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The SR560 is a high-performance, low-noise preamplifier that is
ideal for a wide variety of applications including low-temperature
measurements, optical detection, and audio engineering.
Inputs
The SR560 has a differential front end with 4 nV/√Hz input
noise and an input impedance of 100 MΩ. Complete noise figure
contours are shown in the graphs below. The SR560's inputs are fully
floating (BNC shields are not connected to chassis ground). Both
the amplifier ground and the chassis ground are available on the
rear panel for flexibility in grounding the instrument. Input offset
nulling is accomplished by a front-panel potentiometer, accessible
with a small screwdriver.
In addition to the signal inputs, a rear-panel TTL blanking input
lets you quickly turn off and on the instrument's gain. This is
useful in preventing front-end overloading. The gain turns off 5
µs after the TTL level goes high, and back on again within
10 µs after the TTL signal goes low.
Outputs
Two insulated output BNC connectors provide 600 Ω and 50
Ω outputs. Both are capable of driving 10 Vpp into their respective
loads. Two rear-panel power supply outputs provide up to 200 mA
of ±12 VDC referenced to the amplifier ground. The outputs
provide clean DC power for use as a bias source.
Gain
Gains are selectable from 1 to 50,000 in a 1-2-5 sequence. An adjustable
gain feature lets you specify the gain as a percentage of any of
the fixed gain settings with 0.5 % resolution. Gain can be selectively
allocated before the filters to optimize noise performance, or after
the filters to reduce susceptibility to overloads.
Filters
The SR560 contains two first-order RC filters whose cutoff frequency
and type (HPF or LPF) can be configured from the front panel. Together,
the filters can be configured as a 6 or 12 dB/oct rolloff low-pass
or high-pass filter, or as a 6 dB/oct rolloff band-pass filter.
A filter reset button is included to shorten the overload recovery
time of the instrument when long filter time constants are being
used. Filter cutoff frequencies can be set in a 1-3-10 sequence
from 0.03 Hz to 1 MHz.
Battery Operation
Three internal, rechargeable, lead-acid batteries provide up to
15 hours of battery powered operation. An internal battery charger
automatically charges the batteries when the unit is connected to
the line. The charger senses the battery state and adjusts the charging
rate accordingly. Two rear-panel LEDs indicate the charge state
of the batteries. When the batteries become discharged, they are
automatically disconnected from the amplifier circuit to avoid battery
damage.
No Digital Noise
The microprocessor that runs the SR560 is "asleep" except
during the brief interval it takes to change the instrument's setup.
This ensures that no digital noise will contaminate low-level analog
signals.
RS-232 Interface
The RS-232 interface allows listen-only communication with the
SR560 at 9600 baud. Up to four SR560s can be controlled from a single
computer, with each SR560 being assigned a unique address. A "Listen"
command specifies which SR560 will respond to commands on the RS-232
line. All functions of the instrument (except power on) can be set
via the RS-232 interface. The RS-232 interface electronics are opto-isolated
from the amplifier circuitry to provide maximum noise immunity.
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