Audio Amplifier Testing with an Oscilloscope: Roberto Armani on Square Waves and Bode Plots

In this episode of Elektor Engineering Insights, Roberto Armani demonstrates practical oscilloscope techniques for audio amplifier testing.

Objective Measurement in the Audio Lab

In the latest episode of Elektor Engineering Insights, I speak with long-time Elektor contributor and senior editor Roberto Armani about hands-on methods for analyzing audio amplifiers using an oscilloscope.
 

Rather than relying on subjective listening tests, the discussion focuses on objective, repeatable measurements that can be carried out quickly on the bench. Armani explains why visualising signals often reveals problems long before they become obvious to the ear.

Using Square Waves for Audio Amplifier Testing

Square-wave testing is used to demonstrate how bandwidth limitations, tone-control interaction, and unwanted frequency shaping can be identified rapidly. By observing edge shape, tilt, and overshoot, it becomes possible to spot low- and high-frequency issues that are difficult to detect with sine-wave testing alone.

Examples shown in the video illustrate how even small circuit faults or component tolerances can significantly affect square-wave response.

Bode Plots and Frequency Response

The episode then moves on to Bode plots generated directly on a modern digital oscilloscope. These plots make it possible to visualise frequency response across the entire audio band and to quantify gain variation, roll-off, and channel imbalance.

Armani demonstrates how this approach compares with older, more time-consuming sweep-based methods and explains when Bode plots are worth the extra setup time.

Rise Time, Bandwidth, and Real-World Audibility

Rise time measurements are used to link time-domain behaviour with frequency-domain performance. The discussion highlights how amplifier speed relates to bandwidth, and where improvements cease to have practical audible benefits.

Drawing on decades of experience in electronics servicing and editorial work, Armani also reflects on the gap between measured performance and perceived sound quality.