SRS Labs SR560 manual Gain Mode, Output, Reset, Status, Operation And Controls

OPERATION AND CONTROLS

information on using filters with the amplifier in AC coupled mode.

Gain Mode

The allocation of gain throughout the instrument is set using the GAIN MODE pushbutton The Gain Mode is displayed by two indicator LED’s: HIGH DYNAMIC RESERVE and LOW NOISE. For a given gain setting, a HIGH DYNAMIC RESERVE allocates the SR560's gain toward the output stages after the filters. This prevents signals, which are attenuated by the filters from overloading the amplifier. The LOW NOISE setting allocates gain toward the front-end in order to quickly "lift" low-level (nV range) signals above the instrument's noise floor.

Gain

The instrument's gain is increased or decreased using the GAIN pushbuttons. Gain settings from 1 to 50,000 are available and are displayed as the product of a factor 1, 2 or 5 and a multiplier (none (i.e. 1), 10, 100, 1,000 or 10,000). In addition to these fifteen fixed gain settings, the user may specify arbitrary gains through the UNCAL feature. To set an uncalibrated or arbitrary gain the user must press both Gain buttons simultaneously, lighting the UNCAL LED. In this mode by pressing the Gain Up or Gain Down pushbuttons, the user may reduce the calibrated gain in roughly 1% increments from 100% down to 0% of the selected gain. In contrast to other front-panel functions, when in UNCAL the instrument's key-repeat rate will start slowly and increase to a limit as long as either Gain button is depressed. Simultaneously pressing both Gain buttons once again will restore the unit to the previously calibrated gain setting, and turn off the UNCAL LED.

Output

The outputs of the instrument are located within the OUTPUT section of the front panel. Two insulated BNCs are provided: a 600Ω output and a 50Ω output. The amplifier normally drives high impedance loads and the instrument's gain is calibrated for high impedance loads. When driving a 600Ω load via the 600Ω output (or a

50Ω load via the 50Ω output) the gain of the amplifier is reduced by two. The shields of all the front-panel BNC’s are connected together and form the amplifier's floating ground.

Reset

The OVLD LED indicates a signal overload. This condition can occur when a signal is too large or the dynamic reserve is too low. Reducing the gain, reducing the input signal and/or switching to the HIGH DYNAMIC RESERVE setting should remedy this condition. If an overload occurs with filter settings of long time constants, the RESET pushbutton will speed the SR560's recovery from overload.

Status

The ACT LED indicates communications activity over the SR560's optoisolated RS-

232 port. Please refer to Appendix A: Remote Programming for further details on programming the instrument via RS-232.

The BLANK LED indicates the optoisolated BLANKING input (on the rear panel of the SR560) is active. The SR560 responds to a blanking input by internally grounding the amplifier signal path after the front end and before the first filter stage.

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