do not have a CT1747. I want to know if these work too. We should really broaden this knowledge.

I'll post results when I'm home.

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Sound device guides:
Sound Blaster
Aztech
OPL3-SA

Reply 13 of 15, by Cloudschatze

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SaxxonPike wrote on 2020-07-14, 03:22:

Got a friend to swap a 4.05 onto a CT2290. Going to see how that goes. The trades are generally on cards that do not have a CT1747.

Down-leveling to v4.05 only makes sense with cards bearing the DSP v4.1x and CT1746A/B bus-interface chip combination, all of which exhibit the spurious/latched MIDI byte behavior that would be resolved with such a swap. Where that behavior isn't present with any CT1747-bearing card, there's little point in performing such a modification, assuming it works at all.

Reply 14 of 15, by SaxxonPike

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It does. We will be trying other DSPs on various cards. We would also like to know if the missing note-offs are also resolved as part of this or if that is an intrinsic problem of the CT1747.

Sound device guides:
Sound Blaster
Aztech
OPL3-SA

Reply 15 of 15, by Cloudschatze

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That behavior is a consequence of the SB16/AWE's shared MCU architecture, lack of adequate MIDI output buffering, and sound drivers that either busy/wait things out during concurrent PCM operations (resulting in gameplay slowdown), or simply drop MIDI messages after retry exhaustion. I haven't noticed any difference in this behavior with SB16 cards having the earlier, 4.0x DSP versions, but would certainly be interested in any findings otherwise.