Tube Pre-Amp Audio Amplifiers
Sitting between the source and the amplifier, the preamp provides a clean signal boost so that the amplifier can handle the signal more easily. The two main uses for tube preamplifiers are for instruments like guitars and for turntables in home theatre systems. While some valve preamps are separate from the main amplifier, others part of the amp for convenience. There is no wrong way to do it; there are just different designs to meet different requirements.
Why a Pre-Amp?
The reason for using a vacuum tube preamp is simple. Any audio amplifier can only boost a signal so far without clipping. Clipping is a form of distortion you get when an amplifier reaches its limits so that any further amplification just adds noise. This can be a problem with amplifying very weak signals. Using a preamp gets around this problem by amplifying the signal to the point where a second amplifier can take over and boost the signal to the point where it can drive speakers.
Why Should You Choose Tubes Over Solid State?
The biggest question in the world of amplification is whether to use tubes or go with a solid-state preamp. Each choice has its own set of advantages and tradeoffs and the one that you choose depends on which one you value most:
- Cost: Solid-state preamps are usually less expensive to buy and maintain than tube preamps.
- Power: Tube preamps need much higher DC currents to drive the tubes than solid state, so they pull a lot more power from the mains.
- Sound: Tube preamps are much friendlier when driven hard. They produce warm harmonic distortion, which many people find more pleasing.
In the end, it all comes down to you, but for many musicians the sound outweighs every other factor.
Electric guitars naturally generate very faint signals. By putting a mic preamp directly behind the pickups you can take that signal and boost it so that it reaches the same level as other instruments. This is very useful for mixing different tracks when recording, as you want to be able to balance each instrument. Using tubes gives the warm tone that many players swear by.
One of the most common uses of stereo tube preamps in home Hi-Fi systems is to increase the signal from a phonograph needle. Like a guitar string its vibrations are naturally very quiet, which is why early record players had those huge trumpets. Using a preamp ensures that the amplified signal is both cleaner and stronger than it would be otherwise. It reduces noise and many include an equaliser to ensure the sound that reaches your speakers brings out the best in the music.