History:
The development of Microphone Pre-Amplifiers that were used in recording consoles
before 1970 all used discrete configurations that in many ways were derived from the
tube circuits previously used. In fact the introduction of silicon low noise transistors did
not begin until around 1968. The germanium transistors previously used were not that
quiet and had to be carefully selected to obtain good performance.
The semiconductor industry was changing very quickly back then and had been driven
forwards to a large extent by the USA and the demands of the NASA Space Programs
and the Apollo Program to “Land a Man on the Moon”. Integrated circuits had not yet
been commercially released and any previous operational amplifiers relied on discrete
and hybrid construction. The manufacture of ICs requires a very pure silicon wafer which
as a secondary spin off made low noise discrete devices with both PNP and NPN types
available for the first time. Footprint and line width reduced dramatically to enable all the
circuit components to be shrunk and fitted on the ever decreasing die size used in
making ICs. It soon became apparent that this small die size came with several
important performance limitations with regards to stability, power dissipation and high
frequency phase performance. Also the need for dual complimentary tracking power
supply rails. The almost universal adoption of long tailed pair input stages in the IC also
became popular with this new manufacturing technology and is very beneficial if you are
using the ICs for instrumentation and scientific applications. This input stage
configuration however does not produce the optimum audio performance for ultimate
audio quality. ICs were much cheaper than the discrete equivalent circuit and were used
in commercial consumer products with the marketing people using their skill to
manipulate public perception of this new technology much in the same way as the word
Digital is nowadays used to imply quality when in actual fact the resulting audio quality
produced is inferior to the Analogue information it is derived from.
The top recording studios however in the early 1970’s mostly built their own custom
recording consoles using discrete methods and can be thought of in the same way as F1
Racing Car Manufacturers who are interested in obtaining a technological advantage by
developing and setting new performance standards. The recordings produced by those
top world studios featured on so many famous legendary artist’s albums are considered
today the Benchmark and Holy Grail of Recordings eg: Jimi Hendrix - Axis Bold as Love
(Olympic Studios - London), Stevie Wonder: Innervisions, Music of My Mind (Electric
Lady Studio, Record Plant - New York), Rolling Stones, Jumpin Jack Flash etc. (Olympic
Studios - London).
The concept of the most accurate and direct possible path from microphone to the
recorder was always followed in the quest for ultimate quality.
Using up to a 17 ICs in a chain found in some of today’s recording signal paths of
course degrades the signal as all op-amps will never perform up to their theoretical
performance and their errors all add up. This becomes ever apparent when making a
comparison to a direct path approach design
