BENEFITS
- No color, resulting in extremely high
resolution and tonal purity
- Combines wide dynamic range with wide bandwidth
and both over the entire gain range, not just a "sweet spot"
- High compliance input/output - high
performance with a wide variety of input sources and output loads
- Robust design and build
HIGHLIGHTS
- True variable gain - no
excess gain, no attenuators, no loop feedback
- Output load compensation
for low distortion output into any load
FEATURES
- Overload-proof input clips
after the output and without pads
- Separate gain control with peak
indicator, mute, and phase invert
- Remote control eliminates cable losses and
interference by locating the preamplifier near the microphone or
instrument
- Low noise, high gain (and short mic
cables with remote) for optimal performance with ribbon
microphones
Signal path
-
Balanced,
high-impedance input thru parallel 1/4" and XLR connectors with switchable input impedance
accepts mic, line or DI sources
-
Two megohm input impedance
eliminates current-related losses and load distortion in mics
- Balanced, symmetrical, discrete topology from input to output
– no transformers, no op amps
- FET gain and direct-coupled output
stages with auto-bias
- Select point-to-point wiring
- Non-magnetic enclosure
- Extremely high input-output Z ratio
for other applications including phono preamp, headphone amp, and
line/buffer amp
Support functions
- Local, discrete voltage regulation for each
channel
- Standby mute function enabled during power-up
sequence, low line, and phantom on/off
- Status indicator shows operation of
gain control, output stage, and standby mute
- Shielded internal primary supply with low
leakage current and extremely low noise
Mechanical
- No steel – rugged, anodized aluminum
enclosure and stainless steel fastening hardware
- Removable rack kit and optional outriggers
for
freestanding applications
- Gold-plated
contacts and active retention in all internal connectors
- Fully enclosed, gold-plated contacts
in panel switches and relays
- Low-profile buttons and solid aluminum knobs
with two set screws on ¼" metal shafts – no toggle switch
bats, plastic knobs or terminal strips to break
- Protected panel graphics are printed on the back of clear
overlays
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A standard XLR cable links the GC34 gain
control (top) to the Model 4 single-channel preamp (center) or Model 5
dual-channel preamp (bottom). The Model 4 also includes onboard controls.
SOFT SIGNAL PATH
Preamplifier design concepts have
not changed much since the advent of electronic amplification. Fixed
elements (gain and buffer stages) and variable elements (attenuators or
feedback) are arranged in a fixed signal path. Signal is amplified far
more than is required, attenuated to the desired level, and buffered at
the output with little regard for the load.
Gordon Instruments has developed
a "soft signal path" concept where each stage and the path
itself are variable, optimized automatically for the selected gain and the
output load. This innovation has been incorporated into the Gordon
Microphone Preamplifier System along with high-resolution analog design,
component, and assembly technologies, forming a very powerful sonic
combination.
TRUE VARIABLE GAIN
The primary source of distortion
in any preamplifier is gain. In conventional microphone preamps, the gain
in the signal path (or open-loop gain) is fixed, equal to the maximum
setting of the gain control(s) plus make-up gain for loop feedback,
filters, etc (op amps typically have over 100dB of gain to allow for
feedback). Because the gain is fixed, gain control is actually performed
by variable attenuators or by variable loop feedback. As a result, the audio
input signal is amplified by large amounts of fixed gain only to be cut
back down to the level desired at the output.
In the Gordon mic preamplifier, the
gain in the signal path is variable, equal to the actual setting of
the gain control, with no loop feedback, no attenuators, nor the associated
redundant gain. In addition to gain, dynamic range and distortion are also
optimized for each control setting. The audio signal at the input is
amplified only by gain equal to and optimized for the gain control
setting, significantly improving every aspect of sonic and measured
performance.
OUTPUT LOAD COMPENSATION
Outboard microphone preamp
outputs see a wide range of loads due to signal frequency, cables,
transformer inputs, and electronic inputs, varying from less than a
hundred to over a million ohms. Distortion varies with load and can be
minimized for a particular load by setting the operating parameters of the
typical output stage. Change the load, however, and distortion
increases.
Automated output load
compensation in the Gordon mic preamp couples an output load sensing
circuit to a variable-parameter output stage. The output signal is
monitored to determine the load while the output stage parameters are
adjusted accordingly to minimize distortion.
Extensive support circuitry optimizes a minimalist
signal path. Symmetrical layout helps ensure matching channel
characteristics and extremely low noise and crosstalk.
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