Flinch

I've swapped the Gigabyte card out with an EVGA GTX 750Ti SC (under-clocked the core clock only by 150Mhz to stabilize it), so this is with the EVGA: http://www.3dmark.com/3dm/9758683 Hope that's okay, I don't feel like screwing in the Gigabyte again

Here are some benchmarks: Sky Diver: http://www.3dmark.com/sd/3617810 3DMark 11: http://www.3dmark.com/3dm11/10676285 And the pics:

EDIT: so the TL;DR version is that I'm pretty sure the Akitio does as advertised if you give it a 120W power supply by making 75W available, but the GPU is drawing more under load and either has the power throttled by the Akitio, so starving the GPU, or the Akitio thunderbolt daughter board throws a hiccup and the data pipeline stalls.

Sure, I'll update with pics and benchmarks as soon as I get home (@work at the moment). @Dschijn, thanks for the tip on the PSU, and yes I'm sure that it's 120W. It's a 10A supply with a range of 12V-19V wattages printed on the packaging with the wattage at maximum (120W) with the hypothetical 12V plug attached, and decreasing as the voltage increases which is exactly what you'd expect. It's basically the same thing as the one you linked, just a different brand. Re: not enough power: at first, I did suspect that the PCI slot was really only delivering 25W and that this was the cause of the instability. I really don't think this is the case though. My clocks are still over 1GHZ with the memory clocked at the same frequency as the GTX 750 (not the TI), which is not an extreme underclocking, so I cannot imagine that it can run under load with only 25W. Moreover, the 65W TDP isn't the same as the actual max power consumption (that's just what it can dissipate on average). The peak power consumption is often significantly higher in reality (20-30W is common), so my guess is that the GTX 750 TI under high load with factory settings can peak close to or over the 75W ceiling, and that the thunderbolt circuitry of the Akitio doesn't like it and becomes unstable. PC's are probably more forgiving and have a bit more wiggle room in their PCI power circuitry, so you don't notice if you plug this GPU into a PC, but if you think about it, it almost sounds too good to be true that the GTX 750 TI gives you as much performance as it does for only 65W... because it probably really doesn't promise to *never* go close to or over 75W, but just to dissipate 65W on average with some clever scaling and fan control.

Hi All, I just wanted to share my experiences with setting up a Gigabyte GTX 750 TI eGPU powered only by the PCI slot in the Akitio. My setup: - 2014 Macbook Pro 13", 8GB RAM, 500GB SSD, running OS X 10.10 with Win 8.1 installed via boot camp (EFI) - Gigabyte GTX 750 TI - the slim one with the single fan - Akitio Thunder 2 - 120W Power brick from Trust - external monitor This looked like a really attractive solution to me, since it's as close to plug-and-play as it gets with a cool running GPU which fits tidily in the case and can be closed. I don't recommend that power brick though, it says "automatic voltage selection" on it which is a bit bogus. The thing has a shunt regulator in it, so "automatically selecting" the voltage means choosing the correct plug (which has a built-in resistor) to fit on the end which regulates the voltage, and the correct plug for 12v was NOT included in the packaging (for me at least). So I cut the barrel plug off the Akitio and soldered that along with a 400k potentiometer which I used to regulate the voltage down from 19v to 12.3v (note, this is not the same as simply wiring in a resistor in series, a shunt regulator has a feedback line and the resistor goes between V+ and the feedback). First off, there seemed to be some lack of clarity as to whether simply adding a 120W power brick and powering the whole thing through the barrel plug actually worked in practice. Turns out it works. I was playing the Witcher 3 on high settings at 1080p all evening yesterday. Initially I tried to get it running on my newer 2015 13" MBP 16GB RAM + 1TB SSD running Win 8.1/El Capitan, and I couldn't get it to boot reliably (had to do the hot-plug-after-chime rain dance, and racing a fast SSD was really hit and miss), and most of the time I'd get a black screen or get to watch the pretty spinning dots for hours. I noticed, though, that rebooting worked more frequently than a cold start, so I disconnected the Akitio fan as I suspected that the torque when it starts up might cause a voltage drop which puts the card in a funny state. I then switched to my older 2014 MBP13" (the one on which this all works now), and installed Win 8.1 via boot camp. I also installed the Optimus EFI goodies from here which may have had the effect of inserting a tiny delay via the chain loading from GRUB and could have helped (the theory being that the card needs power a little BEFORE the PCI scan at boot time, but only gets power when the thunderbolt signal comes up, and that there's a race). Once I had it booting reliably without any weird rituals, I had stability issues the first few days, where I couldn't run a game for more than a minute without the card crashing in various interesting ways. I noticed using GPU-Z that the power consumption was spiking as high as 115% TDP and was getting a lot of "PerfCap Reason" "Pwr" notices, so I underclocked it so that it doesn't go over ~98% TDP. And that was the key to getting it stable. After some experimentation, I ended up with both the core and memory clock speeds reduced by 150mhz (I used MSI AfterBurner). Did that, and now it works like a charm Summary: - get a 120W power brick and a GTX 750TI without additional power connectors - disable the Akitio built-in fan by unplugging it from the board (the GPU runs very cool anyway, haven't gotten it over 62 deg. C yet) - install Win 8.1 via boot camp - write the OPTIMUS.dmg to the EFI partition (speculative) - install latest NVIDIA web drivers - underclock the card until stable Thanks for all your advice and discussions. Couldn't have done it without y'all.