Unfortunately the Ampeg fan is 24v, and noctua doesn't make any 24v 60mm fans. 3d printer community is often running a lot of 24v stuff and I've seen many recommendations for these cheap 24v to 12v stepdown transformers you can get 4/$10 on Amazon. They are super tiny and could be stashed anywhere in the enclosure. Most silent PC fans are 12v anyways, so this opens up a lot of possibilities. I'd feel way more comfortable doing this than the above temperature sensor mod, which I agree, is not safe or a good idea without understanding what in the amp needs cooling.
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Noisy fan on ampeg micro vr
- Thread starter krfoss
- Start date
I love the Noctua fans and have used them in loud Avid/Sonnet rack enclosures but unfortunately they don’t make the right size for this application at 24v
NMB makes a lot of very low noise fans, and have more options in 24v, so that might be a good alternative as well.
I emailed NMB to ask, since their site isn't great for comparing their models. They suggest this as a drop in replacement. Slightly lower CFM, but 7db quieter. It is 25mm thick, I'm not sure offhand how thick the ampeg stock fan is.
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Hi, just a question.Why do not use a Noctua with a simple DC voltage changer? For examle a tiny PCB with xl6009... I am now purchasing Micro VR and will probably try it
However, many many thanks for all the helpful info here about the noisy fan!
I'm adding this note about my experience, hoping it might be of some use to others. I'm sure what I did voids my warranty, though it is pretty easily 100% reversible. Good luck out there!
OK, the factory fan was obnoxiously loud.
After studying this thread, disassembly, and testing a bit with an infrared cooking thermometer, my first mod was: to simply remove the fan!
After some further testing, I played a full two hours solid with it with no fan. No drummer, and everyone else acoustic, so I didn't have to be very loud. (But louder than you might think, as there are multiple acoustic guitars and multiple loud singers involved.) The Micro VR was driving a single SVT-210AV cabinet. We were outdoors on a moderate night (ca. 75 F). I checked the temperature of the amp regularly (pointing the thermometer in through the hole where the fan would have been). The readings I got slowly increased from around 85 F to 105 F over the course of the first hour or so, and then sat somewhere around 105. The hottest area of the amp, once it has been on for a while, is internally, near the front, near the power switch, so my measurements were only indirect information. I was a bit nervous about the possibility of overheating. Everything seemed fine at the end of the night, but I thought I should try to find a more confidence-inspiring solution.
I searched for 24v replacement fans, and grew frustrated with the options. So I tried checking (with a multimeter) the voltage at the pins for the fan's power supply.
It was 12V, not 24.
So I ordered a Noctua NF-A6x25 FLX kit.
This paragraph contains some details about the installation process; most will want to skip it. The Noctua fan had three wires leading from it (black, red, yellow), unlike the stock fan, which had only two (black and red only). The little rectangular plastic power connecter that came with the Noctua was a different shape, incompatible with its counterpart on the Ampeg's board. Using a paper clip to press down and release the crimped terminals, I removed the wires with their crimped terminals intact, from their little connector boxes, both from the stock fan and the Noctua. (I did not remove the terminals -- this was a no-solder job.) I placed the black and red wire terminals from the Noctua fan into the little connecter from the stock fan, in the same slots that the stock fan's black and red wire terminals had been in. Since the terminals were a bit different, some fiddling was required to eventually get the Noctua's wires to sit properly and securely on the power pins on the board. But it seems to have worked out. (I did not connect the Noctua's yellow wire to the Ampeg's board. I put some painter's tape over the yellow wire terminal, to prevent unwanted contact.) I used the screws that came in the Noctua kit to mount the fan.
I did compare, in an unscientific way, the amount of air the stock fan seemed to move, versus the Noctua. The Noctua seemed to move less air, but not a huge difference. Again, unscientific, and I am sure that there is more that goes into it, but I decided to play my hunch that the amp, in my particular use case, will be adequately cooled by the Noctua.
The result: the fully reassembled amp with the Noctua fan is much quieter than with the stock fan. Not silent, but no longer obnoxious, to my ears, both in terms of quantity and quality of noise. To test, I left it on for four solid hours, playing through it intermittently at moderate levels, and the exterior temperatures I measured seem stable and acceptable (the highest reading I saw was 89 F at the front, bottom panel, just below the power switch).
OK, the factory fan was obnoxiously loud.
After studying this thread, disassembly, and testing a bit with an infrared cooking thermometer, my first mod was: to simply remove the fan!
After some further testing, I played a full two hours solid with it with no fan. No drummer, and everyone else acoustic, so I didn't have to be very loud. (But louder than you might think, as there are multiple acoustic guitars and multiple loud singers involved.) The Micro VR was driving a single SVT-210AV cabinet. We were outdoors on a moderate night (ca. 75 F). I checked the temperature of the amp regularly (pointing the thermometer in through the hole where the fan would have been). The readings I got slowly increased from around 85 F to 105 F over the course of the first hour or so, and then sat somewhere around 105. The hottest area of the amp, once it has been on for a while, is internally, near the front, near the power switch, so my measurements were only indirect information. I was a bit nervous about the possibility of overheating. Everything seemed fine at the end of the night, but I thought I should try to find a more confidence-inspiring solution.
I searched for 24v replacement fans, and grew frustrated with the options. So I tried checking (with a multimeter) the voltage at the pins for the fan's power supply.
It was 12V, not 24.
So I ordered a Noctua NF-A6x25 FLX kit.
This paragraph contains some details about the installation process; most will want to skip it. The Noctua fan had three wires leading from it (black, red, yellow), unlike the stock fan, which had only two (black and red only). The little rectangular plastic power connecter that came with the Noctua was a different shape, incompatible with its counterpart on the Ampeg's board. Using a paper clip to press down and release the crimped terminals, I removed the wires with their crimped terminals intact, from their little connector boxes, both from the stock fan and the Noctua. (I did not remove the terminals -- this was a no-solder job.) I placed the black and red wire terminals from the Noctua fan into the little connecter from the stock fan, in the same slots that the stock fan's black and red wire terminals had been in. Since the terminals were a bit different, some fiddling was required to eventually get the Noctua's wires to sit properly and securely on the power pins on the board. But it seems to have worked out. (I did not connect the Noctua's yellow wire to the Ampeg's board. I put some painter's tape over the yellow wire terminal, to prevent unwanted contact.) I used the screws that came in the Noctua kit to mount the fan.
I did compare, in an unscientific way, the amount of air the stock fan seemed to move, versus the Noctua. The Noctua seemed to move less air, but not a huge difference. Again, unscientific, and I am sure that there is more that goes into it, but I decided to play my hunch that the amp, in my particular use case, will be adequately cooled by the Noctua.
The result: the fully reassembled amp with the Noctua fan is much quieter than with the stock fan. Not silent, but no longer obnoxious, to my ears, both in terms of quantity and quality of noise. To test, I left it on for four solid hours, playing through it intermittently at moderate levels, and the exterior temperatures I measured seem stable and acceptable (the highest reading I saw was 89 F at the front, bottom panel, just below the power switch).
- Feb 12, 2006
- 60,949
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
This makes sense, thanks. I understand and am personally willing to accept the risk.
Do you by chance have any idea why they would use a fan designated as "24 V" but feed it only 12 V?
- Feb 12, 2006
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- 220,577
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Makes sense. I was wondering if it might have something to do with 110 vs 220. I'm in the US.
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
I like Noctua products, well designed and thought out. Their engineering group is good to deal with.
They do sell a 24V to 12V step down converter (9W, NA-VC1) to drive their fans, they also sell a PWM manual speed controller(NA-FC1).
They do sell a 24V to 12V step down converter (9W, NA-VC1) to drive their fans, they also sell a PWM manual speed controller(NA-FC1).
- Feb 12, 2006
- 60,949
- 5
- 220,577
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
If the original 24V fan was being operated at ~12V, that’s by design.
It seems like folks are struggling to solve a non issue by creating new issues.
I don’t know if it is being operated at 12V. sensor, fan speed. Some fans have control sensors built in as well.
Last edited:
- Feb 12, 2006
- 60,949
- 5
- 220,577
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
There is a base speed and a variable speed input to the 317 regulator. It's common for the base speed to be set to 12V which is in effect an air flow bias that is necessary for the fan speed to track the thermal load effectively. The variable portion is designed around the curves that I mentioned previously. This is why guessing is likely to end up wrong.
The 12V measured by CQE is likely the idle voltage without any thermal load. At a higher internal temperature a test can be done to see if the voltage increases. A higher voltage will damage the fan.
The fan comes with LNA (Low Noise Adapter) cables. There is an inline resistor built into the cable which lowers the voltage, the LNA’s also slow down the speed of the fan.
The fan comes with LNA (Low Noise Adapter) cables. There is an inline resistor built into the cable which lowers the voltage, the LNA’s also slow down the speed of the fan.
- Feb 12, 2006
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- 220,577
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
This all ignores the design metrics of the original product. Why use a 12V fan when the circuit clearly indicates that the variable speed portion of the fan increases above 12V?
This is where all the "seat of the pants" advice is wrong and why modifying a device often results in new problems. I see the results of modifications often enough that my cautions are absolutely warranted. The corrections of incorrect modifications always cost more than the original problem too.
I never said to use a 12V fan. It calls for a 24 volt fan, the control circuit will exceed the spec of the Noctua fan and damage it with time. The proper spec fan is called for.
Testing the circuit under thermal load will demonstrate how much the voltage increases above 12V. The Noctua fan can be used with a 12VDC external power supply. Assuming it has sufficient air flow for the amp’s requirements.
Last edited:
- Feb 12, 2006
- 60,949
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
And how do you propose to know that the air flow is adequate without knowing all of the points of measurement?
I am familiar with the SMPS and power amp design yet I would never be confident in identifying the key points that govern the system reliability. It’s a very complex SMPS in case you haven’t noticed.
There’s a lot of testing involved in tracking all of the thermal elements. The casual fan suggestions being made off the cuff are missing a lot of the important information.
I am familiar with the SMPS and power amp design yet I would never be confident in identifying the key points that govern the system reliability. It’s a very complex SMPS in case you haven’t noticed.
There’s a lot of testing involved in tracking all of the thermal elements. The casual fan suggestions being made off the cuff are missing a lot of the important information.
