Rohde & Schwarz RTB2004 - Fan Noise

[javadesigner]

I'm fairly new to electronics, as a hobby.

Read about R&S RTB 2004 - the touch screen and the improved logic decoding sounded great. On a whim, sold the Rigol 1104Z+ I previously owned and just purchased the R&S RTB 2004 COM4 package from a North American reseller/retailer.

The R&S is definitely an amazing scope - beautiful and lightweight. The lightness is unbelievable and puts a smile on my face. But..the fan noise is way way too loud. At least as LOUD or (LOUDER) than the Rigol (and the Rigol was the loudest thing in the room). Plus the R&S fan cycles through a subtly changing pitch, so that makes it even more annoying than the Rigol. The room is cool (70F) and I'm not doing anything with the scope yet the fan is probably just running flat out. Did a factory reset but that did not help. The unit I received (Jan 2021) is running the 2018 firmware, but the next firmware was only released Oct 2020 so not too surprising.

Another thing: the plastic bags were crinkly and the manual and one probe insert sheet had some minor spots on it. The Rigol scope packaging was factory spotless, not a single crease or crinkle in any of the bags.

This could be a production artifact - maybe the European factory is more hand driven and humans are manually putting stuff in bags, which would explain the crinkles. Or perhaps-  on account of being so damn loud - maybe this unit was previously bought/returned and the retailer shipped that same unit back out to me. I've emailed the retailer and waiting to see what they say. I paid the full promo price (~4K USD).

Would be nice if R&S sold directly (like Rigol does) - which would remove any potential shenanigans but whatever.

Anyway, my questions are:
1) Why is this thing so loud ? It is supposed to be darn near inaudible! It is engineered to be quiet, with the rubber gaskets/mounting/design etc, which is a big selling point in favor of R&S (at least on paper).

2) What are my options when a new 'scope has this sort of issue ? Repair would defeat the reason for buying something new in the first place. Should I return it, ask for swap, try a different retailer ? Luck of the draw if another unit has the same problem ?

Any suggestions or comments from anyone who might have experienced a similar issue would be highly appreciated.

Attached images show:
1) 38.5db value in quiet room with osc off
2) 47.9db value in quiet room with osc on - same db meter position.
3) Some random spots in the manual as well as pack of probe insert

[Harjit]

I use it in my home office and so the environment is quite quiet i.e. I can hear when my laptop fan spins up.

Having said that, I too was (and am surprised) by the sound level of the RTB2004 fan. I did send it in and it came back at the same level. So, that is normal. I think in a normal lab environment with plenty of things humming/buzzing, I don't think it would be noticeable - at least that is what I tell myself.

[Zlotnik]

There seems to be quite some variance in the fan noise level. Mine is my quietest piece of equipment (excluding the fan-less stuff, I mean), the fan is nigh on inaudible.

[javadesigner]

Having said that, I too was (and am surprised) by the sound level of the RTB2004 fan. I did send it in and it came back at the same level.

Hi - thanks for the info/reply!

Where did you send it in ? To R&S repair or to your reseller? If R&S, what did they diagnose ? If reseller, did you get back another new unit and if so, how do you know it was actually new ?

[javadesigner]

Mine is my quietest piece of equipment (excluding the fan-less stuff, I mean), the fan is nigh on inaudible.

Precisely - that's what I was expecting and thanks for confirming. Since you are in the Netherlands, am wondering if this has something to do with either 220v vs 110 volt difference (unlikely) -or- a manufacturing date different than perhaps a large promotional batch that was shipped to the USA and that me (and the poster above) happened to get.

[Hydron]

It may be a consequence of fan to fan variability - there is no feedback of fan speed so it's just controlled open loop.

Mine has a noticeable but not annoying fan - certainly not bad enough to worry about sending in to be checked.

Edit: oh, I can say that it is significant quieter than my DS1054Z was - that was bad enough that I changed the fan.

As for the question about whether you got a brand new unit, did you get a bunch of paperwork with it with serial numbers, packing lists and option keys? Mine came with those and they all had recent dates on them (though note that my unit was a very early one so a cannot have sat in a warehouse for long given they'd only just started to make them).

[javadesigner]

Thanks for the reply/info!

Edit: oh, I can say that it is significant quieter than my DS1054Z was - that was bad enough that I changed the fan.

Complicating all this - hearing is subjective and one persons loud might be another persons inaudible. But for the same person, the differential between 2 sounds should be noticeable objectively. You heard the difference between your Rigol and R&S. In my case, the Rigol (DS1104Z+) and the R&S were equally loud (no difference), and the R&S was worse in that it had a subtly changing whine/pitch in addition to being so loud. Clearly, something is off here.

As for the question about whether you got a brand new unit, did you get a bunch of paperwork with it with serial numbers, packing lists and option keys? Mine came with those and they all had recent dates on them (though note that my unit was a very early one so a cannot have sat in a warehouse for long given they'd only just started to make them).

Yes, actually I got 2 pieces of paper that listed all the accessories in the promo package and a manufucturing date of early Sept 2020. There were no individual option keys but I'm presuming these are perpetual licenses so maybe that's expected? The paper did list a serial number. The scope itself looks new but the stuff in the cardboard box looked like it had been opened before - many of the pastic bags were crinkly. The manual and one of the analog probe inserts had some marks on it. Could be a variation of manufacturing and/or a sign of a previous return. Will see what the retailer says when USA opens again on Tuesday (Monday being a holiday here) but they will probabaly feign ignorance.

Either way, none of this would matter if the scope was just a tad bit quieter but man this particular unit is just a bit too loud. Sonically, it seems like I'm paying Apple prices for a rock bottom Acer laptop. I'm wondering if R&S has any systematic research program to collect some of these reported loud units from the field and diagnose the underlying cause.

Edit: As an aside, many ebm-papst fans (available in different sizes) are rated at 16dbA at full speed - they almost can't even be heard even with your ear against it. I'm assuming R&S is using ebm-papst or similar (or should be)....?

Edit2: This one is 12dbA
https://www.ebmpapst.com/de/en/products/compact-fans/axial-compact-fans/p/8412NGLE.html

[nctnico]

Where it comes to replacing fans you have to make sure the replacement moves the same volume of air and can offer a similar static pressure. Otherwise it won't push enough air through your device causing your device to overheat. Noctua makes very nice low noise fans which usually are much quieter compared to fans from Papst and other brands while providing the same air pressure / air volume.

[vincenza]

hello, I ask for help, I have a rohde & schwarz fsea 30, I would like to replace the hard disk because it causes problems, I cannot access the bios screen, I read in the forums that the procedure to access is: connect a keyboard and start repeatedly click the DEL key on the keyboard, but it remains still at the booting screen but does not access the bios. I ask for your help, thank you and goodbye

[Rydda]

Hello all noise phobics.
I avoid instruments with cooling fans if I can, but the RTB2004 tempted me, and after reading many comments on how quiet it was I decided to give it a try. How bad could it be? Well, I soon found out. After 2 minutes I turned it off in disgust, and realized I had to fix it or get rid of it.

To  give some context: where I live there is no external noise pollution, my computers are all in Hdplex fanless cases and use SSDs for storage. The RTB became the loudest thing in my house. I could easily hear it from an adjacent room.

Initially I had hoped to reduce the noise by just replacing the fan with a better 80mm fan. So I tested with a Noctua NF8, but the difference was minimal. They both run at the same rpm, and the high speed of a small fan is the main contributor to the noise. I needed a larger fan, but the RTB chassis construction and the fan orientation makes it difficult to fit a larger fan inside the case. I did not want to modify the chassis to make space, but opted instead to modify only the plastic case 

Before mods:
------------
Fan = Sunon HA80251 v4   , 1700 rpm  @10.5 volt
Noise:   rear= 40dBA , right= 34dBA , front= 35dBA , left= 34dBA  ( measured at 30cm )
Internal heat sink temp:   adc=34C , micro=50C
Exhaust temp:  32.5C - 40.7C     Air speed=1.2 m/s
Peak temp pcb backside = 62.9C (pic 'before')
 
The RTB fan blows air over the top side of the pcb only. There is no air flow over the back side. The attached pic 'before.jpg' shows the temperature on the pcb back side after one hour. The hottest part at 62,9C was a component (MPKM 3620 246 ?) under the adc.
 
I decided to:
-use a larger slow-running fan placed outside the case.
-modify the case to make the best use of the air flow.

I tested several fans. Some did satisfy my noise requirements when running at reduced rpm, but showed starting problems when the speed was reduced too much. (The RTB monitors the fan, and displays a warning message if the fan stops). The fan I selected was Noctua NF S12A ULN
 
To minimize the needed air flow I decided to open up fan inlet so air can pass through the cavity under the pcb so bottom side acts as heat sink. To allow air to enter the space, the fan cutout must be placed as low as possible. Air exit was created by adding several vent holes ( pic 'bottomview' ).
 
The case was modified as follows:
-all vent holes on the right side blocked.
-the top three vent hole rows on the left side blocked.
-added vent holes to the bottom of the case (pic bottomView). Air exit from pcb back side.
-opened up the rear air intake to suit a 120mm fan.
-added a fan grill and cover (pic 'rearview')

After mods:
--------------------
Fan = Noctua NF S12A ULN   550 rpm  @10.5 volt (with uln resistor) 
Noise:  rear= <30dBA    right,front,left = <26dBA (below noise floor of meter)
Internal heat sink temp:   adc=35C , micro=50C
Exhaust temp:   36.4C - 42C    Air speed = 0.8 m/s
Peak temp pcb backside = 47.3C   (pic 'after')

All measurements taken after one hour.
Ambient temp = 26C
R&S specifies noise as 28.3dBA at 0.8M. I used 0.3M since that is more like the actual distance when I use the scope.
The noise level values tell only part of the story. The greatest change with this modification was the noise character. It is now atonal (like pink noise) and it does not disturb me at all.

 
 
 

[javadesigner]

Hi Rydda!

Thanks for posting about this amazing modification you did  - Very elaborate and impressive!

When you solve a problem, man you do solve a problem

Did you 3D print the external fan casing by any chance ?

Also, it is interesting that R&S are using a cheap Sunon fan. (to confirm, that's what you found in the stock R&S unit?). Given that R&S clearly spent time engineering the fan mounting etc, why would would they then nullify that advantage by using Sunon? I would have expected EBM-Papst, Noctua, etc, at least.

[Rydda]

Hi
@javadesigner
The fan cover/casing just evolved during my testing. It is manually routed from a chunk of oak wood. If I had known beforehand that I would be satisfied with the noise reduction I would probably have printed it, or just heat formed some abs plastic.

I can confirm that the original fan was 'Sunon HA80251 v4', and also that it was not louder than the Noctua NF8. Both the air borne noise and the vibrations seemed to be just about the same. I must admit I was a bit surprised myself. I had previously replaced the crappy original fan (Sunon E80201S1) in an R&S NGE103 power supply with a Noctua NF8, and the difference was remarkable.

Afaik the rubber fan mounting in the RTB comes with the fan. I doubt the R&S people spend many minutes thinking about fan noise. They are probably more concerned with the fan mtbf.

[Harjit]

I went through the reseller and it was a royal pain and slow process.

[javadesigner]

An update:

Got a new unit from a different USA reseller. Talked to the reseller's R&S specialist on the phone and requested they ship from their latest inventory.

The unit I ended up getting has the latest Oct 2020 firmware installed, so it is a very recent manufacture.

Turning it on, this unit immediately feels less noisy than the previous one. The previous unit had felt like something was off/not quite right - was as loud as the Rigol 1104Z that I owned previously. The consensus on these forums seems to be that it was a faulty fan/sensor running full-on all the time without ramping down.

I would guess-timate this new unit to be about 30-35% less noisy than the previous unit. Additionally, the fan in this new unit does not oscillate between frequencies - the fan hum is clearly present but constant - much more like pink noise.

For comparison purposes, I have a benchtop power supply that (despite having a fan) is almost inaudible.

1) This new R&S is noticeably louder than the power supply. But not a whole lot louder. 

2) Compared to the previous unit, this unit is noticeably quieter. Quiet enough that it I don't feel something is wrong when it is turned on. Perhaps no R&S unit is going to be totally silent but mine is definitely on the right side of quiet fence - the pink noise just disappears after a while.

In all, this one is a keeper!  I'm very happy with the outcome...






 

[Rich@RohdeScopesUSA]

In all, this one is a keeper!  I'm very happy with the outcome...

-Rich

[jmw]

2) Compared to the previous unit, this unit is noticeably quieter. Quiet enough that it I don't feel something is wrong when it is turned on. Perhaps no R&S unit is going to be totally silent but mine is definitely on the right side of quiet fence - the pink noise just disappears after a while.

The R&S FPC-1500 is completely fan-less and a pleasure to use! I wish the scopes could share the same thermal design. My unit had to go back multiple times for spurious IF overload problems, but R&S took care of it, and ultimately I think it's just a warm-up issue.

[Ecogeek]

I received my RTB 2004 in Dec 2022 (took 6months from ordering) Serial Number 204357 and the fan noise is almost inaudible.  Looks like R&S has used a new fan to the original?