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From: "Phil Allison"
Subject: Re: Audio noise in diff amps
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Wed, 18 Dec 2002 16:13:28 +1100
NNTP-Posting-Date: Wed, 18 Dec 2002 16:04:10 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"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.
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