sub help please

[Timbre Surfer]

G'day

I have a harmon Kardon AVR130 powering a set of Warfdale diamond 8.1 towers, centre and Yamaha inceiling surrounds. It also powers a Harmon Kardon sub.

About a year ago the sub started making a fast paced "d-d-d-d-d" (like a big helicopter was over the front room) when left in standbye mode. It still does it and i have to manually turn it on when i want to use it, after 5 minutes of no signal it is meant to put itself into standbye but instead does that "d-d-d" noise. so in some quiet movie scenes the sub spoils it due to no signal. Just lately it has started holding a single note and carrying it after a sustained bass heavy section of either movie or song.

what could this be? I think the sub and the amp are 5 years old.

apart from that it is great, when i get a good movie out the neighbours tell me the thunder has come home, hehe.

[soundman]

I'd almost bet my left nut that one or more of the caps has gone out of spec or leaky.
Or maybe one of the semi's has gone out of spec.

No simple solution...needs proper diagnosis and repair.

cheers

[acropolite]

I'd almost bet my left nut that one or more of the caps has gone out of spec or leakyI'd have to agree. Often when caps go they bulge at the top, or show visible signs of leakage, the problem you're describing, used to be called motorboating and is usually caused by faulty caps. It would be worth opening the beast, if you have any technical ability, and replacing any suspect caps (if there aren't too many replace the lot). If you do replace any, look for a place like Farnell where you can buy capacitors specifically made for long life, the average Duck Smuth etc cap has a rated life of just a couple of thousand hours.