206 Pitch Theremin Printed Circuit Assembly

NOTE:  This page is for "REV. 3" (see "Revisions," below)

206 Pitch Theremin

Compared to our previous-generation Pitch Theremins, the 206 Pitch Theremin Printed Circuit Assembly features reduced size, improved sensing distance, and improved audio output drive capability. A wider pitch-zero control range accommodates greater variations in antenna capacitance and grounding conditions. Inexpensive user-supplied materials may be added to the 206 to build a pitch-only instrument. Electrical connections to the external components are easily made with solderless, compression screw terminations. The 206 is ideal for OEM build-in applications where a reliable, affordable pitch theremin is required.


* Ideal for OEM build-in applications, art and technology exhibits, and classroom demonstrations

* Operation from a user-supplied 9 volt battery or 9 to 12 volt power adapter

* Low current consumption for long battery life

* High-fidelity, pleasing sine-like output tone with exceptionally low noise, wide pitch range, and good sensing linearity

* Line output for user-supplied external amplification

* 8 to 16 ohm loudspeaker output capable of delivering sufficient volume for many applications including showrooms, classrooms,  technology displays, and museum environments

* Accommodates user-supplied loudspeaker volume and pitch-zero potentiometers

* Stable, low-drift operation

* On-board static suppression requires no additional components

* Easy calibration with one on-board adjustment

* Excellent sensing range for versatility in exhibits and displays

Technical Specifications
Values are typical, unless otherwise noted., and specified with
Volume Potentiometer fully clockwise (CW).

Dimensions 3.8" x 2.5" x 0.61"
(9.65cm x 6.35cm x 1.55cm)
Weight 1.2 ounces
(34 Grams)
Operating Temperature Range +30F to +90F
(-1.1C to +32.2C)
Storage Temperature Range -10F to +120F
(-23.3C to +48.8C)
Operating Voltage Range 7.5 to 9.0 volts DC (8 ohm load)
7.5 to 13.0 volts DC (16 ohm load)
Loudspeaker Load Impedance 8 ohms or greater (See Item 7, Below)
Operating Current (maximum)
75 milliamperes
Operating Current at Zero Beat
6.5 milliamperes
Operating Current with INH Jumper Inserted  4 milliamperes
Loudspeaker Output Amplitude
2.8 volts, P-P
Loudspeaker Output Power
250 milliwatts (16 ohm load)
Loudspeaker Output Roll-Up Frequency (-3dB) 60 hertz
Loudspeaker Output Roll-Off Frequency (-3dB) 1550 hertz
Pitch Response to Hand Position
(with Circuit Board in Grounded Metal Enclosure
and Using Recommended Antenna)
View Graph
Line Output Amplitude
(10k ohm Load, 440 Hertz)
1.0 volt, P-P
Line Output Impedance 220 ohms
Line Output Noise at Zero Beat 
(Bandwidth = 20Hz to 20kHz)
2 millivolts, P-P
Line Output Signal to Noise Ratio  48 dB
Local Oscillator Frequency
455 2 kilohertz
Total Recommended Antenna Capacitance (typical) 10 picofarads
Test Points TP1:  ground
TP2:  local oscillator waveform
TP3:  variable frequency oscillator waveform
TB1 Terminal Block Wire Range: 24 AWG to 16 AWG (0.5mm to 1.27mm)
Strip Length: 0.19" to 0.23" (5mm to 6mm)
Recommended Torque: 1.7lb-in (0.19N-m)
ANTENNA Terminal Wire Range: 22 AWG to 14 AWG (0.64mm to 1.6mm)
Strip Length: 0.19" to 0.25" (4.8mm to 6.35mm)
Recommended Torque: 2.5lb-in (0.28N-m)


  1. Revision 3 ("REV. 3") has a new type of ZERO CAL tuning capacitor. The location of the adjustment screw has remained the same as in revision 2. Adjustment of the ZERO CAL capacitor requires a tool, available from Knowles Voltronics, their part number TT-400, or from Harrison Instruments (please contact us.) Alternatively, a slot jewelers' screwdriver with a 0.16mm x 0.8mm blade, such as Wiha type 26008, may be used. The new ZERO CAL capacitor can only be adjusted from the top-side of the board.

  2. Revision 3 has relocated the "COUPLING" pad. It is now located below test point 2 ("TP2"), and has a lager diameter to accommodate a 2-56 screw or 2-56 diameter threaded rod. The effectiveness of the coupling has been improved significantly, to more-easily obtain variations in the tone harmonics with relatively short coupling extensions.


206 PCB Dimensions

Connection Diagram


Suggested Sources

Application Instructions

  1. The 206 Theremin Printed Circuit Assembly contains devices that may be damaged by static electricity.  Before removing the product from its protective shielding bag,  discharge static electricity that may have accumulated on your body by touching a grounded metal object near your work area. Remove the product in a work area specifically designed to prevent the accumulation of static electric charges, and use caution to prevent static discharges when handling the assembly prior to its final installation. The assembly has built-in static protection to prevent damage from body static discharge to its antenna input and terminal block (TB1).

  2. The recommended antenna assembly, Harrison Instruments item number 99999-5977-006 may be ordered separately.  It consists of an antenna plate, supporting mast, plug, and jack. The antenna assembly is typically mounted to the enclosure that houses the Printed Circuit Assembly.  The jack provides electrical insulation for the antenna from the enclosure, and the mast provides adequate separation between the antenna plate and enclosure.

  3. Install the Printed Circuit Assembly in an enclosure with four user-supplied 1/4" or longer metal standoffs.  The Printed Circuit Assembly is furnished with its GND (ground) jumper installed. With the GND jumper installed, and the assembly mounted in a metal enclosure with metallic standoffs, the circuit will automatically ground to the enclosure via the lower-right mounting hole. The use of a metallic enclosure will maximize the electrostatic isolation between the antenna and Printed Circuit Assembly, and may be preferred to ensure the ability to obtain maximum fundamental tonality at the lower part of the pitch range. (In this case, the "COUPLING" provision may be used to selectively control the tonality - refer to step 18.) Optionally, a non-metallic (plastic or wood) enclosure may be used.

  4. Provide a hole in the enclosure for accessing the Printed Circuit Assembly ZERO CAL calibration capacitor, to facilitate calibration with the enclosure cover in place.

  5. Connect the antenna assembly jack to the ANTENNA terminal by a wire (item 2, above) not exceeding 6 inches in length. The antenna lead-in wire should be routed in a straight path away from the Printed Circuit Assembly. Do not run the antenna connecting wire against metallic enclosure walls or the Printed Circuit Assembly.

  6. Items 3 through 11, above, may be located in or on the enclosure, or be located away from the Printed Circuit Assembly and connected with suitably-long wires or a cable. Do not connect the 9 volt battery or otherwise apply power to the Printed Circuit Assembly until all the other items have been mounted and connected.

  7. The Printed Circuit Assembly is capable of driving loudspeakers with an impedance of 8 ohms or greater. When driving an 8 ohm speaker, limit the input voltage within a range between 7.5 and 9.0 volts DC. 16 ohm loudspeakers may also be used, in which case the input voltage may extend to an upper limit of 13.0 volts DC. Alternatively, two 8 ohm loudspeakers may be connected in series to provide the equivalent of a 16 ohm load. If a loudspeaker is not used, leave TB1 terminal 9 and 10 unconnected. Terminals 9 and 10, when used, must be connected only to a loudspeaker. These terminals must not be connected to ground or any other circuit, as doing so will damage the assembly. Do not exceed the maximum load recommendations, as doing so will damage the assembly.

  8. The Printed Circuit Assembly has an integrated circuit (located directly above TB1 terminal 9), to drive the loudspeaker. This integrated circuit dissipates heat proportional to to the power supply voltage, and inversely proportional to the loudspeaker impedance. In applications where

              a.  the speaker impedance is at or near the low end of the acceptable range (8 ohms),
              b.  the input voltage is at or near the high end of the acceptable range (9.0 volts),
              c.  the ambient operating temperature is at or near the recommended limit of 90F (32.2C),

    adequate ventilation must be provided so that the case temperature of the integrated circuit does not exceed +140F (+60C). This may be achieved by providing sufficient ventilation for free air exchange, or providing the integrated circuit with a heat dissipater such as Fischer Electronik type SMD A 8 SA attached with 3M™ Thermally Conductive Epoxy Adhesive TC-2707. The suitable attachment of larger radiators will further reduce heat in the integrated circuit.

  9. If required, connect a user-supplied amplifier to the Output Jack with a 1/4" shielded cable ("guitar cable"). To prevent damage to the amplifier or its loudspeaker, initially set the amplifier to its minimum volume level.

  10. Remove objects within 3 feet of the antenna.

  11. To provide optimal sensing distance, ground the theremin to earth with a suitable grounding wire. A grounding wire may be attached to the lower-right mounting pad via a ring terminal under the mounting screw head, or inserted into TB1 terminal block position 1, 5,  or 14.  If the theremin is used with a user-supplied mains-powered amplifier, the grounding will be provided via the amplifier through the shield connection at the Line Output Jack (item 5 above). In this case, a separate ground wire will not be required. If the theremin is used exclusively with a loudspeaker connected to terminals 9 and 10, and no grounding is provided, the theremin will still operate, but with reduced sensing distance.

  12. Set the Pitch Zero Potentiometer (item 3, above) and the Loudspeaker Volume Potentiometer (item 6, above) to mid position. Note that the Loudspeaker Volume Potentiometer does not control the level at the Line Audio Output Jack (item 5, above).

  13. Connect the 9 volt battery or a 9 to 12 volt DC power supply to the Printed Circuit Assembly and set the power switch to the "on" position. Observe the correct power polarity, with the positive connection to TB1 pin 13 and the negative connection to TB1 pin 14.

  14. Using the recommended adjustment tool or jewelers' screwdriver, adjust the ZERO CAL calibration capacitor so that no tone is evident in the amplifier's loudspeaker when the hand is removed from the proximity of the antenna, and a low-pitch tone is evident when the hand is approximately 24 inches above the antenna. The pitch should rise in frequency as the hand is moved closer to the antenna. Do not apply excessive force to the ZERO CAL calibration capacitor. The illustration, below, shows the adjustment range for the capacitor.

    206 Zero Capacitor Positions

  15. After calibration is complete, use the Pitch Zero Potentiometer to fine-adjust the pitch response so that the theremin produces no sound with the hand completely away from the antenna, and a low tone with the hand about 24 inches from the antenna, increasing in pitch as the hand is brought closer. If adjustment of the Pitch Zero Potentiometer does not provide the correct response, then readjustment of the ZERO CAL capacitor may be required.

  16. Output tone quality may be influenced by external interference, which will vary depending on the instrument's proximity to emissive sources such as power lines, fluorescent lighting fixtures, incandescent lamp dimmers, and computers. This interference may be remedied by moving the theremin away from such sources.

  17. If the output is taken from the Line Output Jack (item 5, above), and no loudspeaker is required, current consumption may be reduced by soldering a wire jumper between the two INH pads. Inserting the jumper will place the on-board amplifier section in a low-current, standby mode. This feature will typically reduce the Printed Circuit Assembly operating current from 6.5 milliamperes to 4 milliamperes, and is useful when it is powered from a battery.

  18. The COUPLING pad is provided for optional tone modification via field coupling of the local and variable oscillators. This is accomplished by soldering a short, stiff wire (20 gauge or similar) to the pad and extending it away from the board. The length of the wire is user-selected for the degree of coupling desired. Alternatively, a #2-56 screw or threaded rod of user-selected length may be inserted through the CPL pad and secured with a nut or nuts. The wire, screw, or rod may extend either above or below the board. The tone characteristic will exhibit increased harmonic content with increased wire, screw, or rod length. Do not allow the wire or screw to make electrical contact with other parts of the circuit.

  19. An alternative connection diagram, illustrated below, is useful when the 206 Theremin is used for performance applications in which a P.A. system is present, and a local loudspeaker isn't required. As shown, a wire jumper between the two INH pads places the on-board amplifier into its standby mode to reduce battery current. In addition, by using a "tip-ring-sleeve" Output Jack, the on-off function is provided by the insertion or removal of the output cable's plug, eliminating the need for an On-Off Switch. This automatically disconnects the battery when the cord is removed, lessening the likelihood of inadvertent battery consumption between performances.  Note that this function requires the use of an output cable with a "mono" (tip-sleeve) plug, and not a stereo plug.
    IMPORTANT: When using this connection method, the"tip" of the cable plug will momentarily contact the "ring" contact in the theremin output jack as it is inserted. This will cause a large transient, about equal to the battery voltage, to be present at the P.A. system's input, causing an extremely loud pop in the loudspeakers, and possibly damaging them. It is therefore advised to connect the cable plug at the theremin end first, and the cable plug at the P.A. system's input, last. As previously stated: To
    prevent damage to the amplifier or its loudspeaker, initially set the amplifier to its minimum volume level.

    Alternative Connection Diagram

    Alternative Connections

Important Safety Precautions for Using This Product

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