Macintosh 8100 and variant overclocking.

[macuserman]

Has anyone here actually played with overclocking the 8100? I just picked up the Mach 10 that was listed on trading post so that will be arriving soon, and then I was on ebay this morning and found this listing for a Powermac Bullet https://www.ebay.com/itm/304401825688 so I immediately picked that up as well. This is something I had been searching for info on for awhile and there doesn't seem to be much info online about it. And then there in less than 24hrs I was able to pickup two different overclock setups. What I really want to try and do is to combine one of these overclock setups with one of my sonnet accelerators, and see if I am able to push the speed a little higher, my understanding is that the maximum speed of the accellerator is limited by a multiplier of the base clock speed so if these overclock units will let me push the base clock speed up then perhaps I can squeeze a bit more juice out of an accelerator card. I don't know if this will actually work but in theory at least to me it seems like it would, anyhow I'd love to hear any thoughts or real world experience with any of these types of setups. To my knowledge nobody has tried combining one of these overclock setups with an accellerator, but I welcome thoughts on if you think I'm insane for wanting to try that etc. Anyhow thanks for reading.

 

[Byrd]

I'd overclock the stock CPU first, then install the G3 upgrade with the expectation the Sonnet G3 (which are fairly pedestrian and don't like tweaking) might be closely matched to stock timings and may not like the bus speed overclock. In doing so, you might find you need to lower the bus speed down to get it to play nicely with the G3. Don't forget to re-paste the stock CPU with new thermal paste and what's there will be dust now.

 

[macuserman]

I'd overclock the stock CPU first, then install the G3 upgrade with the expectation the Sonnet G3 (which are fairly pedestrian and don't like tweaking) might be closely matched to stock timings and may not like the bus speed overclock. In doing so, you might find you need to lower the bus speed down to get it to play nicely with the G3. Don't forget to re-paste the stock CPU with new thermal paste and what's there will be dust now.

That’s good advice, and sorta my plan with one caveat the card I’m hoping to bump up is actually a 360mhz G4 the max card they made in g3 form is 500mhz so I’m hoping I can push the g4 a bit more not sure if I can but the 7400 seems to have a much lower multiple it can go for than the g3 or sonnet did some weird trickery to get to 500mhz on the g3 dunno for sure but should be fun to experiment. I do have a 250g3 I can try as well. Those 500 g3 cards are rare and I’ve yet to see one for sale.

 

[macuserman]

Also anyone have thoughts on which board might work best for this project 80/100/110 have some slight differences.

 

[Byrd]

You'll need to check your crystal speeds that you receive before determining what is the best 8100 board choice. Most clock chip upgrades were for the earlier 80, 100Mhz models.

 

[macuserman]

You'll need to check your crystal speeds that you receive before determining what is the best 8100 board choice. Most clock chip upgrades were for the earlier 80, 100Mhz models.

Gotcha, I'm not even sure which boards I actually have I have a couple that need repairs and one good one, but not sure which speeds they are since I"ve been using them with accelerators. I'll have to do some digging and report back. Not sure if anyone else will find this interesting but I'll share what I discover here anyways.

 

[CircuitBored]

I was on ebay this morning and found this listing for a Powermac Bullet https://www.ebay.com/itm/304401825688

Did you notice that that's the version of the Bullet designed for the 6100 and 7100/66 rather than the 8100? It's clearly marked in this image.

You may be able to tweak it in order to get it to work with an 8100 but it definitely seems as though it won't work out of the box. I may be wrong but it's something to keep in mind if you run into trouble with it.

 

[macuserman]

Did you notice that that's the version of the Bullet designed for the 6100 and 7100/66 rather than the 8100? It's clearly marked in this image.

You may be able to tweak it in order to get it to work with an 8100 but it definitely seems as though it won't work out of the box. I may be wrong but it's something to keep in mind if you run into trouble with it.

Nope I didn't catch that, i wonder what the difference between them really is, but I'm still glad I snagged it, gives me something else to tinker with. The Mach 10 is supposed to be for the 8100 for sure so we'll see.

 

[Franklinstein]

The 6100 and 7100 use SMD oscillators so it's easy for the clip-on accelerators to slip over. The 8100 usually has its oscillator soldered through the logic board so it's harder to override it.

I did a mild overclock on an 8100/110, taking it to 120MHz by replacing its 36.6MHz oscillator with a 40MHz one. I don't think the various chips on the logic board are rated for operation faster than 40MHz so I probably wouldn't try taking it much over that.