Amplifiers
How to test a used amplifier by checking channels, controls, noise, speakers and behaviour at different volumes.
Before powering the amplifier on, inspect everything that can be checked externally.
Verify:
- mains cable and power inlet;
- switches and accessible fuses;
- loose or damaged connectors;
- cabinet, grille and visible speakers;
- unusual burnt smell;
- signs of liquid exposure or significant impact.
Do not open the chassis for an informal test. Amplifiers, especially valve designs, can contain dangerous voltages even after being switched off. Internal inspection should be left to qualified personnel.
If anything suggests a serious electrical issue, do not continue the test.
Start at moderate volume with simple settings. Test one input and channel at a time, then work through all advertised functions.
Check:
- clean and drive channels;
- gain, EQ and master controls;
- built-in reverb or effects;
- effects loop;
- footswitch if included;
- any attenuator or power modes.
Move pots and switches slowly to detect drop-outs, noise or unusual changes.
A feature that is “never used” can still affect the amplifier’s value. If it has not been tested, make sure it is clearly described as untested.
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.