Products > Test Equipment
Keysight 34461A Fan Noise
BVH:
I had the 34461A before upgrading. It used the same 5V fan with the identical disturbing "howl". I bought mine from Amazon. I reasoned "Why do all the wire cutting and resistor inserting when the higher quality Noctua fan with it's higher quality bearing system is a drop-in replacement."
iMo:
--- Quote from: BVH on December 08, 2019, 02:57:20 pm ---I had the 34461A before upgrading. It used the same 5V fan with the identical disturbing "howl". I bought mine from Amazon. I reasoned "Why do all the wire cutting and resistor inserting when the higher quality Noctua fan with it's higher quality bearing system is a drop-in replacement."
--- End quote ---
A quick 5cents fix?..
EE-digger:
There's also a 0 cent fix. I held a 1/2" thick pad of loose medical cotton on my 34465A fan exit and it silenced the noise. A thin piece of open cell foam sheet will do the same thing. Just be sure it's open cell and has no adhesive on it. The material used to replace window ac filters is about right.
You're basically building a muffler. Most fan noise is caused by the shearing of the air between the blades and housing, etc.
Messtechniker:
Just replaced the stock fan of my 34465A with a Noctua NF-A4x10 5V fan.
The howl is a bit less now, but still not good enough for me :palm:
The air flow provided by the Noctua is noticeably higher by the way.
1 k 0.05 % resistor tolerance measurement after a 1 hour
warm-up immediately after having made the change.
Before: -0.0021 % to -0.0020%
After: -0.0013 % to -0.0012%
Just for the record: list of parts and tools you will need for the replacement:
Parts:
1.) The Noctua NF-A4x10 5V fan, of course
2.) 2 M4x20 mm metal bolts (doubtful if plastic bolts will be better)
3.) 2 M4 metal nuts
4.) 2 M4 spring washers
Tools for disassembly and reassembly of your 3446x:
1.) T15 bit
2.) T20 bit
3.) Screwdriver for the 2 M4 bolts you will be using.
What I might be trying next (should Xmas be too boring):
Inserting a piece of cotton fabric between casing and fan.
Reducing fan speed a bit.
As a last resort: cut away the metal at the fan exit. Something I will definitely not try.
Edited: Minus sign for tolerance values
Zucca:
--- Quote from: Messtechniker on December 20, 2019, 08:48:25 am ---The air flow provided by the Noctua is noticeably higher by the way.
--- End quote ---
Then the 100ohm 1 watt resistor could be a nice solution.
I would also measured the delta T (inside - ambient) before and after swapping the fan or installing the resistor.
I have a similar problem on my Agilent 66309D, which is lauder than a 1969 tractor compared to all others devices on my bench.
I swapped the old fan with a new high quality papst one:
https://www.tme.eu/de/details/612nn/dc-lufter-12v/ebm-papst/612-nn/
I took the old one out and I did an "outside device test" comparing new and old.
I was so happy to hear almost nothing with the new papst and a stupid rattling noise in the old one.
Unfortunately, after installing the new one in the unit I was not even close to the noise of the outside test, I improved the situation but there was still too much noise.
I am now tempted to try to add some rubber padding where the fan is mounted, to me the fan rotation resonate with that big heat sink.
TLTR: changing the fan with a new high quality one is always good, but sometimes it does not solve the problem.
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