Noise and Grounding 389● Any wire links should be numbered to make it easier to check that they have all
been fi tted.13.1.7 Audio Printed Circuit Board Layout Sequence
PCB layout must be considered from an early stage of amplifi er design. For example,
if a front-facial layout shows the volume control immediately adjacent to a loudspeaker
routing switch, then a satisfactory cross talk performance will be diffi cult to obtain
because of the relatively high impedance of the volume control wipers. Shielding
metalwork may be required for satisfactory performance, which adds cost. In many
cases the detailed electronic design has an effect on cross talk quite independently from
physical layout.
a. Consider implications of facia layout for PCB layout.
b. Circuitry designed to minimize cross talk. At this stage, try to look ahead to
see how op-amp halves, switch sections, and so on should be allocated to keep
signals away from sensitive areas. Consider cross talk at above-PCB level; for
example, when designing a module made up of two parallel double-sided PCBs,
it is desirable to place signal circuitry on the inside faces of the boards, and power
and grounds on the outside, to minimize cross talk and maximize RF immunity.
c. Facia components (pots, switches, etc.) placed to partly defi ne available board area.
d. Other fi xed components, such as power devices, driver heat sinks, input and
output connectors, and mounting holes placed. The area left remains for the
purely electronic parts of the circuitry that do not have to align with metalwork
and so may be moved about fairly freely.
e. Detailed layout of components in each circuit block, with consideration toward
manufacturability.
f. Make effi cient use of any spare PCB area to fatten grounds and high-current
tracks as much as possible. It is not wise to fi ll in every spare corner of a
prototype board with copper as this can be time-consuming (depending on the
facilities of your PCB CAD system) and some of it will probably have to be
undone to allow modifi cations.Ground tracks should always be as thick as practicable. Copper is free.