Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!samsung!munnari.oz.au!metro!otc!brendan
From: brendan@otc.otca.oz (Brendan Jones)
Newsgroups: sci.electronics
Subject: Re: Making a mono VCR into stereo?
Message-ID: <1851@otc.otca.oz>
Date: 14 Aug 90 00:39:38 GMT
References: <1679@oucsace.cs.OHIOU.EDU>
Lines: 45

in article <1679@oucsace.cs.OHIOU.EDU>, 
bwhite@oucsace.cs.ohiou.edu (Bill White ) says:
> 
> 	If I understand things correctly, the second audio track is kept
> on the control track, and can be read by the control head.  If this is
> correct, wouldn't it be possible to tap off the control head, feed a
> second line into a decoder, and get stereo output?  I'm not asking if it
> is _easy_, just possible (I have lots of free time these days to play
> around with stuff like this).

'fraid not.  Lo-Fi stereo VCRs that record stereo on the linear track record 
two tracks very close to each other on the lower edge of the tape.  To be
compatible with mono machines, the upper track is L+R, whilst the lower
track is L-R. 

On playback, a stereo machine can read the lower track, and can add it to,
and subtract it from, the upper track to give you separated Left and Right 
audio signals.

A mono machine just reads the L+R signal as the mono signal.

The control track is in fact written on the upper edge of the tape and 
cannot be used as an audio track.

The only way to do what you want is to put in a new stereo audio head, plus a 
stereo modulator and demodulator, plus stereo audio output jacks.  Sounds
like too much trouble to me.

> 	Oh yes, the annoying problem: the audio buzzes strongly on signals
> with a bright white or with saturated colors.  I don't see any obvious
> adjustments, and RF / IF electronics isn't my field of choice.  Any
> suggestions, besides scrapping the demodulator?

I've had this problem when listening to the *TV* speaker, but not if I 
connect the audio output jacks of the VCR directly to my hi-fi.  Which is 
your problem?  If it occurs with the TV speaker, then don't worry as just
about any TV will do this from interference from the CRT circuits.

If it comes from your VCR, sounds like you got one sick VCR.

-- 
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