The Different Stages of Amplifiers: Why are We Using Them?

The Different Stages of Amplifiers: Why are We Using Them?

You might have wondered why there are multiple stages of amplifiers in your audio system or home theater, but you’ve never really looked into it. Maybe you’ve been to electronics stores and browsed through the different stages of amplifiers, but you just don’t see why you would need more than one.

Let’s take a closer look at these stages of Amplifiers, as well as what they do for your sound system and how much better they can make your overall listening experience.

Why are we using different stages of Amplifiers?

An amplifier takes a weak signal and makes it stronger. The stages of an amplifier refer to the number of times the signal is amplified or increased in strength. The more stages an amplifier has, the more powerful it is.

Voltage Gain

One of the main reasons we use amplifiers is for voltage gain. Voltage gain is the ratio of the output voltage to the input voltage. For example, if we have an amplifier with a voltage gain of 10, and we input 1 volt into it, the output will be 10 volts. If we increase the input voltage to 2 volts, then the output voltage will also be 20 volts.

For this reason, many amplifiers have a minimum level of input needed in order to function properly. In other words, when you’re using an amplifier in your guitar signal chain, you’ll want to start at either your guitar’s pickups or your pedal board’s effects loop so that there’s enough signal going into the amp.

Current Gain:

In order to increase the current gain of a transistor, we need to use more than one amplifier. The first stage is the pre-amplifier, which takes the input signal and amplifies it. The second stage is the driver amplifier, which takes the output of the pre-amplifier and drives the load.

The third stage is the power amplifier, which takes the output of the driver amplifier and amplifies it even further. The fourth stage is the post-amplifier, which takes the output of the power amplifier and filters out any noise from the previous stages. After this filtering process, only clean signals come out of this stage.

Input Impedance

The input impedance of an amplifier is important because it helps to determine the overall load on the amplifier. A high input impedance means that the amplifier can handle a higher load, while a low input impedance means that the amplifier will be less effective at handling a high load.

The different stages of amplifiers help to create a more efficient system by providing different levels of impedance. For example, the first stage provides a relatively high impedance and typically handles relatively small signals from guitar pickups or microphones. In contrast, the final stage provides a lower impedance and handles larger signals such as those from keyboards or synthesizers.

Output Impedance:

The output impedance of an amplifier is the measure of the opposition to current flow (or voltage divided by current) at the output port of the amplifier. It is usually a low number, because we want as much current as possible to flow through the load.

The output impedance affects how well the amplifier can drive a load. A low output impedance is desirable because it means that the amplifier can deliver more current to the load. An ideal situation would be for the amplifier to have zero output impedance and thus be able to provide infinite current (assuming infinite power). That said, most amplifiers have high input impedances on their inputs and low outputs impedances on their outputs.

Stability (Feedback)

One main reason we use different stages of amplifiers is for stability. Without feedback, an amplifier can become unstable and produce distorted output. By using feedback, we can stabilize the amplifier and prevent distortion. The type of feedback depends on the desired frequency response. Negative feedback or a negative loop, for example, would be used to produce a low-pass filter response.

Positive feedback or a positive loop could be used to create a high-pass filter response. A positive loop can also cause oscillation if there is not enough damping in the circuit. Damping resistors (often called dampers) are added in series with RLC circuits to reduce this effect. Other types of feedback include voltage gain (with voltage divider) and current gain (with current mirror). These two types of feedback are used to create preamplifiers and differential amplifiers respectively.


Different stages of amplifiers are used in different situations because of the different benefits that they offer. The first stage, the preamplifier, boosts the signal so that it can be processed by the second stage, the power amplifier. The power amplifier then takes that boosted signal and amplifies it even further. Finally, the output stage clips any excess voltage so that the signal can be sent to the speakers without damaging them.

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