Audio Amplifier Fault Found With a Square Wave

Audio amplifier fault diagnosis does not always require a long measurement session or elaborate test setup. In this short Elektor TV excerpt, Roberto Armani demonstrates a quick bench test that shows why a square wave can be more revealing than a sine wave when checking an amplifier. On the oscilloscope, the sine-wave result appears acceptable, but the square-wave response immediately points to trouble. In this case, the culprit is a faulty loudness switch that alters the amplifier’s frequency response in a way that is much easier to spot with a waveform rich in harmonics.

Audio Amplifier Fault Diagnosis on the Bench

The value of this kind of test is that it gets straight to behavior, not marketing claims or wishful thinking. A square wave contains a broad spread of harmonic content, so it can expose bandwidth limitations, overshoot, rounding, tilt, and other response issues that may stay hidden during a simple sine-wave check. That is why square-wave testing remains such a handy shortcut when you want a quick read on what an amplifier stage is really doing. See the clip here:

In Armani’s demonstration, the waveform makes the problem visible almost immediately. Rather than chasing vague symptoms by ear, he uses the oscilloscope to show that one switch in the signal path is changing the response enough to betray the fault. It is a good example of how audio amplifier fault diagnosis often becomes much easier when you stop treating audio as something mysterious and instead look at the signal as an electrical system with a shape, timing, and spectral content.

Why the Square Wave Still Matters

For students, makers, and repair-minded engineers, this clip is also a reminder that classic techniques have not become obsolete just because modern instruments have prettier screens. A square-wave test is fast, direct, and informative. It can tell you a lot about coupling networks, switching contacts, tone-control stages, and general stability without turning the job into a week-long forensic drama.

If you want more context, Elektor has already covered Roberto Armani’s broader amplifier-testing session in an earlier article on oscilloscope-based audio checks. This new clip works well as a focused example of the same idea: sometimes one waveform is enough to catch a fault that a more polite test signal lets slip by.

That is the appeal here. Audio amplifier fault diagnosis sounds grand, but in practice it can begin with a square wave, a scope, and somebody experienced enough to know when the trace is quietly telling on the circuit.