Minimum Theremin Kit Assembly
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Beginners are encouraged to learn about proper soldering techniques
before assembling this kit.
Click here for
an on-line soldering guide.
You will need:
1) Minimum Theremin Kit
2) Tools (available from an electronics distributor such as Mouser Electronics,
Small-wattage Soldering Iron Station, such as Weller type WTCPT
Tin-Lead Solder with Rosin Core, 63/37 alloy, 0.031" diameter; such
as Kester type 23-6337-0027
IMPORTANT: Only use Rosin Core solder.
Do not use "Water Soluble Flux" or "Acid Flux" types.
Wire Strippers, such as Miller type 100
Diagonal Cutters, such as Xcelite type MS54J
Long-Nose Pliers, such as Xcelite type LN54
1/8" Flat-Blade Screwdriver, such as Xcelite type R186
3) Antenna and suitable enclosure (not supplied in kit)
Unpack the contents of the Minimum Theremin Kit and check that the following
items are included:
Mild Oxidation of the solder pads on the PCB may have occurred
during storage or transit. These oxides will impede solderability. To remove
this oxide, gently rub the pads with an unused pencil eraser. Remove any
eraser residue with a clean paper towel.
Click Here for an
image of the PCB with the components inserted.
You may print the image and use it as a reference for the following
Attach a pair of Standoffs to each corner of the PCB as
illustrated. The Male-Female Standoffs are inserted into the PCB's
component side, which is the side with the white printing. The Female
Standoffs extend from the PCB's bottom side. The standoffs elevate the
board from the work surface to allow the easy insertion of components, and
prevent the components from being crushed. The Male-Female Standoffs may
be replaced with four of the Machine Screws provided, once the PCB
Form the leads of Resistor R1 with long-nose pliers, as
Insert Resistor R1 into the PCB at the location marked
"R1." Note that the resistor may be oriented in either direction, however,
it is conventional to orient the resistor so that its first band (red band,
in the case of R1) is closest to the board's left edge.
Cut off the resistor's excess lead lengths, leaving about 1/16th inch
of each lead extending from the board's bottom, as shown in "METHOD 1," below.
If you wish, you can bend the resistor's leads against the board's pads,
as shown in "METHOD 2," and then cut them. Doing so will help keep the resistor
in place when the board is turned over for soldering. (The same choice of
these two methods applies to all the other components. The disadvantage of
METHOD 2 is that a component will be harder to remove in the event that it
has to be replaced.)
Solder R1 in place. If you used "METHOD 1," above, you can solder one
or both of the leads on the top side of the board to keep it in place. Then,
turn the board over to solder both leads on the bottom side. Top-soldering
the leads is optional, but is useful for keeping the resistor from falling
out of the board when METHOD 1 is used. For either method, it is standard
practice to always solder the leads on the bottom of the board.
Repeat steps 5 through 8 for the remaining 13 resistors.
Prepare the leads of Capacitors C1, C2, C3, C4, and C9
the same way the resistors were prepared, and solder them in place. Note
that these capacitors may be oriented in either direction, however, it is
conventional to orient them so that the numerical marking denoting their
values are readable. The markings are three digits followed by a letter,
as illustrated below. IMPORTANT: These
capacitors are very delicate. Do not apply excessive force to their leads.
Make sure the capacitors fit easily into the PCB before soldering, because
any tension on the leads will cause them to break off the capacitor body
while being soldered.
In the next steps, the rectifier (CR1) and three integrated circuits
(U1, U2, and VR1) will be installed on the PCB.
IMPORTANT: These are "semiconductor" devices
that are sensitive to static electricity. Static electricity is a charge
that accumulates on your body's surface and on other objects. You can often
observe static electricity's effect when you touch a doorknob or other metal
object and feel a brief jolt in your hand. While usually harmless to people,
it can destroy semiconductors such as those used in this kit. To prevent
damage to these devices, discharge any static electricity that may have
accumulated on your body by touching a grounded metal object near your
workstation, immediately before removing the semiconductors from their conductive
foam pad or conductive wrapping. Unwrap the semiconductors at your workstation,
and install them in the PCB immediately.
for more information about handling precautions for
Form the leads of Rectifier CR1 with long-nose pliers as
Insert Rectifier CR1 into the PCB at the location
marked "CR1." IMPORTANT: The rectifier
must be inserted in the correct direction. Make sure that the rectifier's
CATHODE LEAD is inserted into the PCB hole with the SQUARE PAD. As shown
in the picture, the cathode lead is the lead designated by the silver band
on the rectifier's body. Cut off the rectifier's excess lead lengths, leaving
about 1/16th inch of each lead extending from the board's bottom. Once CR1
is correctly inserted, solder it in place.
Refer to the following picture of Integrated Circuits U1
and U2. Note the notch that designates the end of the device with
pins 1 and 14. The ICs may be supplied with their pin rows angled slightly
apart. To facilitate their insertion into the PCB, gently form the
pin rows so that they are 90 degrees (perpendicular) with relation to the
body of the IC. This may be done by carefully pressing each row against a
flat surface (such as a tabletop) just enough to bend them perpendicular
with the body.
Insert ICs U1 and U2 into the PCB at the locations
marked "U1 and U2." IMPORTANT: The ICs
must be inserted in the correct direction. Make sure that Pin 1 is inserted
into the PCB hole with the SQUARE PAD. As shown in the picture, Pin 1
is designated by the notch on the IC's body. Before soldering the ICs into
place, verify that they are oriented correctly and that none of the pins
have been inadvertently bent, preventing them from going through their
hole. Once the ICs are correctly inserted, solder them in
IMPORTANT: Avoid excessive
heat when soldering the ICs.
Form the leads of Voltage Regulator VR1 with long-nose pliers
as shown. IMPORTANT: The regulator
leads are brittle and will break easily. Form the leads gently, avoiding
excessive plier pressure and sharp bends.
Insert Voltage Regulator VR1 into the PCB at the location
marked "VR1." IMPORTANT: The regulator
must be inserted in the correct direction. Make sure that Pin 1 is inserted
into the PCB hole with the SQUARE PAD. As shown in the picture, Pin 1
is the pin on the left, when the regulator is oriented with the flat surface
facing you and the pins are pointing downward. Cut off the regulator's excess
lead lengths, leaving about 1/16th inch of lead extending from the board's
bottom. Once VR1 is correctly inserted, solder it in place.
IMPORTANT: Avoid excessive
heat when soldering the regulator.
Insert the Pitch Zero Trimmer Potentiometer into the
PCB at the location marked "RV1." The adjusting screw of the potentiometer
is closest to the bottom edge of the board. Once RV1 is correctly inserted,
solder it in place, making sure that it is held flat against the
Insert Capacitors C5, C6, C7 and C8 into the PCB
at their respective locations. Refer to the illustration below to identify
their positive (+) leads. IMPORTANT: These
four capacitors must be inserted in the correct direction. Make sure that
their longer (+) leads are inserted into the PCB holes with the SQUARE
PADS. Cut off the capacitors' excess lead lengths, leaving about 1/16th
inch of each lead extending from the board's bottom. Solder them in place.
All of the components have now been attached to the PCB. Inspect each
soldered connection carefully to ensure that there are no solder bridges
between adjacent pads, pads with excess solder, or insufficient solder. Ensure
that the ICs, voltage regulator, rectifier, and capacitors C5, 6, 7 and 8
are inserted in the correct direction.
Before considering the kind of enclosure you want for your theremin,
it is recommended that the parts are temporarily arranged on a surface so
that the circuit can be tested and calibrated.
Refer to the figure below. Using Hookup Wire, connect the
Switch, Battery Connector, Output Jack, and Pitch Zero Control
Potentiometer to the
Note the drawing detail illustrating how the wires
are attached to the PCB. Passing the insulated part the wires through the
strain relief holes will prevent them from breaking off their solder pads.
With the exception of the antenna wire, the lengths of the wires connecting
the PCB to the off-board components are not critical. For the temporary test
arrangement, 4-inch lengths are sufficient. However, plan in advance by making
the wires long enough to allow the circuit board to mount to the internal
surface of an enclosure, with the Switch, Output Jack, and
Pitch Zero Control Potentiometer mounted through the enclosure's side
Note that the Output Jack has two solder
lugs, one called the "Tip" lug, and the other the "Sleeve" lug. These must
not be interchanged. The lugs can be identified by their different shapes:
is the tip and
is the sleeve. The
tip lug is connected to the "LINE OUT" pad on the
PCB, and the sleeve lug is connected to the "GROUND" pad on
Attach the Knob to the
Pitch Zero Control Potentiometer with the Allen
Key provided. The knob has a white index line which indicates the
potentiometer's degree of rotation. You may position the index line so that
it is approximately in the 7 o'clock position when the potentiometer shaft
is fully counterclockwise, and approximately in the 5 o'clock position when
the shaft is fully clockwise. Once the potentiometer is mounted to the enclosure,
the knob may be repositioned as
Power will be "ON" when the switch toggle in the "UP"
position, as illustrated. The top switch lug is not connected. The power
switch wires may be interchanged without affecting operation.
The Antenna is provided by the user. A suggested antenna, suitable for
the test arrangement, is illustrated below. It consists of a 6" x 6" square
of sheet metal supported on a wood stand. Any type of thin sheet metal, such
as the type found in many hardware stores, may be used.
The dimensions of the wood pieces are not critical, but the pole should have
a relatively small cross-section (for example, 3/4" x 3/4"), and be tall
enough (6") to prevent excessive capacitance.
Drill a 5/32" hole through the center of the metal square and attach it to
the wood stand with a #6 x 1/2" long wood screw. One end of the antenna lead
wire is stripped and placed between the stand and the metal plate. The other
end of the antenna lead wire is connected to the "ANTENNA" pad on
The following antenna guidelines are provided:
a) Do not mount the antenna flush against the theremin's enclosure,
because there will be too much capacitance between the antenna and the enclosure.
Elevate the antenna above the theremin enclosure a minimum of four inches,
especially if a metal enclosure is used.
b) Keep the Antenna Lead wire short (less than 8 inches) and route
it directly to the "ANTENNA" pad on the PCB. Keep the antenna
lead as far as practical from other wires or components.
c) While a rod antenna will work in substitution of a plate, using one
will cause a considerable alteration in the theremin's response to hand
positions, making the tone scale "compressed" into a shorter range of hand
distance. This will make the theremin harder to play. If a rod is desired,
use a telescoping antenna such as the type found on portable FM radios, extended
to about 2 feet.
d) The antenna and its lead wire have a certain amount of "capacitance" with
respect to all nearby objects. As the area of the antenna or the length of
the lead wire increases, the value of capacitance increases as well. If the
value of capacitance becomes too large, you will not obtain proper theremin
operation. Antennas with alternative shapes and lead wires of different lengths
are possible, but should not deviate too much from those suggested.
The Minimum Theremin test arrangement is now ready for evaluation.
a) Connect a 1/4" phone cord from the theremin's Output Jack to an
audio amplifier. Set the amplifier's volume control to nearly minimum ("1"
on the volume knob). Connect the 9 Volt Battery to the theremin's
Battery Connector. Set the theremin's Power Switch to the "on"
position. Note: If you don't have an amplifier, you may use headphones. Most
headphones are equipped with a stereo plug, so you will only hear the theremin
in one ear. This may be remedied with a suitable "mono source to stereo headphone
adapter" such as Radio Shack type 274-360 (note that this adapter is designed
for stereo headphones with a 1/4" plug).
CAUTION: Use headphones that have a built-in volume control,
and adjust the volume control for a comfortable level. Hearing experts advise
against the continuous, extended use of headphones.
b) Remove any objects, such as wires, tools, or test equipment, within two
feet of the Antenna.
c) Using a small flat-blade screwdriver, set the RV1 Pitch Zero Trimmer
Potentiometer on the PCB to its extreme counterclockwise resistance
value by turning the slotted adjustment screw at least 15 full counterclockwise
rotations. Note that the potentiometer's mechanism has a slip clutch,
so it can safely be turned an unlimited number of times in either
d) Set the Pitch Zero Control to its middle position.
e) With your hand away from the ANTENNA, slowly turn the RV1 Pitch Zero
Trimmer Potentiometer clockwise. No pitch should be heard with RV1 in
its extreme counterclockwise position. As RV1 is rotated, a very high pitch
will become evident. The pitch will become successively lower with continued
rotation, until it stops abruptly. Stop turning RV1 at this point.
f) Remove the adjustment screwdriver from RV1. Note that the pitch
might return; this is a normal condition resulting from the capacitance change
that occurs when the screwdriver is removed.
g) Slowly adjust the Pitch Zero Control just to the point where the
pitch stops. This point may occur either slightly clockwise or counterclockwise
of its center position.
h) Starting from a distance of about two feet, move your hand toward the
Antenna. Note that the pitch commences at its lowest frequency with
your hand about fourteen inches away, increasing as the distance
An enclosure, if desired, is provided by the user. A cardboard, wood,
plastic, or metal one will work. A metal enclosure will reduce the amount
of capacitive coupling between the circuit and antenna. This will result
in a more sinusoidal tone than would be obtained with an enclosure made from
The Power Switch, Output Jack, and Pitch Zero Control
are each supplied with bushing hardware so that they can be mounted through
the enclosure wall. The maximum panel thickness accommodated is about 1/8",
so if you intend to mount them through material that is thicker (such as
plywood), use a 1/32" to 1/16" thick panel, inset into the wall of the
The Power Switch's antirotation washer and the corresponding 0.093"
diameter hole in the enclosure wall prevents the switch's body from turning
as its bushing nut is tightened, but they may be eliminated at the builder's
option. The Pitch Zero Control has a built-in antirotation tab and
corresponding 0.118" diameter hole in the enclosure wall for the same purpose,
but the tab may be twisted off with pliers, and the hole eliminated, also
at the builder's option. The bushing hardware is arranged in the order
The PCB may be mounted to the wall of the enclosure with the Machine
Screws and 3/4" Female Standoffs provided. The 3/4" standoffs
may be replaced with shorter ones, but keep at least a 1/4" clearance between
the PCB and the enclosure wall. If you want to mount the PCB without screws
going through the enclosure wall (as with a thick-walled plywood enclosure),
replace the standoffs with hollow number 4 spacers and number 4 wood screws.
Mount the PCB in a position that will allow the occasional readjustment of
the RV1 Pitch Zero Trimmer Potentiometer.
Note that metal enclosures will be electrically connected to the circuit's
"ground" in two places; the upper left PCB standoff, and also the output
jack's threaded mounting bushing, which is connected to the jack's sleeve
As previously stated, elevate the antenna above the theremin enclosure a
minimum of four inches, especially if a metal enclosure is used, and keep
the antenna lead as far as practical from other wires or components.
A Minimum Theremin assembled in a plastic box, shown with the lid removed,
is illustrated below. Drill a small hole through the bottom of the box to
access the Zero Adjust potentiometer.
A suitable antenna, which may be used with the above configuration,
is illustrated below. The square metal plate is attached to a 6-32 threaded
rod with two 6-32 hex nuts. The other end of the rod is attached to a banana
plug, which plugs into the theremin's antenna jack. This arrangement is
convenient if the theremin is transported, since the antenna can be detached
2006 09 13
Text, Images, and format ©2006 by Harrison Instruments, Incorporated.
No part of this page may be reproduced without express written consent of
the copyright holder. Minimum Theremin design used with permission
of owner. Specifications may change without notice.