​The difference between pre-amplifier and post-amplifier

                   The difference between pre-amplifier and post-amplifier

Many friends don't understand the difference between the pre-amplifier and the post-amplifier. Today I will explain the difference between the pre-amplifier and the post-amplifier. The professional name of the preamplifier is: the preamplifier is also the part that has the greatest influence on the tone in the whole set of equipment. between). The professional name of the post-stage power amplifier is: pure post-stage power amplifier. This is the real part of the power amplifier, which has a great influence on dynamics and low-frequency control. It is a device that simply amplifies the "pre-stage" audio signal to provide enough power to drive the speaker to sound (always connected before the speaker). The power amplifiers that are common in general households should be called front and rear stage integrated amplifiers, combined power amplifiers.

Power amplifier

Post-stage power amplifier (pure post-stage power amplifier): The input signal of the post-stage is very simple, which is to undertake the output of the pre-stage. But the load of the post-stage 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.

The pure post-stage power amplifier needs the preamplifier to drive. The power of the pure post-stage power amplifier is generally more than several 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, which is used in smaller places, such as home use or KTV.

Preamplifier

Preamplifier (preamplifier): The preamplifier refers to a circuit or electronic device placed between the source and the amplifier stage, and is specially designed to accept weak voltage signals from the source. The preamplifier is used to amplify weak signals. Generally, the signal is passed through an electrolytic capacitor to filter out high-frequency noise signals, and then enters a negative feedback op amp to amplify the signal. A power amplifier generally refers to amplifying the power of an AC signal, that is, amplifying the current and voltage of an 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 achieve impedance conversion and matching.

If we only talk about technology, the requirements of the front stage are more precise than the back stage, 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 back stage because of the large current of the back stage. It should be the front stage. class. 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.

Summary: Power amplifiers are generally divided into front-level power amplifiers, rear-level power amplifiers and combined power amplifiers. The combined machine is a machine that integrates the front-level and rear-level power amplifiers. The front stage is used to initially amplify the signal and adjust the volume; while the rear stage is to amplify the signal from the front stage to drive the speaker.