Audio Engineering

526 Chapter 17

By defi nition the process is nonlinear, and analogue magnetic recorders have to use bias
to linearize it. Digital recorders are not concerned with the nonlinearity, and HF bias is
unnecessary.

Figure 17.1 shows the construction of a typical digital record head, which is just like an
analogue record head. A magnetic circuit carries a coil through which the record current
passes and generates fl ux. A nonmagnetic gap forces the fl ux to leave the magnetic circuit
of the head and penetrate the medium. The current through the head must be set to suit
the coercivity of the tape and is arranged to almost saturate the track. The amplitude
of the current is constant, and recording is performed by reversing the direction of the
current with respect to time. As the track passes the head, this is converted to the reversal
of the magnetic fi eld left on the tape with respect to distance. The recording is actually
made just after the trailing pole of the record head where the fl ux strength from the gap is
falling. The width of the gap is generally made quite large to ensure that the full thickness

No. 1

No. 3

No. 2

No. 4

No. 5

Gap

Pole

Ferrite body

Winding

Figure 17.1 : Typical ferrite head windings are placed on alternate sides to save space, but

parallel magnetic circuits have high cross talk.