Overclock/Voltage Boost OWC Mercury Extreme

If adjusting the CPU clock is merely adjusting the bus speed for the CPU and if this is true, then the other busses usually run at a muplitiple of the cpu bus speed. If this is true, and other busses such as the PCI/AGP bus and the memory bus speed become too high or have less of a running tolerance, you may run into problems there before running into CPU overclocking issues. Usually, at least in PCs(where I have my OC experience) the other busses panic and fail at some speed x before the CPU.

good luck!

In this case, as is the case for most all of the G4 series I believe, is that the CPU speed is dictated by a multiplier which is used along with the system bus speed to determine the CPU clock. In other words, to run a 1.467 clock, you set for a 11x multiplier, if you have a bus clock that runs at 100mhz, you set for 15x. In my case, at the moment I am running 12x by a 133mhz bus for 1.59ghz, or 1.6ghz.

You are correct, this multiplier does impact the speed of the Level 2, and Level 3 cache. Level 2 runs at the core clock, so 1.6 there, L3 runs at a 6:1 ratio, so at stock, L3 is running at 244.5 mhz, at 1.6 ghz, L3 runs at 266 mhz. However, the L3, is rated for 300mhz, as indicated by the -30 at the end of the cache ram part number.

But, as far as I am aware, the overclock is not impacting the other subsystems, unlike, say a G5, where, the timing is all inter-dependent.

Thanks for the advice!

I have this card, it's a big speed bump for the older AGP macs. I'm recalling some of this blurb from memory because it's been a while since I've even tinkered with the jumper settings with it.

My OWC 1.467/1.5 was first installed in a 100Mhz BUS Sawtooth. After some time I tried it at 1.6Ghz, but it would randomly freeze up on me. I decided to keep it at the 1.5. Since then I've upgraded to a Clockwork G4 Digital Audio with a 133Mhz bus. If I remember correctly, I had to move the jumpers a tad because of the 133Mhz bus so it would run closest to the 1.5 as possible (1.467). I did try to go up one more which would be an even 1.6, but to no avail, still randomly unstable.

I understand you're stable at 1.6Ghz? If I recall sometimes during manufacturing, slight differences will amke one CPU more stable than most. That and one's that are rated for 1.5Ghz may fail at 1.5Ghz but work great as say 1.2Ghz. Off to 1.2Ghz cards it goes.

I'm going to venture a guess that the core voltage is set and non adjustable(?). I never did pop off the Warranty Void sticker because well, after coughing up that $$$ for the card, I wasn't gonna fuss with it. I noticed that they upgraded this OWC card with a diff heatsink. Probably other improvements as well. not to mension, I've got jumpers and not dip-switches. I've got the older style one. If you just bought the card, keep in mind you don't want to void this warranty (just my opinion).

Let us know if you are successful with tweeking it more.

-Dk

Yeah, as you suspect, I think I have a newer rev for this card. I have two banks of jumpers, and a low profile copper heatsink, and then a pair of fans blowing down into the heatsink. So far, I've found that it is quite stable at 1.6ghz. I did raise my core volts to 1.70v from the stock 1.65v. I've had a couple of minor issues with freezing, but that usually happens after I've been playing Halo for like 5 hours straight. I suspect that the setup would benefit from some additional airflow, and to that end I am investigating putting everything in an ATX case where I have enough room to add a real fan and perhaps fabricate some sort of a shroud to fit over the cpu module.

I have managed to determine the core voltage dips are identical to the jumper settings referenced on the Gigadesign 1.25 as shown on Accelerate Your Mac's review of the card. I can't speak for the older card, but this one seems to be the same. I have no idea what the 7455b on this card is actually rated for, I would hazard a guess that its probably rated for 1.4ghz since it will tolerate 1.6ghz. I've toyed with the idea of pulling the heatsink and putting some artic silver on the chip, but I'm not sure I care to bother with that yet. You're right about the voltage jumpers/dips, they are normally covered with a small warranty void sticker. However, mine shipped with the sticker not really stuck over the jumpers, so I figured why not fiddle? Way I see it, I've voided the warranty at this point, but, I've only done this after having the card for several months, enough so that I feel more comfortable about it not failing and needing to be replaced. I will mention this, OWC had been using what looked like a mylar void warranty sticker, which doesn't really stop you from peeling back the sticker and changing things, because you can do so without damaging the sticker. I've seen a more recent version of this CPU card, and they appear to have switched to a more conventional sticker that looks like it would rip if you tried to remove it. So, I would say that if you have any concern regarding the warranty for the card, just leave the voltage block alone. (Personally I can't leave mine alone, warranty or not, cause I love this stuff.)

I will also mention, that when I initially tried out 1.6ghz, I didn't have to adjust the core voltage to get the machine to boot and run. I only raised the core voltage after I found it would start to freeze under load. When I tried for 1.73, it would immediatly hang. I had tried raising the core voltage to 1.75, which may have been ill advised, but, it didn't cook the machine, just let it run for maybe 15seconds longer than before. It just drove home the point that 1.6ghz is probably the best the card would muster without ridiculous modding. Also, I retained the original fan from the DA which is blowing cool air over the heatsink and then getting sucked down by the CPU fans. I am not sure why their directions indicate this fan should be removed, as it does help keep cool air fed over the heatsink.

I will comment that the blower fan from a G4 xserve will sit on top of the OWC card and be just about the right height to blow right out the stock vent on the rear of the case above the audio ports. However, the Xserve fan is a PWM fan which can be rigged to run full boar if you short one of the control lines to the +12. When this fan runs at full board it sounds just like a vacum cleaner and you can actually use it to suck stuff up off your desk! The downside to this it is about the same noise level as a shop vac. I have seen someone makes a little widget you can connect one of these PWM fans to and then have a manual adjustment for the fan speed. Its kind of funny, when I would set the fan directly on top of the cpu card, it actually wanted to kind of float around similar to a hover craft. Definetly moves big air. I recall it moves roughly 40cfm at full speed. So, my goal is to either put all this in a PC case, or perhaps get some lexan and then fabricate a duct of some sort to allow the fan to sit on top of the card and exhaust out the back.

Anyway, hope this helps! BTW, whats your take on the 9800? I have a Geforce 4ti, and I have a feeling its getting to be a bit of a restraing factor at this point. Prior to putting the OWC in the machine, I was CPU bound, now its the GPU which is holding me back. I think. I've thought about getting one and having a go at flashing it.