Balanced Audio Preamp

Application

This circuit shows the SSM2017P used as a balanced-input microphone or line preamp that converts a small differential signal into a single-ended output.

Schematic

The balanced inputs enter from the left, the RG resistor sits beside the gain pins, REF is tied to the common return, and the output/load/probe sit on the right. The source row keeps the input references and supply returns on one shared lower bus.

Design Context

VIN+ is 15 mV and VIN- is -15 mV, giving a 30 mV differential input centered around ground. RG is 10 kOhm for a moderate preamp gain, and the 20 kOhm load represents a light line-level load.

Expected Behavior

Vout should be a single-ended amplified version of the balanced input difference, referenced to ground through REF.

Key Values

• VCC / VEE: +15 V and -15 V.
• Balanced inputs: +15 mV and -15 mV.
• RG: 10 kOhm.
• REF: tied to common return.
• RLOAD: 20 kOhm.

Suggested Experiments

• Reduce RG for more gain.
• Set both input sources to the same value to inspect common-mode rejection in the model.
• Move REF to a mid-supply reference for single-supply style output biasing.

Featured Component

U1 is the SSM2017P Audio Instrumentation Amplifier. IN+ and IN- receive the balanced signal, RG sets the preamp gain, REF defines the output reference, and OUT drives the measured load.