Featuring advanced aerodynamic design measures such as Flow Acceleration Channels and an AAO frame. the NF-A4x20 5V PWM is a PWM enabled 5V variant of Noctua s highly optimised. premium quality quiet 40x20mm fan. The custom designed NE-FD3 PWM IC that integrates Smooth Commutation Drive technology and Noctua s reference class SSO2 bearings guarantee superb running smoothness and excellent long-term stability. Topped off with modular cabling. the OmniJoinTM Adaptor Set and 6 years manufacturer s warranty. the NF-A4x20 5V PWM is a premium choice for demanding 5V applications that require PWM control.Being a 5V fan. the NF-A4x20 5V PWM cannot be run at 12V and will be damaged when used with typical 12V power sources such as PC motherboard fan headers.40x20mm sizeCompared to Noctua s award-winning NF-A4x10. the NF-A4x20 is twice as thick. which allows for increased static pressure performance and makes the NF-A4x20 ideal for demanding applications with high flow resistance.5V PWM versionMany devices such as network or storage solutions use 5 volt 40mm fans with PWM speed control. With the same operating voltage. PWM support and the included OmniJoinTM adaptor set that makes it compatible with proprietary fan headers. the NF-A4x20 5V PWM is ideal for replacing noisy or broken 5V 40mm fans with PWM.Polarity protectionAs many devices using 5V fans feature proprietary connectors. and documentation of the pin alignment may not be available. the fan features an integrated diode for polarity protection. This way. you're on the safe side if you accidentally connect it with reverse polarity.Flow Acceleration ChannelsThe NF-A4x20 impeller features suction side Flow Acceleration Channels. By speeding up the airflow at the crucial outer blade regions. this measure reduces suction side flow separation and thus leads to better efficiency and lower vortex noise.AAO frameNoctua's AAO (Advanced Acoustic Optimisation) frames feature integrated anti-vibration pads as well as Noctua's proprietary Stepped Inlet Design and Inner Surface Microstructures. both of which further refine the fan's performance/noise efficiency.Stepped Inlet DesignNoctua's Stepped Inlet Design adds turbulence to the influx in order to facilitate the transition from laminar flow to turbulent flow. which reduces tonal intake noise. improves flow attachment and increases suction capacity. especially in space-restricted environments.Inner Surface MicrostructuresWith the tips of the fan blades ploughing through the boundary layer created by the Inner Surface Microstructures. flow separation from the suction side of the blades is significantly suppressed. which results in reduced blade passing noise and improved airflow and pressure efficiency.Integrated Anti-Vibration PadsIntegrated Anti-Vibration Pads made from extra-soft silicone minimise the transmission of minute vibrations while maintaining full compatibility with all standard mounting systems and fan clips used on heatsinks.Custom-designed PWM IC with SCDSupporting fully automatic PWM speed control. the fan uses Noctua's custom-designed NE-FD3 5V PWM IC that integrates Smooth Commutation Drive (SCD) technology. By providing smoother torque impulses. SCD suppresses PWM switching noises and thus makes the fan quieter at low speeds.OmniJoinTM adaptor setMany devices featuring 40mm fans use proprietary fan headers. so the NF-A4x20 comes with Noctua's OmniJoinTM adaptor set. Just cut the original fan's cable. fix it to the adaptor using the supplied cable connectors and you can plug the NF-A4x20 to proprietary fan headers!Extensive cabling optionsThe fan's short 20cm primary cable minimises cable clutter in typical applications while the supplied 30cm extension provides extended reach when necessary. Both cables are fully sleeved and a 4-pin y-cable allows the connection of a second fan to the same PWM fan header for automatic control.SSO2 bearingThe NF-A4x20 features the further optimised second generation of Noctua's renowned. time-tested SSO bearing. With SSO2. the rear magnet is placed closer to the axis to provide even better stabilisation. precision and durability.6-year manufacturer s warrantyNoctua fans are renowned for their impeccable quality and outstanding longevity. Like all Noctua fans. the NF-A4x20 features an MTTF of more than 150.000 hours rating and comes with a full 6-year manufacturer s warranty.