"Michael Black" wrote in message
news:alpine.LNX.2.02.1508092125250.25787@darkstar. example.org...
On Sun, 9 Aug 2015, Ian Field wrote:


"Bob" wrote in message
...
Hello,

Hoping someone here might know.

Have been using a Radio Shack Mini Amplifier Model No. 277-1008
for many years to help out a person with a disability.
Really important for them

As no longer a R/S, have been trying to find who might actually
make/made this unit, and/or who might still be carrying them.

Anyone have any ideas where I can purchase a few.

Another alternative is an amplified PC speaker, if the input impedance is
too
low just add a JFET source follower. You can use the volume pot as rhe
source
resistor, then all you need is a gate-leak resistor and input coupling
capacitor.

Most types run off a wall-wart, but you can get them with an internal
battery
compartment.

A couple of years back; a columnist in one of the hobby magazines
mentioned a
speaker amplifier unit for Walkman style gadgets in the £1 shop -
needless to
say, all gone by the time I got there. Apparently the unit had a pair of
small speakers driven by a TDA2822.

Ready made amplifiers aren't exactly rare, back in the 70s - 80s, any
number
of component stockists advertised small amplifiers (just a populated PCB)
around the 250mW mark.

An old vest pocket transistor radio is a good candidate for the JFET
modification - but those are often collectibles, such vandalism would
horrify
some people.

And there's sort of a return to all this. In the old days, stereos were
big, now everyone with their Walkman, oops iPod, are throwing out their
stereo system and replacing it with a docking station, which is just an
amplifier with speakers in the same box, so stereo separation is virtually
non-existent.

Oddly, there was a period when boomboxes included auxiliary inputs,
because they wanted to be "ready" for CD players that were either not yet
out, or too expensive to build into the thing. So they also have
auxiliary inputs, if they are of the right vintage.

Anything with an amplifier should be useful, just find a way to feed the
audio into it. In the old days it was easy, the top of the volume control
would be the place, a coupling capacitor would make sure all was safe.
But now, the volume control may not be a suitable marker, the control may
not be attenuating the audio signal, but varying a DC voltage to control a
stage that is controlling volume.

Most of the older shirt pocket items had about 4k7 volume pot, usually this
is too low for most signal sources you might want to patch into it.

My solution is to build a JFET source follower onto the input, you can use
the pot as the source resistor, in front of the JFET you only need a
gate-leak resistor and coupling cap.