Advice on replacement 80mm cpu fan needed - got PWM buzz

[Rick63]

I have an old Asus A8N-SLI dlx MB, just installed Opteron 185 with the stock heatpipe cooler. The thermistor-controlled 70 x 70 x 15 mm original fan didn't work very well in my system, too high rpm when little cooling was needed, and too low rpm at high loads resulting in rather high cpu temps. Bad for my ears and bad for the system in the long run.

Since the actual heat sink seems excellent, I fan swapped to a somewhat larger fan. I took what was available in the local store, a very inexpensive Sunon 2.3W / 0.2A 80 x 80 x 25 mm just to see if I guessed right about what would be suitable fan data.

The choice turned out to be absolutely perfect from a technical point of view! How about this, as measured by AsusProbe 2:

- 28C room temp, Asus QFan controls the cpu fan speed with a target temp of 60C:

Idle, Vcore 1.10 (PowerNow activated)
- cpu: 33 C
- cpu fan rpm: 1300

Full load both cores (standard Vcore 1.35V)
- cpu: 57 C
- cpu fan rpm: 2300

To the purists of silence out there, the rpms may not seem very impressive but this is good enough for me at the moment - below 2000 rpm on the cpu this system is hardly noticable given its placement and other environmental noise. Also, this is summer temps and we have a quite short summer here in Sweden.

I also get the headroom I wished to have, this fan maxes out at 2700rpm in free air and after some experiments with the target temp I know this combo can keep things under perfect control even if room temp should be quite a lot higher.

Problem

This fan has a typical pwm-induced buzz at rpms between 1400 - 2200 that varies with rpm. It is quite faint, especially after I mounted the fan by using soft silicone in between things, but still: this has become the new focus for me. It is the kind of sound that excites resonances in the chassis, probably it could be damped to a significant extent still by chassis mods.

However, I'd much rather like to attack the sources of noise. I would be very grateful for suggestions of 80 mm fans with similar performance, that are known to work well with the pwm as implemented in MB's like Asus A8N-sli (I guess this is a typical implementation).

Alternatively, if there is some kind of inexpensive gadget or easily implementable circuit that could eliminate this buzz. If I try to explain what it sounds like, it is much like a very distant one propeller-driven small private aircraft flying around.

With the fan that came with the boxed cooler for my old Amd64 3000+ Winchester, this fan had no buzz at all when regulated by QFan, Asus MB-based fan control system. Also, no such buzz is generated with other inexpensive fans I use right now, like a 120mm Spire fan that is almost dead silent as regulated by Qfan (save an extremely slight growl if you listen up real close). Overall, I'm very happy with this control method and the cooler performance - except for the buzz it creates with this particular fan.

Please give some advice!

[skiddy]

See if you can adjust the pwm frequency.

If you are using Speedfan, config, advanced, chip...

[vortex222]

the best trick would be to get a small capacitor rated for at least 12 volts. I am unsure what other parts you would need however.

I am sure there are others on here who would be able to tell you exactly how to wire it up. (i think you only need it inline of the positive lead)

[Rick63]

Skiddy: thanks for the suggestion! I checked it out. PWM clock was at the highest available - 48M - and this appears to be the setting where it makes the least sound. Maybe if it was possible to double the PWM fq it would have helped... no luck there I'm afraid.

Vortex, this sounds like a great idea as well! I hope somebody could help me with further information on that, what type of capacitor to use etc.

EDIT: now I checked the archives. There is a gadget TBAN-YA that seems very inexpensive and promises to do what I want.