Keith L. Walker

St. Bernard, Nova Scotia

Magnetic Tuning Pickup

Abstract
Parts Required
Method
Illustrations

Figure 1

Abstract:

This is a really simple, effective, el-cheapo magnetic pickup, suitable for steel-stringed musical instruments. I invented it because my tuner was having a hard time distinguishing the sound of the string I was tuning from the harmonics of all the other strings on my hammered dulcimer.

A piezo or other contact pickup turns the instrument into a giant microphone (not a very efficient one, granted). They are sensitive to loud airborne sounds, and hear all the strings of the instrument simultaneously. A magnetic pickup, on the other hand, is sensitive only to vibrating steel at very close range.

I have successfully used this pickup to tune my instrument while it was only four feet from a speaker tower, with a very loud act on stage. I couldn't hear a darned thing, but my dulcimer was in tune.

Advantages:

It is totally, 100% immune to outside sounds. Very loud sounds may cause the string to vibrate (that's good), but it is only the string's vibrations, not the background sounds that the pickup will sense.
It provides maximum isolation from other strings on the instrument.

Disadvantages:

You have to move it from string to string as you tune.
It is not suitable for audio amplification (not unless you really want to amplify only one string)

Parts Required:

transistor radio earphone (the old mono stick-it-in-your-ear type, nothing fancy)
1/4" plug (or 1/8"-to-1/4"adapter) for tuner input
coat-hanger wire
a small piece of card (3x5 file card, heavy construction paper, etc)
epoxy
your favourite electronic tuner

Method:

Cheap earphones are usually made of two pieces of molded plastic: the part that goes in your ear, and a back molding. Pry off the part that goes in your ear and discard it.

Inside the earphone, you should find a flat metal disc, magnetically stuck to a coil and magnet. This disk is the diaphragm. Remove and discard the diaphragm.

If the coil and magnet are loose in the back molding, you will have to epoxy them in place.

Glue two small pieces of card onto the face of the pickup, as shown in Figure 2. The card is to support the weight of the pickup on the adjacent strings without having it contact the vibrating string. The thickness of the card will depend on the exact geometry of your earphone. You want the core of the magnet/coil to be about 1/16" above the string. See Figure 3.

Make a bracket to hold the pickup in place, using coat-hanger wire. The exact design of the bracket will depend on the spacing of the strings on your dulcimer. Use your ingenuity! See Figure 1 for an example.

Use a 1/8"-to-1/4" adapter to plug the pickup into your tuner. Alternatively, cut off the 1/8" plug and solder on a 1/4" plug.

Illustrations:

Figure 2

Figure 2 shows the underside of the pickup. Note the pieces of card glued onto the face of the pickup. The string being tuned goes in the gap between the two pieces of card.

Figure 3

Figure 3 shows a cross-section of the pickup. Note how the centre string of the course is free to vibrate, while the other two strings support the weight of the pickup.

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