Aphex Studio Dominator 700 - Technical Description; Input Circuit; Crossover

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
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