VOGONS


First post, by BEEN_Nath_58

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I was from the Audigy era, so I never got hand to an ISA Sound Blaster card. Reading about them now and the DOS era, quite a lot of things used to work differently. I saw the card at my relatives' and while I couldn't take a phot, I was able to take the model number and there was a photo of it on the internet, not the best but it works for me. It was a Sound Blaster CT2700.
download/file.php?mode=view&id=136716

Now I would like to know what the following chips do:

  • CT1745A
  • CT1748A
  • The chip below CT1748A (probably it was CT1741)
  • The large chip (CT1746B)
  • That Mitsumi chip (he has a Mitsumi CD-ROM drive, related maybe?)
  • CT 1701
  • YMF262 (I know this one but maybe there's more that can be said here)
  • two RAKON chips
  • chips with MALAYSIA word

Thank you, hopefully I understand this card well.

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previously known as Discrete_BOB_058

Reply 1 of 12, by Disruptor

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The CT1748A is the so called ASP / CSP chip. It may be used for decoding and encoding simple audio algorithms like ADPCM. Re: Tests/Info welcome: Reverse engineering the SB16 ASP/CSP
The Yamaha YMF262 is the OPL3 chip. It is a music synthesizer.
The three? Rakon chips are oscillators. The big one has 46.61512 MHz, the right one has 14.318 MHz. I don't know the frequency of the left one.
The CT1745A is the mixer chip.
The CT1701 is a DAC that is a bit noisy.
The CT1741 is the DSP.
The CT1746B is the bus interface chip.
The 244's are octal buffer and line driver (unidirectional)
The 245's are octal transceiver and line driver (bidirectional)

Last edited by Disruptor on 2022-05-06, 17:36. Edited 4 times in total.

Reply 2 of 12, by BEEN_Nath_58

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Disruptor wrote on 2022-05-06, 08:36:

The CT1748A is the so called ASP / CSP chip. It may be used for decoding and encoding simple audio algorithms like ADPCM. Re: Tests/Info welcome: Reverse engineering the SB16 ASP/CSP
The Yamaha YMF262 is the OPL3 chip. It is a music synthesizer.
The three? Rakon chips are oscillators. The big one has 46.61512 MHz, the right one has 14.318 MHz. I don't know the frequency of the left one.

Thanks for the response. CT1748A, YMF262 and the Rakon chips are understood well. What about the other chips on the board?

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Reply 3 of 12, by RaiderOfLostVoodoo

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A bit more infos about YMF262:
The predecessor YM3812 (OPL2) was used in the original Adlib card. The first Adlib card couldn't play digitized sounds. So it would just play music, while the PC speaker was used for sound effects (like shooting). Creative countered the Adlib card with their Sound Blaster, which had OPL2 plus digitized sounds and was 100% backward compatible to Adlib.
Later both Adlib and Creative released cards with the YMF262 (OPL3) chip. OPL has twice the amount of channels (9->18), so more sounds at once. OPL3 also has a wider variety of sounds, but is backward compatible to OPL2. Also OPL3 has a clearer output. Some people prefer the dull sound of OPL2 for authencity but personally I would pick OPL3 over OPL2 any time.
On their later cards Creative exchanged the OPL3 for their own CQM chip, because they didn't like to share profits with Yamaha. But the CQM is often regarded as a bad copy. It sounds a bit off. This is extremely noticeable in the first level of Doom 1. There are better clones (ESS and Avance Logic for example), but OPL is the real deal for FM synthesis.

Reply 4 of 12, by Gmlb256

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RaiderOfLostVoodoo wrote on 2022-05-06, 21:29:
A bit more infos about YMF262: The predecessor YM3812 (OPL2) was used in the original Adlib card. The first Adlib card couldn't […]
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A bit more infos about YMF262:
The predecessor YM3812 (OPL2) was used in the original Adlib card. The first Adlib card couldn't play digitized sounds. So it would just play music, while the PC speaker was used for sound effects (like shooting). Creative countered the Adlib card with their Sound Blaster, which had OPL2 plus digitized sounds and was 100% backward compatible to Adlib.
Later both Adlib and Creative released cards with the YMF262 (OPL3) chip. OPL has twice the amount of channels (9->18), so more sounds at once. OPL3 also has a wider variety of sounds, but is backward compatible to OPL2. Also OPL3 has a clearer output. Some people prefer the dull sound of OPL2 for authencity but personally I would pick OPL3 over OPL2 any time.
On their later cards Creative exchanged the OPL3 for their own CQM chip, because they didn't like to share profits with Yamaha. But the CQM is often regarded as a bad copy. It sounds a bit off. This is extremely noticeable in the first level of Doom 1. There are better clones (ESS and Avance Logic for example), but OPL is the real deal for FM synthesis.

I would like to complement a bit on this.

OPL2 requires delay code between register writes and many software used dummy reads for delaying but on a faster computer these dummy reads went too quickly before being able to write again to the OPL2 chip, leading to weird noises and glitches. OPL3 is faster than OPL2 thus requiring less delay between writes and clones (CQM, ESFM, etc) are even faster.

That's why we don't see say a Pentium computer with a sound card using OPL2 aside from not being period correct.

Reply 5 of 12, by Cuttoon

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Understanding Soundblaster cards is a fun game, but don't do it to death. You could study that one card for a lifetime and then you'd understand one SB16 of a certain ctXXXX number or, more likely, the third of cards of that number that were actually built exactly that way and not missing some part or featuring some other one.

My point being: They are a mess.
There are several lists like this one and none is perfectly comprehensive, complete or English:
http://www.amoretro.de/guides-workshops/creat … r-modellnummern

My two cents on some parts:

The CT1748A is the so called ASP / CSP chip. It may be used for decoding and encoding simple audio algorithms like ADPCM.
- utterly useless as exactly one game ever supported it. Mainly a joke and collector's item. But in the latter sense, nice if present.

The Yamaha YMF262 is the OPL3 chip. It is a music synthesizer.
- Synonymous with game sound in the 90s but realized in so many variants. That one here is the original one, though.

The CT1745A is the mixer chip.
- That one is important in function, but rarely makes a difference in use, afaik.

The CT1701 is a DAC that is a bit noisy.
- And some are less noisy or noisy AF but most cards are not exactly hifi.

The CT1741 is the DSP.
- The version number decides whether it has a certain bug screwing up MIDI playback.

The CT1746B is the bus interface chip.
- Think that's what makes it a first generation SB16, but don't quote me on that.

General thoughts on that card:
The 2700 seems rare. It looks much like the 1st gen ct17xx cards, but with a Mitsumi CD-ROM interface. For whatever reason they'd call that one 27xx... don't try too hard to make sense of that, I like to think they used dice. But, SB pro 2.0 with Panasonic Interface is ct1600 while the one with Mitsumi port is ct2600 - so that would be logical, for a change.

By basic features, the one pictured here has
- Pre-PNP interface
- ASP / CSP chip present
- real OPL3
- volume wheel on the bracket - only the first ones had that
- single CD-ROM controller for proprietary CD-ROM drives from Mitsumi - since those are almost nonexistant, that's virtually useless. (later ones had IDE)
- a "wave blaster" header for MIDI daughterboards. All full SB16 and AWE32 had those, but not the "value" or budget cards or the AWE64
(While AWE32 and AWE64 are mostly SB16 with extra steps.)
- that silly white "Mitsumi style" CD-audio-in header. Basic cables have only the black 2.54 mm dupont plugs which are much more common, but the white ones can be found.

The ST TEA2025B in the upper right is a very simple stereo amplifier IC providing output levels sufficient for headphones or small passive speakers. AFAIK, the similar chip from Philips is better, and many contemporary sound cards used that one, but not CL. It should be avoided anyway by disabling it via some jumpers or using the alternative "line out" on some cards.

So, think you've hit a bit of a unicorn there, congratulations. Take good care of it.

Chances are, that DSP chip is version 4.05, 4.11 or 4.12 which would mean you could mess around with external MIDI modules or addon cards without the dreaded bug.
And also, it's pretty noisy, but none are perfect.

I like jumpers.

Reply 6 of 12, by Gmlb256

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Cuttoon wrote on 2022-05-06, 22:57:

The CT1748A is the so called ASP / CSP chip. It may be used for decoding and encoding simple audio algorithms like ADPCM.
- utterly useless as exactly one game ever supported it. Mainly a joke and collector's item. But in the latter sense, nice if present.

Yep, but it isn't when used to reduce CPU load while playing audio in Windows. 😀

Chances are, that DSP chip is version 4.05, 4.11 or 4.12 which would mean you could mess around with external MIDI modules or addon cards without the dreaded bug.

Only DSP version 4.05 for that SB16 revision doesn't have the notorious MPU-401 bugs, unfortunately. 🙁

In fairness though, not many bothered with this stuff back then on SB16 cards and played the MIDI music thru the FM synth which is suboptimal but better than nothing.

And also, it's pretty noisy, but none are perfect.

The out-of-the-box experience isn't optimal but the noise can be reduced by tweaking the mixer and muting the unusued outputs. It isn't perfect like you said but much better.

Reply 7 of 12, by BEEN_Nath_58

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Thanks for the information. I would like to know more about the mixer as well as the bus I/F chips, if the knowledge is available.

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Reply 8 of 12, by Gmlb256

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The SB16 mixer chip can control the volume for the following:

  • Voice: For digitized sounds.
  • MIDI: Used for controlling the volume of the FM synth (OPL3) and Wave Blaster. This is why partly people tend to wrongly associate the FM synth with MIDI.
  • CD: Audio transferred from the CD drive into the sound card thru a CD audio connector.
  • Line: Input volume for audio coming from the line-in port.
  • Mic: Microphone input volume.
  • PC Spk: Volume for PC Speaker output when connected to the SB16 PC_SPK header. A feature rarely found on SB compatible clone cards.
  • Master: Overall output level of the sound card.

The SB16 also has bass, treble and gain control, something that the Vibra variants usually lacks.

Reply 9 of 12, by BEEN_Nath_58

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Gmlb256 wrote on 2022-05-08, 15:13:
The SB16 mixer chip can control the volume for the following: […]
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The SB16 mixer chip can control the volume for the following:

  • Voice: For digitized sounds.
  • MIDI: Used for controlling the volume of the FM synth (OPL3) and Wave Blaster. This is why partly people tend to wrongly associate the FM synth with MIDI.
  • CD: Audio transferred from the CD drive into the sound card thru a CD audio connector.
  • Line: Input volume for audio coming from the line-in port.
  • Mic: Microphone input volume.
  • PC Spk: Volume for PC Speaker output when connected to the SB16 PC_SPK header. A feature rarely found on SB compatible clone cards.
  • Master: Overall output level of the sound card.

The SB16 also has bass, treble and gain control, something that the Vibra variants usually lacks.

Seems nothing special, just a regular mixer then. I didn't expect a PC speaker volume feature, never had I seen one.

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Reply 10 of 12, by rasz_pl

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Disruptor wrote on 2022-05-06, 08:36:

The CT1741 is the DSP.

Creative traditionally used 8051 microcontroller here https://en.wikipedia.org/wiki/Intel_8051 https://www.os2museum.com/wp/sound-blaster-th … nch-connection/

Disruptor wrote on 2022-05-06, 08:36:

The CT1748A is the so called ASP / CSP chip. It may be used for decoding and encoding simple audio algorithms like ADPCM. Re: Tests/Info welcome: Reverse engineering the SB16 ASP/CSP

ST18932 DSP, apparently fast enough to fully implement V.32bis (14 400 bit/s modem). It also has quite flexible synchronous serial port able to talk I2S among other protocols. Creative choked its IO and ram size, as a result its useless beyond adpcm.

Reply 11 of 12, by BEEN_Nath_58

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rasz_pl wrote on 2022-05-09, 07:42:

Afterwards, what was it upgraded to?

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Reply 12 of 12, by mkarcher

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BEEN_Nath_58 wrote on 2022-05-10, 06:11:
rasz_pl wrote on 2022-05-09, 07:42:

Afterwards, what was it upgraded to?

An 8052 (double the ROM of the 8051) for the SB16. The part controlled by the "DSP" (it's not what we typically call a "digital signal processor", though) is the same on the SB16, SB AWE32 and SB AWE64, so it was never upgraded. The SB PCI cards do not have a microcontroller like that on the PCB anymore, so the 8052 was never upgraded to anything else.

In all fairness of bashing the 8051 for not being a "real DSP" (we expect a real DSP to provide some MIPS of multiply-accumulate power of at least 16 bits x 16 bits, which the 8051 doesn't nearly achieve - you have to multiply in software on 8 bit registers), Creative Labs actually had the 8051 to some kind of "DSP" work on the SB 1.x: The hardware decompression of 1:2, 1:3 and 1:4 ADPCM compressed sound was indeed performed in software on the 8051. And that's why these modes never exceeded 11kHz to 13kHz mono, and quickly got forgotten, with Duke Nukem II being one of the few games to actually use these modes.