Archives - 1996
Electronic Musician
February 1996
Build the EM Theremin
This classic electronic instrument gives good vibrations and excitations.
By Robert Moog
Most electronic musical instruments are sonic chameleons that try to sound
like a wide variety of other things. However, there is one electronic instrument
that makes no apologies for its single, immediately recognizable sound: the
theremin. This monophonic instrument has added its distinctive, melodic
character to the scores of many horror and suspense movies and made its pop
debut on the Beach Boys’ “Good Vibrations.” It has also appeared on many concert
stages, including Carnegie Hall.
The theremin was named after its inventor, Russian physicist and musician
Leon Theremin, who developed the instrument in the 1920s. Unlike most musical
instruments, the theremin is played with absolutely no physical contact. E’layers
wave their hands in the air near two antennas. As one hand gets closer to the
straight vertical tube (called the pitch antenna), the pitch rises; as the other
hand gets closer to the horizontal tubular loop (called the volume antenna), the
volume decreases. Because the theremin’s pitch and volume are intimately tied to
the player’s hand motions, the tone has a vibrant, wavering quality, not unlike
a human voice or a violin.
Among the requests for DR projects that EM receives, by far the most
common is a do—it—yourself theremin. The instrument presented here is an
authentic theremin, with antenna response characteristics, pitch range, and
tone color that closely emulate Leon Theremin’s original designs. However, it is
reasonably easy to build. It uses currently available components and materials
that you can buy at your local hardware store or from mail—order electronic—
parts distributors. If you know how to read a schematic diagram, solder, and use
a voltmeter, and if you’re comfortable with basic home tools, you should be able
to build and adjust this theremin.
OVERVIEW
When you bring your hand near a theremin antenna, you are actually forming
a variable capacitor: the antenna is one “plate” and your hand is the other.
With the high frequencies and very low currents used by the instrument, your
hand is effectively grounded by being attached to your body, so the antenna and
your hand form a variable capacitor to ground. This variable capacitance is
called hand capacitance. You increase the hand capacitance by bringing your hand
nearer to the antenna. During normal operation, the hand capacitance is less
than one picofarad, which is a very small capacitance indeed!
Each antenna forms a resonant circuit with a group of inductors
collectively called an antenna coil. In this design, the resonant frequencies
are about 260 kHz for the pitch antenna and about 450 kHz for the volume
antenna. At or near the resonant frequency, a tiny change in hand capacitance
results in a larger change in the impedance of the antenna circuit as a whole.
Refer to Figure 1, the functional block diagram, and Figure 2, the
schematic diagram of the entire circuit. The variable pitch oscillator (VPO),
fixed—pitch oscillator (FPO), and detector sections form a beat—frequency
oscillator. Ql, Q2, and their associated components constitute the VPO, the
frequency of which is setslightly higher than the resonant frequency of the
pitch-antenna circuit (established by adjusting L5) . As a player brings a hand
near the pitch antenna, the changing impedance of the pitch antennna circuit
lowers the VPO frequency by about 3 kHz.
Q3, Q4, and their associated components form the FPO, the frequency of which is
set equal to the VPO frequency (by adjusting L6) when the player’s hand is away
from the pitch antenna. The difference, or beat, frequency is extracted by the
detector and appears as an audio waveform at the junction of R23 and R24. As the
player brings a hand near the pitch antenna, the frequency of the audio waveform
goes from 0 to about 3 kHz (31,4 octaves above middle C)
Q5 and its associated components constitute the pitch-tuning circuit. This
circuit presents a variable active impedance that is used to make fine
adjustments to the EPO frequency while the instrument is being played. Front-
panel potentiometer P1 adjusts the current through Q5, thereby changing its
active impedance.
Q6, Q7, and their associated components form the volume oscillator. Its
frequency is set slightly higher than the resonant frequency of the volume—
antenna circuit by adjusting Lll. As the player brings a hand near the volume
antenna, the resonant frequency of the volume—antenna circuit is lowered, and
the DC voltage appearing at the junction of Dl and C12 is reduced. The resulting
current flowing through R14 is amplified and level—shifted by the VCA processor
section (U3-B and associated components) and then fed through R30 to control the
gain of the voltage—controlled amplifier (U3—A and associated components). The
amplitude—controlled audio output is then fed to front-panel jack Jl. The
maximum level is about 0 dBm (0.8V F~MS).
Q8 and its associated components constitute the volume—tuning circuit, which is
nearly identical to the pitch—tuning circuit. Potentiometer P2 is used
to make fine adjustments to the volume—oscillator frequency during performance.
The audio waveform is applied to pin 3 of U3-A at a level high enough to
clip it. This has the effect of reshaping the waveform from a skewed sine to a
quasi—rectangular wave, which is very similar to the waveform of Professor
Theremin’s original instruments. P3 varies the input resistance of U3—A, which
influences the amount by which the audio waveform is clipped. P4 shifts the bias
at the input of U3-A, which changes the waveform width and therefore the
output’s harmonic spectrum. C24 and C26 roll off the high-frequency harmonics to
produce a pleasant, cello—like tonal balance.
ANTENNAS
Making the antennas can be tricky. They should be metallic, rugged, attractively
finished, capable of being rigidly mounted, and easy to fabricate by a home
hobbyist. I have found that 3/8 inch, soft copper tubing of the sort that
plumbers use with bathroom sinks works well. You can buy preplated, straight,
short pieces at your local builders’ supply or hardware store. You can also
purchase a simple tubing bender that will allow you to bend the volume antenna
by hand without collapsing the tubing. You’ll also need a tubing cutter or hack-
saw to cut the tubing to length.
The finished pitch antenna is a straight, vertical tube eighteen inches long and
3/8 inch in diameter, and the finished volume antenna is a horizontal, hairpin
loop with a total length of nine inches. The ends of the volume antenna should
be separated by 31/4 inches, center to center.
I suggest you make the antennas longer than necessary and then cut them to
length after they’re formed and stiffened (discussed shortly) . Start with a
straight, 24— or 36—inch length of tubing for each antenna. To form the volume
antenna, slip the tubing bender over the tube. Then, starting at the midpoint of
the tube, bend it into a semicircular curve. Hold the tube in both hands and
push into the curve with your thumbs while pulling down with your other fingers.
Double—check to make sure that the two ends of the vollume antenna arc -~-parallel
an are the correct distance apart.
Copper tubing has one drawback: because copper is soft enough to bend by
hand, it is easy to put unwanted kinks in the tubing after it has been formed.
You can stiffen the antennas by filling them with polyester resin (the liquid—
plus—hardener type used to repair car bodies) after you’ve formed them. This is
not particularly difficult, but the potential for making a mess is significant,
so be sure you have plenty of time and you’re at peace with the world.
The pitch antenna is straight because this configuration is more sensitive
to changing hand position when the hand is farther away and less sensitive when
the hand is close. The change in hand capacitance is extremely small when the
hand is far away, and the change in pitch as a function of distance must be as
uniform as possible.
The volume antenna is looped because this configuration is less sensitive
when the hand is far away and more sensitive when the hand is close. This gives
you greater control over the low end of the dynamic range and lets you
articulate notes by quickly dipping your left hand into the loop (more in a
moment)
The two antennas are perpendicular to each other to minimize the
interaction between them. For example, as you move your left hand up and down
above the volume antenna, its motion is parallel to the pitch antenna, which
causes little or no change in pitch.
CABINET
The entire cabinet is made of wood. Except for the front panel, large
metal cabinet parts should not be used, as they may add unnecessary capacitance
to the antennas. My materials of choice are hardwood plywood for the top and
solid hardwood for the rest of the cabinet because they are rugged, easy to
shape accurately, and can be attractively finished.
The enclosure consists of a base and cover (see Fig. 3) . The cover should fit
snugly over the base. You may fasten the pieces together with any combination of
nails, wood screws, and wood glue, depending on how you like to put cabinets
together. After the cabinet parts have been assembled, sand them down well and
finish them with the wood finish of your choice, except metallic paint.
The antenna sockets are regular tube—to—pipe connectors that you can get when
you buy the copper tubing for the antennas. The volume—antenna sockets are
straight 3/8—inch—tube—to 3/8—inch—male—pipe connectors, whereas the pitch—
antenna socket is a right-angle, 3/4—inch-tube-to-3/4-inch—male-pipe elbow.
Drill 3/4—inch holes for these fittings; then screw them in by hand. If you
cant screw the %—inch pipe threads into the wood by hand, don’t force it by
using a pipe wrench: you may split the wood. Instead, enlarge the hole slightly
with a large round file or a 3/4—inch pipe tap.
Once you re sure you can screw in the pipe fittings by hand, unscrew them, put a
small amount of epoxy on the threads, and reinsert them by hand. Before the
epoxy hardens, verify that the pitch—antenna socket is vertical by inserting the
pitch antenna into the socket and adjusting the position of the socket as
necessary.
Two 3/4-inch x 3/4-inch blocks and one microphone-stand mounting flange
are attached to the bottom of the enclosure. This lets you set the finished unit
on a microphone stand (preferred) or on a wood (not metal) table when you play
it.
FRONT PANEL
The front panel should be made of 1/16—inch sheet aluminum. It should be about nine inches long and
should have bends at the top and bottom for mounting and stiffening. You can
either cut and bend the panel yourself or have your local sheet—metal shop do it
for you. Alternatively, you can buy a blank, single-space (lU) rack panel, which
is 13/4 inches high by nineteen inches wide, cut it to length with a hacksaw,
and attach the panel to the base from the front instead of from the bottom.
However, that will leave a 1/4-inch gap between the top of the panel and the
enclosure cover.
Four rotary potentiometers, one 1/4—inch phone jack, one 1/4—inch mini—
jack, and one toggle switch are mounted on the front panel. The two tuning pots
should be located in the left part of the panel so your hand is as far from the
pitch antenna as possible when you tune the antennas. Use high—quality, full-
size rotary pots and large—diameter knobs for P1 and P2. P3 and P4 are less
critical; these pots can be miniature, and the knobs can be small. I suggest you
use an insulated, 1/4—inch jack for Ji to avoid a ground loop between the audio
and power grounds.
Eight single—conductor wires and one shielded wire connect the front—panel
components to the main circuit board. I suggest you use a connector for these
wires so you can unplug the panel if you need to work on the main circuit board.
Prototyping boards often have provisions for mounting a DB15 or DB25 connector.
MAIN CIRCUIT BOARD
All circuitry (except the antenna circuits and front—panel components) is
mounted on one circuit board (see Fig. 4) . A plug—in prototyping board of the
sort used to assemble computer I/O circuits provides the space, connection
provisions, and solidity you need. Radio Shack’s prototyping board (catalog
#276—1598) provides ample space for all the circuitry with extra room to try
your own modifications.
The theremin’s power is supplied by a ±12 VAC wall wart, which is widely
available (see sidebar “Where to Get Parts and Materials”) The AC voltage is
converted into DC by two voltage regulators (Ul, U2, and associated components)
Keep the power—supply circuit components as close together as possible, and keep
connections as short as you can. Be really sure that C19 and C21 are very close
to Ul and that C20 and C22 are very close to U2.
The negative side of C19 and the positive side of C20 should be connected
together with a very short lead, and the grounded side ofJ2 should also be
connected to this lead. The voltage regulators are less likely to oscillate if
the connections are kept as short as possible.
Be sure to separate the VPO from the FPO by a couple of inches. These
oscillators are already lightly coupled through C2 and C6, so they tend to
synchronize at low beat frequencies (which is desirable) . Placing the oscillator
circuits close together increases the coupling, which may result in an excessive
tendency to synchronize. In addition, place C4, C8, and C13 very close to the
oscillator circuits with which they are associated to maximize the decoupling.
After the main board is assembled and checked, brush the solder side with
a small wire brush and inspect for unwanted solder bridges, wiring mistakes, and
weak solder joints. Then set the board in the middle of the cabinet base in
preparation for final test and tuning.
ANTENNA CIRCUIT BOARDS
The inductors and other antenna—circuit components are mounted on two separate,
small circuit boards with little or no copper circuit pattern. Li through L4 are
mounted on the pitch—antenna circuit board (see Fig. 4) . Position the inductors
so they arc parallel to one another and about one inch apart, center to center.
The inductors are not polarized per Se, but each terminal is distinct: one
emerges from the center of the coil and the other emerges from the outer layer
of the coil. Arbitrarily select one terminal as the beginning and the other as
the end, and connect the inductors in series so the end of one inductor is
connected to the beginning of the next.
Position the board on the base next to the pitch antenna. The free end of L4
should be close to the main circuit board, and the free end of Li should be
close to the pitch—antenna socket. Connect a short wire from the free end of Li
to the pitch—antenna socket using a heavy soldering iron or by drilling and
tapping a hole for a 4-40 thread and then mounting a solder lug.
L7 through Lb, Dl, C12, and R14 are mounted on the volume-antenna circuit board
(see Fig. 4). As with the pitch-antenna circuit, position the inductors so they
are parallel to one another, about an inch apart, and connected so the windings
are end to beginning. Position the board near the volume antenna, and install
wires to connect the free end of Lb to the volume—antenna socket. In addition,
connect the junction of L7 and C12 to the junction of C14 and CiS, and connect
the free end of R14 to pin 13 of U3.
CHECKING IT OUT
After you’ve assembled and cleaned the main board, take a deep breath and check
all your connections again. Look for shorts, mistakes, missing connections, etc.
Then connect the front panel to the main board, plug in the power supply, and
turn the power switch on.
Use a voltmeter to check the voltages at the inputs and outputs of Ul and U2
(see Fig. 2). Then check the DC voltages at the collectors of Qi through Q8
(they should all be about +12V); the emitters of Qi through Q4, Q6, and Q7
(about 0.6V); and the emitters of Q5 and Q8 (about -2.6V). If you don’t observe
all these readings, check everything until you find the problem.
Next, verify that all three oscillators are working. Read the AC voltages across
L5, L6, and Lil. If you read about 10 VAC, then the corresponding oscillator is
producing a waveform. If you don’t read any voltage at all, the oscillator is
not working. To check the detector, measure the DC voltage across R24. If it’s —
0.5V or so, the detector is working.
Temporarily connect a pair of head—phones or a small powered speaker across
R24. Turn the tuning slugs in L5 and L6 counterclockwise until the tops of the
slugs hit the shield cans. Be careful. Do not force the slugs farther than they
want to go! Turn L5 exactly two turns clockwise. Then turn L6 clock—wise slowly
until you hear a high-pitched whistle. Keep turning until the tone is in the mid
range (about 1 kHz). Now, turn P1 in either direction. You should hear the pitch
change markedly. If you observe all these things, then the entire beat-frequency
oscillator circuit is in good shape.
To check the VCA, temporarily connect pin 12 of U3 to ground. (This should
turn on the VCA.) Connect your headphones or monitor amp across R34. You should
hear a somewhat louder tone. Now, disconnect the temporary ground connection to
pin 12 of U3, and connect that pin to —12V. The audio across R34 should
disappear. If it does, the VCA is working properly.
While pin 12 of U3 is connected to ground, you can also check the
Brightness and Waveform controls (P3 and P4) . Use the Pitch Tuning control (P1)
to set the tone’s pitch to approximately middle C. Then turn the Brightness and
Waveform controls. The Brightness control should change the sound from muted to
bright, and the Wave—form control should change the sound from “reedy” (narrow
waveform) to “full” (wider waveform) . After you have checked all of these
controls, remove the temporary connection to pin 12 of U3.
TUNING
Before tuning, clean off your work—bench and move aside any large,
conductive objects such as desk lamps and test gear. Leave a clear space of two
or three feet around your work area. Place the cabinet base in the middle of the
cleared space, put the pitch antenna in place, and connect the pitch—antenna
circuit board between the antenna and the main board. On the main board,
temporarily connect pin 12 of U3 to ground and connect the instrument’s audio
output to headphones or a monitor amplifier. Now follow these steps to adjust L5
and L6:
1. Set P1 (the Pitch Tuning control) to its middle position.
2. Grasp and hold the pitch antenna with one hand. With the other hand, adjust
L6 until the beat frequency is zero. Then carefully turn L6 counter— clockwise
until you hear a pitch of about 3kHz (3Yn octaves above middle C).
3. Let go of the pitch antenna. Slowly retract your hand from the vicinity of
the antenna. You should hear the pitch go down.
4. If the pitch does not go down to zero when you’ve retracted your hand
completely and stepped back, the inductance of L5 is set too high. Advance the
slug in L5 clockwise by a small amount, perhaps 1/iu turn or so, and repeat
steps 2 and 3.
5. If the pitch goes to zero and then begins to ascend as you retract your hand,
S the inductance of L5 is set too low. Turn the slug in L5 counterclockwise by a
small amount, and repeat steps 2 and 3.
6. If the pitch jumps abruptly as you retract your hand, the inductance of L5
is set far too low. Turn the slug in L5 counterclockwise approximately a
quarter—turn and repeat steps 2 and 3.
Eventually, you will converge on the proper settings for L5 and L6. The idea is
to find the settings at which the frequency (a) is zero when you’ve stepped away
from the theremin, (b) begins to ascend when your body is about two feet from
the pitch antenna, and (c) reaches about 3 kHz when your hand touches the pitch
antenna. Tap lightly on L5 and L6 as you converge on the proper settings, which
will stabilize the tuning—slug positions.
This completes the tuning of the pitch oscillators. In performance, the exact
tuning is established by adjusting the pitch-tuning control (P1).
Now, remove the temporary ground connection to pin 12 of U3. Connect a
voltmeter from pin 12 of U3 to ground, install the volume antenna, and connect
the volume—antenna circuit card between the antenna and the main board. Follow
these steps to adjust Lii:
1. Set P2 to its mid position.
2. Carefully turn the slug in Lii counterclockwise until it is out as far as it
will go. The meter should read about -12V.
3. Slowly turn the slug clockwise. At some point, you will see the voltage begin
to rise from —12V. Stop when the voltage passes through 0 and becomes positive.
At this point, bringing your hand near the volume antenna lowers the voltage;
the meter should read about —12V when your hand is two or three inches from the
volume antenna.
This completes the tuning of the volume oscillator. In performance, the
exact volume is established by adjusting the volume-tuning control (P2).
PlAYING THE THEREMIN
You are now ready to try your theremin. Place the instrument (with
antennas installed) on a microphone stand that is set about 40 inches high.
Connect a small monitor amplifier and speaker to Jl and the 12 VAC wall-wart
power adapter to J2. Turn on SWi and touch the pitch antenna. Set P2 50 the tone
is loud when your left hand is well away from the volume antenna and the volume
begins to decrease noticeably when your left hand is brought within ten to
twelve inches of the volume antenna. Then set P1 so the frequency is zero when
your right hand is well away from the pitch antenna and the tone becomes
apparent when you bring your right hand within 18 to 24 inches of the pitch
antenna. Your instrument is now ready to play.
As with any expressive musical instrument, playing the theremin takes
some practice. You can start by following these simple exercises:
1. Stand slightly left of the center of the instrument with your right shoulder
about 24 inches from the pitch antenna. Relax your wrists. Think of a note and
hum it to yourself. Then move your right hand toward the pitch antenna until the
theremin pitch coincides with the pitch you’re humming. Now hold the note. This
is not as easy as it sounds, but it’s an important technique to learn. At first,
you will find it difficult to stand still, but a few hours of practice will work
wonders.
2. Hum two different notes, one after the other. Find the first note on the
theremin, hold it, and then slowly glide to the second note.
3. Repeat the above exercise, but bring your left hand near the volume antenna
while your right hand glides from one note to the next. Move the left hand
slowly at first and then more rapidly as you learn to move your left hand
independently of your right hand. This exercise teaches you to “feel” where the
notes are and to impart expressive dynamics.
4. While playing a note, introduce vibrato by moving your right hand back and
forth from your wrist several times a second. Concentrate on making the vibrato
even and steady.
These exercises address the basic skills of theremin playing: finding
notes, playing intervals, articulating notes, and introducing vibrato. With
these basic skills, you can play slow melodies. Practicing regular scales and
arpeggios will increase your proficiency. Focus on accuracy of pitch and precise
control of dynamics.
Once you’ve mastered the basic moves, it’s time to develop your own style. Pay
particular attention to shaping envelopes and dynamics with your left hand. The
left hand can also be used to articulate discrete notes by momentarily dipping
into the volume antenna as the right hand quickly moves from one pitch to
another. Try combining audible glides and discrete pitch changes within a
musical phrase. In addition, avoid constant vibrato in the right hand. Instead,
impart expressive nuance by shaping the amount and rate of vibrato. These
considerations are important components of theremin musicianship.
The theremin presented here is designed to meet the needs of musician who wish
to explore the artistic resources of this unique instrument. Build your
instrument carefully, and it will provide many years of reliable service.
Practice with diligence, and you will provide enjoyable music for yourself and
your audiences. Finally, be sure to give an occasional thought to the spirit of
Leon Theremin, to whom we owe so much.
Robert Moog was a pioneer in the early development of commercial
synthesizers and currently serves as Grand Poobah of Big Briar, Inc.
THEREMIN: AN ELECTRONIC ODYSSEY
Leon Theremin lived a long, productive, and amazingly diverse life. He
developed the theremin during the 1920s, a time when most people had never even
heard of radio! He came from Russia to New York City in 1927 and instantly
became the darling of the cultural elite. He set up a laboratory and studio in
midtown Manhattan, where he developed new instruments and tutored a long string
of students. His greatest prot6g~ was Clara Rockmore, a young Russian musician
who was originally trained as a classical violinist.
Professor Theremin’s tenure in the United Stated came to an abrupt end one day
in 1938, when he was taken back to Russia by Soviet agents under circumstances
that are still not fully known. For decades after Theremin disappeared, nobody
in the West knew of his whereabouts. Some publications even reported that
Theremin had died in a Soviet prison during the Second World War. Fortunately,
the rumors of his demise were premature; Theremin actually survived until 1993.
A few years ago, documentary filmmaker Steven Martin (not the comic actor)
became interested in Theremin’s story. He interviewed people who had known
Theremin, located old newsreels and home movies, and dug deep into the life of
this amazing man. The result is a film titled “Theremin: An Electronic Odyssey”.
If you haven’t already seen this movie, watch for it at an amazing array of people appear in the film, including Brian Wilson of the Beach Boys (talking about the use of the theremin in “Good Vibrations”), Clara
Rockmore, Jerry Lewis and Todd Rundgen (doing an on—camera imitation of the
theremin) . In addition, I discuss the technical side of theremins at several
points in the film. But most important, the true story of Leon Theremin is told
in a way you won’t forget.
PARTS LIST
Integrated Circuits
Ul LM78L12 12V positive regulator
U2 LM79L12 12V negative regulator
U3LM13600N dual operational
transcondance amplifier
(National Semiconductor)
Transistors
QI—Q8 2N3904 NPN
Diodes
Dl, D4, D51N4148 signal diode
D2,D31N4001 power diode
Capacitors
Cl, CS 3,900 pF/50V, S%,polypropylene or polystyrene
C2, CS. C16 22 pF/50V, 5%, NPO (zero temperature coefficient) ceramic
C3, C7, CiS, C26 0.01 uF/50V, 10%, polyester
C4, C8, CIO, Cli 1.0 uF/35V tantalum
C13, C17. C18, C25 1.0 uF/35V tantalum
C9 33 pF/50V, 5%, NPO (zero temperature coefficient) ceramic
C12 1,000 pF/SOV, 10%, ceramic
C14 2,200 pF/50V. S%,polypropyiene or polystyrene
C19, C20 2,200 uF/35V aluminum electrolytic
C21, C22, C27 0.1 uF/50V ceramic
C23 4,700 pF/50V, 10%, ceramic
C24 3,300 pF/50V, 10%, ceramic
Inductors
Li, L2, L3, L4 iMh,3—section,RF choke (J.W. Miller#6306)
L5, L6 iOOuH, hi—Q, variable inductor (TokoRWRS-TiOi5z)
L7, L8 2.5 Mh,3—section, RF CHOKE (J.W.Miller #6302)
L9, LlO 5Mh, 3—section RF choke (J.W. Miller #6304)
Lii 68 Uh, hi—Q, variable inductor (Toko 154AN5—TiOi9z)
Potentiometers
P1, P2 5k linear taper, cermet or conductive plastic (Clarostat 53C1—5K or
equivalent)
P3, P4 50k, linear taper
Resistors(i/4W, 5% metal or carbon film)
Ri,R4, R5, R8 1k
R2, R6, R13, Ri6, R21 2.2k
R3, R7, R30, R38 47k
R9, R12, R22 10k
R23, R39, R40 10k
Rb, R15, R17, R19 47 0
Ru, R20 33
R14 560k
Ri8 2.7k
R27, R29 100k
R24,R26, R31 4.7k
R32, R33, R34 4.7k
R25 330k
R28 150k
R35, R36 l.8M
R37 4.7M
Switch
SWi SPST miniature power switch
Connectors
Ji Insulated 1/4—inch phone jack(Switchcraft N—ill or equivalent)
J2 3.5 mm phone jack (Switchcraft 41 or equivalent)
Parts Not on Schematic
16—pin IC socket for U3
Connectors set with at least ten conductors for connections between the main
circuit board and front panel.
Wall—wart transformer to provide 12 to 15 VAC with at least 200 mA(Cui—Stack
DPAi2002O—Pi—SZ)
Two large knobs for P1 and P2
Two small knobs for P3 and P4
Two 24 to 36—inch x 3/8—inch straight copper tubes for antennas
Tube bender for volume antenna
Atlas AD-liBmicrophone stand mounting flange
i0inch x 3-inch prototyping boards
Two 4—inch x 3—inch prototyping boards for the antenna circuits
WHERE TO GET PARTS AND MATERIALS
Most of the electronic parts for this project can be purchased from Digi-Key
(tell. 800/344—4539 or 218/681—6674; fax 218/681—3380; web
http://www.digikey.com). Other suppliers include Allied (tel. 800/433—5700 or
817/595—3500; fax 817/595—6404;