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.
If you had a fire you actually could file a claim with your Home Insurance to re coop your losses..I had a power surge on xmas day many years ago and my Audio Rsearch sp 8 got scortched..I got full replacement value from my insurance.........
I would put it that the stress caused by repeated intermittent dc surges can be cumulative. It's not that energy is getting stored, just that repeated stress eventually causes some component or components to reach a breaking point.

Just as a point of information, resistors don't store energy. Capacitors and inductors (coils) do. And if the units were turned off that energy would pretty much dissipate within a few minutes.

It does sound like intermittent dc surges from the preamp are the cause, very conceivably due to a bad capacitor. If they are brief and/or intermittent chances are your voltmeter wouldn't detect them.

-- Al
If the N.E.W. is DC coupled, avoiding a filter, then it's not a capacitor.

DC offset in audio is an ugly, dry topic and far too complex to scratch the surface here. Some designs handle it better than others. I had one amp that was quite happy with 3V where mV is more typical.

A plug-in solution could be a line level isolator from Jensen transformer. Contact them for advice.
The problem could also be related to a short in the left speaker or speaker cable.
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.

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.
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.
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).

-- Al
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."

-- Al
Al got it. It's just a high pass filter.

I found this. I think it's funny. You might not.

Hi! I'm your friendly amp technician! I live perhaps thousands of miles outside the range of hearing and seeing your amp - even when it's turned up and working! So I've devised this handy questionnaire! In order to help me more efficiently diagnose and repair the problem with your amplifier please respond to the following points:

1. Describe your problem:

2. Now, describe your problem accurately:

3. Speculate wildly based on faulty knowledge about almost everything
just what's the cause of your problem:

4. Please indicate the severity of your problem:
A. Minor___ B. Trivial___ C. Minor___ D minor, the saddest of all keys___

5. Nature of problem:
A. Sounds bad___ B. Sounds really bad___ C. No sound___
D. Strange smell___ E. Smells really bad twice___

6. Was your amp plugged in?
Yes___ No___

7. Was it turned on?
Yes___ No___

8. Did you try to fix it yourself?
Yes___ No___

9. If so, did you make it worse?
Yes___ Yes___

10. Did you have a "friend" who "knows all about amps" try to fix it
for you?
Yes___ No___

11. If so, did they make it worse?

12. Have you read your manual?
No___ No___

13. Do you have the manual?
Maybe___ No___

14. Are you absolutely SURE you read the manual?
I was going to___ No___

15. If you think you read the manual, do you think you UNDERSTOOD it?
Yes___ No___

16. If YES, explain why you can't fix the problem yourself:

17. What were you DOING TO your amplifier at the time the problem occurred?

18. If you answered "nothing", explain why you think there's a problem:

19. Do you have another amp you can use while you wait to take this one
to a repair shop like you should have done in the first place?
Yes___ No, I prefer to be out of commission longer___

20. Are you sure you're not imagining the problem?
Yes___ No___

21. Does the clock on your DVD player always blink 12:00?
Yes___ That's a clock?___

22. Do you have an independent witness to the problem? (Does not
include drummers)
Yes___ No___

23. Have you given the amplifier a good whack on top?
Yes___ No___

24. Did the amplifier catch fire?
Yes___ Not yet___

25. Has the foam or insulation inside your speaker enclosure
ever caught fire?
Yes___ No___ Huh?___

26. Did the insulationy stuff inside your speaker BOX catch fire?
Yes___ No___

27. If so, did you replace it with an approved dampener?
No, enough beer gets spilled in there to keep it safe___
No, the cat whizzes in there after a good scratch on the
carpet anyway___

<-- greenboy ---<<<<
"D minor, the saddest of all keys"- Nigel Tuffnel of Spinal Tap, describing his beautifully haunting "Lick My Love Pump."

LOL- nice one there, NG!