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Can DC power surges cause fires?

My Audio Research D130 (which I was trying to sell- I cancelled it- LOL) caught fire last night. Flames, smoke, the whole nine yards. About a minute later, there was an audible sizzle from a new Jeff Rowland Model 102 power amp as well. This is the FOURTH time the left channel has blown on one of my amplifiers (the AR was recently refurbished after the protection circuitry failed, and an Aragon 2004 MkII is out for repairs with a failed left channel. It was the left channel on the AR that burned last night, and the left channel on the Rowland that sizzled. I thought it may have been a problem with my AC line, but everything else on those lines (which all run via a surge protector) is fine- some fragile stuff like a modem, wireless router, TV, old receiver and CD player. It's like everything that gets hooked up to the preamp- a 12 year old N.E.W. P-3- fries the left channel.

It's strange- I used a voltmeter to look for DC surges just a couple of weeks ago, and both amps and the preamp tested clean....I guess I need to know if DC surges can be cumulative, with the energy getting stored in the resistors and capacitors in the power amps, and after reaching a critical mass, the power amps implode (or, apparently, catch stinking fire- LOL).

Anyone else familiar with problems of this type. A friend of mine who's quite knowledgable says it's definitely bad capacitors on the preamp causing a DC surge into the power amps. Any of you people have any ideas? I just cooked $4000 of amplification last night, and I'm pretty annoyed- any help would be appreciated. All items were shipped out for repair today, including the preamp, although there's nothing obviously wrong with it.

Thanks in advance for any ideas/thoughts.
afc
dcstep
1,518 posts
 
02-19-09: Ngjockey said:
"The problem could also be related to a short in the left speaker or speaker cable."

That's also what I'm thinking, since it only happens to the left channel with a variety of pieces of equipment.

Dave
afc OP
141 posts
 
It's happened with different speaker cables. The fire happened with a brand new pair of Signal Cable Ultras that were bi-wire designs. I don't think it's the cable. The previous fry jobs came with different cables. Also, if it were a short in the cable, wouldn't the protection circuitry just kick on in the amplifiers and prevent them from cooking?

NG, what do you mean by "DC coupled"? I'm not very well versed with that....all I can tell you about the N.E.W. is that it's largely a hand wired unit, with direct wired connections throughout. Don't even know if it has any caps.

It's a baffling, and now, expensive problem.
afc OP
141 posts
 
By the way- it's also happened with two separate speakers, so I don't think an internal short in the speaker wiring itself is to blame.

Thanks for the help, fellas. Guess I'll just have to wait and see what my repair tech comes up with.

The DC coupled thing has me both baffled and curious. I would like to learn more about it.
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almarg
9,670 posts
 
Yes, I didn't think it was a problem with the speaker or cable, because if either of them had a short it would have produced audible symptoms.

"DC coupled" simply means that there is no capacitor in series between the preamp output stage and the output jack. It is the opposite of "AC coupled," which would mean that the preamp incorporates a capacitor in series with its output. Some preamps have an internal switch that allows selection of either configuration (the manual would so indicate). The capacitor, assuming it is working properly, would block any dc offsets that may be introduced in the preamp or further upstream.

DC coupling avoids possible very subtle sonic degradation due to the capacitor, but AC coupling is generally preferable, as a practical matter, if the power amp is DC coupled or if the preamp or any other upstream component is suspected of having significant DC offset. Tube power amps, btw, are AC coupled at their outputs by virtue of their output transformers (aside possibly from OTL designs).

Regards,
-- Al
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almarg
9,670 posts
 
At the end of the last sentence of my previous post, I should have said "aside possibly from OTL designs, which I would think would also be AC coupled, but by virtue of capacitors instead of transformers."

Regards,
-- Al
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