First post, by GabrielKnight123

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Hi everyone, I've built a 486 pc using a Pro Audio Spectrum 16 but when I use the full speed of the CPU at 66Mhz the audio is very scratchy but using the turbo button to slow the pc down it sounds fine and clear, if I change the AT bus clock from CLK/4 to CLK/5 I get clear sound at 66Mhz is this safe to run the ISA clock at CLK/5 for the PAS16 and if it is is it also safe for a MPU-IPC-T card.

Reply 1 of 3, by mpe

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66 MHz 486 CPU uses 33 MHz bus. So:

CLK/4 = 33 MHz / 4 = 8.25 MHz
CLK/5= 33 MHz / 5 = 6.6 MHz.

Both are very safe. AT Bus clock was standardised in ISA standard at about 8.33 MHz.

It is weird that it makes any impact on sound quality though.

Blog||486DX-50|NexGen 586|S4

Reply 2 of 3, by GabrielKnight123

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IIRC someone here said the PAS16 needs a 2/3/486 as using a faster Pentium is too fast for it and I found for this pc build a game could have the audio option for the PAS16 and sound scratchy but the "Pro Audio Spectrum" option has clear sound so i was disabling the motherboard cache to get clear sound but my adventure games characters were walking very slow. Ide rather use CLK/5 and the cache on or use Pro Audio Spectrum setting as I can't hear much difference between PAS and PAS16.

Is it ok to run a MPU-IPC-T card at CLK/5 6.6MHz for an MT32 and SC55


Reply 3 of 3, by Jo22

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Hi! I was using my PAS16 in a 286-12 originally, but kept it up to ca. a Pentium 75 to 133.
I'm not 100% sure, but I believe that 286 ran both CPU and BUS at same speed (12MHz).
The Pentium ran Windows 98SE (and Windows 3.10) and my PAS16 worked out-of-box.

If you encounter trouble, please make sure the PC's PSU has got -5V.
Additionally, try booting DOS without EMM386. That once worked for me..

PS: Happy New Year, too! 😁

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