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From: brown@nicmad.UUCP
Newsgroups: net.audio
Subject: Re: Audio Transformer (Really TV audio)
Message-ID: <185@nicmad.UUCP>
Date: Sat, 25-May-85 23:33:45 EDT
Article-I.D.: nicmad.185
Posted: Sat May 25 23:33:45 1985
Date-Received: Mon, 27-May-85 07:35:35 EDT
References: <1989@topaz.ARPA> <10785@brl-tgr.ARPA>
Organization: Nicolet Instrument Corp. Madison WI
Lines: 32

> The best thing is to grab the audio signal before it gets into the TV's
> own audio stages, and also strip off any garbage like DC offsets or stray
> AC power-line noise or leakage. This is usually done by getting the signal
> at the volume-control pot, and checking it with a DC-coupled 'scope.
> 
> 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!)

WARNING:  Doing the above may be hazardous to your health!

Some TV sets don't use any kind of isolation from the AC line, ie, one side
of the AC line gets connected to the TV chassis/ground circuit.  The headphone
output is done after a audio transformer.  

If the ground of a Hi-Fi system is attached to the chassis of the TV, it is hard
to say which piece will 'blow-up', if not both.

CAUTION IS ADVISED!!!!!!!!
-- 
              |------------|
              | |-------| o|    JVC HRD725U 
Mr. Video     | |       | o|  |--------------|
              | |       |  |  | |----| o o o |
              | |-------| O|  |--------------|
              |------------|     VHS Hi-Fi (the only way to go)
   ({!seismo,!ihnp4}!uwvax!astroatc!nicmad!brown)