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From: kann@savax.UUCP (kann)
Newsgroups: net.audio
Subject: Re: Re: Audio Transformer (Really TV audio)
Message-ID: <276@savax.UUCP>
Date: Tue, 28-May-85 13:58:46 EDT
Article-I.D.: savax.276
Posted: Tue May 28 13:58:46 1985
Date-Received: Sat, 1-Jun-85 04:03:18 EDT
References: <1989@topaz.ARPA> <10785@brl-tgr.ARPA>
Organization: Sanders Associates Inc. Nashua ,NH
Lines: 36

> Some fancy TV's make it hard to do this -- I have a Zenith System III set
> (a real dog!) where the volume pot has only DC on it -- it just varies
> a control voltage and the real audio signal is buried down inside one
> of their overpriced modules! But if you can get clean line-level audio
> at your TV's volume pot, you can tap it off to a line-level-output jack
> which you can install anywhere convenient. (Suggestion: don't put it on
> the back panel were you'll have to disconnect it to take off the rear for
> servicing!)

If you are hacking inside your TV set trying to get clean audio you
should be acutely aware of the 120VAC danger.  Most (almost all) TV
sets today are "hot chassis" sets, where the chassis is directly
connected to one side of the AC line.  If the set has a non-polarized 
plug or the outlet is wired wrong, you could *DIE* connecting to the 
volume control or any other point inside the set.

Even if you can work around this problem, you are still likely to get 
hum and buzz from the sweep circuits, anyway.  You would do better 
buying a separate TV audio receiver or a TV monitor/receiver with the 
connections built in.  Monitor/receivers, may still be hot chassis sets 
but they incorporate special 120V isolation circuitry for the direct 
audio/video connections.

If you are hacking a Zenith set, you may be in luck.  They were one of 
the last companies to go hot chassis, and they are willing to send a 
schematic *FREE* to anybody who calls with a chassis number.  It should
be a simple matter to tap the correct point on the volume control IC.
But again, BEWARE, if your set is hot chassis or you cannot figure out 
whether it is or not, STAY OUT OF IT.

USENET: decvax!savax!kann			Erwin Kann
						Sanders Associates
						Nashua, New Hampshire

(The opinions expressed herein are those of a person who thinks he
knows what he is doing and still gets zapped once in a while :-O)