I put a big fan (140x140mm) on top louvers for cooling, air injected into
... maybe in the future ...
>
> On 6/18/2012 4:42 AM, David Robertson wrote: ( ... a long message I
> won't include here where he improved amplifier cooling by tightening
> heatsink/right panel screws and used heatsink compound.)
>
>
> I operate my KPA500 with the fan speed set to #1 continuously which
> delays the increase in the increase in fan speed once the amplifier
> starts putting out power. My amplifier did not exceed 58 deg C after 10
> minutes at 500 watts carrier output into a dummy load and it stabilized
> at about 60 degrees in a 25 degree C room. My right panel to heatsink
> screws (the ones under the handle) were all tight and that explains why
> my experience was better than was Dave's originally before he tightened
> his heatsink screws and added heatsink compound. I then added heatsink
> compound to the mating surface between my heatsink and the right side
> panel. There was no difference in cooling performance at all. I just
> wanted to know .. and now I do .. and so do you.
>
> The KPA500 fan is as quiet as any muffin fan ought to be but it was
> still annoying to me. That is not an amplifier fault .. it is just that
> I have good hearing and I prefer a *very quiet shack. For those who may
> be like me in that regard here is how I reduced the normal fan noise of
> my amplifier. In my amplifier much of the fan noise was actually coming
> from the sheet metal of the amplifier structure which was being excited
> by the vibration of the fan which is rigidly attached to the amplifier
> structure so that fan vibration was communicated to the structure which
> then resonated and amplified the fan noise. When I removed the fan and
> held it loosely in my hand while it was running I could feel the light
> high frequency 'buzz' produced by the rotating magnetic field of the fan
> and also, crucially, the lower frequency throb caused by a slight weight
> imbalance in the rotor. I used a small piece of sticky pad (normally
> used to mount components to a chassis, etc) and placed this very small
> weight at various points on the rotor blades until, by trial and error,
> found the 'sweet' spot which resulted in greatly reduced throb. That
> reduced fan noise considerably.
>
> Then, to reduce transmission of fan vibration to the amplifier structure
> even further, I mounted the fan loosely to the back of the amplifier
> using soft quarter-inch cushions between the fan and the amplifier. I
> used light wire to do the actual attachment instead of the long screws
> that are standard. The overall effect is considerably less fan noise
> and I am very happy about that. The fan mounting is fragile and not to
> be recommended if the amplifier is to be moved very much but in my
> installation it is just fine. By the way, I carefully compared cooling
> performance before and after the fan mounting modification and found no
> difference at all. I also noticed during my testing that the direction
> of airflow makes no difference.
>
> Don K7FJ
>
>
>
>
>
>
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