G
Gene Gardner
Guest
Earphones are required a lot in our household for TV listening.
On the Toshiba that I just put in use, the Variable-Audio Out was just barely
sufficient for either 8-ohm or 600-ohnm earphones. This would be dangerous
because inevitably, someone would push the "Speakers ON" button while the
volume was on max and blast the loud speakers.
I solved this problem by building a small "scratch-wired"amp on the pins of
a receptacle. I summed (OR'd) the stereos with a 27K from each to a single
1M gate resistor of a 2N5459 FET amplifier, followed by a 2N697 Emitter-follower.
Used 18 volt self-contained wall-plugin-unit....12 volt would be OK too.
Components from junk box and probably not critical. I did seat-of-the-pants
design....using audio osc and oscilloscope and experimental "tack-soldering"
to obtain sufficient undistorted power out. I capactively coupled(330uf)
output to
the two 8-ohm earpieces "In Series"...centerpin to centerpin of the two RCA
phono-plugs (leaving their shields floating). Of course it's no longer stereo
but that's not important.
The earphone volume level is now compatible with that used with "speakers on".
The little "kluge-wired" amplifier dangles at the back with the headphones
and dc-power cable from the wall transformer...attached to the TV power
with a nylon cable-strap......to provide strain-relief.
On the Toshiba that I just put in use, the Variable-Audio Out was just barely
sufficient for either 8-ohm or 600-ohnm earphones. This would be dangerous
because inevitably, someone would push the "Speakers ON" button while the
volume was on max and blast the loud speakers.
I solved this problem by building a small "scratch-wired"amp on the pins of
a receptacle. I summed (OR'd) the stereos with a 27K from each to a single
1M gate resistor of a 2N5459 FET amplifier, followed by a 2N697 Emitter-follower.
Used 18 volt self-contained wall-plugin-unit....12 volt would be OK too.
Components from junk box and probably not critical. I did seat-of-the-pants
design....using audio osc and oscilloscope and experimental "tack-soldering"
to obtain sufficient undistorted power out. I capactively coupled(330uf)
output to
the two 8-ohm earpieces "In Series"...centerpin to centerpin of the two RCA
phono-plugs (leaving their shields floating). Of course it's no longer stereo
but that's not important.
The earphone volume level is now compatible with that used with "speakers on".
The little "kluge-wired" amplifier dangles at the back with the headphones
and dc-power cable from the wall transformer...attached to the TV power
with a nylon cable-strap......to provide strain-relief.