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Old 27th October 2011, 10:21 PM   #1
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Location: Carlisle, England
Default No fool like an old fool.

Been building a pc controlled mixer with digital pots controlled via USB.
Got the pcb up and running but it had a very high frequency on the output signal. Couldnt work out where it was coming from.

Anyway I plugged the mixer into my amplifier and it sounded ok.
Next thing I knew my amplifier burst into flames. Silly me had a cardboard box with parts on top of the open amplifier and it started to burn. So threw it outside and turned off the amplifier.

Turned the mixer back on again and still there was the high frequency.
I turned off my light in disgust and was about to walk to my pc when I noticed the high frequency on the scope had gone.

It then hit me the lamp is fluorescent and has an oscillator inside it which had been interfering with my mixer. The mixer then passed this high frequency to my amplifier which had cooked it.

Doh !
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Old 28th October 2011, 05:51 AM   #2
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
Yep, welcome to the real world of electronic noise.

Over in the guitar amp forums we regularly have guys writing in to complain their amp makes a steady ticking sound. We tell them to stop putting their cell phones on top of the amps.

Don't feel bad, we have all been bit by some environmental noise source at some time.
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Old 31st October 2011, 09:53 AM   #3
Mooly is offline Mooly  United Kingdom
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Many years ago as a repair tech we had a problem with a VCR where the drum servo would lose lock and take off.

Cause was eventually found to be a radio transmitter (radio amateur) down the road.
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Old 31st October 2011, 10:14 AM   #4
ODougbo is offline ODougbo  United States
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Default Yikes!

It's a good thing you were home!!
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Old 31st October 2011, 12:10 PM   #5
ODougbo is offline ODougbo  United States
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Location: Maryland USA
Default Ham Radio

My dad is a "ham"; back when I was a teenager, I could hear him loud and clear in my speakers in my room. My stereo system was totally tuned off and not really that close to the cables, transmitter or antenna.

** Might want to pick up some hard hats for the shop....chuckle




Quote:
Originally Posted by Mooly View Post
Many years ago as a repair tech we had a problem with a VCR where the drum servo would lose lock and take off.

Cause was eventually found to be a radio transmitter (radio amateur) down the road.
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