Preamplifier vs Amplifier (What’s the Difference?)

A preamplifier (preamp) is a device that converts a weak electrical signal into a noise-tolerant audible output signal, while an amplifier (power amp) is a device that can increase the power of the output level of any signal, albeit with some added noise.

Both devices use voltage to increase the power of sound signals, but they do it differently and have distinct functions. While preamps are generally used to boost the level of microphone recordings without significantly increasing its noise floor, power amps are used to boost sounds that are already audible, like electric guitars and speakers. In doing so, they can add a noticeable amount of noise to such sounds.

What’s the exact difference between preamps and power amps?

Preamps are necessary for powering quiet sounds without increasing their noise floor, whereas power amps are necessary for powering sounds that are too loud to be processed by a preamp. Both are used to convert small signals into bigger signals, but what is it exactly that makes them different?

In technical terms, it all has to do with the impedance level. Defined as the opposition to current flow, impedance is used to hold back (i.e., impede) the level of noise and power of an output signal. High impedance means less power and more noise, while low impedance means more noise and less power.

How does impedance affect preamps and power amps?

Preamps have high impedance, meaning they can power weak signals into line-level signals without adding too much noise. For this reason, preamps are favored by audiophiles and are commonly used to process microphone recordings. However, they’re virtually useless in dealing with speaker-level signals: since the level of impedance in the preamp is very high, they do not have the required wattage to drive a loud signal.

Power amps, on the other hand, have low impedance, meaning they can successfully drive any sound. Power amps have a voltage amplifier input (just like preamps) but also a current amplifier output. This means that, while power amps can audibly increase the noise level of a sound signal, they can also effectively power sounds at any volume, from speaker-level samples to an electric guitar power chord.

To sum it up, preamps count on voltage input and voltage output amplifiers only, while power amps have a voltage input amplifier and a current output amplifier.

What are preamps used for?

Unless you’re making music using nothing but digital sound sources, a preamp makes for an indispensable piece of equipment for music production. While there are various creative applications for preamps, they’re most commonly used to boost sound signals recorded by microphones. Due to their sensitivity, microphones cannot capture high-quality sounds at a significantly loud level, which means they need to be powered by an external amplifier.

Preamps are used to power microphone signals instead of power amps due to their ability to contain noise-floor levels. If you use a power amp to boost a mic input, you’ll notice the recording will sound very noisy, causing a significant reduction in sound quality. On the other hand, preamps will increase the level of the mic input without sacrificing its sound quality.

What are power amps used for?

In music production, power amps are often not required. However, they’re essential for creating genres such as rock, punk, and metal music. Commonly known as amplifiers, power amps are mainly used to boost the level of instruments such as bass and electric guitars.

They can serve more esoteric functions too, such as coloring pre-recorded sounds with a layer of “grit” and noise and purposely reducing the sound quality of a signal (which can be useful for creating lo-fi samples, for instance).

While preamps are an absolute must-have during the recording process, power amps are mostly used for performing live music, powering electric instruments, and compensating for the lack of power in certain sound systems.

During recording, sounds processed by a power amp will regularly be recorded through a microphone powered by a preamp: audio engineers do so because simply recording the output signal of a power amp would carry too much noise and affect the overall quality of a mix.

Do I need to buy a preamplifier and an amplifier?

There’s nothing bad about having both, but if you have to choose between the two, you should go for a preamp.

A preamp is a much more essential tool to music production, as it can be used to record all sorts of sounds with a decent level of sound quality (please keep in mind you’ll also need a microphone). Preamps are great for vocals, acoustic instruments, field recordings, and even sounds powered by power amps—such as bass and electric guitars.

If you’re a guitar player who wants to record high-quality riffs and solos, you’ll need a preamp and a microphone. Counterintuitively, you may not even need a power amp! Nowadays, you can connect your guitar to an audio interface (which works as a preamp) and use digital power amps to make it sound like, well, an electric guitar.

There are many quality options out there, from the fan-favorite Guitar Rig 6 Pro to the vintage-sounding BIAS Amp 2. Alternatively, you can also download one of the many free virtual amplifier plugins available on the Internet.

Conclusion

Preamps are a must-have for any audio engineer, as they allow the user to maintain a high level of sound quality without sacrificing a loud signal. Power amps, on the other hand, are more useful during live performances and compensate for weak sound systems, as opposed to common music production jobs such as recording.

In conclusion, preamps are best equipped to improve the quality of a sound signal, while power amps are better at powering instruments such as electric guitars and basses.

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