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From: gnome@olivee.UUCP (Gary Traveis)
Newsgroups: net.audio
Subject: Re: Installing a Varistor
Message-ID: <182@olivee.UUCP>
Date: Wed, 15-Aug-84 18:07:13 EDT
Article-I.D.: olivee.182
Posted: Wed Aug 15 18:07:13 1984
Date-Received: Sat, 18-Aug-84 00:14:51 EDT
References: <1691@inmet.UUCP> <465@houxt.UUCP>
Organization: Olivetti ATC, Cupertino, Ca
Lines: 45


There are a few different types of power-line related
noises that can pop up in an audio system.

1) Hum - a 60hz hum that is sitting in the background
   and stays mostly the same amplitude over time.
	:This could be caused by the following circumstances.
	a) A ground loop caused by too little or improper
	   grounding.  AC neutral is NOT the same as ground!
	b) A transformer nearby a sensitve area of the system.
	   Namely a power transformer or video device too close
	   to preamp or pickup.
	c) A bad power supply with ripple in preamp or power amp.

2) Buzz - A constant buzz (low freq) that comes and goes.
	a) Flourescent light or ballast near audio system.
	b) A light dimmer being used on the same or nearby
	   AC power line.
	c) Bad or dying rectifier in amp(s).

3) Whine- A variable or intermittant whine/buzz that comes and
	  goes.  Often in bursts.
	a) A blender, variable speed drill, vacuum cleaner
	   or other AC/DC motor that uses brushes internal to
	   the motor or unit itself.

4) Pops - A loud or moderate pop heard from time to time.
	  (sometimes random crackling)
	a) Any capacitive or inductive load being turned
	   on or off.  Flourescent lights that use starters
	   will flicker and cause popping on power-up.
	b) Non-positive switches.  Bad wall switches, or
	   aquarium heater thermostats can induce noise on
	   both audio and TV/video systems.

That covers most cases -- oops! I forgot HAM and CB interference!
Well, once the cause of a problem is discovered, then the
proper fix can be sought.

A power line filter (a good one) can get rid of most of the
above problems, but not all!

Gary
(hplabs,ios,fortune,allegra)oliveb!olivee!gnome
- with no more time today...