SR 560 Low Noise Preamplifier

The SR 560 is a high-performance, low-noise preamplifier suitable for a variety of applications, including cryogenic measurements, optical detection, and audio engineering.

Input

The SR 560 features a differential front end with 4 nV/√Hz input noise and an input impedance of 100 MΩ. Complete noise figure profile. The inputs of the SR 560 are fully floating (BNC shields are not connected to chassis ground). Both amplifier ground and chassis ground are available on the rear panel for flexible grounding of the instrument. Input bias nulling is accomplished via a front panel potentiometer, which can be adjusted with a small screwdriver.

In addition to the signal input, a rear panel TTL blanking input allows you to quickly turn the instrument's gain off and on. This is useful for preventing front-end overload. The gain is turned off for 5 seconds when the TTL level is high and recovers within 10 seconds after the TTL signal is lowered.

Output

Two isolated 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 amplifier ground. The outputs supply clean DC power for use as bias sources.

Gain

Gain can range from 1 to 50,000 in 1-2-5 steps. The adjustable gain feature allows you to specify the gain as a percentage of any fixed gain setting (with 0.5% resolution). Gain can be selectively allocated before the filter to optimize noise performance or after the filter to reduce susceptibility to overload.

Filters

The SR 560 includes two first-order RC filters whose cutoff frequencies and types (HPF or LPF) can be configured from the front panel. These filters can be configured as 6 or 12 dB/oct low-pass or high-pass filters, or as 6 dB/oct roll-off bandpass filters. When using long filter time constants, a filter reset button is included to shorten the instrument's overload recovery time. 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. When the unit is connected to line power, the internal battery charger automatically charges the batteries. The charger senses battery status and adjusts the charging rate accordingly. Two rear panel LEDs indicate the battery's charge status. When the batteries are discharged, they are automatically disconnected from the amplifier circuit to prevent battery damage.

No Digital Noise

The microprocessor operating the SR 560 is in "sleep" mode except when changing the instrument's settings for a short period. This ensures that no digital noise contaminates low-level analog signals.

RS-232 Interface

The RS-232 interface allows listen-only communication with the SR 560 at 9600 baud. Up to four SR 560 units can be controlled from a single computer, with each SR 560 assigned a unique address. The "listen" command specifies which SR 560 will respond to commands on the RS-232 line. All functions of the instrument (except power) can be set via the RS-232 interface. The RS-232 interface electronics are isolated from the amplifier circuitry to provide maximum noise immunity.