Newsgroups: sci.electronics.design
Subject: Re: Question about Schematic found in Magazine?
References: <[email protected]> <[email protected]>
From: Tomi Holger Engdahl 
Date: 13 Jan 1997 10:41:40 +0200
Message-ID: 
Organization: Helsinki University of Technology, Finland
Lines: 26
X-Newsreader: Gnus v5.3/Emacs 19.34
bwilson@newshost (Bob Wilson) writes:

> : I heard that the outputs of amplifiers are subject to 60 Hz line noise
> : without a proper filter.  How much noise does this multimedia subwoofer
> : have? 
> This is not so. Amplifier outputs are inherently low impedance and not
> at all subject to stray noise pickup. Inputs may be is normal shielding
> practices are not observed, but the use of a 60 HZ filter makes no
> sense. You must deal with the problem, not try to eliminate the
> symptom.

60 Hz filter on the output does not make sense. The most common
reasons for getting 60 Hz noise are:
1. Ground loops (usually happens when your system is connected to cable TV
   or multipple power outlets)
2. Poorly designed electronics which do not hve enoug filteing in their
   power suppply (cheap multimedia speakers go to this category)
3. Wires or electronics picking it from nearby transformer 
   or high current mains wiring

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