I am working on a friend's Imsai 8080 that we just pulled out of his storeroom after 40+ years. Back then he was into computer generated music and there is one mystery card I cannot find info on. I'm focusing first on the basics - MPU and front panel - but I'd like to get info on this mystery sound board that neither Claude or ChatGPT can tell me about. I have attached front and back images and I can provide closeups if necessary. The markings seems to say this a DMC SB-64 card made in 1979. Any ideas?
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What is this sound generator board?
- Thread starter kyrbee
- Start date
twolazy
Veteran Member
From what I could find, its pointing towards a MicroDASys SB-64 12bit DAC/ADC.
Istarian
Veteran Member
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From the pictures of a couple boards here, I think you'd know if the board was made by MicroDASys. And MD or MDS is a more likely three letter sequence to appear on early products by them.
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Unless the 'DMC' logo made out of pcb trace is a red herring, that would seem to suggest it is a company's name or an abbreviation thereof.
It looks like datamedia corporation might have used 'dmc' on some of their marketing materials, but I can't tell if they made anything other than terminals.
Of course DMC could be just about any company since lots of words (data and digital being two options) and plenty of names start with D, M could easily stand for Micro or Microcomputer, and C is likely (but not guaranteed) to stand for corporation.
Thanks for all the ideas. A followup with Claude (sometimes you get different answers the next day, and sometimes they're better) summarized : "Digital Music Corporation SB-64, circa 1979 — a 64-oscillator digital sound-generation board used in an early DMC/Synclavier computer-music system, implemented as a large self-contained processor and waveform-generation subsystem." This makes sense since my friend was quite into music, especially digitally created content. "Synclavier" also rings a bell as he was discussing that back then. Claude also cautioned me to better understand the card before plugging it into an 8080 bus since the card has processing and nothing is known what to do with it. I'll keep digging, and thanks again.
pbirkel
Veteran Member
The first part of that description is pretty consistent with the on-board circuitry, where we see an 8-bit equal-to comparator for addressing, a 64x9 bit RAM, a 12-bit DAC (probably only 8-bit employed), and then 64 channels of analog steering followed by 64 channels of op-amp driven output.
The second part is, IMO, completely confabulated as the visible circuitry appears to expect a CPU (somewhere) to be updating the RAM with the desired waveforms (step by step) for all 64 channels in real time. I don't see evidence of circuitry to support DMA to the RAM so the interface would be programmed I/O. Perhaps there's something sophisticated going on with the extra 4 bits supported by the DAC but at first blush it seems to me that there would have been a second board perhaps cabled to the upper-left OTT connector that would have added the missing "sophistication" of a "large self-contained processor" _or_ the description is of an entire system of which we're seeing just the output portion. The part-whole confusion wouldn't be unexpected from a LLM.
You don't mention a second board that had a top-left edge connector that matches the one on this board which thus might have been cabled to it?
Istarian
Veteran Member
@pbirkel Any thoughts why there are 5 separate sets of 2x10 horizontal pin headers on the upper edge of the board? They each appear to be missing a single pin (not snapped off, absent) in a different sequential location starting from the upper right.
Also the upper group of chips includes 8x MC14051B which are SP8T digitally-controlled analog switches...
It is also referred to as an "8-channel Analog Multiplexer/Demultiplexer"
So maybe there are 64 units of something on here, like signal paths? And presumably you can route 8 of them to an output.
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If OP has more boards, they should post pictures of all of them so that they can be at least identified and potentially ruled out as connecting to this one.
Also the upper group of chips includes 8x MC14051B which are SP8T digitally-controlled analog switches...
It is also referred to as an "8-channel Analog Multiplexer/Demultiplexer"
So maybe there are 64 units of something on here, like signal paths? And presumably you can route 8 of them to an output.
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If OP has more boards, they should post pictures of all of them so that they can be at least identified and potentially ruled out as connecting to this one.
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hjohnson
Experienced Member
I think Istarian is correct that "DMC" is some arbitrary company logo. Search of MicroDaSys documents as online simply don't mention a multichannel audio board, they have a different logo, so that's a dead end. Search for Synclavier finds hardware references but they don't identify S-100 architecture. Searching for "DMC" is kinda fruitless., even if it means "Data Music Company", too common a phrase. Image search for the DMC logo didn't find anything matching but logo images are hard to search. The US has a trademark federal registry, look for that.
History suggests this board like many, came from some company that produced only a few S-100 boards, maybe some other computer-based products (or not). The docs may not be findable (anytime soon). But this board looks interesting and non-trivial, but not too obscure.
1) Talk to the friend who owned this board, pick their brains for any clues. check their disks/tapes for files with clues,check their papers for docs or clues. Did they go to an event where this product was sold or shown? Hopefully that IMSAI had cabling for that board, document the cabling. Note the IMSAI's disk controller; that may determine the disks formats for any data/code recovery. It is, after all, 45 years old
2) The original poster did not ask for diagnostic advice. But I suggest without details, that forensic examination of the board (check for shorted caps is a real good idea) and docs of chips, will reveal general function. Tracing of the S100 signals and one of the many connectors ought to be informative. Careful powering of the board and careful I/O and memory search, plus knowledge of the complex chips on it, ought to reveal basic functions. My point is, "sometimes the hard way, is the easiest way" to make sense of this board. It ought to be interesting if you like digital audio.
Good luck, regards - Herb Johnson
History suggests this board like many, came from some company that produced only a few S-100 boards, maybe some other computer-based products (or not). The docs may not be findable (anytime soon). But this board looks interesting and non-trivial, but not too obscure.
1) Talk to the friend who owned this board, pick their brains for any clues. check their disks/tapes for files with clues,check their papers for docs or clues. Did they go to an event where this product was sold or shown? Hopefully that IMSAI had cabling for that board, document the cabling. Note the IMSAI's disk controller; that may determine the disks formats for any data/code recovery. It is, after all, 45 years old
2) The original poster did not ask for diagnostic advice. But I suggest without details, that forensic examination of the board (check for shorted caps is a real good idea) and docs of chips, will reveal general function. Tracing of the S100 signals and one of the many connectors ought to be informative. Careful powering of the board and careful I/O and memory search, plus knowledge of the complex chips on it, ought to reveal basic functions. My point is, "sometimes the hard way, is the easiest way" to make sense of this board. It ought to be interesting if you like digital audio.
Good luck, regards - Herb Johnson
twolazy
Veteran Member
I am in agreement. Its all that I could find scouring the web for round an hour... Seems more likely.
Heres the jist, I found another board almost identical, with that same company/title/name.
*shrug*
Only reason I said anything... Its def an DAC/ADC of some sort. Now my best guess its some sort of digital measurement, rather then audio. Good example, an oscilloscope.
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pbirkel
Veteran Member
Front PCB traces show that four are wired to op-amps; the fifth on the left is an unknown based on the front traces. The missing pin(s) on each male IDC-type connector are used to ensure that the associated ribbon cable isn't attached upside-down or to the wrong connector; the associated female connector will have one or more of those positions blocked.
mark0x01
Experienced Member
Could the DMC be Dartmouth College referenced here as where the Synclavier was created?
Thanks for all the ideas and suggestions. There was no second board and my friend has no recollection of one, and there were no remaining cables. Sorry for the lack of info. I think the next best approach is what was suggested, the hardest/easiest, and just trace it out. The four similar IDC-type connectors with different missing pins, plus a fifth IDC with different circuitry suggests a four channel something with a controller or monitor port. But first, I'll be working on the Imsai itself.
Istarian
Veteran Member
While it does potentially fit the letters, I think that's somewhat unlikely
It's not impossible that there's some kind of loose connection to the development of the Synclavier. But as far as I can tell from searching online neither the Synclavier I or II seem to use S-100 style boards or obviously use the Intel 8080/Zilog Z80.
While an S-100 compatible system could probably have ben used to control the synthesizer, the actual synthesizer boards don't appear to have any appreciable similarity.
hjohnson
Experienced Member
Okay ..... where did you find this? Web link please? - Herb
To wrap up the potential Dartmouth thread I emailed them. Their comm person routed my email to appropriate departments and the concluding comment was "There is no indication I can see that the board had anything to do with Dartmouth ("DMC" is not an abbreviation for anything Dartmouth-related that I'm aware of.)". So, I'm going to pack this card back in its anti-static bag and go onto other activities, including finishing the Imsai refurbishment. I'll probably get back to the card at some point and try to trace it. Thanks to those who weighed in here.
twolazy
Veteran Member
I found it using Gemini after a bunch of different searches and refining.
Istarian
Veteran Member
FWIW doing a 'reverse image search' can sometimes turn up useful results that are otherwise difficult to find because most searches are text queries (i.e. is this word or a particular phrase present)
E.g. a website with archival materials like a folder full of images doesn't necessarily contain any searchable text OR there might be an ebay listing by a clueless seller who has not include ANY useful keywords.
Suppose they have an S-100 bus RAM card but know zero about such things. So to them it's just a 'printed circuit board with IC chips'.
Even "expansion card" is far too vague, but would suggest the seller think it's part of a more general purpose computer and not some oddball industrial system or embeddee system
jlang
Veteran Member
After looking a bit its a 64 channel DAC
It has a single 12 bit DAC routed to 8 analog switches
followed by 64 op-amps.
the analog switches (MC14051) route the DAC output to 1 of the op-amp channels.
it operates like this:
a value is written to the DAC then routed by the analog switches to a single op-amp (per channel) operating as a simple sample and hold.
this is repeated for each channel to produce 64 different analog outputs.
Do this fast enough and you get the illusion of 64 DAC channels. You have to refresh each channel before it drifts to far off the desired value.
It's not a smart board. It's as dumb as they come.
It has a single 12 bit DAC routed to 8 analog switches
followed by 64 op-amps.
the analog switches (MC14051) route the DAC output to 1 of the op-amp channels.
it operates like this:
a value is written to the DAC then routed by the analog switches to a single op-amp (per channel) operating as a simple sample and hold.
this is repeated for each channel to produce 64 different analog outputs.
Do this fast enough and you get the illusion of 64 DAC channels. You have to refresh each channel before it drifts to far off the desired value.
It's not a smart board. It's as dumb as they come.