Fig. A: Cordless phones found in a trash can.
Fig. B: Searching for recoverable parts inside the
Fig. C: Could these handset earpiece speakers be
repurposed as guitar pickups? Fig. D: An earpiece
speaker temporarily attached to an acoustic guitar
I normally leave components that require desol-dering on the board until I turn up a use for them.
In this case, an hour or so with a soldering iron will
yield another 3 crystals, 25 momentary switches,
another electret mic, adjustable coils, and transformers, along with a few small signal transistors.
There are also a number of diodes and capacitors
well worth harvesting as needed. Each phone base
unit also has an RJ11 jack that can be put to future
use, as well as standard 2.11mm wall wart jacks.
Inspired by Les Paul, I turned my attention to
the handset earpiece speakers from the 2 phones
(Figure C). Could these work as guitar pickups?
My first experiment involved connecting one of
the mics to a shielded audio cable and ¼" phone
plug. I temporarily taped the mic facedown on the
soundboard of an acoustic guitar and plugged it into
a traditional guitar amplifier (Figure D).
It actually had quite good sound. I experimented
further by moving the mic around on the face of
the guitar for the best sound pickup and tone. This
mic would also work well with the electric Cigar Box
Guitar featured in MAKE, Volume 04.
With the earpiece mic properly repurposed, it was
not hard to think of ways to amplify the device with
scrounged parts. My junk box of recovered radio,
142 Make: Volume 15
TV, and other electronic gadgets is brimming with
transistors and chips that could make a basic amp.
For example, the $5 Cracker Box Amplifier in
MAKE, Volume 09, is built around the LM386 audio
amplifier chip, a common item in many radios and
electronic toys. You could also use the LM380 or
the older LM383. The National Semiconductor data
sheets for all 3 chips are readily available online at
national.com and they include schematics to guide
you in the process of building your own amp.
Many other simple circuits supporting these
chips can be found on the internet. The nicest thing
about recovering one of these chips from an old
radio or toy is that the few additional resistors and
capacitors needed to bring the chip to life are often
found nearby on the same scrounged printed circuit
board. If not, keep scrounging! These amplifier
chips are like cockroaches in modern electronics.
If you want to go “old school” and you have a few
high-gain NPN transistors lying around (common
enough in old radios), a simple 2-stage amplifier
circuit can be made.
T.J. Arey has been a freelance writer to the radio/
electronics hobby world for more than 25 years and is
the author of Radio Monitoring: The How-To Guide.
Photography by Thomas Arey