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toddalin
10-24-2005, 10:05 AM
I have a dBx subwoofer amp. Several years ago it began letting out a "pop" after being on for about 10 minutes. Over the years it has gotten progressively worse, and now lets out a few garbled pops, at 10 minutes. Other than that it works fine (even before and after it pops). My thought was that this could be caused by the filter caps going bad over time. I figure that the 10 minute mark represents a period of thermal expansion. I know from the Bose system in my Corvette that the filter caps on those amps go and can produce similar (and worse) problems.

Yesterday I opened the unit and sure enough, there is some waxy material at the base of the two 10,000 mfd, 80 volt power supply filter caps, one worse than the other. It actually looks more like a sealent to seal the caps to the board, but that wouldn't make any sense. Also the one with more wax around wiggles when rocked even though the solder joints are sound.

Unforetunately, these are not so easy to come by, except of course on ebay where I would need to buy at least 5 for about $35 plus about $15 s/h.

I would sure hate to put in the new caps if this doesn't cure the problem and that being the case, would rather put the $$$ toward a new amp. Before I invest the time and $$$ on this fix, does anyone concur that leaking filter capacitors could be the source of the popping?

On another note, if I do replace the caps, I can get caps of similar size and voltage, but up to 15,000 mfd. The replacement of the two 10,000 mfd caps with 12,000 or 15,000 mfd should help beef up the power supply reserves. Does anyone see a problem with this change???

Thanks guys

John
10-24-2005, 11:01 AM
Well I would not use that amp till it is serviced as you are risking your sub driver. If the cap shorts it could send DC voltage to the voice coil and fry it.:(

Mallory has a cap. part # CGS103U100W4C
10,000 MDF 100VDC
Should work and buy new ones,forget ebay!!!

What do you think??? LE15-Thumper :hmm:

scott fitlin
10-24-2005, 11:06 AM
Mallory was and is widely used by amp manufacturers, buy new, get em fresh, and have em installed by a technician!

Earl K
10-24-2005, 11:08 AM
A Few Observations; ( in no order of priority )

- Personally, I'd retouch all the solder joints on that pc board before making any more assumptions .

- You haven't mentioned if the "popping" occurs when the amp is just "on" but not amplifying ( okay, call that a standby mode or an idle mode ) .

- Pics of any suspected problem area are really crucial to avoid confusion ( at least in semantics and vernacular )

- These days, silicone sealants are used to affix all sorts of things to pc boards / especially if those boards are working inside mechanically challenging environments - such as a subwoofer .

- If I was in a similar situation ; I'd start any part-swapping with the cheaper sorts first ; such as the voltage regulators within that power supply .


The replacement of the two 10,000 mfd caps with 12,000 or 15,000 mfd should help beef up the power supply reserves. Does anyone see a problem with this change???

- This upping of the supply reserve capacitors is not the "no-brainer" it's sometimes made out to be. Afterall , the supply transformer must still supply those supply capacitors with adequate current. It'll depend on the design margins built into the amp. Likely a 15% increase in capacity falls into a safe zone .

- The DIY forum has many more posters who specialize in this sort of off-hand advice . Though, there are a few posters here who can and have helped others with similar problems .

:)

toddalin
10-24-2005, 11:10 AM
Well I would not use that amp till it is serviced as you are risking your sub driver. If the cap shorts it could send DC voltage to the voice coil and fry it.:(

Mallory has a cap. part # CGS103U100W4C
10,000 MDF 100VDC
Should work and buy new ones,forget ebay!!!

What do you think??? LE15-Thumper :hmm:

The noted Mallory caps are way to large to fit the chassis/case.


OK, I plugged the unit in with nothing connected. While I was waiting for it to warm up (case open), I could rock the caps and get static/popping from the woofer, so it's pretty sure that these are a problem, if not the problem. (At that point, I stopped the test.) I'll look for new ones in the 10,000-12,000 range. (BTW that single Mallory is about $30.)

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/caps.jpg

pelly3s
10-24-2005, 07:39 PM
I would go with Earl on the solder joint thing. 80% of the repairs I handle are bad solder joints. They are normally noticed after a peice of gear has had time to heat up a little bit. You can find those caps somewhere like MCM or Mouser

John
10-24-2005, 09:50 PM
The Mallory cap I mentioned is 2-9/16" dia. x 4-1/4" high

What size are the present ones???

toddalin
10-25-2005, 10:50 AM
The Mallory cap I mentioned is 2-9/16" dia. x 4-1/4" high

What size are the present ones???

1-3/8" dia x 2-1/2" tall

toddalin
11-13-2005, 06:06 PM
I ended up getting a lot of five 12,000 80 volt surplus caps on ebay (exact case size to replace the two 10,000 mfd units). I looked for the newest ones (most recently out of production) and found some that were in production just two years ago. (None of the caps I saw on ebay that would work carry current listings.) While I was in the amp, I also enlarged the heat sink, shielded some signal wires, and silver soldered some wire-wrap connections.

Amp works like new and the popping is totally gone.:bouncy: