Preamplifi ers and Input Signals 211masking layers can be applied. The results are seldom very satisfactory. Such a lateral
PNP device has a very poor current gain and HF performance.
In recent IC designs, considerable ingenuity has been shown in the choice of circuit
layout to avoid the need to employ such unsatisfactory components in areas where
their shortcomings would affect the end result. Substantial improvements, both in the
purity of the base materials and in diffusion technology, have allowed the inherent noise
background to be reduced to a level where it is no longer of practical concern.
7.15.2 Modern Standards
The standard of performance that is now obtainable in audio applications, from some of
the recent IC op–amps, especially at relatively low closed-loop gain levels, is frequently
of the same order as that of the best discrete component designs, but with considerable
advantages in other respects, such as cost, reliability, and small size.
This has led to their increasing acceptance as practical gain blocks, even in very high-
quality audio equipment.
When blanket criticism is made of the use of ICs in audio circuitry, it should be
remembered that the 741, which was one of the earliest of these ICs to offer a satisfactory
performance—although it is outclassed by more recent types—has been adopted with
enthusiasm, as a universal gain block, for the signal handling chains in many recording
and broadcasting studios.
This implies that the bulk of the program signals employed by the critics to judge whether
or not a discrete component circuit is better than that using an IC will already have passed
through a sizeable handful of 741-based circuit blocks, and if such ICs introduce audible
defects, then their reference source is already suspect.
It is diffi cult to stipulate the level of performance that will be adequate in a high-quality
audio installation. This arises partly because there is little agreement between engineers
and circuit designers, on the one hand, and the hi-fi fraternity, on the other hand, about
the characteristics that should be sought and partly because of the wide differences
that exist between listeners in their expectations for sound quality or their sensitivity
to distortions. These differences combine to make it a diffi cult and speculative task to
attempt either to quantify or to specify the technical components of audio quality or to
establish an acceptable minimum-quality level.