wanttaja@ssc-vax.UUCP (Ronald J Wanttaja) (08/29/85)
One of the problems I have had since my student days is understanding what
is said on the radio. Intelligibility is the issue... not terminology. I
always blamed it on waxy ears and squinted to hear better :-).
When I bought my 150, the owner threw in an old set of headphones, and boy,
what a difference! Nearly every transmission came in perfectly
understandable. However, as I have a rather large head (oh, come on now,
be serious!:-) ) the pressure was excessive- the earpieces felt like they
were trying to meet at my Medula Oblongata. So I made my own, which
are comfortable, cheap, and have excellent sound quality.
Aircraft headphones are 600 ohm impedance, while standard home stereo
headsets are 4 to 8 ohm. All that you need is an impedance matching
transformer. Radio Shack sells a small audio transformer with a 1000 ohm
centertapped primary and an 8 ohm secondary. The transformer is stocked in
one of those little cards with the plastic around it; if you say
"transformer" to a Radio Shack clerk, he/she will lead you to the 25 pound
power transformers and say "this is all we have." Remind me to flame about
Rat Shack clerks, someday. You will also need a 1/4 inch mono headphone
plug, also carried at RS. Total parts cost: $4.
Now, you have two ways to go: 1. Convert an existing headset, or 2) make
an adaptor so you can plug in any headset.
1. If you convert an existing (stereo) headset, start by cutting off
the plug on the cord. Strip away the outer sheathing, and strip about 3/4
inch of insulation from each of the wires revealed. The wires should be
color coded, and one may be bare metal braid instead. Install the mono
plug, noting which of the two wires you used. Use the metal braid, if any,
as one of the wires. Be careful to slide the plastic cap onto the cord
before you solder, so it'll screw onto the plug when you're done.
Now go inside the headpieces and strip out all switches and volume
controls... all you want left is speakers and the wires that go to the
other side's speaker. Put tape over the holes to plug them. Since my
headphones had slide controls, I cut pieces of white plastic to size and
glued them in place. What you'll have left is two wires hanging free from
each speaker, and two wires that go through the headstrap between
headpieces. Take the right headpiece (the one that doesn't have the
plug-in cord) and solder the two speaker wires to the headstrap wires. Do
the same in the other headpiece. Now, look at the transformer. It has
five color-coded wires; one set of three, and a set of two. Take the group
of two wires and solder them to the junction of the headstrap wires and
speaker wires in the left headpiece. Look at the back of the card the
transformer came in, and find the color of the center tap wire. The
schematic will show a "curlicue" transformer symbol, and the line coming
off the middle of the left side is the centertap. Solder the centertap and
one of the remaining two wires to the end of the cord that comes into the
left headpiece, making sure the colors of the wires from the cord are the
same as the two wires you connected to the plug, earlier.
new plug cord trans.
--@@@@==================l=88=:=|< speaker in headpiece
headstrap \
\=|< other speaker
2. The other way is to build an adaptor, which sell for about $26 but you
can make for less than $10. In addition to the transformer and the mono
plug, buy a stereo jack (about $1.50). You may want to pick up a small
"experimenters" box to mount it all, or use some castoff box from something
else. You'll need some two-conductor wire, too... speaker wire is fine.
Connect some wire to the plug, connect this wire to the centertap and one
other primary wire, and connect the secondary leads of the transformer to
the stereo jack. Solder one to the lug that contacts the metal shaft of
the stereo plug, and solder the other secondary lead to one of the
two tip lugs, with a short wire to the remaining lug. That's it!
---------------------------------------------------------------------------
I converted a headset (#1) for my first try, but the environment turned out
too rough on it so I'm making an adaptor. The broken headset was an old
cheap one just sitting around, so no great loss. Now, next week, I'll tell
you boys and girls how to take Daddy's old CB and some popsicle sticks to
add a boom mike to your headset...:-).
Ron Wanttaja
(ssc-vax!wanttaja)
NOTE: When I say, "take these two wires and solder them to those two
wires, I do *not* mean, "wrap them all together!" Take one wire, solder
it to a wire in the other set, wrap some tape around for insulation, and do
the same to the remaining two wires. I knew a guy who cut an extension
cord with a mower. He took the three wires from one side, twisted them all
together, did the same with the three on the other side, then twisted the
two sets together into one big copper mass. He then (very professionally,
I might add) wrapped electrical tape around the "splice."kellym@iddic.UUCP (Kelly McArthur) (08/30/85)
> >When I bought my 150, the owner threw in an old set of headphones, and boy, >what a difference! .....[didn't fit].... >..........So I made my own, which are comfortable, cheap, and have >excellent sound quality. > This is useful information, but only solves half my problem. I have a very comfortable old headset with a boom mike of about WWII vintage that I'd like to retrofit, and I need information on the microphone end of things. I was wondering if the "electret" recorder microphone elements are compatible with the aircraft radios. How do they wire up? Also, does anyone have information on the transmit switch wiring schemes? Thanks IA for any information you can provide...... Kelly McArthur tektronix!iddic!kellym --
dmmartindale@watcgl.UUCP (Dave Martindale) (09/01/85)
Not all stereo headphones are 8 ohm. A goodly number (AKG and Sennheiser immediately come to mind) are either around 600 ohms or above 1K ohms. For these, no matching transformer is necessary, just a mono-to-stereo adapter cable. However, I don't think you'll find any stereo headphone with the noise attenuation of the real aircraft headsets. By the way, the most common aircraft headsets (David Clark and Telex) are 150 ohms - two 300-ohm transducers in parallel.