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Adding fan-noise decibels.
Adding fan-noise decibels.
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Old 30th October 2002, 02:18 PM   #11
daatkins is offline daatkins  United Kingdom
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Join Date: Aug 2001
Location: Bath, UK
The fans I used (four 12v 40mm diameter) are rated at 24.5dB each and are certainly too noisy when running at full speed so I limit them by using a simple PWM speed controller. I use a thermistor screwed into the heatsink to sense the temperature and increase the fan speed as the amp heats up.

I designed the PWM circuit to start with a minimum of 15% duty cycle (the slowest speed before the fans begin to stall) at ambient and run up to a maximum of 50% (the point where the noise becomes objectionable) at around 40'C.

I did the following measurements by replacing the thermistor with a fixed resistor to give a constant fan speed:
No fans: 54'C
Fans @ 25% duty cycle: 43'C
Fans @ 33% duty cycle: 41'C
Fans @ 50% duty cycle: 35'C

I'd still like to replace the fans with some quieter units though, hence my original question. Even at 50% duty cycle, the fans are only audible in the gaps between songs but are still a bit too noisy during quiet dialogue passages in movies.

I'm half way through updating my Hiraga web page and will probably include details of this circuit.

Nice one.

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Old 30th October 2002, 02:48 PM   #12
bob4 is offline bob4  Germany
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Join Date: Oct 2002
Location: (Black Forest, Germany) currently southern Finland
Talking Re: BABYLON II

Originally posted by fdegrove

Because his ears are too small a stork is no rabbit at all!
Porque sus orejas son tan pequenitas la cegogna no puede ser conejo!
Puisque ses oreilles sont tellement petites une cigogne ne peut pas etre un lapin!

Still missing:German,Portuguese,Italian,Svensk,Norsk.... .


Roger Rabbit.
Here's the german and finnish translation:

Weil seine Ohren so klein sind, kann ein Storch kein Hase sein.
Koska sen korvat ovat niin pienet, haikara ei voi olla jšnis.

But wait a second.................
What are you trying to say??
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Old 30th October 2002, 02:53 PM   #13
wuffwaff is offline wuffwaff  Netherlands
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Join Date: Aug 2001
Location: Ingolstadt Germany

my first try was also with a PWM circuit (MIC502) but this turned out to make the fans more noisy as with a constant (lower) voltage.
The other thing was that I found the PWM frequency back in the signal although I used a seperate power supply.

After that I just used some resistors to get the right voltage and this works just fine.

Silent fans are for example the papst 8412 NGL at 12dB wich runs without problems at 8V.

een ooievaar is geen konijn want zijn oren zijn te klein!
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