Handbook for Sound Engineers

858 Chapter 25

25.10 Input Amplifier Design

A console is expected to accept signals of wildly
varying input level and impedance while producing a
uniformly consistent output capable of being deposited
in the tightly defined container that is a recording track,
or similarly defined output.

Fortunately, industry standards provide at least some
clues as to what mixers are likely to have applied to
them. Nevertheless, these standards can obviously do
nothing to alter the physics of the operation of the
assorted transducers and sources in common use; the

disparity in the treatment required between a dynamic

microphone and a recorder output totally precludes a

universal input stage.

Mixer front-end design tends to be a little like

working on a grown-up jigsaw puzzle where all the

important pieces perversely refuse to fit. It’s delightful

to discover or cultivate some that fit nicely, like in

line-level input stages. This euphoria is chipped away

by the problems inherent in other areas, notably micro-

phone input stages.

Optimizing input noise performance in a dynamic

microphone preamp is quite an operation, juggling a

Figure 25-34. Matrix channel-decoding logic.

Enable

Individual

card

select

outputs

Binary

card

address

bus