Noctua Fan Swap on a Calnex Rb/GPS Frequency Reference | Hacker News Reader

Noctua Fan Swap on a Calnex Rb/GPS Frequency Reference

jeffgeerling.com

46 pointsaray0731 comments

One issue I've had with swapping fans for Noctuas is the airflow matching. The louder fans aren't louder just because they're lower quality (which they definitely are), but also because (almost always in my experience) they force more air through.

That unit from the article sounds very temperature sensitive. I'd be wary of throwing a precision unit like that out of spec and out of calibration.

FWIW I've noctua-swapped so many things including an oscilloscope.

You can just look at the airflow charts and buy accordingly?

The best way is to measure temps before (ideally over at least 1-2 hours), then to measure temps the same amount of time after and compare.

In the case of this Rb oscillator, it is temperature sensitive, but also built for pretty extreme environments.

I'm not too worried about this particular application, because the clock will be in an air conditioned environment, and I'm monitoring the clock accuracy to +/- 2ns from another GPSDO / rubidium clock. The performance before and after the fan swap is within my measurement noise for 24H, though I haven't done 30+ day measurements and ADEV comparison. Still working on a consistent test setup.

The GRClok datasheet[0] gives its operating range as -10 to 55 °C (14-131 °F). The integrated Calnex unit only says it should be kept at +/- 1 °C for rated stability, but otherwise it just mentions 25 °C.[1]

Considering the new airflow rating is 9.4 m^3/h (vs 16.8[2]), yes it sounds like plenty of headroom.

[0] https://safran-navigation-timing.com/wp-content/uploads/2023...

[1] https://cdn-adepci5.actonsoftware.com/acton/cdna/28343/f-bf4...

[2] https://www.delta-fan.com/Download/Spec/EFB0412HHD.pdf

If you do you'll often find there isn't an equivalent noctua part.

> You can just look at the airflow charts and buy accordingly?

Not with Noctua and the likes, not always at least. These fans are quiet, but they are not made of magic fairy dust. They simply max out at lower flow rates than some of the the noisy, high-RPM fans people replace with them. Those 40 mm Noctuas, apart from voltage options, don't really come in many varieties.

It's a trade-off - you definitely lose the upper end of the device's original temperature range, but if it's stable under your conditions - great. How do you find out? Well, you replace the fans and check if it sizzles or not.

And funnily enough, a LOT of equipment these days isn't made with formal thermal design, they simply throw in high-cfm fans and... check if it sizzles. It usually doesn't because there's plenty of headroom. It's loud, but who cares since it's not meant to sit on your bench.

Source: replaced PSU and chassis fans in countless pieces of network and test & measurement equipment.

He mentions that he's running it in an air-conditioned studio, so presumably if the unit's datasheet lists an environmental range warmer than that, it has plenty of cooling headroom in this environment.

The last rubidium oscillator I played with, had to heat the vapor cell within the physics package, but then prevent that from overheating the rest of the unit, so it specified mounting to a heatsink. There was no heatsink recommendation given, just a certain package temperature as reported by sensor value X in the diagnostic data page. Get below that and you're golden. Get too much below that and you're wasting extra energy in the heater. Which is harmless, it just drives power consumption up.

So depending on how the unit's thermals work out, a slightly less aggressive fan may end up being mildly beneficial.

I wish Noctua fan fans realized they're fan equivalent of "unsafe languages such as C++" Rust fanatics. Even actual Rust fanatics would see how that kind of attempted advocacy is counterproductive.

I have no idea what you’re trying to say.

They are trying to say you cannot blindly swap for noctua if you don't know what specs you need for a fan.

I've also noctua swapped many of my things!

One of my slightly embarassing ones was the fan on one of my Nanlite lights was always on, do I thought to swap it with a noctua one so at least it'll probably be quieter.

When I took it apart, it turns out it was already a 12cm noctua... Black edition.

Airflow is typically measured for worst-case scenarios or not measured at all but just something pulled off a datasheet and then they install the cheapest fan they can find that meets the specs. My SOP is to open the case, get thermal readings, drop in a Noctua, and keep dropping the voltage while taking thermal readings to make sure nothing is getting too hot. I've got an NVR where I've dropped the speed to the lowest at which it will still start and it's still blowing cold air through the vents, so the 40mm screamer that was there initially was total overkill.

You can also get non-Noctua hydrodynamic bearing fans with polycarbonate blades and silicone mounts which are supposed to be very quiet, but I've never compared one against a Noctua. Anyone done a comparison?

I prefer installing a generic fan that's one size bigger but lower RPM instead of a fancy Noctua. You end up with similar or higher CFM. Downside is it may require drilling extra holes. But it's much cheaper and I didn't measure but I bet it's quieter too.

I have done a few casemods for that exact reason, but also taken a few approaches other than a step-up in fan size. Based on the pictures of this case, for example, I would have drilled holes to add a second and third fan (of the same size) on the sides, and have all three run slower.

They unfortunately arent cheaper anymore, but phanteks makes a line of 30mm thick fans that I've been using everywhere that will fit where I used to use noctuas. So you can avoid the extra holes if you can fit the thickness.

I got a ThinkStation P8 thinking it would be a nice workstation, but the fan noise was just unbearable. Not loud (although it could get LOUD), but extremely annoying. A cooling solution created for a rack mount system where the person buying the machine will never hear it. Absolutely unsuitable at home. I was looking into doing a Noctua Fan Swap here as well, but after reading the fan specs, I found out that this would be impossible, or possibly melt the machine. The 60mm fans on the PSU were rated at something like 25 watt _each_ and push more air at way more pressure than the strongest 120mm Noctua fan.

The Mac Studio that replaced it is practically silent and very energy efficient, while not being significantly slower.

My tinnitus requires loud fans. Also fan noise is always a good indicator of power.

When I was in highschool, I bought a secondhand Poweredge 1800-something hoping to make it my new home server after the Pentium 4 desktop I had been rocking. It was so fucking loud, I couldn't find a place to keep it that wasn't audible throughout the house. My parents were not happy.

Funny this is popping up, just ordered a noctua and buck converter to replace the very annoying fan in my rack mounted UPS this morning. The fan is audible through some sliding doors and has been driving me nuts.

Anyone know why that heatsink is that weird hedgehog spines design and not the more common regular extruded fin?

The design is called a splayed pin fin heat sink.

The rounded pins present minimal resistance to incoming air streams and Incoming air streams can enter from all directions (omnidirectional).

Round pins generate extensive air turbulence.

I'm guessing the more splayed the pins, the greater the air turbulence and it allows for air movement in all directions; the time / gps chipsets are meant to run cool.

Straight long fins heatsinks would be greatly hampered by the small fan that only produces a big airflow for a small number of fins.

Anyone else remember the WarmTek Hedgehog? The Kanie was better-known but wasn't really as much of a hedgehog design.

I assume Jeff used an industrialPPC variant here, but I kind of wonder if there isn't an EBM Papst or Sanyo Denki part that would have been sufficiently quiet and a better fit. The Noctua parts are usually at least decent, but they're really not the end all for fans.

I never understood why so many devices were using such poor quality and noisy fans. They fail earlier, they move less air and they're noisier. Now I understand there's a cost issue, but it's not only that: a lot of it is also just poor design / poor research / poor parts sourcing.

For the little story, back in the early beige PC days (think 386 and 486), quiet PC fans didn't exist. It was all super noisy, and typically at a fixed speed.

And, coming from the Commodore 64 and then Commodore Amiga that were silent machines, this was driving me crazy.

So 18 y/o me managed to source some proper fans out of Japan (Panaflo fans IIRC) and I went bug my neighbor, who was studying to become a chip engineer...

I came to my neighbor with an idea: "Why not lower the fan speed when the PC ain't too warm and then only speed it up when the PC gets too warm, you know, like a car's fan adapts to temperature?" (cars would do that: they'd start spinning a huge fan to cool down the water in the car's radiator, but only once the water would be too warm).

And so my neighbor drew a little electronical circuit and we bought "thermistors": I would "calibrate" them with boiling water in my mom's kitchen and then we'd install the circuit with the thermistor in the PC's PSU, with Panaflo fans.

So basically: back in the 386 and then 486 days, I already had quiet PCs. I'd "muffle" my HDD in an enclosure, opened on top (so that heat could dissipate, on which I'd put a 7V panaflo fan [I'd take the 12V and the 5V and create 7V]).

Once the PC world began to wake up and the likes of Be Quiet! and Noctua became a real thing, I was delighted. My current main rig has a Be Quiet! PSU and a Noctua fan for the CPU. I cannot thank such companies enough.

P.S: for what it's worth my neighbor later on moved to southern California and became an early Broadcom employee and he's been much more successful than me for he was the real smart cookie. We're still friends to this day.

This particular fan is a high quality / high CFM fan meant for servers and industrial gear.

Usually these boxes are at remote sites or in already-loud test racks, so the noise isn't a concern.

The Noctua is rated for lower CFM, so if you are already at a slim margin for thermals, switching to a quieter fan is not necessarily a good idea.

I do wish more manufacturers would go to 60 or 80mm fans instead of the 40mm ones common in this gear. Power supplies especially!

> And I guess it wouldn't be, since it's not exactly cheap (they don't publish a price for the unit online).

Any idea how much it costs?

Starting price of $835 after a quick search.

Used, AFAICT. New is a bit more.

This popping up on hn is quite satisfying. I’m in the middle of (procrastinating) swapping out a noisy fan for a noctua in my kramer 728 which i use for improving the video quality out of a laserdisc player.

That heatsink looked quite inefficient, somehow. Wouldn't it be better if there were branching on them to increase surface area multifold?

Real Engineers at work.

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