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Old 4th February 2014, 10:55 PM   #1
ro9397 is offline ro9397  United States
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Default Dummy load for cooling fan?

I use 2003 Pioneer VSX-D912 receiver (analog chip power amp modules) as unbalanced pure analog line preamp, sum total purpose for gain and remote volume, nothing else.

Compared to RCA unbalanced preamp outputs, performance audibly improves employing speaker outputs through "bridging circuit" comprising 9k Ohm series resistor (source side) followed by 1k Ohm parallel (load side). The load is practically invisible/non-existent; the top remains cool at any level. Still though, the cooling fan operates past a certain volume threshold.

Adding large amounts of rope putty and two fishing weights significantly damped fan noise, but my room is dead quiet and fan noise is still audible for a few seconds when I pause music. Plus even though higher playback level masks fan noise, I presume fan noise masks some detail.

I removed the fan, which the 912 "sensed" was gone, and would not turn on.

Fan label: 24VDC, 0.11A.

Can I replace the fan with a dummy load, thus tricking the program into thinking the fan is present? Please specify appropriate load and how to wire it per the fan's three conductors. I have only standard DVM. I'll risk frying the 912 to test.

Thanks very much for your help.
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Old 4th February 2014, 11:01 PM   #2
Einric is offline Einric  United States
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Is the fan only 2 wires?
If Yes.......
Measure the DC resistance of the fan.
Try to find a resistor of that value that will handle at least 3W or so.
That's what I'd try.
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Old 4th February 2014, 11:03 PM   #3
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Fan label: 24VDC, 0.11A.
220R and 5 watt resistor.
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Old 4th February 2014, 11:08 PM   #4
ro9397 is offline ro9397  United States
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Thank you sirs!

Any ideas re. three wires to the fan? I will dis-assemble fan if necessary to confirm purpose of three conductors.
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Old 4th February 2014, 11:26 PM   #5
Einric is offline Einric  United States
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3 wires means that there is either an RPM sense lead or PWM control over fan speed.
The 220Ω 5W resistor would go across the red and black wires generally, the standard color code is Red + Black - Yellow RPM.
If it does care that the fan is actually spinning then the 220Ω resistor might not work.
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Old 4th February 2014, 11:34 PM   #6
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3 wires means that there is either an RPM sense lead or PWM control over fan speed.
The 220Ω 5W resistor would go across the red and black wires generally, the standard color code is Red + Black - Yellow RPM.
If it does care that the fan is actually spinning then the 220Ω resistor might not work.
If it needs an RPM sense then you could stick in a 555 timer that output pulses.
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Old 5th February 2014, 12:10 AM   #7
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Default fan

Or just replace the fan with a quieter fan. There are many computer fans specifically designed to be very low db output. Available in most common fan sizes.
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Old 5th February 2014, 12:22 AM   #8
Einric is offline Einric  United States
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Z - This is true but the system requires a 24V fan.

I suppose a 12V Zener on a nice quiet computer fan would be ok.
But as with servers if the RPM is out of a certain range then it will throw a fault.

At that point I suppose the best you could hope for is that the Receiver only senses that the fan is spinning & doesn't care the actual RPM.

Last edited by Einric; 5th February 2014 at 12:25 AM.
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Old 5th February 2014, 12:34 AM   #9
Einric is offline Einric  United States
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Maybe try THIS 20V Zener diode on the Red lead, it will make the fan slower and quieter.
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Old 5th February 2014, 12:56 AM   #10
ro9397 is offline ro9397  United States
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On the one hand, too bad for the third wire. I'm hopeful it's irrelevant, as I never noticed RPM vary (good pitch sensitivity).

OTOH, this place is loaded with generous members! Thanks again. Will report results later.
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