Minimum Theremin Kit Assembly Instructions

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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, http//:www.mouser.com/):

3) Antenna and suitable enclosure (not supplied in kit)


Assembly Instructions:

  1. Unpack the contents of the Minimum Theremin Kit and check that the following items are included:

    Bag Label

    Quantity
    in Bag

    Checked

    100 Picofarad Capacitor (C1, C9)

    2

    0.01 Microfarad Capacitor (C2, C4)

    2

    0.1 Microfarad Capacitor (C3)

    1

    10 Microfarad Capacitor (C5, C6, C7, C8)

    4

    1N4004 Rectifier (CR1)

    1

    270,000 Ohm Resistor (R1, R3, R4, R6, R9, R13)

    6

    27,000 Ohm Resistor (R2, R11, R12)

    3

    22,000 Ohm Resistor (R5, R7, R14)

    3

    100 Ohm Resistor (R8)

    1

    470 Ohm Resistor (R10)

    1

    Pitch Zero Trimmer Potentiometer, 10,000 Ohm (RV1)

    1

    CD4069UBE (or equal) Integrated Circuit (U1, U2)

    2

    LP2950ACZ-5.0 Integrated Circuit (VR1)

    1

    9V Battery

    1

    Pitch Zero Control Potentiometer, 1,000 Ohm
    Includes: 1 Nut, 1 Washer

    1

    Output Jack
    Includes: 1 Nut, 1 Washer

    1

    Hookup Wire

    5 Feet

    Switch
    Includes: 2 Nuts, 1 Lockwasher, 1 Anti-Rotation Washer

    1

    Mounting Hardware
    Includes: 4 Standoffs, 4 Male-Female Standoffs, 8 Screws

    1 Set

    Knob
    Includes: 1 Set Screw, 1 1/16" Allen Key

    1 Set

    Battery Connector

    1

    100-PCB Blank PC Board

    1


  2. 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.

  3. 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 steps.

  4. 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.



  5. Form the leads of Resistor R1 with long-nose pliers, as shown:



  6. 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.

  7. 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.)



  8. 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.

  9. Repeat steps 5 through 8 for the remaining 13 resistors.

  10. 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.



  11. 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. Click here for more information about handling precautions for semiconductors.

  12. Form the leads of Rectifier CR1 with long-nose pliers as shown:



  13. 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.

  14. 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.



  15. 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 place. IMPORTANT: Avoid excessive heat when soldering the ICs.

  16. 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.



  17. 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.

  18. 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 board.

  19. 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.



  20. 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.

  21. 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 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, with the Switch, Output Jack, and Pitch Zero Control Potentiometer mounted through the enclosure's side or sides.

    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 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 as needed.

    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.

  22. 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 PCB.



    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.

  23. 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 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 shortens.


  24. 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 non-conductive materials.

    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 enclosure.

    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 illustrated.



    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 lug.

    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 easily.

2006 09 13

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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.