System specs:
Apple Mac Mini 2018 i5, 32Gb
Zotac Amp Box Mini 230W version
Sapphire Radeon RX 570 Mini ITX 4Gb + customized cooling solution
Installation instructions
1) Remove the Sapphire RX 570 fan+shroud assembly (4 screws must be unscrewed in the back of the card).
2) Attach a 14cm fan on top of the heatsink. Connect it to the GPU using a GPU-CPU PWM fan adapter.
3) Install the modded Sapphire RX 570 Mini ITX in the Zotac Box.
4) Connect & enjoy - plug and play in MacOS.
Comments/overview
My goal was supplement my Mac Mini with an inexpensive, silent eGPU. Power delivery wasn't a requirement as it is not needed for the Mini. I have a gaming PC with a proper RTX card, so I only wanted a reasonable but not overly powerful GPU which will drive my 4K display better than the Mini's UHD 630. I went with the Zotac Box Mini because it was the most affordable, fanless (therefore silent) eGPU case I could find. I installed a Sapphire Radeon RX 570 Mini card in it since this was the fastest card available that fits both the form factor and the power limit of the Zotac box and is compatible with MacOS.
The Sapphire Radeon RX 570 ITX is a nice card (especially considering it's price) but turned out to be a minor disappointment. The card is supposed to be able opreate in fanless mode, but the heatsink is obviously not up to the task. The temperature slowly rises to 55C even with modest desktop usage, then the fan kicks in and remains on until the temperature drops to 45C. This the whole warming + cooling process just repeats endlessly. The card has a small fan, and its lowest setting of 37% PWM spins it up to 1300+ RPM creating an irritating noise every 2-4 minutes.
My solution was to strip the card from its shroud+fan assembly, install a custom PWM fan on top of the heatsink and connect it to the GPU's PWM header (using a VGA fan adapter like this).
I tried several replacement fans:
- attach a 12cm fan with zipties -> works well and absolutely silentl, but during gaming the fan and noise ramps up.
- attach a standard sized 14cm fan with zipties -> the fan is too bulky to put the cover back on.
- attach a slim 14cm fan with zipties -> should work well and looks nice, but unfortunatelly the Rajintek 14cm slim fan has control issues with the RX 570 (it always runs at 100%)
- What I ended up doing is to get rid of the outer assembly of the standard sized 14cm fan (by cutting it off) and attach the fan motor itself to the card (using the "spikes" of the bottom part of the fan assembly to fasten it to the heatsink).
The resulting setup is now perfect for my needs. Small, completely silent, inexpensive. A rough equivalent of the Breakawy Puck RX 570 but for half the price. The Zotac Box Mini is somewhat larger than the Puck and has no Power Delivery, but on the positive side, it is upgradeable. the Puck retails for EUR 600 (in my area), but my setup costed approximately EUR 300.
Benchmarks
Hardware pictures
Fan options
Rajintek 14cm slim fans (PWM control does not work properly):
Size comparison for the 12cm and 14cm standard sized fans:
The 14cm standard sized fan with the outer assembly intact - not enough room, eGPU cover does not fit:
The 14cm fan without the outer assembly (my preferred solution):
Apple Mac Mini 2018 + Zotac AMP Box Mini + Sapphire RX 570 ITX
2018 Mac Mini [8th,6C,B] + RX 570 @ 32Gbps-TB3 (Zotac AMP Box Mini) + macOS 10.14.5 [build link]
@steve4332 Thank you for sharing this build. Very nice work fitting the 140mm cooling fan! I use the RX 580 out of the Gigabyte Gaming Box (130mm fan) and it's quiet. Your custom cooling should be silent by comparison. We'd love to see a side-by-side with the Mac mini. Perhaps custom cooling for the Mac mini is next. 😀
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2020 15" HP Spectre X360 [11th,4C,G] + RTX 2080 Ti @ 32Gbps-TB4 (AORUS Gaming Box) + Win10 2004 [build link]
Nice to see more pics of the Zotac mini box... also love the GPU mod - I've often considered whether the shrouds are really needed in eGPU's, might look into running my Vega shroud less as it should help with cooling a bit (not sure if that's even possible).
As @itsage said, would love to see some side by side / full set up shots, although it might tip me over the edge of buying one of these....
2017 13" MacBook Pro Touch Bar
GTX1060 + AKiTiO Thunder3 + Win10
GTX1070 + Sonnet Breakaway Box + Win10
GTX1070 + Razer Core V1 + Win10
Vega 56 + Razer Core V1 + macOS + Win10
Vega 56 + Mantiz Venus + macOS + W10
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LG 5K Ultrafine flickering issue fix
2017 13" MacBook Pro [7th,2C,U] + RX 5700 XT @ 32Gbps-TB3 (Mantiz Venus) + macOS 10.15.4 & Win10 2004 [build link]
Here are some additional photos for size comparison to the Mac Mini. I think astethics-wise the two units don't go very well together, so I keep the Zotac Mini hidden away under my desk... The Zotac Mini is obviously not so mini compared to the Mac Mini. 
As you might see, there is a blue smear behind the Zotac box on the wall. It is caused by the light of two rather bright blue internal indicator LED-s soldered to the Zotac Mini's motherboard leaking through the vent holes. At night it can be a nice wallpaper effect or annoyance (depending on what level of darkness one might prefer). I did some close ups of the green and red LED in the front (red is the off state, green is the on state) and the blue LEDs leaking through the vent. During standby only the green LED remains on, the blue LEDs turn off, so if you have your system in your bedroom it will not cause any annoyance.
Finally, here are some screenshots - to show how the unit shows up at System Preferences. Also a printout of the fan speed at the default 37% PWM fan level using the Arctic P14 fan (this is when the cooling kicks in during normal desktop usage when the GPU temp reaches 55C - the fan turns off completely after the temperatures go below 45C). The fan cannot be controlled under MacOS, but I tried removing the fan altogether - the temperature then just keeps increasing to a dangerously high 80-85C even showing a completely blank screen without any movement, both the GPU and memory at the lowest speed step - this means that the Sapphire RX 570 ITX cannot work at all in passive mode without the fan kicking in periodically at normal room temperature.
The fan spins at 680-690 RPM which is impercetible even if I put my ear next to the unit at night. The original fans have an audible kick-in sound, but luckily the Arctic fan spins up absolutely gracefully without any audible noise whatsoever.
ps. in order to claim my AMD rewards for purchasing the RX 570 I had to run the AMD product verification tool which works under Windows only. Therefore I had to attach the eGPU unit to my Windows PC (which is also thunderbolt equipped thanks to the ASRock Phantom Gaming ITX motherboard). I did not experience any issues, after I installed the Intel Thunderbolt software downloaded from ASRock and the Radeon drivers, everything went smoothly (Windows 10 ver 1903). I didn't experiment with it much however, since the PC has an RTX2070 card which is more powerful obviously.
Apple Mac Mini 2018 + Zotac AMP Box Mini + Sapphire RX 570 ITX
2018 Mac Mini [8th,6C,B] + RX 570 @ 32Gbps-TB3 (Zotac AMP Box Mini) + macOS 10.14.5 [build link]
Lovely clean full set up!
Do you have a link to your mobo? Thinking of building a mitx set up.
2017 13" MacBook Pro Touch Bar
GTX1060 + AKiTiO Thunder3 + Win10
GTX1070 + Sonnet Breakaway Box + Win10
GTX1070 + Razer Core V1 + Win10
Vega 56 + Razer Core V1 + macOS + Win10
Vega 56 + Mantiz Venus + macOS + W10
---
LG 5K Ultrafine flickering issue fix
2017 13" MacBook Pro [7th,2C,U] + RX 5700 XT @ 32Gbps-TB3 (Mantiz Venus) + macOS 10.15.4 & Win10 2004 [build link]
This is the mobo:
It's a really decent board, packed with features. But it's Thunderbolt is PCIe x2 only (Intel JHL6240), which limits its speed. 🙁
Apple Mac Mini 2018 + Zotac AMP Box Mini + Sapphire RX 570 ITX
2018 Mac Mini [8th,6C,B] + RX 570 @ 32Gbps-TB3 (Zotac AMP Box Mini) + macOS 10.14.5 [build link]
I updated the original post with pictures of my various fan mod attempts.
Apple Mac Mini 2018 + Zotac AMP Box Mini + Sapphire RX 570 ITX
2018 Mac Mini [8th,6C,B] + RX 570 @ 32Gbps-TB3 (Zotac AMP Box Mini) + macOS 10.14.5 [build link]