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Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!hplabs!hao!seismo!mcvax!turing!haring!jaap
From: jaap@haring.UUCP
Newsgroups: net.periphs
Subject: Re: terminal noise
Message-ID: <375@haring.UUCP>
Date: Sun, 9-Dec-84 00:21:44 EST
Article-I.D.: haring.375
Posted: Sun Dec  9 00:21:44 1984
Date-Received: Mon, 10-Dec-84 02:59:27 EST
References: <36@mot.UUCP>
Organization: CWI, Amsterdam
Lines: 9
Apparently-To: rnews@turing.LOCAL

A lot of hardware have ``switched power'' supplies. They are based on
the effect that at higher frequency AC less smaller transformers are
needed. Usually they bump the frequency up to 40kHz or more, however
cheaper ones have lower frequencies.
When the transformers are cheap as well, you and up hearing the
noise made by these.

It is the same effect as in cheap/old television sets (In Europe
15.625 kHz.