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 Post subject: Noctua NF-P14 FLX low noise adapters
PostPosted: Tue Oct 02, 2012 4:39 pm 
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Joined: Tue Aug 15, 2006 6:46 pm
Posts: 21
Location: Canada
I have tried searching and have been unable to find an answer. I bought some NF-P14s which come with a low noise adapter (UNA, black) and ultra low noise adapter (ULNA, blue). Even with the ULNA I find the fans louder than I was hoping. Is the ULNA meant to be or can I chain it with the LNA?

Additionally, if I want to plug the fan into a motherboard header, can or should I use the adapters as well? I tried attaching with the ULNA and Asus's UEFI monitor showed a really low RPM of ~300 I think in red text. Is the red text due to the voltage being too low or perhaps it's an indication that I plugged in a 3-pin fan into a 4-pin header?


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 Post subject: Re: Noctua NF-P14 FLX low noise adapters
PostPosted: Wed Oct 03, 2012 12:52 am 
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Joined: Fri Aug 05, 2005 3:29 am
Posts: 1426
Location: UK
ctag wrote:
Additionally, if I want to plug the fan into a motherboard header, can or should I use the adapters as well?

The supplied LNA adapter and ULNA are simple resistor cables. The LNA reduces the voltage to the fan from 12V to around 9V and the ULNA to something like 7V. So used individually they give a choice of two fixed fan speeds of about 900 or 750 rpm.

The normal alternative to the adapters is to set the Silent profile in the BIOS. For a chassis fan header on an Asus motherboard this will give thermal control equivalent to around the 7V to 12V range. With the NF-P14 this would be a rpm range of 720 to 1230 (using the figures from the SPCR review of the Noctua NH-D14 cooler). In other words under idle conditions you should see around 700-800 rpm, and only under load and/or higher ambient temperatures would the fan speed increase.

You can of course put one of the adapters between the fan and the motherboard header. But instead of say 7V to 12V range it is going to be a lower voltage at both ends. So a lower minimum fan speed but equally it will reduce the maximum speed as well. The potential problem as always with 3 pin fans is that it may reduce the voltage to less than what the fan needs to start. It it easy to check that by rebooting the system and observing whether the fans run.

ctag wrote:
I tried attaching with the ULNA and Asus's UEFI monitor showed a really low RPM of ~300 I think in red text. Is the red text due to the voltage being too low or perhaps it's an indication that I plugged in a 3-pin fan into a 4-pin header?

The Asus BIOS has a minimum fan speed setting for both the CPU and chassis fan headers, you need to set this to Ignore which will remove the red text.


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 Post subject: Re: Noctua NF-P14 FLX low noise adapters
PostPosted: Thu Oct 04, 2012 7:49 pm 
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Joined: Tue Aug 15, 2006 6:46 pm
Posts: 21
Location: Canada
Thank you for your help. I was just afraid that I might damage the fans in some way. Plugging the fan into the motherboard with a LNA did wonders; the fan operates at ~500 RPM (UEFI) or ~400 RPM (in Windows 7) with the silent profile and my CPU and motherboard probes all report in the 30-40 degrees range at idle.

Oddly, I sometimes could not boot or the mouse didn't operate properly in the UEFI when chaining the ULNA and LNA with the front fan but not the back fan, even though both fans always spun up. Luckily, I don't need the front one right now.


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 Post subject: Re: Noctua NF-P14 FLX low noise adapters
PostPosted: Sun Jan 17, 2016 6:23 pm 
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Joined: Sun Jan 17, 2016 6:00 pm
Posts: 1
I know this is an old post but I thought o would try to post my question here since it falls within the same subject. I have the NOCTUA NF-A14 PWM 3000 RPM Industrial and I k kW that NOCTUA recommends against using their low noise adapters with their Industrial versions of their fans but I was just testing a few fans and not using them in a build. Anyways , I hooked one of the NF-A14 to the low noise adapters NA-SRC7 and the fan did not start up however if I give the fan an initial push it starts and keep spinning. That's is weird because according to what everybody is saying , the LNA brings down the vintage to 9 volts or even 7 volts at most. According to NOCTUA website , the starting vintage for the NF-A14 is somewhere between 5.5 volts to 6 volts. So what am I missing here ?


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 Post subject: Re: Noctua NF-P14 FLX low noise adapters
PostPosted: Mon Jan 18, 2016 12:05 pm 
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Joined: Mon Mar 17, 2008 1:49 pm
Posts: 1568
Location: UK
ikthos wrote:
That's is weird because according to what everybody is saying , the LNA brings down the vintage to 9 volts or even 7 volts at most. According to NOCTUA website , the starting vintage for the NF-A14 is somewhere between 5.5 volts to 6 volts. So what am I missing here ?

I see what this is. We need to consider some physics here. The LNA does NOT bring the voltage down to a specific voltage. It acts as an inline resistor. The voltage across the fan can then be found by dividing 12V by the total resistance of the fan and the LNA, then multiplying for the resistance of the fan. The voltage therefore varies according to the resistance of the fan. A high power fan like the NF-A14 has a very low resistance. If you add in a resistor the voltage going through it will drop by more than it would for a fan with a higher resistance.

If you want to slow down the NF-A14 then measure it's resistance and buy a resistor accordingly (let's say one with half the resistance of the fan, then you will have 8V across the fan), then solder this inline.

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