I just got an Ashly FET-500 off ebay; the seller had a bunch of them for sale at a great price. 8 pairs of K135/J50 laterals on +/-80vdc rails for 400w/4 ohm.
However, the ~5" 120VAC fan they use to suck air through the front panel is pretty loud. Fine for the PA rack, but annoying in the HT room. The heat sinking in these amps is fairly generous, but with a sealed top/bottom the amp would get too hot with no air flow.
Is there a simple way to slow down the fan?
However, the ~5" 120VAC fan they use to suck air through the front panel is pretty loud. Fine for the PA rack, but annoying in the HT room. The heat sinking in these amps is fairly generous, but with a sealed top/bottom the amp would get too hot with no air flow.
Is there a simple way to slow down the fan?
AC fans
I have slowed an AC fan down by using a small transformer with dual 120v primaries as an autoformer. Connect the two 120V primaries in series, connect the fan across only one of the primaries. Don't connect the secondaries at all. Now you have half (approximately) the voltage going to the fan, slowing it down and quieting it.
I have slowed an AC fan down by using a small transformer with dual 120v primaries as an autoformer. Connect the two 120V primaries in series, connect the fan across only one of the primaries. Don't connect the secondaries at all. Now you have half (approximately) the voltage going to the fan, slowing it down and quieting it.
Rikard Nilsson said:I would try connecting a diode in series with the fan. This removes one half wave, could do the trick.
Induction motors don't like DC in the stator. It will slow it down, but it will run very very hot.
If there are already +/-80V rails in the amp, that puts the secondary at 56-0-56. Just run the fan off one side of the main trafo (56VAC).
Thanks for the replies.
I think connecting the fan across one of the secondaries would be the easiest way to slow it down. This type of fan seems to draw around 100mA so i don't think the extra load on the transformer will be a problem. What about noise on the supply lines?
If i wanted to use a cap, how would i calculate the value?
I think connecting the fan across one of the secondaries would be the easiest way to slow it down. This type of fan seems to draw around 100mA so i don't think the extra load on the transformer will be a problem. What about noise on the supply lines?
If i wanted to use a cap, how would i calculate the value?
I use the series capacitor method. It works very well and without heat.
I suggest you start with 0.1uF and go up or down from there to make sure the fan starts reliably and provides the air flow / noise level you want.
Make sure you use a mains rated capacitor and put a 200k resistor (2 x 100k in series) in parallel with the capacitor so that it discharges when the power is turned off.
Cheers
Q
I suggest you start with 0.1uF and go up or down from there to make sure the fan starts reliably and provides the air flow / noise level you want.
Make sure you use a mains rated capacitor and put a 200k resistor (2 x 100k in series) in parallel with the capacitor so that it discharges when the power is turned off.
Cheers
Q
Oops, important safety note;
Make sure you discharge all the capacitors you try. They could retain a voltage as high as the mains voltage x 1.4. This voltage will remain indefinately unless discharged and you would not want these waiting in your parts bin. I use a 1k resistor on a croc-clip lead.
Also insulate the arrangement or arrange it so it is out of harms way.
Cheers
Q
Make sure you discharge all the capacitors you try. They could retain a voltage as high as the mains voltage x 1.4. This voltage will remain indefinately unless discharged and you would not want these waiting in your parts bin. I use a 1k resistor on a croc-clip lead.
Also insulate the arrangement or arrange it so it is out of harms way.
Cheers
Q
How about a thermal cutout switch in series with the fan (NO normal open)? Usually can mount the switch on the output heatsink. Make sure the HS is isolated or chassis grounded, even better if the fan is operated off the XFMR secondary.
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similar to http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=90936
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I would take the approach given by infinia: a thermal switch.
If, with a thermal switch, you find it is operating most of the time anyway in spite of the "generous" heat sinking. then make sure there is ample clearance around the amp and use a quieter external fan to push air in the same direction as the internal fans.
You will find that small room (table) fans produce a lot less noise then your average high speed muffin and has a higher cfm rating.
You may be also be able to find a quieter muffin fan ( with the same cfm ) to replace the existing one.
If, with a thermal switch, you find it is operating most of the time anyway in spite of the "generous" heat sinking. then make sure there is ample clearance around the amp and use a quieter external fan to push air in the same direction as the internal fans.
You will find that small room (table) fans produce a lot less noise then your average high speed muffin and has a higher cfm rating.
You may be also be able to find a quieter muffin fan ( with the same cfm ) to replace the existing one.
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