If I had to guess, Diamond simply made several different versions using the same board and stencil.
I've seen versions of the SpeedSTAR 24 with a Sierra SC11483 15-bit DAC too.
Fitting a 24-bit capable RAMDAC (try looking for the SS2410 or Music MU9c1880, those are the same chips that the 24-bit DAC the 'high end' versions came with) ought to give you the higher color depths you want.

Eep386 wrote on 2020-11-07, 18:36:

If I had to guess, Diamond simply made several different versions using the same board and stencil.
I've seen versions of the SpeedSTAR 24 with a Sierra SC11483 15-bit DAC too.
Fitting a 24-bit capable RAMDAC (try looking for the SS2410 or Music MU9c1880, those are the same chips that the 24-bit DAC the 'high end' versions came with) ought to give you the higher color depths you want.

I will just swap out the RAMDAC for one of those that you suggested. Thanks!

Yes, there were at least three variants of SpeedSTAR24, see the pictures in this thread:
Diamond Speedstar24 Bios versions

Grzyb wrote on 2020-11-07, 21:25:

Yes, there were at least three variants of SpeedSTAR24, see the pictures in this thread:
Diamond Speedstar24 Bios versions

Thank you for pointing out that thread. It appears that different RAMDACs may require specific BIOS from Diamond to work properly. I could put another RAMDAC in only find out I am no better off. I am just going to run the card with 256 colors. It is currently in a Tandy 1000 TL/2 anyway. I have a Micro-Labs ET4000AX board with an AT&T 24-bit RAMDAC I can you use for other builds. Glad I asked about this card.

I have a SpeedStar24 with the 15bit SC11483CV-80 DAC:

if you get one I can dump the bios so you can at least use 32K modes

Just out of curiosity I am doing some searching for a SS2410 or a Music MU9c1880 RAMDAC for purchase. So far I can't find anything. I checked Digikey, AliExpress, JameCo and eBay, plus searching on Google. Any ideas where to find one of these? If one is not too expensive, it may be worth trying to swap the RAMDAC after all. I remember putting in a HiColor RAMDAC in my Orchid Prodesigner II ET4000AX many years ago. It worked without a BIOS update.

It should be possible to use >8-bpp modes even without upgrading the BIOS, by using UniVBE.
UniVBE is good at detecting the RAMDAC, and if not, it's possible to select one manually:

Still, it would be a good idea to do the BIOS upgrade, as there's some software which uses non-VBE modes.

SS2410 was a DAC made for diamond or a rebranded one - I doubt you'll find that
the 15bit one should be available and in reality it will be fine for an isa card

The SC11483CV from Sierra is available from quite a few sources. I will look into getting one.

keropi wrote on 2020-11-07, 22:13:

I have a SpeedStar24 with the 15bit SC11483CV-80 DAC: […]
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I have a SpeedStar24 with the 15bit SC11483CV-80 DAC:

if you get one I can dump the bios so you can at least use 32K modes

please dump them! I'd love to give a 15bit DAC a try in my card

BTW please dump the actual EPROMs in a programmer, software dump is not helpful here since they are encoded

will do!

I'm surprised and wonder - what are >256c acctually being used for? Photoshop? watching Video CDs?

I always sticked to 256c, because that colour depth fits so nicely to applications of this era.
For example, colour-cycling works nicely in 256c.
It's also causing less overhead on ISA bus.

This is no critique, I'm simply surprised. 😅

24-bpp is highly recommended for viewing JPEG picures, ray-tracing, etc.

Interesting topic.

I happen to have 2 of these cards. One with 24-bit DAC and a second with 8-bit one.

24bit

8bit

They are identical, except a "made in USA" print.

The second card produces subtle and hard to describe with just words incorrect background color fill during palette transitions in some games. Where it should be black it is sometimes dark blue.
Not sure if this is because of the .01 difference in the BIOS between the two cards, or maybe it is the DAC. The problem is so minor that i never bothered to investigate.
Other than that i didn't actually notice much difference in picture quality, but i use them mostly on 286 and 386 class computers where 8bit graphics are the norm and there is a chance i missed something obvious.

can you name a specific game? because mine has the exact same DAC, I'd be curious to try that.

Captured 2 short videos from Wolf3D running on a 286 PC:

This one shows the video card with 24 bit DAC and BIOS version 5.01:
https://www.petershipkov.com/temp/retro_pc_im … x_24bit_dac.mp4

And another one showing the card with 8 bit DAC and BIOS version 5.00:
https://www.petershipkov.com/temp/retro_pc_im … ax_8bit_dac.mp4

Notice the blue color fill flashes.
I cannot remember which other 2 or 3 games i have seen this artefact in.
Was it Indiana Jones and the faith of Atlantis ?

I never looked at what may be causing this minor issue, so take the info for what it is.

did you try just swapping DACs ? maybe this fixes it?

looks perfectly fine on mine ^^

Then it looks like a BIOS version specific issue, assuming you are running 5.01

I can swap DACs and BIOSes around, but i doubt it is DAC specific.