How does this work?

Chris Beard · 2 Aug 2021 at 16:25

I'm interested in reducing the intensity of the 'jerk' of the pwm pulse that propels my fans in an attempt to reduce the volume of the pwm 'click'.

Does anyone know what the anatomy of these are please?:

Noctua NA-SRC7 4-Pin PWM Low-Noise Adaptors, 3 pack

Are they just a resistor, a series of diodes, a switching voltage regulator, something else? If someone has one - do they get warm to the touch?

Chris Beard · 3 Aug 2021 at 08:58

Mr Mcgoo said:
i believe they reduce the fan form 12v to 7v via an internal resistor, thus reducing the speed by around 30%

Thanks - this is my working assumption too. I'll pick up some resistor laden fan connectors then, and let's see how it goes.

Chris Beard · 3 Aug 2021 at 17:39

LuckyBenski said:
Although if that's the case, I don't know what happens with PWM fans, because these usually have a fixed voltage and pulse it. So between pulses, with theoretically no current, the voltage will increase back up to 12V.

Interesting; this may be exactly what I want, to 'soften' the pulse, as with increased current draw to power the fan it will deaden the movement. I never considered the non-instantaneous current increase.

LuckyBenski said:
That said, we're overthinking this - it won't kill anything so give it a try!

This is probably also true :-)

Chris Beard · 3 Aug 2021 at 18:22

chroniclard said:
Should there even be a click.....all mine don't click....

It's incredibly subtle, and only audible at very very low rpms, but it's the difference between a fan that I can hear and one that I can't. It's only my Akasa Apache fans (my pwm fans) that do it.

Noctua described the clicking here: https://noctua.at/es/noctua-announces-new-pwm-fans

Chris Beard · 13 Aug 2021 at 07:39

Silicon Si said:
Quote from the advert 'The NA-SRC7 contains three resistors for reducing the speed of 4-pin PWM fans by around 30%.' I would imagine that's one resistor per cable, I have one of those and it feels like a resistor under the the outer covering. Athough mine is a NA-RC7

Thank you! This is exactly what I wanted to know

Chris Beard · 13 Aug 2021 at 20:14

Meddling-Monk said:
Hmmm, just a quick question. Are you sure you've got pwm fan headers and not just voltage control with 4 pin pwm header?

Thanks for the heads up!

I'm running a pwm hub, so voltage control wouldn't alter the fan speed. There is a very considerable difference in volume between the different PWM settings for the fans, so I'm very confident the PWM signal from the mobo is working.

I'm also using an ASUS board, and whilst I am using the CPU header, I think all the headers support both PWM and Voltage control. There's a setting somewhere that I had to change for a fan from another header - seemed to work for me.

Your board is a lot lot nicer than mine. I'm surprised your board doesn't also have this setting and only offers voltage control. Especially as voltage control is more expensive to implement for the board maker!