This article is the second half in our series on the analog tape recorder, excerpted from Huber & Runstein’s book Modern Recording Techniques, Seventh Edition. For the first half, click here.

The Magnetic Tape Head
Most professional analog recorders use three magnetic tape heads, each of which performs a specialized task:

• Record
• Reproduce
• Erase.

The function of a record head (Figure 9) is to electromagnetically transform analog electrical signals into corresponding magnetic fields that can be permanently stored onto magnetic tape.

In short, the input current flows through coils of wire that are wrapped around the head’s magnetic pole pieces.

Since the theory of magnetic induction states that “whenever a current is injected into metal, a magnetic field is created within that metal” … a magnetic force is caused to flow through the coil, into the pole pieces and across the head gap.

Like electricity, magnetism flows more easily through some media than through others. The head gap between poles creates a break in the magnetic field, thereby creating a physical resistance to the magnetic “circuit.” Since the gap is in physical contact with the moving magnetic tape, the tape’s magnetic oxide offers a lower resistance path to the field than does the nonmagnetic gap.

Thus, the flux path travels from one pole piece, into the tape and to the other pole. Since the magnetic domains retain their polarity and magnetic intensity as the tape passes across the gap, the tape now has an analogous magnetic “memory”  of the recorded event.

Fig. 9: The record head.

The reproduce or playback head (Figure 10) operates in a way that’s opposite to the record head. When a recorded tape track passes across the reproduce head gap, a magnetic flux is induced into the pole pieces.

Since the theory of magnetic induction also states “whenever a magnetic field cuts across metal, a current will be set up within that metal” … an alternating current is caused to flow through the pickup coil windings, which can then be amplified and processed into a larger output signal.

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