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Sol-20 Reproduction

Good choice. If ever there was a vintage computer that was worth replicating, it has to be the SOL-20 and it is a manageable size.

I have been keen on replicating some S-100 boards in the past, such as the Dazzler and some others for vintage computers, but a whole computer, that is really something.

One interesting thing is practically all the IC's are still available and not expensive. Though there is the temptation to replace large gate arrays with FPGA's.

When I do a replica I try to make it exactly as the original, even the shapes of the pcb tracks. It is not to pass it off as the original, but just make it as close as possible. I think of it like "making spare parts" and the main pcb might be one of those parts. And then the parts are interchangeable for the originals. This is one very big advantage. For example if you made the cabinet parts identical (the woodwork, the paint color & texture, metalwork geometry etc), they would be a great source of spares for people with original SOL-20's.

One part I found hard to get for the SOL, but finally found them, are the plastic slides that support the S-100 boards, the ones in mine had cracked. The original SOL cooling fans are still available. It might take a batch of transformers to be wound for the power supply. Though you could use an SMPS, but I find the analog supply part of the charm of the whole thing.
 
isn't he just making a case with a PI in it?

I wasn't sure how close the replica would be, the case looks pretty good.

One thing about emulators of logic circuits is they can get the input vs output functions pretty close or maybe even bang on so that two completely different hardware setups appear to do the same thing. But sometimes there are things that are very very difficult to emulate, or at least I don't know any way of doing it without constructing the exact original circuit.

One good example, say in the SOL, is the function of the circuitry that processes the Tape signals. Because its mixed analog in function, has specific issues of signal dynamic range and noise immunity, PLL locking properties all combined to make a "thing" with unique functional properties.

Though I guess people using a SOL emulator/replica might not want tape storage. I did for mine initially before I moved to a pair of disk drives and a N* card. But I liked the tape signal process circuitry in the SOL so much I did up an article on it because it was a very interesting and clever circuit they created in there :

https://www.worldphaco.com/uploads/The_SOL-20_tape.pdf
 
Although the RPi doesn't contain an ADC/DAC converter, there are plenty of simple add-ons for it, so the analog aspect isn't as daunting as it used to be.
 
Retro “Reproduction” projects that concentrate on the case/look/feel of the complete unit while leveraging emulation for operation are a fairly popular sub-genre these days. It’s not quite my cup of tea but I’m not going to “yuck someone else’s yum”, as we tell the kids.
 
Definitely a cool project. For those into a 100% reproduction, you could always take the case that megardi is designing and use it to house your own innards.

There's nothing wrong with emulating original hardware, anyway. That's been done in production often enough, due to evolution or unavailability of spares, or a mountain of other reasons.

- Alex
 
Thank you all for posting. I just realized that I had not Subscribed to my own post so missed getting Emails.

As has been posted yes I am emulating the Sol-20’s internals. I am trying to provide a hands on Sol-20 experience for people who would never get the opportunity given how rare they are (like me ;-).

Right now my emulator has “virtual” cassette tapes that make it easy to load and run the original Sol-20 programs that can be downloaded from Jim Battle’s Sol20.org site. Adding a physical tape interface is a cool idea I hadn’t really thought about.
 
Right now my emulator has “virtual” cassette tapes that make it easy to load and run the original Sol-20 programs that can be downloaded from Jim Battle’s Sol20.org site. Adding a physical tape interface is a cool idea I hadn’t really thought about.

That is very very cool that you made virtual cassette tapes ! These are bound to be much better than the originals with no dropouts.

It could be an interesting idea, for all retro computers that use cassette tape interfaces, to make an external solid state cassette recorder interface with lots of memory to eliminate the real recorders and cassettes. This might even be more reliable than a floppy disk drive, albeit slower. Though I suppose these exist to some extent already with items like solid state dictaphones made by the people at Olympus, though the one I have in front of me on my desk uses a USB port to send the files in digital format to the computer where the Olympus software lives.
 
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