Theremin for Tube Enthusiasts
|WHAT YOU CAN DO
|Nearly everyone who has ever watched television
or attended a motion picture has heard music and background effects produced by a Theremin,
yet relatively few could recognize the instrument, and fewer still have had the chance to own
or play one. With its astounding tonal and dynamic ranges, it has been used to produce
background music and special effects in scores of science-fiction, fantasy, horror, and
|USING THE THEREMIN
|For about the price of an inexpensive guitar,
plus a few hours assembly time, you can own and enjoy what is perhaps one of the most
versatile of all musical instruments: the unique and amazing Theremin. Named after its
Russian-born inventor, Leon Theremin, its frequency range exceeds that of all other
instruments, including theater pipe organs, while its dynamic range is limited only by the
power capabilities of the Amplifier and speaker system with which it is used. Above all, it is
a true electronic instrument, not just an “electronic version” of a familiar string, reed, or
percussion instrument. Its tone is unlike that of any conventional instrument.
|A musician playing a Theremin seems almost like
a magician, for he or she can play a musical selection without actually touching the
instrument itself! As he or she moves his or her hands back and forth near two metal plates,
he or she seems to “conjure up” individual notes at any desired volume; he or she can “slide”
from one musical note to another with ease, can produce tremolo and vibrato effects at will,
and can even sound notes which fall outside the standard musical scale. He or she can play
tunes or melodies, produce unusual sound effects, or can accompany a singer or another
instrument- all by means of simple hand movements.
|The Theremin is ideal for amateur as well as
professional musicians and can be used for “fun” sound effects as well as for serious music.
It makes a wonderful addition to the home recreation room, and can be used equally well by
rock ‘n’ roll groups or larger bands. Theatrical groups find it just the thing for producing
eerie and spine-tingling background effects to accompany mystery or horror plays, and for the
budding scientist or engineer, it is an excellent Science Fair project.
|The typical Theremin has two r.f. oscillators,
one having a fixed, the other a variable, frequency, with their output signals combined in a
mixer/oscillator stage. At “tune-up,” the oscillators are preset to “zero beat” at the same
frequency. The frequency of the variable oscillator is controlled by an external tuning
capacity-the “antenna”- which is a “whip” or a simple metallic plate.
|As the musician’s hand is moved near this
antenna, the variable oscillator shifts frequency and a beat note is set up between the two
oscillators. The pitch is proportional to the difference in frequency between the two
oscillators. This beat note, Amplified, is the Theremin’s output signal. The more advanced
Theremin designs- such as the version presented here- use a third oscillator to control output
volume, and two antennas. This Theremin also uses a unique tube V3 to control the Amplitude of
|It should be noted; that in constructing the
Theremin–that the coils L1, L2, and L3 are mounted at least 18” apart from L6, L7, and L8,
while L4, L5 and at right angles to both pitch and volume coils. As an electronic instrument
using tubes, a Theremin may be constructed at a very nominal cost, especially if you use
salvaged parts. And give completely satisfactory performance. In the instrument about to be
described, the tone is produced by two RF oscillators beating at an audible frequency. The
addition of hand capacity to the pitch control antenna lowers the frequency of one of the RF
oscillators, and the pitch of the beat frequency is correspondingly changed. The outputs of
the two radio frequency oscillators V1, and V2 in the schematic are mixed, and the RF
components of the resultant signal removed by means of a diode detector.
CRAIG KENDRICK SELLEN
164 SOUTH MAIN ST.
CARBONDALE PA, 18407-2655