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Soldermizer 21st February 2012 06:16 AM

Behringer iNuke NU3000 w/o any fan...?
The Behringer NU3000 arrived today. I needed "twist lock" speaker cables and what Radio Shack lacked, the pro audio store had. Presidents' Day is a holiday? OK, there was no mail today. Made my DIY cables and sure enough the new amp puts out a nice signal to my 4x Bose 901 II. But the noisy fan. It may or may not be variable speed, but even at start-up it's too noisy for me.

Consulting the wisdom of the great Google, I found such info as this DIY video:

Behringer iNuke Amplifier Fan Swap DIY - YouTube

While putting in a quieter fan is a worthy goal, left unanswered is the ultimate question( especially if I currently have no suitable new fan). Besides being emminently cheap, the quietest fan is no fan, of course. Why not disconnect and remove the old fan, its shroud, and for extra cooling, leave the lid off? Well, it least 1/2 hour into a test. I am relying on the "thermal shutdown" failsafe if it gets too warm. This would be the most elegant solution...perhaps passive cooling will work because (1) no cover to impede the updraft, (2) this may be "pro gear" but it will be on its own shelf in a normal bedroom, not crammed in a rack of other heat-generating devices; and (3) the amp probably won't get pushed too hard in my bedroom, but I will blast it tomorrow.

:att'n: Other than presumably voiding the warranty, I see no problem in doing this mod but one must keep in mind that the top is open and high voltages are exposed. :cuss: If the Soldermizer fanless mod works, some type of vented cover would seem to fit the bill. So go to your drill press and start making the thousands of holes it will need

Last year I did a similar "ghetto mod" on a PC fan. See it here:
SPCR &bull; View topic - Fanless PSU with (almost) no soldering for < $12

This mod has proven itself safe (or at least, didn't melt) in 8 months of use. I basically took a stock ATX PSU, opened up the case, removed the fan, put a resistor in its place to fool the shutdown and crossed my fingers. Also I disconnected a 2nd case fan in the PC box. One side panel of the case had to be left open to allow enough air in. The only fan remaining on that PC is the CPU fan.

If anyone is inclined to do a rigorous power test of these amps, perhaps do one with the fan disconnected to see what its limits are.

zerokelvin99 22nd February 2012 02:51 AM

The thermal protection is useless if you insist on running without the fan (!!!)

I have recently seen these "modifications" on youtube and they are painful to watch..

The issue is that the thermal protection systems rely on specific airflow across the components in order to achieve predictable thermal characteristics. Without this airflow certain components will heat far faster than normal, while the monitored components will stay cool.

Result: Something will probably go BANG before protection activates!

Your best option is to KEEP the current shroud and either run a quieter PC fan or install a resistor in series with the fan. Either way you don't want to push the amplifier.

Eva 22nd February 2012 03:48 AM

New class D amplifiers without heat-sinks are the most evolved (and evil) form of programmed obsolescence that I know. They are designed to fail after a few years (just out of warranty) due to thermal cycling, dust build up and corrosion. A fair engineer would never throw air directly at a PCB. This is easy money for a few ones today and lots of garbage and ruin for the planet and us tomorrow.

Consider adding some heat-sinks with thermo-conductive gap filler rather than keeping a fan blowing air directly at a PCB. This is not a trivial work, indeed, it's the work that Behringer was supposed to do.

Soldermizer 22nd February 2012 04:09 AM

I hope to learn more about the NU3000, such as specifically where are the thermal sensors? I intend to keep running it fanless right now. In its present use (a home stereo in a bedroom) it surely is not being pushed as hard as its typical user (e.g. a heavy metal bass player shaking books off the shelf on the other end of the house.)

aandy 22nd February 2012 07:25 AM

I puke

Soldermizer 22nd February 2012 03:41 PM

Yes! That's it!!! The new improved iPuke NaUsea3000 -- a workhorse amp for the headbanging professional. If the Airbus A380-like sound of the cooling fan is objectionable, you may be trying to use this in a home environment. While it will certainly void your warranty if a fly so much as defecates on the unit, some modders replace the cooling fan with a less raucous one, or even remove it entirely. The thermal protection may or may not work in such cases. Please note that vomiting upon the unit will likely etch the aluminum (due to stomach acids). Such damage is not covered by the warranty.

noah katz 22nd February 2012 05:00 PM

If you run it fanless, keep your nose handy for smell of overheated electronics, even at idle.

Some components may need air cooling that are not in the output stage.

I ran my Peavey IPR 3000 fanless (by mistake while putting in a quieter fan); I could smell it and the thermal protection lights went on in less than a minute.

Eva 22nd February 2012 09:08 PM

I have repaired many amplifiers placed at bars and clubs and I know the kind of dense dust that builds up over time anywhere the air from the fan is hitting (had to clean it too many times). It's not usually a problem, at home it will never be, but in this case it's a semi-pro PA amp and there is exposed solder (no solder mask) with strong AC at a few hundred khz and +/-90VDC, it may be enough for some electrolysis fun.

Concerning idle operation without fan, due to class D nature, each of the 4 power devices near the fan can be easily dissipating 3W at idle, that's why some air is always required. Definitely best fix would be adding some heatsinking.

gmarsh 23rd February 2012 04:06 PM

Can't say I like the design of that thing one bit. Rather than hacking the thing with a different fan, holes in the top, heatsinks soldered on, etc... have you considered just selling the thing and getting a different, fanless amp?

Soldermizer 24th February 2012 02:50 AM

I got the NU3000 partly for fun. If I don't kill it, it will replace either a Sunfire (ca. 1996) or a Carver M400t (ca. 1984), both of which work well but are just "old." In building the Sunfire, based on the "white paper", Carver effectively used a class D power supply and a class AB power amp stage. Works, but huge!

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