[sci.electronics] stereo TV hookup

phil@osiris.UUCP (Philip Kos) (05/27/88)

Well, I finally got around to checking out my TV's "external speaker"
jacks (remember my TV?  no?  oh well..) and they certainly are NOT
isolated.  My DMM even loaded them down enough that the built-in speaker
for the left channel switched in and out as I connected and disconnected
the DMM probe.  :-)  For those of you who are interested and/or
concerned, the TV is a Montgomery Ward model 12868.  (Free karma points
to anyone who can tell me what it *really* is, but that's not important
now...)

I suggested before that if the jacks turned out to be hot, it might be
a cute trick to use audio impedance-matching transformers (hooked up
"backwards") and L-pads to connect them to my receiver.  The responses
that I got mainly said "I doubt the jacks are hot, but check to make
sure" and didn't contain any commentary on my hookup method.

So now I really need to know - does anyone want to volunteer?  Will my
idea work?  Is there a better way that won't cost more than the TV?  And
what about Naomi?

For those who missed the original posting, the TV in question has two
output jacks on the back that (according to the manual, at least) want
an 8 ohm impedance connected to them.  The 8 is probably just a minimum
load, but I've had bad experiences before with connecting low-impedance
output stages to high-impedance input stages so I don't want to bet on
what the sound quality would be like if I just used 1:1 isolation
transformers.  My idea is to use audio impedance-matching transformers
and L-pads to isolate the two ends of the chain and attenuate the signal
a little.  I know that I can probably get by without the L-pads but the
incremental cost is so low that I feel I don't have any excuse not to
put them in.

So, anyone who wants to help me out is more than welcome.  I would also
appreciate explanations as to why my idea will/won't work - I might as
well learn something from this...

                                                                 Phil Kos
                                                      Information Systems
...!uunet!pyrdc!osiris!phil                    The Johns Hopkins Hospital
                                                            Baltimore, MD