On Jul 23, 8:27 pm, Ernest Christley wrote:
I've been looking into building a in-the-ear type headset using low-end
earphones, following the example given athttp://www.canardzone.com/members/nickugolini/CuplessHeadet/cupless_h...

I bought the Phillips ANR headphones from Target. I've got Jim Weir's
impedance matching circuit article describing how to use the audio
transformer, so the headphone portion is in the bag.

The hangup is with the microphone. I found some discussions where Jim
said that an amplifier is needed to use an electret element. Well, I
picked up Item# 270-090 from Radio Shack today.http://www.radioshack.com/product/in...mary&techSpecs...

It has a wiring diagram on the back of the package that seems to
indicate that the single transistor amplifier is already built into the
package. I was going to post here and ask if that was in fact what it
indicates, and inquire whether it would work with the RST-443 intercom.

Then I got antsy and just went and tried it. With only two leads, you
know I had to hook it up backwards and feel disappointed for a minute
until I figured out to turn the leads around. Then it was "WOOHOO!!"
all the way.

I'm now well on my way to having the equivalent of a $500, in-the-ear
headset, and it's only costing me about $50. (Testing is incomplete,
but others have reported resounding success.)

I built a headset (the usual passive type) using the speaker
elements from old telephones (dial or early touch-tone types) which
are around 300 ohm and give the necessary 150 ohm overall impedance
when connected in parallel. The microphone was an electret that came
out of a cheap ($6) touch-tone corded phone. You know the sort; they
can be had at any Wal-Mart or liquidation center. No preamp was
necessary; it worked without, and maybe has a tiny preamp built into
it. I carved a wooden mike holder for it and made the articulated
support from 3/32 welding rod.
The most expensive parts were the plugs (the 7/32" mike
plug is hard to find) and the ear protectors ($19 Peltor muffs). I
built another headset using $6 Princess Auto muffs, but they're not as
good.
I wonder if I can build an airplane using old telephone
parts?

Dan