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Old 4th June 2004, 08:18 PM   #1
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Default Bad ground = radio, but why?

Can anyone explain this phenomena?

I was testing the plate amp Iím building and I didn't have the signal ground tied to the power ground. I wanted to see what would happen, since the opamps don't have a power connection for ground. Well I could sort of hear what I was playing, although there was a lot of distortion.
But what I could mostly hear was some other voice and then some other music. Something totally unrelated to the CD I was playing. After hooking up the ground in the proper way the distortion went away, and so did the voices.
Can anyone explain why this happens?
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Old 4th June 2004, 08:36 PM   #2
markp is offline markp  United States
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Your bad ground acted like the diode in an old crystal radio. Look up 'crystal radio' on the web and you'll see what was going on.
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Old 4th June 2004, 09:11 PM   #3
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Very interesting. Thanks.
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Old 4th June 2004, 09:50 PM   #4
sreten is offline sreten  United Kingdom
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Look up AM radio principles.

For analogue circuitry any HF assymetry will demodulate AM
RF, you don't need a rectifier as such. Found this out with a
vengeance with a friends system with a Taxi firm nearby.

sreten.
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Old 4th June 2004, 10:05 PM   #5
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Quote:
Originally posted by markp
Your bad ground acted like the diode in an old crystal radio. Look up 'crystal radio' on the web and you'll see what was going on.
I had this: Solid wire into a ordniary screw connector, badly decoupled phono amp. This made the phono amp tune in russian radio equally strong as the vinyl signal at the output! When it not was normal radio from russia I tuned in the russian woodpecker = shortwave radar with huge output power. Some russian guys here maybe can tell me more about this beyond horizon radar?

When I tightened the screw the radio signal disappeared! Copper+oxid+copper+ rather bad cap= diode + small capacitor = AM detection.
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Old 4th June 2004, 10:25 PM   #6
markp is offline markp  United States
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Quote:
Originally posted by sreten
Look up AM radio principles.

For analogue circuitry any HF assymetry will demodulate AM
RF, you don't need a rectifier as such. Found this out with a
vengeance with a friends system with a Taxi firm nearby.

sreten.
In this case the assymetry is created by the diode like junction of his ground. Just like peranders said, the 'oxide-copper' junction forms a crude diode so current flows one way = assymetry.
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