Case fan noise

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  • Question
  • Updated 6 months ago
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Just wondering ??  After 5 months of living with a Flex 6500 and Maestro,  I have gotten use to all the quirks that happen and the long learning curve.  It is a great radio, and no doubt the newest versions will be even better.

I have just one issue, and maybe it is just me.  The exterior case cooling fans.  I fully understand that cooling is needed, but to me the noise is more than I wish to have on a constant basis.  Unlike many I don’t really like headphones.  The 6500 sits on a desk top about 3 feet away.  Is it maybe just my fans, or are they all pretty noisy  ??  Is there a replacement fan(s), that are better.

Just wondering are the new 6400 and 6600 a lot better in that regard  ??

For now I have gone back to my Kenwood 590SG and an SDR play for a panadapter, and much less noise. 


Photo of henrylance


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Posted 7 months ago

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Photo of David


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Have you tried put the radio under the desk or isolated way from your operating position? I have mine under the desk behind me in a shelf unit. I don't hear it.
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Jim Gilliam

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That is an excellent question. I, also, have a 6500 and find the fan noise unreasonable while sitting in front of it. Fortunately, I do most of my operating with my IOS device in another location. I have two 6500's and both of them have too much fan noise. I have even blown out the radios according to Tim's fine explanation, but the fan noise was unreasonable. I have 6600 on order and, hopefully, the fan noise will be less annoying. I have the 3000 and 5000 and they are about half or less loud than the 6500's.

Jim, K6QE

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Bill English

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I have a 6300 and I don’t hear anything objectionable. My PC makes a lot more noise than the Flex. I know it’s cooling by looking at the temperatures in DDUtil. Even in Rtty at 50-60 watts in a contest it doesn’t get that hot, and when I stop transmission, the temp drops very fast.. Maybe you have a fan issue. A bearing perhaps?
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Larry Williamson

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Like Bill, I don't hear anything on my 6500. Only when the fan revs during RTTY at about 50 watts.
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Bill English

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Yes sir, when I get the temps up the fan does increase but not bad. I guess this is kind of a per case deal, Some of us have more sensitive hearing than others, more ambient noise in our shacks, headphones, etc. Lots of factors make this about impossible have a one case fits all situations
Photo of W5AP


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I have a 6600M and so it sits on the desk in front of me
and yes....the fan noise is excessive. i was surprised
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Mike - WB8CXO

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My 6600M is quiet! The huge fan inside looks to be running at quarter speed. Perhaps my hearing is worse than I thought
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Ria - N2RJ, Elmer

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The fan noise even from my 6700 is not what I'd consider excessive. What kind of noise do you get? Mine is less than a computer power supply fan. The 6600 is supposed to be even quieter.
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Duane, AC5AA

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My 6600 (not M) is nearly silent - I can barely tell a fan is running.  My prior 6500 had some fan noise, but nothing near what I'd call objectionable.  It never really bothered me.  But I did notice how quiet the 6600 is by comparison.
Photo of N5LB - Lionel B

N5LB - Lionel B

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My 6300 fan noise was low and not an issue two feet away. My 6400 is much quieter. Except for the green button and the blue waves it would difficult to tell the radio was running.
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Gary L. Robinson

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I have had a similar experience having owned a 6300 for two years and then upgrading to a 6400.  The 6300 was fairly quiet unless I did a very long digital transmission.  The 6400 is even better - I have, so far, never heard the fan get louder even on very long digital transmissions (4-5 minutes on Olivia - I'm a rag chewer hihi).  And I monitor the temperature and it runs cooler than the 6300.

---Gary WB8ROL
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I'm sure they have a goal set to improve with every generation.
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Mike Presnell

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I guess I never realized the issue of fan noise with these radios.  I have my 6700 right next to me (less than 2 feet from my ear),  but I have rack-mounted it into a rack cabinet that is convenient for my shack, only about 4 feet high.  With the 6700 rack mounted (no front door - the front is open) I cant hear any fan noise from my Flex.  If racking it is a possibility for you, I'm sure you would be very pleased with the results.
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Bill -VA3WTB

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To me the fan noise on the 6500 is not objectionable. It is about the same as my computer power supply. I think some expect the radio to be almost silent. Too bad your using a much lower performance radio because of fan noise.
And yes the 6400 and the 6600 make much less noise because of the larger fan and slower RPM.
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Steve - K6SRS

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My 6500 is quiet enough I never gave it a thought.
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KY6LA - Howard, Elmer

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Perhaps you have a noisy fan with bad bearings...

My 6700 is very quiet... sits underneath one of the monitors on my desk about 20" from my ears

I did put a $10 Laptop Cooler underneath the radio (powered from the Radio USB Port- yes I know Tim does not like that use of the radio as a power source) which definitely helps keep the fans from spinning up even under heavy loads.

Did some tests on FT8 with and without the laptop cooler...   Without the cooler running SO2R, the 6700 fans will start to spin up after about 10 minutes.. With the cooler, they never spin up.

Even when they spin up the noise level is never as bad as some of my computers in the shack

Photo of Jeff-W7NEE


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My 6600 sits on the desk right next to my operating position and it is super quiet. I can’t say I have ever noticed the fans running!
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Mike - WB8CXO

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I can’t confirm 6500 fan noise but my 5 year old ( has it been that long already) 6700 has been running 24/7 and the fans are still quiet! Seems like with fans YMMV...
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Same here.
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Alex - DH2ID, Elmer

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Well, I haven't got a Kenwood TS590SG, but my TS2000X is very loud! Much louder than my Flex-6500, in fact. And you should hear my VAIO I7 notebook under full load. It howls like a jet engine, when under full load although not as loud ;-) I run all my TRX in my micro shack with this one notebook.
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John G3WGV

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Noise levels are subjective! As I get older I find myself less tolerant of unnecessary noise and nowadays I build my PCs into soundproofed cases. That makes the 6500 the noisiest thing (apart from me!) in the shack. Mine is under the desk and the noise level is just about OK. I keep on thinking about putting it in a small cabinet. I can see why some people get irritated by it.

PC cases with large slow running fans and a bit of soundproofing material do a pretty good job and are only marginally more expensive than the cheap noisy ones. It sounds like the 6600 has at least gone some way towards appeasing those of us who crave a quiet life.

73, John, G3WGV
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Cal Spreitzer

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Both my 6300 and 6500 had noisy fans which was mildly annoying.  My new 6600 is nearly silent and not annoying at all! 

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Lawrence Gray

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I find the 6500 fans noisy, but I know I have sensitive hearing. The 6500 is the noisiest item in my shack—even the Acom 600S is quieter. I use headphones, so the noise isn’t an issue, other than when using digital modes. I like Howard’s laptop cooler suggestion. I ordered one to try. My fans are clean, the noise is not bearing noise, and the equipment is in a rack, no door, on the operating desk.
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Gene - K3GC

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Fascinating, It sounds to be purely a matter of perception.  I have, over time had three Flex 6xxxs and I think they all had the same noise level. My computer is almost totally silent.  I can hear the fan on the CPU cooler - just.  My 6300 is a small bit louder but far from objectionable.

No one has said anything about amplifiers which, in my experience drown out all the rest.  My present amp is a Palstar LA-1K solid state rf sensing 1kw. It is the quietest Amp I have ever had blut still completely drowns out every thing else. 

I think this is just as individual as your choice of radio or microphone.  I use my Radiosport head set 90% of the time anyway. :) 
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Bob N0IS

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Sounds to me as though your 6500 fans are running in a speed other that just idle.  Every once in a while my 6500 will suddenly go to a faster speed for no apparent reason at all and it is noticeable.  It will then stay at that speed until it is turned off and then on the next time I wish to use it, but it then comes on at what I call "IDLE".  Would be nice if there were something to look at to see what speed setting the rig cooling fan was running at.  Ran the 6500 in a contest over the weekend and it just broke out of idle on a couple of occasions.  Oh yes, on hot days without the A/C on in the house, I have come into the shack and found the 6500 working hard to cool itself.  I am talking about 85 to 90 degrees "F".

Bob, N0IS

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John G3WGV

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A moot point! My (small by US standards) linear only makes a noise when it's being provoked and soon quiets down again after the QSO is done. That's rather different to the radio, which tends to be on whenever I am in the shack, fans and all.

It's a non-issue as far as I am concerned but it is unusual - most radios don't have fans running continuously.
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Bill -VA3WTB

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Good point Bob
I don't do anything with my radio to make the fans increase. The only time I have heard them ramp up was when doing an up date.
If they stayed ramped up I don't think I would like that much either.

Henry, make sure your radio is in the open and nothing blocking the fans,,it really should not be so noisy when the fans are on Idle.
Photo of Bill -VA3WTB

Bill -VA3WTB

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John, it is important that the fans run all the time. Most any other radio's do not use the same processors the flex does. These processors create lots of heat that need a lot of cooling.
Much the same way as your computer processor fan, or video card fan.
Photo of henrylance


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Thanks for all the above, see my reply below
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Ria - N2RJ, Elmer

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My fans started making quite a racket shortly before they failed, came up with the dreaded "ERR CPU FAN SPEED." My radio had to take a trip to the mothership in Austin. Now smooth as silk.
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Burch - K4QXX

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I have never heard my fan on my 6700.  I don't think I've ever seen the temperature get above 65 degrees.  Is there a certain speed that the fans kick in?

Photo of Ted  VE3TRQ


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I cannot hear the fans in my 6600M, and I sit maybe a foot from it. I can't speak for all 6600's, but mine is certainly quiet. But then I run QRP, never more than 20 or 30 watts out, often only 10 or 15 watts on digital modes, so do not stress the PA chips at all.
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John - W8AGS

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I have a 6600 that sits right in front of me. I can barely hear the fans spin up from time to time. The fans on my 6500 were a little louder but still not objectionable for me. Love the 6600. The fans on both my laptops are louder than either the 6600 or 6500.
Photo of Wim


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My 6500 was louder but these fans on the 6600 are still very noticeable to me, 
the transceiver is on my desk in front of me.
Putting it in a remote rack is an option ...
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Thanks, see my comment below
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When the 6500 fan`s kick in high speed you will know it.

Sounds like a jet air plane taking off. Over all running just sounds like an older desktop computer tower to me that had no modulating fans just full on unlike the new computers do as they modulate up and down.

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See my comment below, thanks
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Mike W1BFA in Maine

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I experienced the 6500 rev up this morning for the first time in two years. I typically run 40-50 watts in digital modes but had turned it up to 75 on a hard QST. I forgot to back it down and called cq and ended up running half a dozen stations and all of a sudden the fan stepped up, pretty impressive noise. It took it about 30 seconds to drop back to normal. I have been thinking of doing a DNC on it... annual thing with the pc’s etc. so imagine it’s due. Temp was around 135 F I think when it came up in speed.
Photo of henrylance


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Thanks everyone for your replies and comments. I should add some more info, in reply to thoughts.

First off, having had desktop computer since the 80's, and just about every rig and amp made, I'm a good judge of cooling system noise, as well and laboratory instrumentation. The current computer is a Apple Mac Mini, and there is no noise. My Macbook Pro and Samsung laptops are noise free. I had an actual Windows Desktop here a few weeks back and it had hardly any fan noise.

My Kenwood 590SG will only cycle the cooling fan on if it is pushed hard on digital modes, and its fan is about 1/3 of the 6500. I did have a icom 7300, and sold it because on transmit ( keying of any kind ), the fan ramped up to full take off and was awful. Some people have replaced the fan with a better unit with better bearings, and better shaped blades and a better frame.

But .... some people have hit upon something I have been thinking of, but haven't seen in the Flex manual. Is/does, the 6000 series of radios have temperature controlled case fans ?? This is not new and is actually common ?? What I maybe failed to mention, but I thought it was normal, is that right from the turn on ... the fan speed to me seems to high and loud. It does not change at all ( either up or down ), depending on work load. I have run 30 min or more of FT8 station after station, and been watching the temps, and the speed stays the same. The temps go up, but never to a level that is dangerous, and if there is a 30 second break the temps will come right back to basically base line.

From what I am reading others seem to have a change in fan speed vs load.

Yes I have done the case fan and CPU fans cleaning, as recommended by Flex. Thought I had a CPU fan problem, but Tim Emailed me the outline to check the RPM's and they were fine, and yes I can hear them, and know that they will have a sound of their own.

So my question now would be, are the case fans temp controlled. If they are, then than would be my answer.

Lastly, as some people have pointed out, noise is a matter of each persons perception, as well as how good their own hearing is. To me the 6500 I have is louder than 95 % + of all other rigs I have heard, for standby mode. I have no problem with rigs that ramp up the cooling fan/blowers speeds and the temps rise.

Could I build up a special enclosure to dampen the sound, sure. But why should that be needed.

What I am seeing is that other people also feel the same way, and others don't, as well as, some people are feeling that way about the new radios.

Does any one, or has anyone done a retrofit of the fans ?? I am sure they are not the best fans that can be had.

FYI: My hearing is tested on a regular basis ( abt every 2 years ), and I have a slight fall off in the midrange, but only very, very slight, so I am probably about like most people in my age group.

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Bill -VA3WTB

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The chassis fans will spin up to high when the internal temp reaches 60 deg C (140 deg F)
It is best to replace any fan with the exact fan, or at least the same air flow.

The 6500 is so well engineered everything was taken into consideration. The fans are what they are.
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Don't think I have seen the temp get that high.  If ..... I had the exact specs, I'm sure I could find a better fan.  The Flex is well engineered, but, it was or is not a price was no object product, and yes that can be said of almost anything.  I don't have a sound good sound level meter to take readings.
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Alan - KA4B

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Henry, I just tested my 6500, tuning at 35 watts into a dummy load for a few minutes, and using Flex Meter V1.2 to measure temperature.  The fan goes into high speed mode at 70C, which is about 158F.  At that point it is quite loud.  When the temperature came back down to about 56C, the fan speed dropped back to the normal mode.  Like you, I prefer not to have extra noise, and I think the 6500 at idle is the loudest thing in my house.  I think it would be a significant improvement if they had a multistep temperature control for the fan.
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Have you followed the procedure for cleaning the fans? This is really important in order to lower noise and increase fan life.