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Old 11th December 2006, 04:40 PM   #1
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Default EMI and RFI -- what you thought you knew

last week the folks at TI put on one of their webinar's dealing with opamps, RFI and EMI. they compare the front end differential amp of an opamp to a crystal radio

i wonder if the exotic cable industry would go away if engineers paid more attention to the huge amount of radiated energy from cell phones, bad power connections, smps etc. where they showed dramatic changes in opamp offset were in applications like electrocardiograph -- not dissimilar from what goes on in a moving coil preamp.

the engineers demonstrated offset shifts on bipolar opamps in the presence of various radiated energy fields, and you don't need a 1GHz network analyzer to perform the test, a simple FRS walkie-talkie will deliver enough RFI to cause significant offset even in opamps designed to minimize the effect.

fwiw, shielding is a last resort -- they talked about the potential for kinks in MuMetal which may serves as radiators (reflectors) for radio frequency interference.
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Old 11th December 2006, 04:59 PM   #2
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D/A digital residuals (spikes), EMI and RFI are most influencing factors of the sound of current digital audio. It is behind hobbyist approach to solve this issue.

P.S.: I especially mean all that non-harmonic mess you can analyze at the output.
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Old 11th December 2006, 05:58 PM   #3
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Quote:
Originally posted by PMA
D/A digital residuals (spikes), EMI and RFI are most influencing factors of the sound of current digital audio. It is behind hobbyist approach to solve this issue.

I don't think so. Good bypass, shielding of inputs, use of ferrite beads etc. really knock down RFI.
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