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SRS SR865A DSP Lock-in Amplifier

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  • FFT Display
  • Trend graphs
  • Large numeric readout
  • SR865A iOS app
  • Strip chart recording
  • SRS SR865A DSP Lock-in Amplifier
  • SRS SR865A DSP Lock-in Amplifier
  • SRS SR865A DSP Lock-in Amplifier

SRS SR865A DSP Lock-in Amplifier, 4MHz

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Availability: In stock

Excl. VAT: £8,126.00 Incl. VAT: £9,751.20
Product Code: 55449
Manufacturer: Stanford Research Systems

  • 1 mHz to 4 MHz

  • Low noise voltage and current inputs

  • 1 µs to 30 ks time constants

  • High bandwidth outputs

  • Touchscreen data display - large numeric results, chart recordings, & FFT displays

  • 10 MHz timebase input and output

  • GPIB, RS-232, Ethernet and USB

  • HDMI video output

The new 4MHz SR865A Lock-in Amplifier is the latest in a line of innovative lock-ins from SRS. With unparalleled analogue performance, sophisticated new digital signal processing features, a modern, intuitive user interface, and a wide range of computer connectivity options, the SR865A is the ideal choice for any synchronous detection application.

With over 30 years design experience, SRS optimize each detail from a toroidal transformer that eliminates switch-mode noise, iOS mobile connectivity, to advanced DSP filters that eliminate more noise while speeding up your experiment, the SR865A is truly the ultimate lock-in amplifier.

Signal Inputs

Lock-in performance starts at the front end. The SR865A offers both state-of-the art voltage and current input amplifiers. The voltage input is a switchable single-ended/differential JFET-pair amplifier with 2.5nV/√Hz of noise at 1 kHz and under 10nV/√Hz of noise at 10Hz. The voltage input has a 10MΩ input impedance and can be AC or DC coupled. Input connector shields can be connected to the instrument ground through a user selectable 10Ω (Ground) or 10kΩ (Float) resistor.

The SR865A’s built-in current amplifier represents a significant improvement over previous designs. The current input range is selectable from 1μA or 10nA. The 1μA range has 400 kHz of bandwidth and 130 fA/√Hz of noise, while the 10nA range offers 2 kHz of bandwidth and 13 fA/√Hz of noise.

While the built in voltage and current amplifiers are suitable for most applications, the SR865A is also compatible with the complete range of specialized pre-amplifiers offered by SRS.

Sensitivity and Input Range

As with previous instruments, the Sensitivity setting of the SR865A is the voltage (or current) which produces a full scale output. But unlike previous designs, the input range of the SR865A can be set from the front panel without having to consult a confusing “dynamic reserve” equation. Simply choose the sensitivity required by your experiment and then select the smallest input range that doesn’t overload.

The SR865A’s effective dynamic reserve is simply the ratio of these two settings. E.g. a 10nV sensitivity setting and a 300mV input range the effective dynamic reserve of the SR865A is 3 × 107, or nearly 150 dB.

Output Time Constants and Filtering

The SR865A offers traditional RC-response output time constants from 1µs to 30ks with rolloffs of 6, 12, 18, and 24dB/oct. In addition, advanced digital filters can significantly reduce measurement time. Synchronous filtering may be selected at reference frequencies below 4 kHz.

Reference Channel

The SR865A has a specified reference frequency range of 1mHz to 4MHz. Detection can be done at the fundamental of the reference frequency, or at up to the 99th harmonic. Several reference modes are available: Internal Mode, External mode, Dual Mode or Chop mode.

Sine Output

The SR865A offers a precision sine wave output which can be set with 6 digits of frequency resolution and from 1nV to 2V. The SR865A output is unique in that it can be configured as a single-ended or differential (balanced) signal. A DC offset of up to ±5 V can be applied to the sine output.


Rear-panel 10 MHz inputs and outputs are provided allowing the SR865A to be locked to an external frequency reference (such as the FS725 10 MHz Rubidium Frequency Standard).

FFT Displays
Lock-in amplifiers are traditionally time-domain instruments but sometimes it’s easier to understand in the frequency domain. An FFT display shows the spectrum of the input signal, the post-mixer signal, or the spectrum of the signal after the time-constant filters.

Front-Panel Touchscreen Display

The centre of the SR865A’s front panel is a colour 640 × 480 touchscreen which can display up to 4 channels of data. Each data channel can be configured to display X, Y, R, Θ, Aux In (1-4), Aux Out (1-2), X noise, Y noise, Sine Amplitude, Sine Out DC Level, Reference Phase, or Reference Frequency. The screen can be set up to show the data channels as large numbers or as a “strip-chart” display showing a complete history of each channel with selectable time scales from 0.5 s/div to 2 days/div. The touchscreen continually displays key lock-in setup parameters such as phase, reference frequency, and sine amplitude.

All commonly used controls are controllable with dedicated front panel knobs or buttons. Infrequently accessed configuration settings, such as the TCP/IP settings and other communication settings, are accessed through menus shown on the touchscreen.

Computer Connectivity

GPIB, RS-232, USB (Test and Measurement Class) and Ethernet (VXI-11 and telnet) are fitted as standard. The SR865A hosts its own webserver allowing the instrument to be monitored and controlled remotely with just a browser. The SR865A can be controlled remotely from an iPhone. The front USB port allows data and screen-shots to a USB flash drive.

Additional Information

Signal Channel
Voltage Inputs Single-ended or differantial
Voltage input range 10mV to 1V (peak)
Current input range 1μA or 10nA (peak)
Max input 1V (peak) or 1μA (peak)
Input impedance
   Voltage input 10 MΩ + 25 pF, AC or DC coupled
   Current input 1 kΩ or 100 Ω to virtual ground
Gain accuracy ±1% (<200kHz), ±2% (to 4MHz) Signal amplitude must be less than 30% of input range
Noise (rms) 2.5nV/√Hz at 1kHz (10mV input range, typ.)
Harmonic detection –80dB (100kHz), –60 dB (>100 kHz)
CMRR 90dB to 1kHz (DC coupled),decreasing by 6dB/oct above 100kHz
Dynamic reserve >120 dB
Reference Channel
Frequency range

0.001 Hz to 4MHz (specified) 

Timebase 10MHz In/Out (phase locks the internal frequency to other SR865As)
Input impedance 1MΩ or 50Ω
Phase setting resolution 360/2³²°
Phase noise
   Int. ref

 <0.0001° rms at 1kHz  (100ms, 12 dB/oct)

   Ext. ref (typ)  

<0.001° rms at 1kHz  (100ms, 12 dB/oct)

Phase drift <0.002°/°C below 20kHz (DC coupled)
  <0.02°/°C below 200kHz
  <0.2°/°C below 4MHz
Harmonic detection Detect at N × fref  (N<99 and (N × fref)<4MHz)
Dual F reference Detect at fdual = abs(fint – fext)
Chopper reference SR86A drives SR540 Chopper (via Aux Out 4) to lock the chopper to fint
DC stability Digital output values have no drift
Time constants  1μs to 30k s
Low pass filters

Typical RC-type filters or Advanced FIR/BiQuad filters

Filter slope 6, 12, 18 or 24 dB/oct rolloff
Synchronous filter Available below 4kHz
Harmonic rejection –80 dB
Low latency output

Rear-panel BlazeX output with <2 μs delay (plus LPF rise/fall times)

Internal Oscillator  
Frequency range 0.001Hz to 4MHz (specified) 
Frequency accuracy 25 ppm + 30 μHz (with internal timebase)
External timebase 10 MHz timebase input/output (on rear panel)
Frequency resolution 6 digits or 0.1 mHz, whichever is greater
Sine Output  
Outputs Single-ended or differential
Output impedance 50Ω source
Amplitude 1 nVrms to 2 Vrms (amplitude is differential into 50 Ω loads). Output is halved when using in single-ended mode. Output is doubled when driving a high impedance load.
Amplitude resolution 3 digits or 1 nV, whichever is greater
DC offset ±5 V, differential or common mode
Offset resolution 3 digits or 0.1 mV, whichever is greater
Output limit ±6 V, sum of DC offset and peak amplitude
Amplitude stability  50 ppm/°C
Sync  Logic level sync on rear panel (via BlazeX output)
Distortion  <–80 dBc (f < 1 kHz)
Data channels  Four data channels are displayed and graphed (green, blue, yellow, orange)
Data sources Each data channel can be assigned any of these data sources: X, Y, R, θ, Aux In 1 to 4, Aux Out 1 to 2, X noise, Y noise, Sine Out Amplitude, Sine Out DC level, reference phase, or fref.
Data history All data sources are continually stored at all chart display time scales. The complete stored history of any data source can be displayed sat any time.
Offset  X, Y and R may be offset up to ±999% of the output scale
Expand X, Y and R may be expanded by ×10 or ×100
Data buffer 8 Mpoint internal data storage. Store (X), (X and Y), (R and θ), or (X, Y, R and θ) at sample rates up to 1.25 MHz. This is in addition to the data histories for the chart display.
Scanning  One of the following parameters may be scanned: fint, Sine Out Amplitude, Sine Out DC Level, Aux Out 1 or 2
Inputs and Outputs  
CH1 output   Proportional to X or R (±10V full scale thru 50Ω)
CH2 output  Proportional to X and Y (rear panel) (±10V full scale thru 50Ω)
X and Y outputs  Proportional to Y or θ (±10V full scale thru 50Ω)
BlazeX  Low latency ouput of X, ±2.5 V full scale or logic level reference sync output, either thru 50Ω
Aux outputs  4 BNC D/A outputs, ±10.5V thru 50Ω, 1mV resolution
Aux inputs 4 BNC A/D inputs, ±10.5V, 1 mV resolution, 1MΩ input
Trigger input TTL input triggers storage into the internal data buffer
Monitor output  Analog output of the signal amplifier
HDMI  Video output to external monitor or TV (640×480, 60Hz)
Timebase I/O 1 Vrms, 10 MHz clock to synchronise internal reference to other units




GPIB (IEEE-488.2), RS-232, USB and Ethernet
USB flash Front-panel slot for USB flash storage of screen shots and data
Preamp power  9-pin D connector to power SRS preamps
Power  60W, 100/120/220/240VAC, 50/60Hz
Dimensions  17”×5.25”×17” (WHD)
Weight  30 lbs.
Warranty  One year parts and labor on defects in materials and workmanship






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