Tonight I did fan mods on both an iNuke NU3000DSP and an EP4000.
A week or two ago, I ordered a fan for the NU3000DSP mod. I was looking at these two, and ended up accidentally buying them both:
Nexus 80mm Real Silent Case Fan
Noctua NF-R8 80mm Fan
I compared them by hooking them up to an adjustable power supply. They are both really, really quiet compared to the stock fan on the NU3000DSP.
The Noctua comes with two optional resistors that can be plugged into the wires. So you can run with no resistor for full speed, or use one of the resistors to slow the fan down a little or a lot. With no resistor, the Noctua flows a lot more and is slightly louder than the Nexus. So if you are looking for a quiet fan with more air flow, the Noctua is a good choice. If you install the "low noise" resistor, the flow and sound level seems roughly comparable to the Nexus, but note that this is just a rough impression -- I did not actually measure the air flow or noise level with any precision. With the "ultra low noise" resistor, the Noctua is even quieter and lower-flowing than the Nexus.
The Nexus does not come with any resistors, and it is quieter and flows less air than the "bare" Noctua.
I have no idea which fan flows more for a given sound level. I did not do any precision measurements of flow or sound level. But I just wanted a simple install (no resistors) and the Nexus is quieter than the "bare" Noctua, so I installed the Nexus fan in my NU3000DSP.
Both fans come with rubber mounting things/posts, but you can't really use them for the amp fan mods because the fan grill is held on by the fan screws. So you have to use the fan screws that came with the amp. I did not try it, but you could probably use one of these isolators if you were pursuing the lowest possible sound level while still having a fan:
I saw that people were also modding the fan shroud in some YouTube videos, but I did not modify my shroud. Be careful when removing the fan shroud -- I accidentally cracked mine a bit, and used some packing tape to repair it. The shroud is held in place by double-sided tape attached to the top of the fan. You can just pull it off the old fan and stick it to the new fan -- no additional tape is required.
I cut the wires and soldered the Behringer connector to the replacement fan. I used a little heat-shrink tubing over the wire splices. I accidentally pulled the connector off the Behiringer circuit board at first, but it was easy to stick back on once I removed the glue. I would normally recommend more caution than I used, but I don't actually think it hurt anything to pull the connector off the board. So go ahead an pull yours off, too -- just make sure you pull straight up so you don't bend the pins.
After the fan swap, the NU3000DSP is way, way quieter than it was with the stock fan. It is now really quiet, and totally acceptable for use in my rack.
The NU3000DSP fan swap was super easy, so I decided to swap the fan in my EP4000, too. Physically, the EP4000 is a massive beast compared to the NU3000, so it is much harder to move around. The EP4000 has more screws, too. You must remove the four little screws in the top of the case as well as the screws around the sides and back. The fan blows air through big aluminum channels, from the back of the case and out the front.
The EP4000 uses a 24v fan. But the fans I ordered are 12v. If I had searched the internet before I opened my EP4000, I would have discovered this, and the fact that Digi-key and other vendors sell low-noise 24v fans. However, I now had my EP4000 open, and I just happened to have a Noctua fan that comes with resistors, so I did a little experimentation. I cranked my power supply up as high as it would go, which was only 16v, but that is enough for my test. I installed the "low noise" resistor, and measured the voltage drop across the fan. 10v, which is a little too much. At 24v, the fan would be getting about 24 * 10/16 = ~15v. So next I tried the "ultra low noise" resistor, and got about 6v. That means that the fan would get 24 * 6/16 = ~9v maximum, which means that I can use the Noctua fan + "ultra low noise" resistor in the EP4000. I did one final test to make sure that the fan would get enough volts to spin upon startup, and it did, so I proceeded to install the Noctua fan and "ultra low noise" resistor into the EP4000. I took a little care to cable tie the connectors inside the case so that they don't rattle or disconnect themselves. I don't have a lot of time on this mod yet, but I am confident that it will work fine long-term.
So, the Noctua NF-R8 with the "ultra low noise" resistor is another option for the EP4000 fan mod. I bet that it is quieter than the common alternatives, but it probably also flows less air.