Blown Polk subwoofer?

Joe Kesselman <
In all fairness, when I replaced the caps the sub did a pretty good job
of shaking the living room, so it's not as if the thing is malignantly
ill-designed like some stuff I could mention *cough* B*se *cough*, but
more like an engineer made a booboo in a reasonably ok piece of gear.

Francois.

The art of engineering is figuring out how to build something that is
Just Barely good enough. Sometimes that leads to gambles which don't
work out. I suspect that this is a matter of their original parts having
a little leeway beyond the rated voltage, which was lost when they
changed suppliers (or when the supplier made their own product more
precise).

They aren't the first to dance too close to an edge; they won't be the
last. At least it's a relatively easy retrofit and it doesn't seem to
damage anything else.

Thanks for pointing this out. A friend has offered me a used PSW202, and
I'd certainly rather know about this fix _before_ making an offer!

Amazing a company would try such a stunt and think they could get away with
it. Apparently, they didn't : )
John

The amp works ok modulo the cap problem getting fixed, so you might want
to save your money, especially if you can find a decent electronics
surplus store in the area.

Francois.

Thanks very much for the info, it gives me a place to start. I may just
replace the amp. The cabinet is mint and the driver looks good.

Regards, Tom

These subs have a design flaw in the power supply: the filter capacitors,
while rated at 35 volts, actually filter 36 volts at nominal wall voltage,
on top of which the parts are somewhat undersized (read: high ESR) for
the task. Every one I've run across has behaved exactly as yours -
the barking is a function of the supply caps deteriorating over time
not filtering as well as they should, thus leaving a lot of ripple on
the supply rails which then gets superimposed on the signal.

Replace both power supply capacitors with 50 volt parts, and all should
be well. There's not a lot of room on the board, so you might have to
mount them somewhere else and run wires to the caps.

If this sounds sporty for your taste, show this post to a technical friend.

Good luck,
Francois.