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Old 5th September 2008, 01:04 AM   #1711
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Originally posted by Magura
I have tested this sort of abuse for approx. 2.500 hrs. Heatsink running at 35C.

I for one don't care if I have to do some maintenance every 2.500 hrs., if it means that I can get better sound

Magura

Just keep in mind that you may also have to do some maintenance your loudspeaker or your home. I had an amp go DC at the output and ruined one of my Thiel CS1 speakers. We initially thought it was the house on fire and called the fire department. But later realized it was the speaker enclosure burning.

The voice coil of the tweeter was real close to the back of the cabinet. There was a big black burn mark behind the tweeter. A well known speaker designer once told me a tweeter looks like a short to DC. This makes no sense to me since tweeters are capacitively coupled to the amp through the crossover.

Maybe the amp was oscillating at a high freq and the tweeter broke and got hot? I don't know. The woofer was also melted.
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Old 5th September 2008, 02:53 AM   #1712
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that is a real danger in what we do, I have lost a few tweeters from r.f. oscillationsbecause I was to impatient to fully test. An RC network connected right at the output binding posts is good insurance, and has arguably no effect on the sound.

Years ago I repaired a Klipsch LaScala that was completely charred around the woofer, and the cone was ashes.
It seems the drummer From the Rock band Foghat decided to drum directly on a microphone totaly smoking a phase linear 700B amplifier. The amp was not in much better shape than the speaker. Believe it or not Klipsch covered the speaker under warranty. Even overnight expressing it to us.

My advice buy a scope, even an old limited bandwidth one .
Run your new projects into loads as long as you can stand, before chancing your hard earned speakers to it. It much easier to build a power R.F. oscillator than a stable high bandwidth amp . Of couse you can always connect a small wattage resistor , and run the amp with no input and see if the resistor becomes hot ( or becomes smoke)
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Old 5th September 2008, 04:04 AM   #1713
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Originally posted by amp-guy
It seems the drummer From the Rock band Foghat decided to drum directly on a microphone totaly smoking a phase linear 700B amplifier.
Weren't the lyrics "Slow ride...take it easy"?

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Old 5th September 2008, 05:37 AM   #1714
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Heehee...

It's pretty cool when passive devices catch on fire from the inside out. When poly cones do it drips down the front of your speaker like syrup on a sundae. I have some pics of some older B&W's that did this...DC caused the adhesive bonding the voicecoil to the former to ignite.

Chris
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Old 5th September 2008, 11:48 AM   #1715
Magura is offline Magura  Denmark
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Quote:
Originally posted by Johnloudb



Just keep in mind that you may also have to do some maintenance your loudspeaker or your home. I had an amp go DC at the output and ruined one of my Thiel CS1 speakers. We initially thought it was the house on fire and called the fire department. But later realized it was the speaker enclosure burning.

The voice coil of the tweeter was real close to the back of the cabinet. There was a big black burn mark behind the tweeter. A well known speaker designer once told me a tweeter looks like a short to DC. This makes no sense to me since tweeters are capacitively coupled to the amp through the crossover.

Maybe the amp was oscillating at a high freq and the tweeter broke and got hot? I don't know. The woofer was also melted.

When running mosfets this hard, you usually don't get DC at the output if they go south. They simply blow, and that's it.

A simple and nice way to make sure you don't get DC at rail voltage, to your speakers, is to use output caps.

I find it a bit strange, that people whom are pushing the limits of quality amps, somehow are reluctant to do a bit of maintenance.
I see this game, like with hefty sports cars. A hefty sports car, is usually not particular durable, and for a car that's perfectly acceptable......but not for an amp?


Magura
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Old 5th September 2008, 11:52 AM   #1716
Magura is offline Magura  Denmark
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Oh, and BTW, all this talk about amps catching fire, has little to do with failure of the parts, but is rather a matter of building the chassis, using the right materials.
Whenever I build a power amp, there is close to nothing that possibly could burn in it, and the bit that can burn, is made of self extinguishing materials.


Magura
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Old 5th September 2008, 12:12 PM   #1717
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Quote:
Originally posted by Magura
Oh, and BTW, all this talk about amps catching fire, has little to do with failure of the parts, but is rather a matter of building the chassis, using the right materials.
Whenever I build a power amp, there is close to nothing that possibly could burn in it, and the bit that can burn, is made of self extinguishing materials.


Magura
Well, they do sell "flame-proof" resistors -- and Sony just recalled a batch of laptops (battery related again). (The accountants become too involved in the design of power supplies, batteries and other components.)

I use flame-proof 10R/2W resistor in my F5.
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Old 5th September 2008, 05:13 PM   #1718
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Default OT Warning!

jackinnj,

That was pretty quick with the avatar swap!
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Old 5th September 2008, 08:29 PM   #1719
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Quote:
Originally posted by Magura



When running mosfets this hard, you usually don't get DC at the output if they go south. They simply blow, and that's it.

A simple and nice way to make sure you don't get DC at rail voltage, to your speakers, is to use output caps.

I find it a bit strange, that people whom are pushing the limits of quality amps, somehow are reluctant to do a bit of maintenance.
I see this game, like with hefty sports cars. A hefty sports car, is usually not particular durable, and for a car that's perfectly acceptable......but not for an amp?


Magura
I'm sure there are many scenarios here, but a push/pull amp will likely have some amount of DC at the output when one of the output transistors fail.

Yes, there are a number of ways to protect against DC including caps. The amp I mentioned was and old 150 Watt commercial design, and it didn't have DC protection unfortunately. I do miss those speakers.

Whatever you enjoy.
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Old 5th September 2008, 08:46 PM   #1720
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Default Re: OT Warning!

Quote:
Originally posted by chrismercurio
the avatar swap
Original, looks and no brains is a change.
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