VIDEO RGB BUFFER BOARDS

[exxos]

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Some of the biggest annoyances of the ST line of computers is the bad video quality. Some people may remember when we were developing the remake boards I produced a test board such as THIS ONE. The effort was to provide a much sharper and cleaner noise free video signal.

In amongst a tidying up I have been trying to do lately. I have come across the boards which were revised but never made it into mass production. I hooked up one of these later boards and was extremely impressed by how well it cleaned up the video signal.

I threw up a quick page on this project here.

https://exxosforum.co.uk/atari/last/VIDEODAC/

I have several more of these boards. They have the SMT birdseed on them. But not the VIDEO DAC IC itself. It of course requires the headers and the socket to complete it. Plus the usual few bodge wires.

I will put the remaining boards in the store. If there is significant interest I will consider getting a small run of these boards fully assembled.

https://www.exxosforum.co.uk/atari/store2/#0253

[Steve]

Wow! This, is absolutely amazing. I think you're on to a winner with these boards. Something a lot of people want!

[Cosmic Puppet]

I like this!

[BigSteve]

Does this DAC widen the frequency range so that we are not so constrained with VGA monitors in colour mode?

[PhilC]

Does this DAC widen the frequency range so that we are not so constrained with VGA monitors in colour mode?

The output from the board is still the same frequency wise. Just of a much better quality. I have one to build up over the next few days and will show the quality difference between a standard STFM and ATX st and with this board fitted.

[exxos]

. I have one to build up over the next few days and will show the quality difference between a standard STFM and ATX st and with this board fitted.

Be interesting to see the difference. So is this the first step of mods to bring the atx inline with the H5 now then :lol: it will make it to the alpha level next :lol: :hide:

[PhilC]

@exxos its certainly an easy and quality upgrade for the ATX, along with HD floppy and a couple of other ideas

[exxos]

Looking at the mother board I posted on my website. There are 2 sets of power cables going above and below the shifter. I first thought they could be there as power wasn't routed on the PCB. But now wonder if it was a "quick fix" by Atari to couple the digital noise via the cables directly back to the PSU.

So it would be interesting to unsolder them and see if the power still gets to the right side of the board. Also interesting to what part they play in video noise.

It looks like this could have been the revision before viewtopic.php?p=90292#p90292

[exxos]

I did some very quick tests just. It seems both power rails are completely missing on the upper cables.

The bottom two cables only 5V is actually doing anything. I cannot see any visual difference on the interference on the screen with or without the ground cable connected.

The problem could be the impedance of the wire is probably greater than the impedance of whatever crazy ground there is on the motherboard anyway. It would really need something like Litz wire with a suitable gauge to have any significant effect.

I did not see any visual differences with or without the extra ground wires. But it was at least interesting experiment anyway.

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The camera and rescaling of the image pretty much ruined the illustration of the vertical noise. Can only really notice it on the left side in the plane blank white area. But that vertical bar interference is present throughout the picture.

[exxos]

I also had the idea to put the 4MB RAM adapter connector on the DAC board. As if anyone wanted to use the MMU style RAM upgrade, along with the DAC board, it would create a rather tall "stack" of it all. Apologies to those people who like building towers but it just made sense to do this :lol:

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I see A few of you have purchased the current board from the store (thanks!). Please post your installs and results on the forum somewhere and see if there is any oopies which need to be addressed before I consider getting any more boards done.