New FPGA-based MSX

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By George.rm

Supporter (13)

George.rm's picture

19-04-2018, 23:49

I'll look into it. Funny thing is, I have found some serial A/Ds in the trash a few days ago. Never would've happened to me, using those to route cart audio to the FPGA. Thanks for the suggestion!

By blackmsx

Expert (70)

blackmsx's picture

25-04-2018, 11:54

hardwaremaker wrote:

OK, sorry, the OCM don't uses the 74HCXX IC's. Only the Zemmix uses them.

Those chips are only used for the scanlines effect and can be stripped out without much changes.

By Eugeny_Brychkov

Paladin (962)

Eugeny_Brychkov's picture

27-04-2018, 13:50

I hope that this new machine will have proper sound mixing hardware designed on opamps, not just copy of the ugly circuit from original OCM.

RetroTechie wrote:
gdx wrote:

If you can also improve the sound mixing, do not hesitate!

Better yet: include a small 2-channel A/D converter, put cartridge slot audio signals in there with minimum filtering on the input, and do mixing in the FPGA logic. That way it's easier to fix/enhance mixing later. Or make it programmable through some I/O port, provide a hotkey or whatever.

I disagree on this approach. There's no need in such complexity making analog sound distortion and depending on the sampling rate.

You must buffer FPGA DAC outputs using op-amps in voltage follower modes, and then mix with also buffered outputs of slot connectors, and buffer all that mixed stuff before outputting to the outer world. Ideally.

By George.rm

Supporter (13)

George.rm's picture

02-05-2018, 06:57

I was gonna put a TL084 in there, but to be honest space was at a premium. Maybe in future revisions I can figure something out. This was just a first attempt at making any kind of moderately complex PCB.

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