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From: Don Pearce
Subject: Re: Audio noise in diff amps
Date: Wed, 18 Dec 2002 08:02:49 +0000
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On Wed, 18 Dec 2002 16:13:28 +1100, "Phil Allison"
>"Glenn Gundlach" wrote in message
>> I work in video duplication and we're in the process of moving the
>> equipment to a new building. One of the router inputs is 'black' and
>> no audio. The router input is a differential opamp with 22K resistors
>> to the inputs. In the past, the 'black' input was simply left floating
>> but one of the guys said to short them together. FYI, the noise level
>> floating is -74 dbm (Fluke 8060) with operating level at +4. SO, the
>> question is: is it theoretically quieter shorted or floating? Is the
>> Johnson noise of the input resistors significant? When the inputs
>> float, those resistors are essentially not there so they can't
>> contribute to the noise, can they?
> ** The noise from a 22 kohm resistor in the audio band is about 2.4 uV
>rms or -110 dbm.
> .............. Phil
Make that -126dBm
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