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Old 23rd April 2004, 12:10 AM   #1
roibm is offline roibm  Romania
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Question The noise and where it is comming from

I am really interested to properly understand what is generating the noise as we hear it(the hssss that we all hate).
Taking as a source a CD for example, and assuming that there is no noise in it's tracks, after the signal travels through some devices(like cd player, dac, preamp, amp etc) we get a sound that also contains some noise(sometime more, sometimes less, depends on the devices).

What I would like to understand is what generates this noise. Is it the PSU that is the biggest noise generator? DAC? opamps? RF? For sure all of these, but whichs is the worst?

Thank you
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Old 23rd April 2004, 12:24 AM   #2
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- every resistance makes johnson noise

- there is a lot electromagnetic noise around from computers, radio stations, TVs, cellulars etc, straying into the audio device and power line

- artifacts from the sampling in case we have a digital part in the audio chain, i donīt know the word in english "Quantisierungsrauschen"
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Old 23rd April 2004, 02:14 AM   #3
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Hi,

Quote:
- every resistance makes johnson noise
Actually those are relatively quiet, dependant on technology and value.Their type of noise is known as white noise.

Any active device will generate some Johnson noise, aka thermal noise also shot noise.

Thermal noise:
The noise generated by thermal agitation of electrons in a conductor.
The noise power, P, in watts, is given by P = kT f, where k is Boltzmann's constant in joules per kelvin, T is the conductor temperature in kelvins, and f is the bandwidth in hertz.

Note 1: Thermal noise power, per hertz, is equal throughout the frequency spectrum, depending only on k and T.
Note 2: For the general case, the above definition may be held to apply to charge carriers in any type of conducting medium. Synonym Johnson noise.

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Old 23rd April 2004, 02:27 AM   #4
Magura is offline Magura  Denmark
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I have found that some types of resistors almost works like antennas. Especially the big wirewound ceramic power resistors can be tricky to shield adequately well. A celluar phone goes right in those resistors. On the other hand I have found that most discrete devices are relatively un-impressed by the presence of a celluar phone. Caps also dont seem to care. For power resistors I stick to thick film types, they also seem to not be influenced by a celluar.

Note that theese tests were conducted with a celluar phone(most noise problems in this end of the world tends to have connection to celluars), it may differ with the frequenzies the components are exposed to.

Magura
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