Can the mixer be upgraded on the SB16 CT1740? \ VOGONS

Can the mixer be upgraded on the SB16 CT1740?

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First post, by FinalJenemba

Posted on 2023-03-11, 01:21

FinalJenemba Offline

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Own one of these and it’s one of my favorite overall cards. Has some of the best sounding OPL3 support and the 16bit playback sounds great, and bug free MIDI, no PNP. But as everyone knows, it has the noise issue. Mainly with 8 bit lower sample rate stuff. Is this issue directly because of the 1701 mixer chip? If I was willing to sacrifice a newer card, that had the newer 1703-a mixer revision, could I swap the mixer chip over to this card? The soldering would not be particularly difficult. But would it be compatible and would it solve the noise?

Reply 1 of 2, by Joseph_Joestar

Posted on 2023-03-11, 05:15

Joseph_Joestar Offline

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If you're referring to actual noise, and not the DMA clicking bug, check this post by Cloudschatze.

By setting the OPSL/OPSR jumpers to the correct position, you should be able to bypass the card's internal amplifier and get cleaner output.

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Reply 2 of 2, by Cloudschatze

Posted on 2023-03-11, 21:25

Cloudschatze Offline

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The CT1701 and CT1703 are CODECs; the CT1745 is the mixer IC.

Regarding the single-cycle DMA "clicking" behavior that Joseph_Joestar mentioned, here are a couple of mitigation efforts to try:

Set the DOS stacks value to zero (STACKS=0,0)
Forgo the use of EMM386.EXE if/where possible
Temporarily set the SB16's treble setting to zero

The first two points relate to the speed/response of interrupt servicing, where the third is an application of low-pass filtering that reduces the frequency response of the SB16 to more-closely match that of the earlier Sound Blaster cards.

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