I have AMD stock cooler with 4 pin fan. It runs by default between 1600 -3300 RPM (PWM controlled). Now, I have managed to increase RPMs all the way to 6136 RPM (Note: CPU still varies the fan speed according to core temperature, but in different RPM ranges).
I have gained control of fan RPMs with intervention on fan PCB electronics, by adding RESISTOR and POTENTIOMETER in parallel with SMD RESISTOR on fans PCB.
NOTE: Value of fan resistor is 5 Kohm; Value of added resistor is 10 Kohm; Value of added potentiometer is 10 Kohm (Potentiometer is in series with 10 Kohm resistor and than both of these are in parallel with fan resistor). I have also installed a switch to have turn off possibility of added circuitry (Off = default)
Turning the potentiometer towards higher resistance increases RPMs and vice versa. Now, when computer add his pulses when temperature increases, fan RPMs raises too and vice versa.
RPM range control with potentiometer is between min/max: 3300 - 6136 (6136 RPMs are on 100 % CPU load when the potentiometer is set on maximum value of 10 Kohm).
So in practice it's like this:
Turbo fan operations mode switch - ON & STOCK with RPM range adjustment possibility (potentiometer).
ON MODE (potentiometer in zero position): Min/Max RPM: 3300 - 5000; Potentiometer in Max position: Min/Max RPM: 4436 - 6136. STOCK MODE (Switch Off): Min/Max RPM: 1600 - 3300. In every RPM range CPU variate fan speed according to core temperature.
However, in your case, to decrease fan speed ranges, you must replace FAN SMD RESISTOR with one which has higher resistance value, in that way that keep RPMs below 2100.
Also, if you wish to have automatic fan RPM control (fans with 3 wires), you'll need to install PTC resistor somewhere near the CPU, since PTC resistors changes its resistance (towards higher values) with raise of temperature, therefore fan RPM will also variate according to CPU temperature.
2What does the fan connect to for power: the mainboard or a powersupply lead? – music2myear – 2011-07-15T14:50:13.107
The fan is connected to the mobo to the cpu_fan input and it has 3 wires. I can read actual rpm of the fan in BIOS and in the software, I just can't change the speed. – user20196 – 2011-07-15T15:26:43.193
14-pin socket on the mobo? – Aki – 2011-07-15T15:50:10.693
Yes, the cpu_fan socket has 4 pin but the fan has only 3 wires. – user20196 – 2011-07-15T15:52:12.517
4http://www.allpinouts.org/index.php/Motherboard_%28CPU%29_4_Pin_Fan "Note: when using a 3-pin power connector with a 4-pin fan header, the fan will always be on; there is no fan control." – Aki – 2011-07-15T16:00:18.030
thx aki, if you move the comment as an answer i can set it up as a proper respond/answer to the question. – user20196 – 2011-07-15T16:05:08.590
Are there any other 3-pin fan headers on the motherboard? If so try plugging your cpu fan into one of those. Your bios may complain about there being no cpu fan installed, in which case there should be an option somewhere to ignore it. – Shane Kearney – 2011-07-15T17:18:03.163
2nope, all fan sockets are 4 pins. I think i got wrong fan, since PWM indicates that it can be controlled and thus it should have 4 pins. – user20196 – 2011-07-15T17:22:18.753