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High Frequency Oscillation hurt resistors in Magico A5 crossovers

Hi,I am looking for help understanding how HFO could blow crossover resistors in Magico A5 speakers. Equipment playing at the time of the incident is as follows...
Magico A5 speakersHegel H30 mono blocksHegel P30 preamp (lt and rt inputs on the Aux inputs from the laptop and Dragonfly Cobalt)
Dell laptopAudioquest Dragonfly CobaltAmazon Hi-res streaming
I was listening to Amazon music at a very moderate level when the application said there was an update available.I instinctively clicked accept while music was paying. It was only off for a few seconds to update and when complete and I restarted music the A5 tweeters were not on. These happened simultaneously and there was no audible noise what so ever indicating a potential issue. After multiple source tests and tweeter test, I was certain the tweeters were fine and it was an electronic issue. The cross overs were removed and sent to Magico and that was when I was told that HFO blew the resistors.
Can anyone explain how/why this happened so I can ideally avoid it happening again?
Thank you!
128x128howaanders8
rsf507
2,222 posts
 
Wow very unfortunate. Sounds a bit of a lame excuse since music has LOTS of high frequency and a download? You were lucky as others have pointed out the tweeters are ok. 
mlsstl
1,378 posts
 
Actually, music played at any volume that the speaker was designed to handle rarely contains enough high frequency material to damage a tweeter.  

Most often tweeter damage is caused by amp clipping -- the clipped signal basically becomes square waves which generates much more high frequency energy than was present before clipping.  Another culprit from days of old was when one fast-forwarded an open reel recording without muting or reducing the volume. And if an amplifier went bad and started oscillating, that too could damage a tweeter.  

Have to say that I've never seen a program software update generate high frequency noise. Usually the program simply stops running during the update and then restarts after the update is completed. But, then I'm not a computer expert and don't use your particular setup, so its hard to say exactly where the HF noise came from. The OP did say he was listening at "a very moderate" level which seems a polite way of saying it was fairly loud. Maybe the resistors were already pretty hot and it didn't take much to push them over the edge.  

Good luck with your inquiries. It would be interesting to have a more complete answer. 

sciencecop
180 posts
 
How about a quick Google search on what is ’high-frequency oscillation’ in audio (Parasitic oscillation). It’s straightforward, real, and distractive. If you are using a PC as a source, you never know what it is sending out, best to turn-off the amps when you are doing updates.
fuzztone's avatar
fuzztone
5,496 posts
 
misstl has a point maybe they’re fuses in operation. Still, I would hope to get something in writing.
Good point that using a computer for source is dirty AND dangerous. Especially today with so many alternatives.
erik_squires
15,647 posts
 
Yep.  Makes sense to me.  What sent your amp into oscillation is the question.  This is one of the potential problems with very high bandwidth electronics.  If they can reproduce FM signals, you won't hear it, but your speaker wills smoke, one way or another.

I'd actually reach out to Hegel, as they may be better able to help you.

Best,

E
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