How to understand pre-amplifier and pure post-amplifier ?

                      How to understand pre-amplifier and pure post-amplifier

1. Concept

The preamplifier is generally a differential amplifier circuit or a common collector amplifier circuit. It mainly selects the differential mode signal that needs to be amplified from the signal, and it is generally connected with a multi-stage common-emitter amplifier circuit to amplify small signals. Most of the boost in the front is the signal voltage rather than the current. The function of the front stage is to initially amplify the signal and realize volume adjustment.

The input signal of the pure post-stage power amplifier is very simple, which is to undertake the output of the previous stage and increase the power of the signal. The current stage is connected to the high-impedance post-stage, which mainly provides an appropriate output voltage, and the post-stage amplifier is connected to a low-impedance speaker to provide not only an appropriate voltage, but also sufficient current.

Two, characteristics

A preamplifier is a circuit or electronic device placed between the source and the amplifier stage, designed to accept a weak voltage signal from the source

The preamplifier is used to amplify weak signals. Generally, the signal is first passed through an electrolytic capacitor to filter out high-frequency noise signals, and then enters a negative feedback op amp to amplify the signal. Preamplifier generally refers to amplifying the power of the AC signal, that is, amplifying the current and voltage of the electrical appliance without distorting the signal. The pre-amplifier is 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 with high input impedance and low output impedance to realize impedance conversion and matching.

If we only talk about technology, the pre-amplifier requires more precision than the pure post-stage power amplifier, and it is more difficult to do well. If you want to add a special power line, you must not use a good line for the post-stage because of the large current of the post-stage. It should be the previous class.

The input signal of the pure post-stage power amplifier is very simple, which is to undertake the output of the pre-stage. But the load of the pure post-amplifier is the speaker, which is what makes many audio fans and even magazine comment writers confused. The latter stage is the load of the former stage, which is a high-impedance load; the speaker is the load of the latter stage, which is a low-impedance load. It looks almost the same, only one word is missing, but the high and low impedance makes it easy to push or not to push. The current stage is connected to a high-impedance post-stage, which mainly provides an appropriate output voltage because of the post-stage amplifier.

3. Application scope

The preamplifier is generally connected to the pure post-stage power amplifier, the output of the pre-stage is connected to the input of the post-stage, and the post-stage is connected to the speaker. The preamplifier is to amplify the voltage, and the pure post-stage power amplifier is to amplify the current. The preamplifier is the link device between various audio source equipment and the power amplifier. The output signal level of the audio source equipment is relatively low, which cannot promote the normal operation of the power amplifier. The preamplifier plays the role of signal amplification. It is mostly suitable for residential, commercial, office and other public places.

The pure post-stage power amplifier needs the preamplifier to drive. The power of the pure post-stage power amplifier is generally more than a few hundred watts. It is usually used in some professional places, and multiple units work at the same time to drive different speakers. Therefore, there is no low-level input port for the amplifier circuit, and there is no jack for high-impedance input signals such as microphones. This requires adding a preamplifier or a mixer to the signal to control it. The preamplifier and the pure post-amplifier are also combined into one, usually with a power of less than 300 watts, and are used in relatively small places, such as home use or KTV.

Written by : Davecl Audio
The Audio Equipments Manufacturer
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