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Old 08-10-2018, 08:23 AM   #1
Deep South
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Default AC/DC variable voltage adaptor for Noctua NF-S12A ULN fan

Hi,
I'm hoping someone knowledgeable can point me to the right adaptor to use the Noctua fan as cooler for 2 pieces of audio gear - a Dark Voice 336SE and a Parasound Zamp.

Both produce a lot of heat and both the components and the sound benefit from cooling - passive cooling is a joke that so many in the audio world refuse to let go of.

I have a Maplin AC/DC adaptor that I bought years ago and that has a 3V-12V slider control . it seems to be malfunctioning and I do need 2 adaptors.

Nowhere can I see this type of adaptor anymore. The amp sits on an open backed slate box well above the my old Noctua fan giving me room to have airspace beneath the fan. The box is lined with bitumen sound dampening sheet.

I doubt if I will need to run the new Noctuas at full speed to achieve a reasonable temperature with the 2 amps - the variable voltage slider control is neat - any ideas?
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Old 08-10-2018, 08:32 AM   #2
eccerr0r
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Default Re: AC/DC variable voltage adaptor for Noctua NF-S12A ULN fan

pictures?

wattage?

Usually electronics are good at one voltage, what's the adjustment for?
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Old 08-10-2018, 12:59 PM   #3
Curious.George
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Default Re: AC/DC variable voltage adaptor for Noctua NF-S12A ULN fan

Quote:
Originally Posted by Deep South View Post
I have a Maplin AC/DC adaptor that I bought years ago and that has a 3V-12V slider control . it seems to be malfunctioning and I do need 2 adaptors.
What you've not said (but appears to be implied) is your belief that this adapter would be a suitable power source for the fan (which, apparently, is a DC fan hence the variable voltage gives you speed control).

How is the old/existing unit "failing"? One problem with "slide pots" is that they tend to get dirty (their design opens their innards to the environment to allow for the range of travel of the slider). This might manifest as the voltage bouncing all over as you move the slider. Or, being "wrong" for the current position of the slider (and possibly "right" if you nudge the slider just a wee bit as the wiper regains contact with the linear resistive element).

You can try cleaning the pot (spray cleaner and work it in by exercising the slider).

Or, if cosmetics aren't an issue, you can extract the slide pot from the adapter and connect a rotary potentiometer (or even a 'selector switch" as you probably only need a few settings, not an infinite number of them!) in its place.

BTW, there's nothing wrong with passive cooling (does your adapter have a fan in it? what about your cell phone? BT earpiece??) The error is not sizing the heat sink for the ambient and power being dissipated.
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Old 08-10-2018, 01:50 PM   #4
redwire
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Default Re: AC/DC variable voltage adaptor for Noctua NF-S12A ULN fan

Try to find a voltage you like for the fans, say 9V and then use a (transformer-based) wall adapter.
But these have poor regulation and 9V usually gives 11V, so nice to switch to 6V. Or use a resistor to lower speed. The Noctua and Scythe fans are very good I find.

Multi-voltage (transformer tap switch) AC adapters are harder to find now, there are switching power supplies that do the same. Pic is from fleabay.

I'm against using SMPS wall-adapters here because they make a lot of RFI which can get into the audio gear. PWM fan controllers also are noisy.
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File Type: jpg ac adapter.jpg (63.4 KB, 4 views)

Last edited by redwire; 08-10-2018 at 01:51 PM..
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Old 08-11-2018, 03:09 AM   #5
Deep South
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Default Re: AC/DC variable voltage adaptor for Noctua NF-S12A ULN fan

Curious George,
I've used a Noctua fan for years to cool both a Bada power and h/amp, very successfully. In the 50s white papers stated categorically that lowering operating temps. for caps and resistors by 10C effectively doubled their life. The idea was mooted by a Dutch friend of mine and a useful by-product was that the sound (we both had the same Bada h/amp) improved, not by a lot but it was noticeable.

I've just bought a Parasound Zamp and if it is used in a restricted space they also sell a boxed fan to use beneath.

Mosfets are an excellent for amplification but do create as part of their function a lot of heat as do valves and power resistors. Sadly there are those on audio forums who state that mosfets perform best when 'hot' but provide no evidence that they have ever performed tests on actively cooled mosfets - another classic example of 'received wisdom.

Passive cooling simply isn't as effective as active cooling as proof just look at all the development of active cooling in PCs.

What has always impressed me in PC development is the industry wide open mindedness, out of the box thinking compared to audio.

Enclosures could be designed to encourage convection cooling - heat rises but I've never seen any such examples. Of course it's not in the interests of the audio business to design longevity into products.

Your suggestion about spray cleaning the pot is of course spot on, I did this when I bought a Technics SL120 years ago.

Redwire - totally agree about SMPS adaptors IF they are connected to a piece of equipment but I use the adaptors independently.

I have seen this argument used about inter/connects and shielding - theoretical b/s. In fact shielding seriously interferes with signal conduction that's from 4 years I spent creating various designs of analogue i/cs.

As it happens yesterday I saw an Irish seller on Ebay with exactly what I wanted so have bought 2. Thanks for the replies.
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Old 08-11-2018, 02:54 PM   #6
Curious.George
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Default Re: AC/DC variable voltage adaptor for Noctua NF-S12A ULN fan

Quote:
Originally Posted by Deep South View Post
Passive cooling simply isn't as effective as active cooling as proof just look at all the development of active cooling in PCs.
Apples vs. Oranges.

Do you need active cooling for a 20W audio amp made of discrete semiconductors? (No, because the heat is dissipated in various components separated by large enough distances that convective cooling -- at STP -- can move enough of that heat away from the die to prevent their melting.)

Do you need active cooling for a 20W integrated CPU? (Yes, because all of that heat is concentrated in one die and you can't get the heat away from the die fast enough to prevent the die from going "poof")

Not often you see someone trying to make a 1KW linear in something the size of a laptop case! OTOH, you do see folks trying to get laptops running as fast as desktops (despite the reduced volume). Audio tends to be more tolerant of packaging than digital.

[You don't see roadies lamenting the size of the amps they have to haul around -- cuz the speaker stacks will still be there even if the amps were reduced to "pocket sized"]

Quote:
What has always impressed me in PC development is the industry wide open mindedness, out of the box thinking compared to audio.
There's just as much mumbo-jumbo touted in the digital realm as in audio. And, just as many wide-eyed proponents of their favorite belief systems (dogma).

How eagerly would you increase B+ beyond the V(br)dss of the mosfets in the output stage? Yet, folks willingly overclock CPUs -- with no easy way to know when they have introduced (functional) failures. At least an overstressed FET will go poof to tell you of the error in your ways! Are you sure the calculations performed by that overclocked processor were ALL correct?

Quote:
Enclosures could be designed to encourage convection cooling - heat rises but I've never seen any such examples. Of course it's not in the interests of the audio business to design longevity into products.
The whole back end of my Phase Linear 700's was devoted to heat sinks for the power transistors. No fan. Never melted any silicon or let any magic smoke escape.
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