Matt circuit

We published a design for a stereo microphone preamplifier with balanced inputs and a phantom power supply. The heart of this circuit was a special Analog Devices IC, the SSM2017. Unfortunately, this IC has been discontinued. In its place, the company recommends using the pin-compatible AMP02 from its current product line. However, and again unfortunately, the specifications of this opamp make it considerably less suitable for use as a microphone amplifier. By contrast, Texas Instruments (in their Burr Brown product line) offer an integrated instrumentation amplifier (type 1NA217) that has better specifications for this purpose. Incidentally, this IC is also recommended as a replacement for the SSM2017. It features internal current feedback, which ensures low distortion (THD + noise is 0.004 % at a gain of 100), low input-stage noise (1.3 nV/√Hz) and wide bandwidth (800 kHz at a gain of 100). The supply voltage range is ±4.5 V to ±18 V. The maximum current consumption of the 1NA217 is ±1...

This add-on board is designed to provide a pair of balanced audio outputs for the High-Quality Stereo DAC (Digital to Analog Converter). Two 3-pin male XLR connectors are used for the new outputs and they can either replace or augment the existing unbalanced outputs without affecting their performance. Balanced audio is used in recording studios and on stage because of its improved noise immunity. Picture of the project:      This is due to the fact that the signal is sent differentially (ie, as two signals 180° out of phase) and then converted to a single-ended voltage signal at the far end. If any noise is picked up in the cable, it affects the two out-of-phase signals equally so that when the signals are subsequently subtracted, most of the noise is eliminated. Parts layout: In addition, the DAC’s performance at the balanced outputs generally exceeds that of the unbalanced outputs, although only by a small margin. The signal-to-noise ratio, frequency response and chann...