In high power class D amplifiers like the Vera P400/1000 the output coils of the NC500 gets quite hot at high power levels. Since these are located close to the surrounding capacitors it will heat them up as well. 90 degrees celcius (194F) is not uncommon, and I have in fact managed to push the temp up to 105 degrees celcius (221F) under really heavy load.
The picture below show the situation after a while with music at 800W peak levels (Bridged). The coil is 98,4C (211F), and the capacitors are 74C (165F)
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To reduce this heat problem we use this aluminum heat block that removes the heat from the coils. The heat block is pushed down with the spring (shown on top) that is attached to the lid. Heat is dissipated to the cabinet through the slot/channel in the middle
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We measure the temperature on each coil with two NTC temperature sensors glued to the coils. Fan speed is controlled dynamically based on the temperature on the coils.
When the temperature exceeds 65C (149F) the fans starts at 500RPM. The Noctua fans are truly totally silent at this low speed, but the slight breeze directed towards the modules through the fan ducts is enough to keep the temperature under control even under extreme load.