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9.0
TECHNICAL DESCRIPTION
Since
the
studio
Dominator
is
basically
stereo system, many circuits are identical in the
channels.
Therefore,
component
designations
descriptions
of
these circuits
will
be taken
channel only for simplicity.
9.1 INPUT CIRCUIT
a symmetrical
left and right
used
in
the
from
the left
A unique precision instrumentation topology is incorporated
which employs
a common
mode signal
cancelling servo.
Due to
common
mode
cancelling by
the servo
at
the input
(prior to
signal amplification), common mode signal distortion
mechanisms
which
exist
in
conventional
balanced
input
circuits
are
eliminated.
The
instrumentation
amplifier
operates
on
the
same
principles as the well known classical circuit, except where the
common mode servo is concerned.
Therefore, only the servo
will
be described.
The outputs of buffers
UIOIA and UIOIB are
normally equal
and out of phase for differential mode input signals
.
Rloa
and
RI09 sum
these signals
into inverting
gain stage
UI02B.
Any
output
signal
from
UI02B
represents
amplified
common
mode
information out
of phase
with the
common mode
signal at
the
buffer inputs.
The signal
from UI02B is summed
passively with
the input
signals through
RI02
and
RI03
to
cancel the common
mode
signals
at
the
input buffers.
The
operation
of this
circuit
may
alternately be
described as
a servo
stage which
monitors
the
difference between
zero
volts and
the detected
common mode signal, then outputs a correction signal to null the
common
mode
signal
at
the
input
to
the
instrumentation
amplifier.
9.2
CROSSOVER
Three
frequency
bands
are
generated
by
the
crossover
circuit composed of U508, U509, U5l0, and associated components.
The high and low
band generators are essentially
passive first
order highpass
and lowpass
filters buffered
by output voltage
followers U510, and USD8, respectively.
The mid band generator,
U509, is a
differencing amplifier which
subtracts the low
and
high
band
information from
the total
input signal.
In this
manner, three
phas~-matched
frequency bands are
produced which
can be directly added to perfectly reproduce the input signal.
Tuning
the
crossover frequencies
switching
of
timing
components.
Low
is accomplished
by FET
crossover
tuning
is
29
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