My MacSD Upgrade for the Colour Classic [and Stereo Mod]

[MacinJosh]

I finally got a chance to upgrade my SCSI2SD to MacSD today. Nothing wrong with the SCSI2SD but the CD-ROM functionality and other features really sold me on the MacSD.

I created long wires for my RGB LED and positioned it into the holes on the bottom of the CC. You can see it in the video below. I realized I needed a way to transfer my stuff from the SCSI2SD and I didn't have a 50pin to 25pin SCSI adapter so I created one myself. Worked the first time The noise in the video is the exhaust fan that happened to be on at the time (someone was in the shower).

 

[YMK]

Very nice, that is one clean machine!

Do you plan on connecting the CD audio?

 

[MacinJosh]

Very nice, that is one clean machine!

Do you plan on connecting the CD audio?

Thank you! And thanks for the great product. I do have a cable plugged in for the CD audio but I haven't decided how/where to connect it. Probably the speaker in the video above right next to the CC. Or is there a way to keep it internal in the CC?

 

[YMK]

I don't know that much about the CC's audio circuitry.

It should be possible for a Mystic since the LC575 LB is built for CD audio.

If you don't have an external mixer, you can run the CC's audio to the CD audio input on the MacSD.

 

[MacinJosh]

I don't know that much about the CC's audio circuitry.

It should be possible for a Mystic since the LC575 LB is built for CD audio.

If you don't have an external mixer, you can run the CC's audio to the CD audio input on the MacSD.

This sent me down a rabbit hole. There is no information on the web that I can find with any pinouts for the wiring harness on the LC 575. Not having an actual LC 575 chassis, I have still managed to narrow the CD-audio signals down to a section on the LC 575 logic board edge connector based on some pictures online. Next time I remove the logic board (this week) I will investigate further.

So far I know for a fact that on the LC 575 chassis, the CD-audio is transferred over to the internal chassis connector though a CD audio adapter on the drive and then via a narrow ribbon cable alongside the SCSI ribbon cable. The Developer Note states:

​

Each channel has its own ground return; the computer’s audio circuits have differential inputs. The maximum signal level for the audio is 0.7 V ± 0.1 V RMS at 47 kΩ.​

These four signals/traces end up on the bottom side of the logic board and will/should end up connected to the DFAC II sound input IC. Once I have identified the signals I will probably have to solder a connector and wires to the edge connector on the logic board.

 

[YMK]

Is your CC a Mystic or stock?

The maximum signal level for the audio is 0.7 V ± 0.1 V RMS at 47 kΩ.

If this is 1.4V peak to peak, then the MacSD's 2V output might be a little hot.

If it ends up clipping, I'd try a 10K resistor across each channel.

 

[MacinJosh]

Is your CC a Mystic or stock?



If this is 1.4V peak to peak, then the MacSD's 2V output might be a little hot.

If it ends up clipping, I'd try a 10K resistor across each channel.

Yes, this is a Mystic CC.

Ah, good to know about the output, cheers.

 

[MacinJosh]

@YMK - Glad to report that I was able to get the CD-audio to work.

I took the board out and looked at the connections. I was not able to tone them out to any chip as much as I tried, but when I looked at it logically, I was 100% confident that I had the right signals.

So far I've verified that it works. I have not looked into the levels.

But this is brilliant! Next I will do the stereo-mod on the analogue board.

@JDW Your video got me to buy this MacSD in the first place and wanted to thank you for it. It think it would make for a good video if you're keen on doing this mod yourself.

I'll report back with more findings later and give more detailed information once I've verified everything.

Josh.

 

[JDW]

I appreciate this thread very much. My plan is to do a video on MacSD in a Color Classic, and also a video on the Stereo Mod, which concludes taking the speaker from a junked Quadra 630 and using it inside the Color Classic. But I must do my overclocking and Kai Robinson SE Reloaded videos first. I am working on the Overclocking video now.

I had not given thought to CD Audio in the Classic because unlike the LC575, the CC has no CD-ROM drive internally. (@Kay K.M.Mods might know more about this than I do right now.) I do know that there are many Color Classics sold on Yahoo Auctions Japan with internal CD-ROM mods, so this issue has no doubt been tackled. I will look into more later when I can find the time.

The most important and critical point seems to be that the absolute maximum limits of the aforementioned circuit is "0.7 volts" and such is not clear if it is PEAK, which would imply 1.4v p-p. YMK said MacSD is 2.0v p-p. So if it is 1.4 p-p max, then MacSD's 2.0v p-p output would present a problem. Did you use a 10KΩ resistor that YMK recommended in order to get it to work without distortion even at the maximum speaker output volume?

 

[YMK]

Nice work @MacinJosh ! You might be the first to do this.

If the CD inputs are clipping, you should hear distortion at all volumes. I'd apply the resistors in that case.

If there's distortion only at high volume, I wouldn't be as concerned. The additional gain might be good to have for quieter CDs.

I had not given thought to CD Audio in the Classic because unlike the LC575, the CC has no CD-ROM drive internally. (@Kay K.M.Mods might know more about this than I do right now.) I do know that there are many Color Classics sold on Yahoo Auctions Japan with internal CD-ROM mods, so this issue has no doubt been tackled. I will look into more later when I can find the time.

One of many nice things about a solid state CDROM replacement is there's no need for a 5.25" bay, or to carve up the chassis. Warcraft II runs nicely with CD music on my LCIII. The same should be possible on your 640x480 Mystic. Great video by the way, and I think you chose the best method.

I agree that the CD audio mod would make for a good video, and would complement the stereo speaker mod nicely. There's not exactly a wealth of high fidelity, stereo material available for 68K Macs to play otherwise.

 

[MacinJosh]

I appreciate this thread very much. My plan is to do a video on MacSD in a Color Classic, and also a video on the Stereo Mod, which concludes taking the speaker from a junked Quadra 630 and using it inside the Color Classic. But I must do my overclocking and Kai Robinson SE Reloaded videos first. I am working on the Overclocking video now.

I had not given thought to CD Audio in the Classic because unlike the LC575, the CC has no CD-ROM drive internally. (@Kay K.M.Mods might know more about this than I do right now.) I do know that there are many Color Classics sold on Yahoo Auctions Japan with internal CD-ROM mods, so this issue has no doubt been tackled. I will look into more later when I can find the time.

The most important and critical point seems to be that the absolute maximum limits of the aforementioned circuit is "0.7 volts" and such is not clear if it is PEAK, which would imply 1.4v p-p. YMK said MacSD is 2.0v p-p. So if it is 1.4 p-p max, then MacSD's 2.0v p-p output would present a problem. Did you use a 10KΩ resistor that YMK recommended in order to get it to work without distortion even at the maximum speaker output volume?

Nice. I have spare Color Classics for parts so I will get a speaker from one of them.

Having a solid state CD-ROM as @YMK stated is the whole beauty of the MacSD (amongst other things) and will allow all audio to be outputted to the CC speaker/s.

I did go ahead and put the 10K resistors in place just in case. I did not experience distortion but the audio was loud even at low volumes. I'm not sure if this changed anything. I'm still testing various CD images.

 

[MacinJosh]

Nice work @MacinJosh ! You might be the first to do this.

If the CD inputs are clipping, you should hear distortion at all volumes. I'd apply the resistors in that case.

If there's distortion only at high volume, I wouldn't be as concerned. The additional gain might be good to have for quieter CDs.



One of many nice things about a solid state CDROM replacement is there's no need for a 5.25" bay, or to carve up the chassis. Warcraft II runs nicely with CD music on my LCIII. The same should be possible on your 640x480 Mystic. Great video by the way, and I think you chose the best method.

I agree that the CD audio mod would make for a good video, and would complement the stereo speaker mod nicely. There's not exactly a wealth of high fidelity, stereo material available for 68K Macs to play otherwise.

Thank you! Yes, I suspect that I may indeed be the first to do this. Funny how we still come up with new stuff for 30-year old machines.

As I replied to @JDW, I applied the resistors just in case. I did not experience clipping or distortion but the output seemed really high at low volumes.

I'm no audio guy so this goes a bit over my head at times. Heroes of Might & Magic II has some awesome music but it plays super loud at minimum volume and almost drowns the sound FX. But playing the same tracks in AppleCD Audio Player let's me pull the volume down more so it might be the game itself.

Anyway, I guess it doesn't hurt to have the 10K resistors in place? It's plenty loud at max volume.

 

[YMK]

Anyway, I guess it doesn't hurt to have the 10K resistors in place? It's plenty loud at max volume.

Do you have the resistors between signal and ground or in series? If I was unclear, I meant the former. If it's still loud, try a lower value.

MacSD's volume control is done in software, so reducing the volume in AppleCD player (and probably other applications) will cost you some resolution.

Does the LC575 LB have a mixer for the CD input in the sound control panel? That would be a better place to adjust it.

 

[MacinJosh]

Do you have the resistors between signal and ground or in series? If I was unclear, I meant the former. If it's still loud, try a lower value.

MacSD's volume control is done in software, so reducing the volume in AppleCD player (and probably other applications) will cost you some resolution.

Does the LC575 LB have a mixer for the CD input in the sound control panel? That would be a better place to adjust it.

Doh! I have them in series. I'll try fix this but it might take a couple of days. There shouldn't be any harm having them in series?

 

[YMK]

Doh! I have them in series. I'll try fix this but it might take a couple of days. There shouldn't be any harm having them in series?

No harm, but they'll be ineffective if the logic board has a high input impedance.

 

[JDW]

If one of you could sketch out a simple wiring diagram for the connections, including the resistors, that might help others who are following this thread with interest. No rush. Just whenever you have time.

 

[MacinJosh]

If one of you could sketch out a simple wiring diagram for the connections, including the resistors, that might help others who are following this thread with interest. No rush. Just whenever you have time.

Yes, that's the plan. Once I've verified everything. I'm actually already trying to think of how fancy do I want to get with the sketch.

 

[MacinJosh]

If one of you could sketch out a simple wiring diagram for the connections, including the resistors, that might help others who are following this thread with interest. No rush. Just whenever you have time.

Ok, here is the pinout diagram to start with. Still testing resistors.

 

[MacinJosh]

@YMK I did the resistor mod again but this time across the signals to ground. I did not notice any change or improvement in terms of volume. I think it is fine without the resistors from my brief testing so far as I didn't hear clipping or distortion.

It must be a sound mixing issue but I can only find a "Monitors & Sound" control panel that doesn't offer any mixing options. I'm trying to find something in Macintosh Garden but not finding any. I'll have to check the Mac OS 8 Bible.

 

[JDW]

@YMK I did the resistor mod again but this time across the signals to ground.

So you put one 10kΩ resistor from the RED wire (Right) in your picture above to the BLK (GND), and then put another 10kΩ resistor from the WHT (Left) wire to BLK (GND), correct?

And previously, you had the two 10kΩ resistors inline with each of the RED & WHT wires (i.e., not going to GND), correct?