fans and LNA cables - strange results - any explanations please?


New Member
Jun 13, 2015
I have an x51 R1, and recently decided to see if I could lessen fan noise at all.
it is a stock machine, i5, GTx660, 2TB HD, except that I have taken out the blu ray drive to improve airflow, as I never use it. I have the X51 laid down horizontally.

So I studied lots of discussions including speedfan solutions ( but had trouble implementing those)

I will now name my fans like so, as they appear in open hardware:
fan 1 = 60mm front case Fan - 4 pin
fan 2 = 80mm CPU fan - 4 pin
fan 3 = 40mm power baord fan under optical drive - 3 pin

This is what i did: equipped with some noctua LNA cables , and using open hardware to eerport fan speeds, I made these changes & got these results:

1. I put a 4 pin noctua RC7 LNA on the CPU fan - that is a 50 ohm resistor. . before that FAN2 was at 860 on boot up, but with the LNA it went up to 1010 when it shoudl have gone down ???

2. removed that. CPu fan reverted to 860. I traced the connector for fan 1 and put the same LNA on that instead. It dropped the FAN1 start up speed from 1280 to 800. that is good, so the LNA is working, more powerfully than expected even.

3. I added a 3 pin noctua SRC10 LNA ( also 50 ohn I think) ,to fan 3. but the FAN3 speed here was unchanged. ~2200 at boot. I added another in series, but still no change. so I removed both . Also whatever instructions I followed with speed fan ( now removed) , I could not change that speed!

result 3 may be explainable if that fan has non standard wiring?

result 2 is a mystery. but I was able to figure out the snap on connects and replace that delta CPU fan with a noctua AF8 PMW that runs at same speed ~860 at boot & I think it is quieter. I kept the fan orientation the same as for the stock fan.

NB I do not have a fan shroud to worry about. I bought he X51 "new" on ebay & it came with no shroud. though google semms to think that all X51s should have one. but as it has worked fine for 2 years without, and as they seem impossible to source and buy, I will continue without one.

I would like to swap out the front casefan, but the instrucitons forgetting to that are so complex, I doubt that i have the nerve!