Minimum Theremin Kit 101 Assembly
(Back to "Technical
Beginners are encouraged to learn about proper soldering
before assembling this kit. Internet instructional videos on the topic
Basic Soldering Lesson 1
"Solder & Flux" (PACE,
Incorporated; 8 additional lessons available)
here for images of a properly soldered kit.
here for the Minimum
Theremin Troubleshooting Guide. The
troubleshooting guide contains
valuable advice that will be helpful to you in your construction. It
is highly recommended that you read this guide, before you
You will need:
1. Minimum Theremin Kit
2. Tools (available from an electronics distributor such as Mouser
- Small-wattage Soldering Iron Station, such as
Weller type WTCPT
Note that the components and printed circuit board in this
kit are compliant with the recent "RoHS" (Restrictions of
Hazardous Substances) directive. This directive was, in part, developed
due to concerns about the toxicity of lead and its impact on the
environment. Either traditional lead-containing solder, or the newer
lead-free solder may be used to construct this kit. Use the lead-free
type if you desire to comply with the RoHS directive. However, note
that there are differences in the characteristics of the two solder
types; lead free solder requires a somewhat higher melting temperature
which may be more damaging to the printed circuit board and components.
Also, the appearance of lead-free soldered connections is duller than
connections made with the traditional, leaded type. Click here
for more information on the RoHS directive.
The recommended solders are:
Lead Type: Kester type 23-6337-0027
63% Tin - 37% Lead Alloy with Rosin Core, 0.031"
Lead-Free Type: Kester type
24-7068-1402 96.5% Tin - 3% Silver - 0.5% Copper
Alloy with Rosin Core, 0.031" diameter
use Rosin Core solder. Do not use "Water Soluble Flux" or "Acid Flux"
- 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
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.
This is an image of the PCB
with the components inserted. Use this 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 is complete.
- Form the leads of Resistor R1
with long-nose pliers, as shown:
- 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.) If you choose METHOD 2, make sure that the bent-over
leads do not touch each other or adjacent leads.
- 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 11
- 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 two diodes (CR1
and CR3), rectifier (CR2),
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. Click Here
for more information about handling precautions for semiconductors.
- Form the leads of Diodes CR1 and
CR3 with long-nose pliers as shown:
- Insert Diodes CR1
and CR3 into the PCB at the
locations marked "CR1" and "CR3." IMPORTANT:
The diodes must be inserted in the correct direction. Make sure that
each diode'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 black band on the rectifier's body. Cut off the
diodes' excess lead lengths, leaving about 1/16th inch of each lead
extending from the board's bottom. Once CR1 and CR3 are correctly
inserted, solder them in place.
- Form the leads of Rectifier CR2
with long-nose pliers as shown:
- Insert Rectifier CR2
into the PCB at the location marked "CR2." 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, the end of the IC with Pin 1 is designated by the
U-shaped notch on the IC's body. Do not confuse the U-shaped
notch with the circular recess that may be present at the other end of
the IC's package. 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 place. 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
- 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
- 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
- Refer to the figure below. Using Hookup
Wire, connect the Switch, Battery
Connector, Output Jack, and Pitch Zero Control
Potentiometer to the PCB. 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 (if an enclosure
is desired), with the Switch, Output Jack,
and Pitch Zero Control Potentiometer mounted
through the enclosure's side or sides. If you plan to mount any of the
items further away from the PCB, consider this before you commit to
specific wire lengths. (The kit is supplied with a five-foot length of
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 sleeve lug may also be identified as the one with
"SWITCHCRAFT" stamped into the metal where it extends from the
jack. The tip lug is connected to the "LINE
OUT" pad on the PCB, and the sleeve lug
is connected to the "GROUND" pad on the PCB.
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
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.
- An optional, quick antenna arrangement suited
for testing the theremin is illustrated below. It consists of a 6" x 6"
square of sheet metal supported on a wood stand. (Many users
will want to combine the theremin and all the related components,
including the antenna, into one assembly. A typical method is described
and illustrated in step 27.)
The "Materials" chart next to the illustration specifies the Internet
distributor McMaster-Carr and their stock numbers for the plate and
screw, however, these materials and the wood parts may often be
obtained in many local hardware stores. Any type of thin sheet metal
and wood 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 provide adequate capacitive isolation between
the plate and the PCB that will be located beneath
Drill a 5/32" hole through the center of the metal square and attach it
to the wood stand with the 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 PCB.
- 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 direction.
d) Set the Pitch Zero Control to its middle
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 shortens.
- An enclosure, if desired, is provided by the
user. It can be constructed from any material such as cardboard, wood,
plastic, or metal. A metal enclosure will reduce the amount of
capacitive coupling between the circuit and antenna. This may result in
a more sinusoidal tone and a larger sensing distance than would be
obtained with an enclosure made from non-conductive materials.
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 lug.
Note the following guidelines pertaining to the antenna and enclosure:
a) If a cardboard, wood, or plastic (non-conductive)
enclosure is used, do not mount the antenna flush against it, because
this may result in too much added capacitance between the
antenna and the enclosure. For such enclosures, it is further suggested
that the antenna is elevated at least six inches to provide adequate
capacitive isolation between the plate and the PCB that
will be located beneath it.
b) If a metal (conductive) enclosure is used, it is suggested that the
antenna is likewise elevated at least six inches to prevent too much
added capacitance between the antenna and the enclosure.
c) 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. If you do not use a plug and
socket for your antenna, pass the Antenna Lead wire
through the enclosure so that it is perpendicular to the wall. For
metal enclosures, take care not to damage the wire's insulation where
it passes through the hole.
d) 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.
e) 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.
f) Antennas with alternative shapes and lead wires of different lengths
may work, but should not deviate too much from those suggested.
- A typical Minimum Theremin using a plastic box
with a plug-in antenna is illustrated below. The "Materials" list
specifies the additional (non-supplied) items required for this
arrangement. The detail drawing shows the hole patterns and recommended
hardware arrangements for mounting the Switch, Output
Jack, and Pitch Zero Control Potentiometer.
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, allowing easy detachment for
The PCB is mounted to the wall of the enclosure
with the eight Machine Screws and four 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 (not supplied in kit). Drill a small hole through the bottom of
the box to access the Pitch Zero Trimmer Potentiometer
The items indicated with an asterisk (*) are available as a kit from
Harrison Instruments, Inc. as stock number 99999-5977-006.
2011 01 17
Text, images, and format ©2006-2018 by Harrison
Incorporated. No part of this page may be reproduced without express
consent of the copyright holder. Minimum
Theremin design used
with permission of owner. Specifications may change without notice.