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valterdaw 28th September 2007 04:10 AM

MTX class-D amps inductor is VERY hot
Inductor on double-stacked toroids is VERY, VERY hot. To the point, that adjacent capacitors becomes very unhappy. Is it normal ??? Thunder 4250D, sub channel on 4405 and others.

Perry Babin 28th September 2007 05:48 AM

These inductors run hot. That's why they have the thermally conductive pads between the inductor and the cover. If it gets too hot to touch within ~2-3 minutes, with no load, there is likely a problem. If it only runs hot when the amp is run hard, it's probably normal.

Check the operating frequency of the class D section. If it's below ~80khz, that could cause the inductor to overheat. If you have one or more defective capacitors, that could cause the inductor to overheat.

These amps (from experience with the 250D, which I believe to be similar) have a problem with shorted windings on the inductors. Where the terminal winding comes out from under the inductor, the insulation is often worn away. If yours shows signs of damage to the enamel insulation, glue a piece of thin cardboard inbetween the winding and the body of the inductor. Keep pressure on the inductor until the adhesive dries/cures. There is essentially no clearance and if the added insulator isn't compressed, the cover may not go on without placing excessive pressure on the inductor. I usually apply the adhesive and replace the cover until it dries.

valterdaw 28th September 2007 03:58 PM

Wow, thank you very much for all information!
It runs VERY hot (on 4405) after ~10 min of moderate load I got a burn on my hand from this inductor :o There is no thermally conductive pad on this amp between inductor and cover, I definitely should add one.
I test-installed it today in my car, it worked very well, but I can smell that inductor :hot: I'll check the frequency.
BTW, It's been a long time since I had an MTX amp in a car and I can tell that it sounds excellent! Better then 5x more expensive amp it replaced.

valterdaw 12th November 2007 02:55 AM


Originally posted by Perry Babin
...If you have one or more defective capacitors, that could cause the inductor to overheat. ...
Sorry for digging an old thread, just had some time to spend on this amp... Yes, it was 2 defective capacitors. Couldn't tell that without desoldering them. Thanks a lot, Perry, you fixed one more amp :worship: Inductor temperatures are back to normal and power output is increased :D

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