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SM5 Signal Mixer

SM5 Overview

The SM5 is a three-channel signal mixer. The relative contribution of the three inputs to the final output can be adjusted using a variable gain for two of the inputs. In addition, the signal on the two adjustable channels can be inverted before addition. The input signal range is ±10 V for each channel, with the additional caveat that the amplified signal for each channel may not exceed ±10 V without clipping. The range for the summed output is ±10 V.


The SM5 Signal Mixer is powered via the System 3 zBus (ZB1PS). No PC interface is required.

SM5 Features

The SM5 Signal Mixer is a three-channel weighted summer with variable input weighting and channel inverting.


Three signals input channels (A, B, and C), with a range up to ±10 V peak, are accessed through front panel BNC connectors. Input channels A and B are multiplied by a weighted, signed constant, K, before being added to the final output. The weighting range for these two channels is adjustable from -20 dB to +20 dB (i.e. |K| = 0.1 to 10) using a GAIN knob on the front panel. The sign of K for channels A and B can also be selected using front panel toggle switches, labeled INV-A and INV-B.

If an input is not being used, it should be grounded by attaching a shorted BNC cable. This will prevent unwanted noise from being added to the output.


The variable weighting provides a great deal of flexibility in input and output signals. However, care should be taken to avoid clipping any signal component. The SM5 output signal = (Ka*A) + (Kb*B) + C is limited to ±10 V peak. In addition, the raw inputs, A, B, and C, as well as the weighted inputs, Ka*A, and Kb*B, are limited to ±10 V peak.

SM5 Technical Specifications

Input Signal Range ±10 V peak
Weighting Range -20.0 to +20.0 dB
Max Output ±10 V
Spectral Variation <0.1 dB from 10 Hz to 200 kHz
S/N (typical) 111 dB (20 Hz to 80 kHz)
THD <0.002% (1 kHz tone ±7 V peak)
Noise Floor 19 uVrms
Output Impedance 20 Ohm
Input Impedance 10 kOhm
Inversion Channels A & B

SM5 Frequency Response

SM5 Total Harmonic Distortion