Amplifiers: listen for noise, vibration and speaker behaviour

Listen to the amplifier both when idle and while playing single notes, chords and stronger transients.

Pay attention to:

• excessive hum;
• intermittent crackle;
• cabinet vibration;
• a speaker scraping or distorting abnormally;
• unstable volume;
• noise that changes when touching pots or jacks.

A high-gain amplifier may naturally be noisier than a clean channel, so always judge the behaviour in relation to the channel and settings being used.

If a problem appears only after several minutes, note it. Intermittent faults can be harder to diagnose.