The Ultimate Behringer iNuke NU3000DSP Fan Mod (CLICK HERE FOR PICTURES):
After purchasing an iNuke, I found the stock fan far too loud for home theater use. I liked seeing what people were experimenting with here (slower fans, inline resistors to slow down the stock fan, natural convection), but I didn't like the compromise that in almost all cases the capabilities of the fan were reduced or eliminated. Aside from the lowered cooling ability, I was concerned that any fan bearing, no matter how silent, would not address the issue of the noise form the air rushing out of the louvers in the front bezel. This mod not only reduces the fan noise to imperceptible levels, but also substantially increases the heatsink area and CFM of air flow.
I chose a fluid dynamic ball bearing because it is the quietest and longest lasting type of case bearing available. I went with the Cougar 140mm fan because it has a true Matsu****a designed fluid dynamic bearing. Here is an excellent write up and a list of fans with the best fluid dynamic bearings: fan bearings.
Another benefit of the Cougar, aside from its impressive build quality, is the inclusion of an inline resistor that will drop the fan from a maximum of 1200rpm (19.2dB) to 700rpm (16.4dB). I did not use the resistor since the system is absolutely imperceptible at a couple meters, but even with the resistor installed, this fan will still push as much air as the stock fan. Without the resistor, this fan flows 70.5CFM (19.2dB) compared to the stock fans 55.5CFM (40.9dB). Make sure to get the 3-pin design and not the 4-pin PWM fan. This fan has some awesome rubberized insulation that I didn't want to screw up, so I just used a cheap 3-pin to 2-pin adapter listed below. The one down side of the Cougar is it doesn't include a fan grill. I picked up a 2-pack from newegg.com for $5. I'm not into a flashy home theater, so I went with the black fan, but it is also available in a bright orange blade fan that will match the iNuke.
As for the heatsinks, I used black anodized aluminum 28x28x15mm IC heatsinks. I would have used straight fin heatsinks below the fan for improved cooling performance, but I ultimately chose the cross cut style because I could not predict how air would flow across the heatsinks on the power supply side and I didn't want to buy two different types. I first cleaned all of the tabs with a little alcohol to remove any oils. By bending the output stage MOSFET heat tabs up to about a 60 degree angle a heatsink can be mounted on the top and bottom. I left the power supply heat tabs flat and placed a single heatsink on top of each. Make sure none of the adjacent heatsinks are able to touch each other, and also make sure the power supply heatsink fins are inline so they don't block flow from each other or cause unnecessary turbulence.
I masked off the lid and took measurements of the internal components to be able to layout the cutout for the fan. Make sure to measure repeatedly and keep track of the front, back, left, and right. After determining a center point, I took a nail a punched in an impression to guide the pilot bit of the hole saw. I fortunately already owned a 5 1/4" hole saw, but if you don't, then you will have to figure in an additional $35 for a hole saw from amazon.com. Once the hole was cut out, I used a pocket square and the fan grill as a guide to punch and drill the fan mount holes with a 13/64" drill bit. I then cleaned up the cut aluminum with a rat-tail and flat bastard file.
I installed the fan utilizing the included rubber mounting tabs and then snipped off the ends. I didn't want to have a gaping hole in the back (that's what she said), so I purchased a few 8-32 machine screws and reinstalled the stock fan grill. I was considering cutting a piece of the stock fan shroud and limiting the amount of air that could flow directly out of the back, but after running it, I believe there is plenty of cold air flowing out of the front of the amp even with the back completely open. In the end I have an amp that is effectively silent, yet is cooled far better than the stock Behringer design. I am very pleased with it, and I do not baby it in anyway. The obvious limitation is that nothing can be set on top of the top-mounted fan, and if it is rack-mounted, it will have to have an open slot above it. My total cost was $42.04. If you have to buy the hole saw and a role of masking tape, figure the price at about $80. This puts a silent "3000w" home theater amp with on board DSP at about $360.
(CLICK HERE FOR PICTURES)
The Stock Fan
For anyone wondering, the fan in a recently shipped iNuke300DSP is a "Bi-Sonic BP802512HL-03-W". It is a 12V 80x80x25mm 2-pin fan with a maximum of 55.53CFM at 4000rpm and a stated 40.9dB-A
Here is the datasheet: http://datasheet.octopart.com/BP8025...eet-525890.pdf
These are a couple interesting links I found when looking for the best heatsink design:
Why you should consider straight fin heatsinks, if possible, when you know the direction of airflow:
Why you should choose anodized heatsinks for natural convection systems:
COUGAR CF-V14HB Vortex Hydro-Dynamic-Bearing (Fluid) 300,000 Hours 14CM Silent Cooling Fan (Black) - $17.99
APEVIA G-140MM 140mm Fan Grill 2 in 1 pack - $4.99
FREE Shipping 10pcs 28x28x15mm Cheap CPU Black Aluminum Heatsink With Blue Thermal Conductive Double Sided Adhesive Tapes - $15.00
30cm Fan Adapter Cable Case Ventilation 3-Pin Plug 2-Pin Jacket Coupling - $2.50
4x 8-32 Machine Screws with Washers and Nuts - $1.56