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Similar name, different functions! ---Preamplifier & Amplifier

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Similar name, different functions! ---Preamplifier & Amplifier

Issue Time:2019-08-28
Similar name, different functions! ---Preamplifier & Amplifier

Many friends don't understand the difference between the preamp and the power amp. Today, let's explain the difference between them. Their names are might look similar, but these two devices perform very different functions in the signal chain.


A preamplifier (preamp or "pre") is an electronic amplifier that boosts a weak signal into an output signal strong enough and adjust sound quality. The preamplifier is also the most influential part of the sound in the whole equipment set. It is connected between the sound source and the amplifier. Without this device, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups (Microphone is the most common input device that has a weak signal.).

Generally, the signal is filtered through the electrolytic capacitor to filter out the high-frequency noise signal and then enters the negative feedback op-amp to amplify the signal.  The Preamp is placed close to the detector, the transmission line is short, the distributed capacitance Cs is reduced, and the signal-to-noise ratio is improved. The signal is initially amplified by the preamplifier to reduce the relative influence of external interference. The preamplifier is designed for high input impedance and low output impedance for conversion and matching impedance


An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals to a level that is high enough for driving loudspeakers. Amplifier is has a great influence on the dynamic and low-frequency control. In simple, it increases the volume so that we can hear it through the speakers.

But that is not all. The amplifier can also perform other signal manipulations. It can modify the balance between different channels, it can mute a signal, it can add filters to modify the output and more.

The input signal of the power amp is very simple, that is, the output of the preamp is taken. But the load in the power amp is the horn. The power amp is the load of the pre amp, which is a high impedance load; the horn is the load of the power amp and is a low impedance load.When the preamp is connected to the high-impedance power amp, it mainly provides the appropriate output voltage

Power amplifiers need to be driven by preamplifiers. Its power is generally more than a few hundred watts and used in some professional venues, and the need for multiple amplifiers simultaneously to drive different speakers.Since it does not have a preamplifier circuit, there is no low-level input port, no socket for high-impedance input signals such as a microphone, which needs a preamplifier or mixer to control signal for it.

Sum up

The preamplifier is generally connected to the power amplifier, the preamp output is connected to the input end of the power amp, and the poweramp is connected to the speaker. The preamp is amplifying voltage, and the power amp is amplifying current. The preamplifier is a linking device between various audio source devices and a power amplifier. The output signal level of the audio source device is relatively low, and the power amplifier cannot be driven normally. The preamplifier acts as a signal amplifier.

The preamp is used to initially amplify and adjust the volume; while the power amp is to amplify the signal from the preamp to drive the speaker.


1. General engineering recommends that the power of the amplifier be 1.5 times, and the bass part should be 2 times, in order to get enough power.

2. In the demanding sound, such as studio monitoring, concert hall, etc., the best power of the amplifier should be twice the power of the speaker.