Amp Classification - What's the difference?
We often get asked questions regarding tube amp 'classification'. Is Class A superior to Class B? What are the differences? Here are a few simple tips to help demistify the wonderful world of tubes!
Amp Classification The 'Class' rating system for amplifiers refers to when each system was invented (Class A being the oldest).
Class A
- Runs hottest - like controlling a cars speed with the brakes, Class A amps run at full power constantly and thus will wear cause the most amount of wear on the power tubes.
- Least efficient use of power
- Sounds warm, smooth & natural even when pushed to clipping
- The oldest, simplest and most traditional way to wire a tube amplifier
Class B
- Uses two transistors to amplify the signal.
- Runs fairly 'cool' - when not being pushed, very little wear is being put on the tubes
- Very efficient use of power
- Produces 'objectional crossover' distortion
Class AB
- Comprises elements of both the Class A and Class B amplifier
- More efficient use of power
- Produces some distortion but not 'high gain' from power amp stage
- Produce a tight, firm and 'punchy' sound
- More power and greater volume capabilities
- Many of the most influential and premium tube amps run a Class AB design (Fender '59 Bassman, Ulbrick Arena 50)
Class C
- Not used for audio
Class D (solid state)
- New technology that uses width modulation to amplify the signal
- Extremely efficient - are quite small in size and produce high output
- Runs very cool
- Heatsinks are much smaller, enabling a smaller, lighter and cooler amp
- Used in Fender Passports, Bass amplification and other lightweight devices