Difference between Power Amp and Preamp?

In summary, the difference between a power amplifier and a preamplifier is that a power amplifier provides both current and voltage gain, while a preamplifier only provides voltage gain. The preamplifier amplifies low level signals and prepares them for the power amplifier, which amplifies the signal to a level that can operate a speaker. The circuit provided is considered a Class A Power Amp, which operates in push pull mode and is considered inefficient. There are 4 main types of power amplifier classes for audio: Class A, B, AB, and D. Each has different characteristics and efficiency levels.
  • #1
saad87
85
0
Hello all,

I was wondering what the difference between a power amplifier and a preamplifier was. Someone told me that a power-amp provides current and voltage gain whereas a pre-amplifier only provides voltage gain.

If this is the case, why are circuits like the following considered Class A Power Amps?

amp21.gif


Does this circuit provide current gain? I think it only provides voltage gain, but I could be wrong.
 

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  • #2
I can answer a couple of your questions. The preamp amplifies what is called a low level signal like a guitar pickup, turntable cartridge or microphone signal. These are typically very low like 3mV. The preamp amplifies the signal to line level and provides filtering, ie tone control. The power amplifier amplifies the signal from the preamp so it is "powerful" enough to operate the speaker and produce sound.

I don't know if you attached a schematic or not but I can't see it. There are 4 main types of power amplifier classes for audio.

Class A amplifier operates in push pull mode which means one transistor amplifies the positive cycle and the other transistor amplifies the negative cycle. The key here is a class A has both transistors active at all times so it's considered inefficient.

Class B amplifier has each transistor on only half the time. This helps with power efficiency but introduces something called crossover distortion when the signal switches from pos cycle to neg cycle.

Class AB tries to remedy this by keeping both transistor very close to being active to minimize crossover distortion but keep Class B efficiency.

Class D is bit more complicated and there are different types. Basically it uses pulse width modulation and relies on filtering to extract the audio signal.
 

What is a power amp?

A power amp, short for power amplifier, is an electronic device that increases the amplitude of an audio signal to a level that can be used to drive speakers.

What is a preamp?

A preamp, short for preamplifier, is an electronic device that amplifies a low-level audio signal from a source, such as a microphone or instrument, to a level that can be processed by other audio equipment.

What is the difference between a power amp and a preamp?

The main difference between a power amp and a preamp is the type of signal they amplify. A power amp amplifies a high-level audio signal, while a preamp amplifies a low-level audio signal. Additionally, a power amp is typically used to drive speakers, while a preamp is used to prepare the signal for further processing by other audio equipment.

Do I need both a power amp and a preamp?

It depends on your audio setup. If you have a source, such as a microphone or instrument, that produces a low-level audio signal, you will need a preamp to boost the signal before it can be processed or amplified by a power amp. If your audio source produces a high-level signal, you may not need a preamp and can directly connect it to a power amp.

Can a power amp be used as a preamp?

In some cases, a power amp may have preamp functionality built-in, allowing it to amplify both low-level and high-level signals. However, a dedicated preamp is typically preferred for its specialized features and more precise amplification of low-level signals.

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