DC OUTPUTS and SCALING

The SR850 has X and Y outputs on the rear panel and Channel 1 and 2 (CH1 and CH2) outputs on the front panel.

X and Y

The X and Y rear panel outputs are the outputs from the two phase sensitive detectors with low pass filtering, offset and expand. These outputs are the traditional outputs of an analog lock-in. The X and Y outputs have an output bandwidth of 100 kHz.

CH1 and CH2

The two front panel outputs can be configured to output voltages proportional to X, Y, R, θ, or Traces 1-4.

If the outputs are set to X or Y, these outputs duplicate the rear panel outputs.

If they are set to R or θ the output voltages are proportional to the calculated values of R and θ. These calculations are performed at a rate of 512 Hz and the R and θ outputs are updated at the 512 Hz rate.

If the outputs are proportional to a data trace, then the output is also updated at 512 Hz. The traces are defined in the TRACE menu as A•B/C where A,B,C can be X, Y, R, θ, Xnoise, Ynoise, Rnoise, Frequency, Aux Inputs 1-4, or unity (C may also be any quantity squared). If a trace is defined as simply X, this trace, when output through CH1 or CH2, will only update at 512 Hz. It is better in this case to set CH1 to output X directly, rather than the trace defined as X. The output scale of a data trace is discussed later in this section.

X, Y, R and Output scales

The sensitivity of the lock-in is the rms amplitude of an input sine (at the reference frequency) which results in a full scale DC output. Traditionally, full scale means 10 VDC at the X, Y or R BNC output. The overall gain (input to output) of the amplifier is then 10 V/sensitivity. This gain is distributed between AC gain before the PSD and DC gain fol- lowing the PSD. Changing the dynamic reserve at a given sensitivity changes the gain distribution while keeping the overall gain constant.

The SR850 considers 10 V to be full scale for any

SR850 Basics

output proportional to simply X, Y or R. This is the output scale for the X and Y rear panel outputs as well as the CH1 and CH2 outputs when configured to output X, Y or R. When the CH1 or CH2 outputs are proportional to a data trace which is simply defined as X, Y or R, the output scale is also 10 V full scale.

Lock-in amplifiers are designed to measure the RMS value of the AC input signal. All sensitivities and X, Y and R outputs and displays are RMS values.

Phase is a quantity which ranges from -180° to +180° regardless of the sensitivity. When the CH1 or CH2 outputs a voltage proportional to θ, the output scale is 18°/Volt or 180°=10V.

X, Y and R Output Offset and Expand

The SR850 has the ability to offset the X, Y and R outputs. This is useful when measuring deviations in the signal around some nominal value. The offset can be set so that the output is offset to zero. Changes in the output can then be read directly from the display or output voltages. The offset is specified as a percentage of full scale and the percentage does not change when the sensi- tivity is changed. Offsets up to ±105% can be programmed.

The X, Y and R outputs may also be expanded. This simply takes the output (minus its offset) and multiplies by an expansion factor. Thus, a signal which is only 10% of full scale can be expanded to provide 10 V of output rather than only 1 V. The normal use for expand is to expand the measure- ment resolution around some value which is not zero. For example, suppose a signal has a nomi- nal value of 0.9 mV and we want to measure small deviations, say 10 µV or so, in the signal. The sen- sitivity of the lock-in needs to be 1 mV to accom- modate the nominal signal. If the offset is set so to 90% of full scale, then the nominal 0.9 mV signal will result in a zero output. The 10 µV deviations in the signal only provide 100 mV of DC output. If the output is expanded by 10, these small deviations are magnified by 10 and provide outputs of 1 VDC.

The SR850 can expand the output by a factor from 1 to 256 provided the expanded output does not exceed full scale. In the above example, the 10 µV

3-13

Page 66 Page 68
Page 67
Image 67
SRS Labs SR850 manual DC Outputs and Scaling, CH1 and CH2, R and Output scales, R Output Offset and Expand
Page 66 Page 68

SR850 specifications

The SRS Labs SR850 is a high-performance audio processor designed to enhance the listening experience across a variety of applications. With its advanced technologies, the SR850 delivers superior sound quality that is particularly noticeable in environments where audio clarity and fidelity are paramount. This device caters to audio professionals, audiophiles, and casual listeners who demand exceptional performance from their audio systems.

One of the standout features of the SR850 is its proprietary SRS 3D Audio technology. This innovative feature creates a more immersive soundstage, allowing users to experience audio as if they were in a live performance setting. By adding depth and dimension, it elevates the listening experience, making music, movies, and games far more engaging.

Additionally, the SR850 incorporates SRS dialog clarity technology, which enhances speech intelligibility in dialogues and vocals. This is particularly beneficial in film and television viewing, where dialogue can sometimes be drowned out by background music or sound effects. With dialog clarity, users can enjoy crystal-clear conversation tracks without adjusting volume levels continuously.

The device also supports various audio formats, ensuring compatibility with a broad range of media. It boasts inputs for both digital and analog sources, allowing connections to various devices such as TVs, laptops, gaming consoles, and more. The versatility of inputs makes the SR850 a convenient addition to any home entertainment system.

Another impressive characteristic of the SR850 is its compact and user-friendly design. The intuitive interface makes it easy for users to adjust settings to their preference, whether they are a novice or an audio expert. The device is equipped with programmable presets, enabling users to store their favorite sound profiles, making switching between settings quick and hassle-free.

Furthermore, the SR850 features advanced EQ capabilities, granting users the ability to tailor the audio output to their specific tastes. This personalized approach to sound adjustment enhances the overall experience, allowing users to get the most out of their audio content.

In summary, the SRS Labs SR850 is a sophisticated audio processor packed with features designed to significantly uplift sound quality and listening pleasure. With its cutting-edge technologies such as SRS 3D Audio and dialog clarity, an array of connectivity options, and customizable EQ settings, the SR850 stands out as an outstanding option for anyone looking to enhance their audio experience. Whether for professional use in sound engineering or personal enjoyment in home entertainment, the SR850 proves to be a valuable asset.
Top Page Image Contents