Blown Polk subwoofer?

Archived from groups: rec.audio.tech (More info?)

In article <1113153034.801214.224110@g14g2000cwa.googlegroups.com>,
<tomrp@juno.com> wrote:
>I have a 2 year old Polk PSW202 10" sub that started making distorted
>"barking" noises. It got worse and worse, finally unseable. Is this the
>driver itself? Or could it be something in the amp. It was never driven
>hard, but I knew that these inexpensive subs had short life spans.

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.

Archived from groups: rec.audio.tech (More info?)

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

Archived from groups: rec.audio.tech (More info?)

In article <1113222393.954382.135540@g14g2000cwa.googlegroups.com>,
<tomrp@juno.com> wrote:
>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.

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.

Archived from groups: rec.audio.tech (More info?)

"(null)" <fps@idiom.com> wrote in message news:1113188366.308250@smirk...
> In article <1113153034.801214.224110@g14g2000cwa.googlegroups.com>,
> <tomrp@juno.com> wrote:
>>I have a 2 year old Polk PSW202 10" sub that started making distorted
>>"barking" noises. It got worse and worse, finally unseable. Is this the
>>driver itself? Or could it be something in the amp. It was never driven
>>hard, but I knew that these inexpensive subs had short life spans.
>
> 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.
>
Amazing a company would try such a stunt and think they could get away with
it. Apparently, they didn't : )
John

Archived from groups: rec.audio.tech (More info?)

JohnR66 wrote:
> Amazing a company would try such a stunt and think they could get away with
> it. Apparently, they didn't : )

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!

Archived from groups: rec.audio.tech (More info?)

Joe Kesselman <keshlam-nospam@comcast.net> wrote:
>JohnR66 wrote:
>> Amazing a company would try such a stunt and think they could get away with
>> it. Apparently, they didn't : )
>
>[...]
>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!

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.

Archived from groups: rec.audio.tech (More info?)

"Joe Kesselman" <keshlam-nospam@comcast.net> wrote in message
news 3fd95$tq2$1@domitilla.aioe.org...
> JohnR66 wrote:
>> Amazing a company would try such a stunt and think they could get
>> away with it. Apparently, they didn't : )
>
> The art of engineering is figuring out how to build something that
> is Just Barely good enough.

NOT always true, at least outside of consumer goods. My company
engineers large margins in our industrial instrumentation products to
give lots of headroom and very long service life in adverse
environments.

> 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).

(snip)

Not just Polk. Just check out the Infinity BU-120 subwoofer saga -
many dead Class D amplifiers! I found a website full of complaints...
Clearly a design problem in the Class D chip (rest of the circuit
looks OK).
I had one and replaced the original "POS" amplifier with a
PartsExpress FET Class AB linear. Great results! You may want to
consider this if the cap replacement suggestion does not work.
Cheers,
Roger

Archived from groups: rec.audio.tech (More info?)

Thanks, Francois. You were right. I replaced the power supply caps with
63 volt capacitors(had a friend do it for $25)it now works better than
new, plus no more hum, like it used to have, even before the barking
noises.

Thumpin' in Portland, Oregon

Tom

Engineer wrote:
> "Joe Kesselman" <keshlam-nospam@comcast.net> wrote in message
> news 3fd95$tq2$1@domitilla.aioe.org...
> > JohnR66 wrote:
> >> Amazing a company would try such a stunt and think they could get
> >> away with it. Apparently, they didn't : )
> >
> > The art of engineering is figuring out how to build something that
> > is Just Barely good enough.
>
> NOT always true, at least outside of consumer goods. My company
> engineers large margins in our industrial instrumentation products to

> give lots of headroom and very long service life in adverse
> environments.
>
> > 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).
>
> (snip)
>
> Not just Polk. Just check out the Infinity BU-120 subwoofer saga -
> many dead Class D amplifiers! I found a website full of
complaints...
> Clearly a design problem in the Class D chip (rest of the circuit
> looks OK).
> I had one and replaced the original "POS" amplifier with a
> PartsExpress FET Class AB linear. Great results! You may want to
> consider this if the cap replacement suggestion does not work.
> Cheers,
> Roger

This is exactly the info i was looking for, I have the same issue, started years later yet I barely used the sub. I called Polk, they wouldn't wanna fix the design flaw under warranty (never buying Polk again, their service sucks in Canada)..I got a Bic America F12 and will be swapping the capacitors now that i know what value to swap them with.

Thx