The CMRR is adjusted by the single turn potentiometer located at A1 under the single hole at the front of the signal shield. (The shield is the aluminum box on the left side of the main board). Using a small screwdriver, carefully adjust the potentiometer to minimize the 100 Hz output on the scope. Set the DISPLAY to R,Ø and the sensitivity to 5µV and minimize the R output on the Channel 1 meter.

Notch Filters

Set the reference frequency to 60.0 Hz (50.0 Hz). It is convenient to use the SYNC output of the signal generator as the reference input if it is available. Connect the sine output of the signal generator to the A input and set the input selector to A. With the SENSITIVITY at 100mV, adjust the amplitude of the input signal to 100 mV (full scale).

Set the LINE NOTCH to IN, the SENSITIVITY to 10mV, and the DYN RES to LOW. Connect the scope to the SIGNAL MONITOR output on the rear panel. Set the scope to AC coupled, 0.2V/div, 10mS/div. Trigger the scope externally using the reference input signal.

The LINE NOTCH frequency and depth are adjusted by the pair of 20 turn potentiometers located under the middle two holes in the signal shield (row 4 on the circuit board). Using a small screwdriver, carefully adjust one pot until the line output on the scope is minimized. Then adjust the other pot until the output is minimized. Iterate between the two pots until there is no further improvement. Set the SENSITIVITY to 5mV, 2mV, and 1mV, repeating the adjustments at each sensitivity.

Repeat this procedure using a reference frequency of 120.0 Hz (100.0 Hz) and the LINEX2 NOTCH filter. The LINEX2 NOTCH is adjusted by the pair of 20 turn potentiometers located under the back two holes in the signal shield (row 5 on the circuit board).

Replace the top panel.

Replacing the Front-End Transistors

Both the voltage and current front end transistors (Q101 and Q102) are 2N6485 (IMF6485) dual JFETS. These transistors are selected at the factory to meet the noise specifications.

This section outlines their replacement procedure in the event that they become damaged during use.

1)Remove the AC power cord from the unit.

2)Remove top and bottom panels.

3)Release the signal shields by removing the four screws which hold it onto the circuit board. Be careful not to lose the nuts. Carefully slide the shields back and then lift them out.

4)The input transistors are located on the main board, just behind the input selector switch. Q101 is the voltage (A, A-B) front end, and Q102 is the current (I) front end. Desolder and replace the appropriate transistor.

5)Replace the signal shields. Be careful to check that the shields do not touch any circuit board traces around their edges.

6)Replace the top and bottom panels.

7)If Q101, the voltage front end has just been replaced, the Common Mode Rejection needs to be readjusted using the procedure described in the Amplifier Adjustments section.

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SRS Labs SR530, Lock-In Amplifier manual Notch Filters, Replacing the Front-End Transistors
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SR530, Lock-In Amplifier specifications

The SRS Labs Lock-In Amplifier, model SR530, is a powerful tool designed for high-precision measurements in the realm of scientific research and industrial applications. This state-of-the-art instrument excels in extracting small signals from noisy environments, making it an invaluable asset for experiments in fields such as physics, engineering, and materials science.

One of the main features of the SR530 is its ability to perform synchronous detection, which is key to improving signal-to-noise ratios. By utilizing a reference signal, the device correlates the incoming signal with the reference to effectively filter out noise, allowing for the accurate measurement of weak signals that might otherwise be obscured. This process of phase-sensitive detection is fundamental to the operation of the Lock-In Amplifier.

The SR530 offers a wide frequency range, covering from 0.1 Hz to 100 kHz. This broad frequency response allows it to handle a diverse array of signals, making it suitable for various applications including optical detection, capacitance measurements, and in many cases, voltammetry. The device is also equipped with multiple inputs and outputs, facilitating the integration with other laboratory equipment and enabling complex experimental setups.

Precision is further enhanced with its adjustable time constant, which allows users to optimize the response time based on experimental needs. The user can choose time constants from 10 microseconds to 10 seconds, accommodating fast dynamic measurements as well as those requiring stability over longer durations.

Another remarkable characteristic of the SR530 is its digital processing capabilities. The device features a highly accurate digital voltage measurement system, minimizing drift and ensuring long-term stability. Additionally, the use of microprocessors enhances data handling and allows for features such as programmable settings, facilitating automated measurements.

Moreover, the SR530 includes a range of output options, including analog outputs, which can be used for direct signal processing, as well as digital interfaces for integration with computers. This ensures that users can not only capture high-fidelity data but also analyze and display it efficiently.

In conclusion, the SRS Labs SR530 Lock-In Amplifier stands out due to its sophisticated technology, versatile features, and robust performance. Its precision, flexibility, and ease of use make it an ideal choice for researchers and engineers looking to unlock the potential of weak signal measurement in complex environments.
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