VOGONS


First post, by BadGoldEagle

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Hi all
This is my first post here. I'm a Mac enthusiast and I've just bought myself an Apple PC Compatibility card for the Powermac 6100. This is basically a full PC with a 66MHz 486DX2, SVGA graphics and a Vibra 16 sound card. The card uses the Mac's keyboard and mouse, and can output to the same monitor. The sound can be passed through to the Mac side via internal CD Audio cables.

The card is used with a specific cable that breaks out into multiple ports, including a joystick port. However, the MIDI signals are absent from this port and pin 15 has 5V so it cannot be used with MIDI devices at all.

The particular VIBRA 16 on this card uses a CT2501 chip. I was wondering if it would be possible to hack a MIDI port from this chip's pins. I'm sure this is doable, plus since I only need midi out, I wouldn't need to modify it too much.

Problem is, I can't find any info about this Creative CT2501 chip or any schematics... Can someone here help me figure out where the MIDI pins are?
Thanks!

Reply 3 of 19, by derSammler

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You wrote you only need MIDI out. MIDI out does not even use pin 15! MIDI out is pin 12, with pin 8 supplying 5V and pin 5 being GND.

Also, you most likely counted the pins wrong, as no company would connect a pin to 5V that is normally used for something else. Pin 15 is the last in the upper row, pin 8 is the last in the lower row.

ps: you need the cable anyway, unless you want to build the TTL to current-loop converter yourself.

Reply 4 of 19, by keropi

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well I looked at my stash but I have no CT2501-based cards...
it would not surprise me that a compatibility card would not have all features available , still it worths a shot to try with a gameport->midi cable

🎵 PCMIDI mpu site buy+info
🎧 WIP Orpheus soundcard site
💻 WTB Amstrad PC7486SLC-33 system

Reply 5 of 19, by BadGoldEagle

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Sorry for not getting back to you guys sooner. I don't have this card in front of me at the moment. I just bought it, it's in the mail and it'll take quite some time before it arrives. All the information I got about it came from a pal on another forum who has one. So I haven't tested it myself. I sure will when it gets here.

I found this schematic while writing this post:
midi_1a.gif

Apparently, on a joystick only port, pin 15 is tied in to pin 9, which is connected to 5V. That seems to be in accordance with what I said above...However, a Game MIDI adapter (that would be the port traditionally found at the back of the sound card, right?), doesn't have 5V on pin 15. Could the port on the breakout cable be just a joystick port and not a gameport? Perhaps...

If so, what kind of circuitry is needed from the creative chip to the midi out port?

Reply 6 of 19, by keropi

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I don't know about the rest but

BadGoldEagle wrote:

[...]
If so, what kind of circuitry is needed from the creative chip to the midi out port?

this is hard to answer without examining an actual card. It could just be straight connections from the chip, there could be pullups, pulldowns, etc... we don't have the specs so we can't really guess. What I can answer though is what is needed between the gameport and the midi device:

tzvAwcJ.png

this is a simplified midi-out-only version I built for use with SB cards and it works fine , it is based on info discussed here: Good schematic for simple joystick->midi-out adapter?
Maybe you can do the same and test when the addon arrives?

🎵 PCMIDI mpu site buy+info
🎧 WIP Orpheus soundcard site
💻 WTB Amstrad PC7486SLC-33 system

Reply 7 of 19, by BadGoldEagle

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I guess I better get myself a CT2501 equipped card (They aren't that expense anyway) and track down where exactly the Midi out signal comes from. Worse case scenario, it would be just one or two 74 series chips, right?

Reply 9 of 19, by BadGoldEagle

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Good to hear, that'll probably help keep the complexity as well as the costs down (no custom daughterboard required).

It might be worth trying to contact Creative about this? You never know, I once tried to contact Sanyo's customer support about a 25 year old fan and they replied...
I could grab 5V and Ground from any other chip or via so the only unknown is the midi out signal itself.

Reply 11 of 19, by BadGoldEagle

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My Quadra died back in February. I had to gut the PSU and build an adapter which allowed me to use a standard ATX PSU (https://68kmla.org/forums/index.php?app=forum … &comment=652901).
It's still in the testing phase so I'd like to make sure it's stable before I put the DOS card back in.

The only way to get MIDI out is to get a PC CT2501-equipped card (CT2810 or CT3930 for example) and check how the signal is routed with a multimeter. As fellow collector Der Sammler suggested, it's probably going to be quite easy (I don't think there are any passives between the chip and the port). I just need to find a cheap card.

Reply 13 of 19, by Tyrantulas

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BadGoldEagle wrote on 2020-10-04, 18:47:

My Quadra died back in February. I had to gut the PSU and build an adapter which allowed me to use a standard ATX PSU (https://68kmla.org/forums/index.php?app=forum … &comment=652901).
It's still in the testing phase so I'd like to make sure it's stable before I put the DOS card back in.

The only way to get MIDI out is to get a PC CT2501-equipped card (CT2810 or CT3930 for example) and check how the signal is routed with a multimeter. As fellow collector Der Sammler suggested, it's probably going to be quite easy (I don't think there are any passives between the chip and the port). I just need to find a cheap card.

I found a card on eBay. I'll poke around with the multimeter and share my results.

Reply 14 of 19, by stevenh

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Tyrantulas wrote on 2020-10-09, 16:24:

I found a card on eBay. I'll poke around with the multimeter and share my results.

Sorry for the necro-posting!

Tyrantulas, did you ever poke around with the card?

Reply 15 of 19, by Tyrantulas

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stevenh wrote on 2021-03-17, 02:08:
Tyrantulas wrote on 2020-10-09, 16:24:

I found a card on eBay. I'll poke around with the multimeter and share my results.

Sorry for the necro-posting!

Tyrantulas, did you ever poke around with the card?

I got the card in, and indeed MIDI-IN / MIDI-OUT / 5V / GND can be toned directly off the Vibra chip with no discrete components between the chip and the gameport on the back of the card.

My next step is to find a second DOS Card Vibra module (so I don't sacrifice my original) and create an adaptor for MIDI.

Reply 16 of 19, by stevenh

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Tyrantulas wrote on 2021-03-17, 12:53:

I got the card in, and indeed MIDI-IN / MIDI-OUT / 5V / GND can be toned directly off the Vibra chip with no discrete components between the chip and the gameport on the back of the card.

My next step is to find a second DOS Card Vibra module (so I don't sacrifice my original) and create an adaptor for MIDI.

That's great news! Any chance of a photo/pinout!?

Last edited by stevenh on 2021-03-23, 05:17. Edited 1 time in total.

Reply 17 of 19, by stevenh

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Talking to myself, it occurred (to myself) that I could just find hi-res images on Google and trace the traces. I've managed to determine MIDI-OUT Pin 12 is hooked to the 11-th pin 'up' (aka Pin 30) from the bottom-left of the CT2501 when looking at it with the text level.

In the images, blue is midi IN (pin 15), red is midi out (pin 12). On the chip side, MIDI OUT is followed through and traced in yellow, directly on the bottom-left of the CT2501 IC.
MIDI IN runs somewhere under an IC bottom-left and I am not able to trace it from web images.

From here, the goal is to run a trace from this pin on the DOS Compatibility Sound Card and then somehow feed it to the joystick port plug.
I'm thinking a 3.5mm audio jack in the plate with a secondary plug that comes from the hydra cable (of which I made my own, so wont need to try and rip one apart)
Also unhook the +5v and GND in the joystick cable port as they're hideously wrong.

Will update as the project progresses.

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Last edited by stevenh on 2021-03-23, 05:20. Edited 4 times in total.

Reply 19 of 19, by BadGoldEagle

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Great detective work!

And I'm glad you of all people managed to do this. Because of your excellent write-up on the Quadra 950, I managed to get hold of one in the hope to get the DOS card to work with it. I eventually did while the donor ATX PSU was spilling its guts next to the Quadra to power it up. The mod isn't quite done yet but I would definitely have revisited the Vibra16 MIDI hack after the fact. At least now I know it'll work! Thanks!