Electronic Musician - DIY theremin

Build the EM Theremin
This classic electronic instrument gives good
vibrations and excitations.
By Robert Moog
ost electronic musical instru-
ments are sonic chameleons
that try to sound like a wide
variety of other things. How-
ever, there is one electronic
instrument that makes no
l
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 in-
ventor, 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 con-
tact. Players 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 play-
i
86 Electronic Musician February 1996
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.
er's hand motions, the tone has a
vibrant, wavering quality, not unlike a
human voice or a violin.
Among the requests for DIY projects
that EM receives, by far the most com-
mon is a do-it-yourself theremin. The
instrument presented here is an au-
thentic 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
OVERVIEW
When you bring your hand near a
theremin antenna, you are actually
forming a variable capacitor: the an-
tenna is one "plate" and your hand is
the other. With the high frequencies
and very low currents used by the in-
strument, 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 dia-
gram of the entire circuit. The variable-
pitch oscillator (VPO), fixed-pitch oscillator
(FPO), and detector sections form a beat-
frequency oscillator. Q1, Q2, and their
associated components constitute the
VPO, the frequency of which is set
The theremin's main circuitry is mounted on a single prototyping board, and the two antenna
circuits are mounted on their own smaller boards.
to make fine adjustments to the vol-
ume-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 hacksaw 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 horizon-
tal, hairpin loop with a total length of
nine inches. The ends of the volume
FIG. 1: This functional block diagram reveals how the theremin works.
the DC voltage appearing at the junc-
tion of D1 and C12 is reduced. The re-
sulting 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-con-
trolled audio output is then fed to
front-panel jack J1. The maximum level
is about 0 dBm (0.8V RMS).
Q8 and its associated components
constitute the volume-tuning circuit,
which is nearly identical to the
pitchtuning circuit. Potentiometer P2 is
used
slightly higher than the resonant fre-
quency of the pitch-antenna circuit (es-
tablished by adjusting L5). As a player
brings a hand near the pitch antenna,
the changing impedance of the pitch
antenna circuit lowers the VPO
frequency by about 3 kHz.
Q3, Q4, and their associated compo-
nents form the FPO, the frequency of
which is set equal to the VPO frequen-
cy (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 (3½ octaves
above middle C).
Q5 and its associated components
constitute the pitch-tuning circuit. This
circuit presents a variable active im-
pedance that is used to make fine ad-
justments to the FPO frequency while
the instrument is being played. Front-
panel potentiometer P1 adjusts the cur-
rent through Q5, thereby changing its
active impedance.
Q6, Q7, and their associated com-
ponents form the volume oscillator. Its
frequency is set slightly higher than the
resonant frequency of the volume-
antenna circuit by adjusting L11. As the
player brings a hand near the volume
antenna, the resonant frequency of the
volume-antenna circuit is lowered, and
The EM theremin closely emulates Leon Theremin's original design, although it is housed in a
smaller cabinet.
February 1996 Electronic Musician 87
February 1996 Electronic Musician 89
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 attrac-
tively 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.
∙ ∙∙ ∙ DIY
antenna should be separated by 3¼
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. Doublecheck to
make sure that the two ends of the
volume antenna are parallel and are the
correct distance apart.
Copper tubing has one drawback: be-
cause 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 po-
tential 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 sen-
sitive 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 interac-
tion between them. For example, as
you move your left hand tip and down
above the volume antenna, its motion is
parallel to the pitch antenna, which
causes little or no change in pitch.
FIG. 2: The schematic for the EM theremin.
∙ ∙∙ ∙ DIY
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,
3/8-inch-tube-to-3/8-inch-male-pipe
elbow. Drill 3/8-inch holes for these
fittings; then screw them in by hand. If
you can't screw the 3/8-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
3/8-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 4/4-inch X 3/4-inch blocks and
one microphone-stand mounting flange
are attached to the bottom of the enclo-
sure. 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 ei-
ther 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 (1U) rack panel,
which is 1¾ 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 1/8-inch mini-
jack, and one toggle switch are mount-
ed 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 PI and P2, P3 and P4 are less
critical; these pots can be miniature,
and the knobs can be small. I suggest
90 Electronic Musician February 1996
you use an insulated, 1/4-inch jack for
J1 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 Von 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
THEREMIN: AN ELECTRONIC ODYSSEY
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 (UT, 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
Leon Theremin lived a long, produc-
tive, 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 mid-
town Manhattan, where he
developed new instruments
and tutored a long string of
students. His greatest protege
was Clara Rockmore, a
young Russian musician who
was originally trained as a
classical violinist.
Professor Theremin's
tenure in the United States
came to an abrupt end one
day in 1938, when he was
taken back to Russia by So-
viet agents under circum-
stances that are still not fully
known. For decades after
Clara Rockmore was Leon Theremin's greatest protege
Theremin disappeared, nobody in the An amazing array of people
West knew of his whereabouts. Some appear in the film, including Brian
publications even reported that Wilson of the Beach Boys (talking
Theremin had died in a Soviet prison about the use of theremin in
during the Second World War. For- "Good Vibrations"), Clara Rockmore,
tunately, the rumors of his demise Jerry Lewis, and Todd Rundgren (do
were premature; Theremin actually ing an on-camera imitation of the
survived until 1993. theremin). In addition, I discuss the
A few years ago, documen- technical side of theremins at several
tary filmmaker Steven Martin (not the points in the film. But most impor-
comic actor) became interested in tant, the true story of Leon Theremin
Theremin's story. He interviewed is told in a way you won't forget.
people who had known Theremin, -Robert Moog
located old newsreels and home
movies, and dug deep into the life of
this amazing man. The result is a
film entitled Theremin: An Electronic
Oddessy. If you haven't already
seen this movie, watch for it at your
neighborhood cinema.
that C20 and C22 are very close to U2.
The negative side of C19 and the posi-
tive side of C20 should be connected
together with a very short lead, and the
grounded side of J2 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 os-
cillators are already lightly coupled
through C2 and C6, so they tend to
synchronize at low beat frequencies
(which is desirable). Placing the oscil-
lator 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 un-
wanted 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.
FIG. 3: Fabricating the cabinet requires some basic woodworking skills.
ANTENNA CIRCUIT BOARDS
The inductors and other antenna-cir-
cuit components are mounted on two
separate, small circuit boards with lit-
tle or no copper circuit pattern. LI
through L4 are mounted on the pitch-
antenna circuit board (see Fig. 4). Po-
sition the inductors so they are
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 se-
ries 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 Ll should be
close to the pitch-antenna socket.
February 1996 Electronic Musician 91
∙ ∙∙ ∙ DIY
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 L10, DI, 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 con-
nected so the windings are end to be-
ginning. Position the board near the
volume antenna, and install wires to
connect the free end of L10 to the vol-
ume-antenna socket. In addition, con-
nect the junction of L7 and C12 to the
junction of C14 and C15, 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
PARTS LIST
Integrated Circuits
U1 LM781L12 12V positive regulator
U2 LM79L12 12V negative regulato
U3 LM1360ON dual operational
transcondance amplifier
(National Semiconductor)
Transistors
Q1-Q8 2N3904 NPN
Diodes
D1, D4, D5 1N4148 signal diode
D2, D3 1N4001 power diode
Capacitors
C I, C5 3,900 pF/50V, 5%, polypropylene
or polystyrene
C2 C6, C 16 22 pF/50V, 5%, NPO (zero
temperature coefficient) ceramic
C3, C7, C15, C26 0.01 µF/50V, 10%, polyester
C4, C8, C1O, C11 1.0 µF/35V tantalum
C13, C17, CI8, C25 1.0 µF/35V tantalum
C9 33 µF/50V, 5%, NPO (zero
temperature coefficient) ceramic
C12 1,000 pF/50V, 10%, ceramic
C14 2,200 pF/50V, 5%, polypropylene
or polystyrene
C19, C20 2,200 µF/35V aluminum
electrolytic
C21, C22, C27 0.1 µF/5OV ceramic
C23 4,700 pF/50V, 10%, ceramic
C24 3,300 pF/50V, 10%, ceramic
Inductors
L1, L2, L3, L4 10 mH, 3-section, RIF choke
(J. W. Miller #6306)
L5, L6 100 pH, hi-Q, variable inductor
(Toko RWRS-T1015Z)
L7, L8 2.5 mH, 3-section, RIF choke
(J. W. M i ller #6302)
L9, L10 5 mH, 3-section, RF choke
(J. W. Miller #6304)
L11 68 µH, hi-Q, variable inductor
(Toko 154ANS-T1019Z)
Potentiometers
P1, P2 5 kΩ linear taper, cermet or
conductive plastic (Clarostat
53C1-5K or equivalent)
P3 P4 50 kΩ linear taper
Resistors (¼ ¼¼ ¼W, 5%, metal or carbon film)
R1, R4, R5, R8 1 kΩ
R2, R6, R13, R16, R21 2.2 kΩ
R3, R7, R30 ,R38 47 kΩ
R9, R12, R22 10 kΩ
R23, R39, R40 10 kΩ
R10, R15, R17, R19 470Ω
R11, R20 33Ω
R14 560 kΩ
R18 2.7 kΩ
R27, R29 100 kΩ
R24 R26, R31 4.7 kΩ
R32, R33, R34 4.7 kΩ
R25 330 kΩ
R28 150 kΩ
R35, R36 1.8 MΩ
R37 4.7 MΩ
Switch
SW1 SPST miniature power switch
Connectors
J1 Insulated ¼-inch phone jack
(Switchcraft N-1 11 or equivalent)
J2 3.5 mm phone jack (Switchcraft
41 or equivalent)
Parts Not on Schematic
• 16-pin IC socket for U3
• Connector set with at least ten conductors for connections
between the main circuit board and front panel
• Wall-wart transformer to provide 12 to 15 ILIAC with at least
200 mA (Cui-Stack DPA120020-P1-SZ)
• Two large knobs for PC 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-11 B microphone-stand mounting flange
• 10-inch x 4-inch prototyping circuit board
• Two 4-inch x 3-inch prototyping boards for the antenna
circuits
92 Electronic Musician February
∙ ∙∙ ∙ DIY
for shorts, mistakes, missing connec-
tions, 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 U1 and U2
(see Fig. 2). Then check the DC
voltages at the collectors of Q1 through
Q8 (they should all be about +12V); the
emitters of Q1 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 L1 I. 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
headphones 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
clockwise slowly until you hear a high-
pitched whistle. Keep turning until the
tone is in the mid range (about I 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 some-
what 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 Bright-
ness and Waveform controls (P3 and
P4). Use the Pitch Tuning control (PI)
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 Waveform
control should change the sound
FIG. 4: The position of certain components is critical to minimize unwanted oscillations and capacitances
February 1996 Electronic Musician 97
∙ ∙∙ ∙ DIY
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, con-
ductive 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 PI (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
3 kHz (3 ½ 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 in-
ductance of L5 is set too high. Advance
the slug in L5 clockwise by a small
amount, perhaps 1/10 turn or so, and
repeat steps 2 and 3.
WHERE TO GET PARTS AND MATERIALS
Most of the electronic parts for this
project can be purchased from DigiKey
(tel. 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; BBS
800/433-5003; Web http://www.allied.
avnet.com), Mouser (tel. 800/346-6873 or
817/483-4422; fax 817/483-0931), and
Newark (tel. 800/463-9275 or 312/
784-5100; fax 312/907-5378). Radio
Shack is a good place to shop for
prototyping boards. You should be able
to get wood for the cabinet and all the
materials to make the antennas at your
local hardware superstore.
A complete kit and many of the
individual parts are available from Big
Briar, Inc. (tel. 800/948-1990 or
704/251-0090; fax 704/254-6233; email
[email protected]). The kit includes an
assembled and tested circuit board (with
antenna circuits), completely fabricated
front panel and antennas, and precut
cabinet parts. Also included are The
Complete Theremin Video starring Lydia
Kavina, Clara Rockmore's The Art of the
Theremin CD, and Bob Moog's detailed
and illustrated booklet on theremin
technology and history. The price of the
kit is $229, including shipping within the
United States.
98 Electronic Musician February 1996
5. If the pitch goes to zero and then
begins to ascend as you retract your
hand, the inductance of L5 is set too
low. Turn the slug in L5 counterclock-
wise 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 fre-
quency (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 L11:
1. Set P2 to its mid position.
2. Carefully turn the slug in L11 coun-
terclockwise 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 vol-
ume 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 J
I and the 12 VAC wall-wart power
adapter to J2. Turn on SW1 and touch
the pitch antenna. Set P2 so the tone is
loud when your left hand is well away
February 1996 Electronic Musician 99
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 PI 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 follow-
ing 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.
∙ ∙∙ ∙ DIY
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
musicians 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 de-
velopment of commercial synthesizers and
currently serves as Grand Poobah of Big
Briar, Inc.
100 Electronic Musician February