Motor Speed Control Box for Vibraphone

A musician that I know recently purchased a Saito Vibraphone which had the motor control box missing. The Vibraphone is an instrument kind of similar to a Xylophone or Marimba but with two major differences. The Xylophone has bars made of wood while the Vibraphone has bars made of metal. The other major difference is that the Vibraphone has little pipes underneath each reed which act as resonant chambers and they have butterfly valves that open and close at a speed determined by the rotation of the motor. This gives the instrument a distinctive vibrato sound. The Vibraphone also has a pedal which allows the musician to pick long or short notes, it is widely used in jazz and was used in 1950's and 60's "Tiki" music led by the well known Arthur Lyman.

I built this control box for the motor that was in improvement on the original as this one allows the motor speed to be continuously varied from stop to the fastest speed that the motor is capable of. The motor is typical of that used in many appliances except that it has a torque multiplying gearbox. The motor has two windings, one (blue wires) has a higher resistance from the other (red wires). The higher resistance one is connected in series with the capacitor. The lower resistance one goes directly to 120 volts. The series circuit is then connected in parallel with the AC also. I broke the AC connection on one side to connect in the fuse, on/off switch and rheostat in series. Make sure you break the "hot" side to do this.

Note: Do not fool around with this circuit unless you are experienced in working on line powered equipment. The voltages used in this circuit could be fatal.

1) Plastic project box 2" deep by 6" long by 3" wide (Radio Shack)

2) Single pole single throw switch (Electronics supply store) I used a double pole single throw switch and soldered two poles together. It doesn't really matter what type of switch you use as long as it is rated for 120 volts and can handle 1.5 amps.

3) 25 watt, wire wound rheostat, 250 - 350 ohms would be good value, but not mandatory. The important thing is the power rating, as the rheostat needs to be able to handle the full power of the motor without excessive heating as it might melt the plastic box. (Well stocked electronics supplier or online)

4) 3 mfd 660 volts AC motor starting capacitor. (Electrical supply house)

5) Chassis mount fuse holder and 1 amp fuse. (Electrical supply house or online)

6) Solder, hookup wire, and hot melt glue and gun. (Hardware store)

7) Electric drill, screwdriver, and a soldering gun. (Hardware store)

8) Control knob (Radio Shack)

9) Electrical tape, reamer or rat tail file. (Hardware store)

10) Line cord (Electrical supply house)

Drill (2) 1/4 inch holes on top side of box, 1/2" from the bottom and at 1 1/2" and 3" from left side. These are for the motor wire and supply cord. If they aren't big enough, ream them out with a reamer or rat tail file. On opposite side drill a 1/2" hole, 1/2" up from bottom approximately 2" from left side, this is for the fuse holder. If fuse holder doesn't fit, ream out with file or reamer. On the lid of the box, drill (2) 1/4" holes for the Rheostat and on/off switch. The holes should be drilled 1 1/2" and 3" from the left side and should be in the middle of the box or 1 1/2" from either side. If these holes aren't big enough, ream them out. Making holes bigger to fit is always a better practice than drilling them too large.

Mount capacitor on the bottom of box with hot melt glue. Mount rheostat, on/off switch and fuse holder in place as shown in photos.

Do wiring as per schematic and pictures. Wrap a few layers of electrical tape around both the motor connections and power cord so as to keep the wires from slipping out of the box. After mechanically connecting wires, solder them together for strength and a good electrical connection.

Visually inspect and check all connections again, plug cord into wall and test operation. Once you are satisfied that the unit is working satisfactorily, close lid and fasten with screws provided. Once the motor is mounted on Vibraphone and attached to the motor pulley, the control box can be mounted in a location that is out of the way but accessible.