Classic Rock Amplifier Glossary

GLOSSARY

Breakup - the point at which an amplifier begins to overdrive/distort, especially when chords are struck hard.

Cabinet (Cab) - a speaker box designed to be used with an amplifier head. The 4x12 configuration is most popular, followed by the 2x12 format. A 4x12 cab is also known as a Quad Box.

Channel Switching - amps that have two or more channels that can be set up with different levels of volume/gain, and in some cases EQ. Channels are usually selected with a footswitch. The JCM 800 2210 & 2205 introduced in 1981 were the first Marshall amps to feature channel switching.

Clean - a signal free of overdrive/distortion.

Combo - an amplifier that contains the head and speaker/s built into a single, smaller cabinet. Most Fender amps are in this format.

Compression - when a tube/valve amp is turned up loud it will begin to overdrive/distort. The more overdriven the signal is, the more compressed it will be. A compressed sound is smoother and has more sustain.

Crunch - a mild overdrive sound - think AC/DC!

Distortion - is that a term that is interchangeable with overdrive, although most people will consider distortion to be more extreme than overdrive.

Headroom - the clean volume threshold of an amplifier. A high headroom room amp can be turned up very loud before it begins to overdrive, while a low headroom amp will begin to distort at lower volume levels.

Preamp Distortion - controls the level of overdrive, allowing more overdrive at quieter volumes, however, Preamp Distortion can sound fizzy at lower volumes.

Powertube Distortion - controls the overall volume, and the level of overdrive when turned up loud. Powertube distortion is 'fatter' but less overdriven than Preamp Distortion.

Master Volume - amplifiers that effectively have two volume controls, one for preamp distortion to control the level of overdrive, and a master volume to control the overall volume. The first Marshall Master Volume amps came out in 1975.

Non-master Volume - amplifiers that have only one volume control. As a result these amplifiers must be turned up very loud do achieve overdrive tones.

Overdrive - is a term that is interchangeable with distortion, although most people will consider overdrive to to be less extreme than distortion.

Pedal Platform - this term is used to describe high headroom amps with relatively 'flat' EQ sections. Effects pedals can be used with these amps with minimal 'colourisation'.

Reverb - is an effect designed to emulate the experience of playing in a large space. Many Fender and Vox amps have this effect built in, and have done so since the 60's. Marshall began adding this effect to their amps in the early 80's.

Single Channel - an amp with one channel.

Solid State - an amplifier that uses transistors rather than valves/tubes, such as the Roland JC-120.

Speaker Configuration - the size and number of speakers in the combo or cabinet. 4x12 means four 12 inch speakers, 2x12 means two 12 inch speakers, 4x10 mean four 10 inch speakers, etc.

Speaker Efficiency - is a measurement of how effectively a speaker handles a signal. A 25w speaker with a Speaker Efficiency rating of 97db will sound louder than a 25w speaker with a Speaker Efficiency rating of 90db.

Stack - a combination of amplifier head and separate speaker cabinet, typified by Marshall amps. A half stack is a head sitting on a 4x12 cab or quad box. A Full stack is a head sitting on top of two 4x12 cabs (quad boxes).

Tube - a vacuum tube. In America it will be simply called a Tube, while in the UK it will be referred to as a Valve.

Transistor - a type of amplifier built without valves/tubes, such as the Roland JC-120. The terms Solid State and Transistor are relatively interchangeable.

Transformer - this is the final connection in your tube amplifier that takes the signal from the tubes and transforms them into impedances and power suitable for your speakers.

Tremolo - a pulsing modulation effect built into many Fender and Vox amplifiers.

Valve - the British name for a vacuum tube.

Wattage - the power or potential volume of an amp. A 100w amp is about 3db louder than a 50w amp. A 50w amp is about 3db louder than a 25w amp.

A 100w amp is perceived as double the volume of a 10w amp.

High wattage amps will have much higher headroom before they overdrive, and will often be perceived as having more bass. In fact, I find that as I turn an amp up louder, I need to compensate by reducing the bass.

Some guitarists prefer 50w amps over 100w amps as they can get them to 'overdrive earlier', meaning that the amp sounds overdriven at a reduced volume compared to a higher wattage amp. I read an interview once that said Angus Young of AC/DC was at the time using 100w Marshall Amps for his rhythm sound, and 50w Marshalls for his lead sound.