PCBs are still not tested...
But I've moved the project a little bit further.
Small update for MIDI host block (due to WaveBlaster header integration into design).

- MIDI (HardMPU-based) @2019-08-01
Interface parts with external connectors were added as well as internal
WaveBlaster header.
Next, some things were re-thought in process of integrating all of the blocks into
FMonster main board.
Now it is not just an outline and some blocks that were thrown in.
I've tried to implement the sound mixer.
At first I thought that I'll pull output traces from each block to the right side of the board and then mix all of them there. But I quickly realized that there will be no place for all those traces on top of the board. AND I have to squeeze WaveBlaster header between those somehow.

So, I've transitioned to an idea of "distributed mixer" with "pseudo-differential" buffers to prevent ground loops via outputs of multiple blocks.
Here is debug block of the mixer (with low-pass filter):

- Mixer @2019-08-01
After several iterations of buffer amp design I've managed to squeeze it into 7.7 mm of height.
Than I've redesigned ISA bus along the bottom of the card.
And...
CMS (Creative Music System) block didn't fit in between. At was the tallest block (about ~70 mm). Last revision of it was made almost a year ago. So... It was time to retrace CMS block.
And I've done it.
New version is 2 mm thinner and (what mattered most) more than 10 mm lower. And now it fits.

- CMS @2019-07-28
In the process I've added two linear regulators (one for each
SAA1099, because one regulator will not supply enough current to both SAAs).
The next achievement - I've finished the right side of the main board that was not touched before.
What was done?
- determined set of connectors (line output 3.5 mm, 2x MIDI outputs mini-DIN, MIDI input mini-DIN)
- added mounting points for
Keystone 9202 metal bracket (I will not supply it, I will supply PCB bracket, but Keystone 9202 can be installed if desired)
- added output low-pass filter
- added MIDI interface circuitry
All that resulted in a clear line from which I can put all synth-blocks.

- FMonster @2019-08-09

- FMonster @2019-08-09
And that is almost ready
FMonster main board!
Only
AY (CSM) block is not ready yet, everything else is in place and is fully connected (ISA, power, output, mixer).
I've changed order of the blocks, now
2xSID (DuoSID) block is on the right side of the main board and clock circuit is to the right side of this block. This was done to decrease number and length of clock traces on the board. For example, the only part that requires 14.318 MHz is
OPL3 block. And now it is right to the right side of clock block with a shortest clock line.
Also there was one problem with sorting synth blocks... The
WaveBlaster header. It should be as closest to the right side of the main board as possible.
Because, first, MIDI data trace should be short to prevent interference and, second, not to overweight the right, not supported, part of the board.
But
WaveBlaster header is pretty long and spans for overall distance between main board and optional MIDI synth board. So, if there will be an output level trimmer below the header - it will become useless. And that was the problem - I had almost none combination of blocks that will give me that long distance without any trimmers! But I've managed to find and implement one.
