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What Is The Function Of The Amplifier? 4 Amplifier Classes


What is the function of the amplifier? The function of the amplifier is to increase the amplitude of an input signal. It takes a weak electrical signal from the signal source of any electronic equipment and amplifies it to a higher level, providing a stronger output signal.

Have you ever paused to think about how you can enjoy the music blasting your headphones or the strong sound of a concert? This is all thanks to a small device that packs a small signal with a massive punch—the amplifier.

You know, that mysterious piece of audio and music equipment hidden away in the corners of the sound systems. For those who have always been curious about the inner workings of gadgets, I am here to explain: “What exactly is the function of an amplifier, and why is it such a major part of our audio experience?”

What’s an Amplifier and How Does It Work?

An amplifier is an electronic device that strengthens an electric current. If you use a hearing aid, you might know it has a microphone that picks up sounds and turns them into a changing electric signal. Basically, the voltage amplification process tries to match the input waveform to the output waveform in a faithful way.

An electronic amplifier with transistors takes this signal, makes it much stronger, and sends it to a small speaker in your ear. This lets you hear sounds much louder than they were before. You can find operational amplifiers in most electronic devices, like television and radio receivers.

To see how much an amplifier helps, we look at the difference between the loud, larger output signal and the small input signal. This difference is called the amplifier’s “gain.” If an amplifier doubles in size, it gains 2. We often measure gain in decibels for sound amplifiers, which shows how much the sound power increases.

What Is The Function Of An Electronic Amplifier?

The function of an electronic amplifier is to increase the amplitude or power of a signal. This allows for better signal transmission and improves the overall quality of the audio output. Amplifiers play a crucial role in enhancing the performance and efficiency of various electronic devices, making them an essential component of modern technology.

The current gain control on your amplifier will allow you to increase the magnitude of the signal applied to the input, resulting in a louder output sound. Here are the types of resistance that are commonly used in amplifier electronic circuits:

Input resistance (RIN): The input resistance is an important characteristic of amplifiers that determines their ability to receive and amplify signals without distortion. It is typically measured in ohms and should be as high as possible to minimize the loading effect on the source.

Output Resistance (ROUT): This resistance is an important characteristic of a device or an electronic circuit. It determines how much the circuit or device can resist the flow of current through it. If too much current flows through the circuit or device, it may cause damage or malfunction.

Some amplifiers have heat dissipation systems to prevent overheating and ensure safe operation. You can find power amps that have vacuum tubes in them, which can provide a unique and vintage sound.

The Different Amplifier Types That You Need to Know

If you’re assembling your first hi-fi system, you’ve probably realized you’ll need an amplifier. This important part acts like the ‘muscle’ for your setup. No matter what you’re using to play music, it connects to the amplifier, which powers the speakers and lets you control the volume.

Which operational power amplifier circuit is the right one for me? Before you rush to buy any audio amplifier you see, let’s pause for a moment.

There are different types of audio amplifiers and power amplifiers you should understand first, and we’re going to explain their roles in simple terms:

#1 Pre-Amplifier

The pre-amp’s task is to take the quiet audio signal from your music source and prepare it for the next boosting stage. Some electronic devices, like network players, already have a pre-amp, so you might not need to add one to your setup.

#2 Power Amplifier

The power amp takes the feeble signal from the pre-amp and gives it the extra power supply needed to make it audible through the speakers. It’s design is based on a differential amplifier that uses two inputs instead of one.

#3 Integrated Amplifier

The integrated amplifier works with the pre-amp and power amp all in one box. This is handy if you’re on a budget or don’t have space for two separate devices. However, remember that in the world of hi-fi, a general rule is that having each stage of the music journey in its own individual unit usually results in better sound quality overall.

Power Amplifier Classes by Signal Type

Let’s talk about voltage Amplifier Classes, specifically in the context of integrated and power amplifiers. When it comes to instrumentation amplifiers for audio, there are different “Classes” that describe how they work.

These classes have been around for a while, dating back to the days of vacuum tube designs and, more recently, solid-state electronics that started gaining popularity in the 1950s.

I’ll focus on solid-state amps here and exclude tube amps, which have their own unique sound characteristics and are often appreciated by enthusiasts who seek that specific kind of sound from power amps.

For high-quality solid-state amps, three main design types are commonly used. However, there can be a bit of overlap and variation among them.

Class A:

Transistors, the electronic components in these amps electronic amplifiers, deal well with direct current (DC), but the audio is alternating current (AC). This presents a challenge. One solution was to use two complementary transistors. One transistor handled the positive parts of the signal, while the other handled the negative parts of the weak signal. They were then combined.

However, merging these signals seamlessly proved tricky, leading to a phenomenon called “crossover distortion.” During moments when the signal crossed zero (neither positive nor negative), both transistors turned off briefly, causing a kind of distortion known as odd-order harmonic distortion – generally an unpleasant kind.

These designs were labeled as “Class B,” but they aren’t usually used in quality hi-fi amplifiers. Class A amps tackle this issue by applying a significant bias to the signal. Bias might sound complex, but here, it just means adding some DC to the signal, shifting it to either the positive or negative side.

Instead of being an AC signal centered around zero voltage, it becomes a varying DC signal centered on the voltage. This prevents the signal from crossing the positive-to-negative boundary, resulting in low distortion. The negative feedback from DC bias is filtered out before the signal reaches the speakers.

But there’s a trade-off. One major drawback is inefficiency. The voltage is set at half the maximum voltage. So, for a 100-watt amp, it would run around 14 volts. And that 14 volts is active whenever input power to the amp is on, even if there’s no signal. This constant operation generates high gain and heat and consumes electric power.

Because of the voltage gain and substantial heat management needed, these amps tend to be large and heavy. Nonetheless, many audiophiles aim for Class A when possible due to its power gain and its lack of crossover distortion.

Class A/B:

Class A/B amps strike a balance. They use bias voltage to shift the crossover slightly away from zero. This reduces the distortion found in Class B while preventing the extreme inefficiency of Class A. Class A/B stays the most common design for high-quality amps. With modern design techniques, they often deliver impressive performance.

There are various design choices, including the level of bias input voltage. For instance, Moon by Simaudio sets its bias output voltage much higher in some models, so the first few watts of power are pure Class A.

Class C:

Class C amplifiers are known for their high efficiency but also for their high distortion levels. They are commonly used in applications where efficiency is prioritized over audio quality, such as in RF amplifiers and radio transmitters. Despite their drawbacks, Class C amps can still be suitable for certain specific applications where fidelity is not a primary concern.

Class D:

Class D, a switching amplifier, is quite different and tricky to explain. If it doesn’t make sense, don’t worry – we’ll get to the practical aspects soon. Even though the “D” in Class D doesn’t represent digital, the confusion is understandable. The signal remains mostly the same in Class A and B designs as it goes through the electronics. It rises and falls with the music. That’s how it works in the transistors and reaches the speakers.

But in Class D, the incoming signal is turned into pulses. These pulses might resemble digital signals, but they’re still analog because they don’t have specific numbers defining the edges of the pulses. The pulses’ width and frequency represent the waveform’s high and low points.

A simple filter converts the output signals of these pulses back to an analog signal at the speaker end of the ideal amplifier. This output circuit might seem unconventional, but it has its benefits. The main advantage is efficiency.

Instead of the signal going up and down in the power output transistors, they are either fully on or off at all times. The pulses determine when they’re on or off. Transistors are most efficient when fully on, so they don’t waste as much energy as heat.

So, if you need a lot of power but want a lightweight package without massive heatsinks, Class D can be a good solution. It’s even used in many subwoofers. While it’s not uncommon in high-end audio amps, it’s gaining ground. So, you might start to see more of them around.

4 Features To Look For On Power Amplifiers

Whether looking at a pre/power combo or an integrated amp, it’s important to consider the features you’d like in your amplifier. Here are a few features you might find on amps, along with my thoughts on them – though your preferences might differ.

#1 Remote Control

This is pretty straightforward. At the very least, you should be able to adjust the volume from a distance. However, there are different ways to achieve this. I prefer a volume knob that directly controls a high-quality potentiometer or serves as a control for a series of attenuating resistors. This setup allows a remote to adjust a motor that turns the knob.

#2 Line-level Subwoofer Output

This RCA socket could be handy for starting your high-fidelity journey on a tight budget. For initial speakers, I usually suggest investing in the best stand-mount speakers you can afford rather than opting for full-range floor-standing speakers.

Generally, the quality is better, but they might lack a bit of bass. The sub-output, available on certain stereo amps, combines the left and right channels, though usually without filtering. Once you’re ready, you can connect an active sub, adjust its level and crossover settings, and enhance the bass of your main speakers.

Pre-out on an integrated amp – That stereo output offers a simple upgrade path: switch to a better and higher-quality operational amplifier and use the integrated amp as a pre-amp.

Power in on an integrated amp – This feature adds flexibility, especially if the amp has pre-outs. For instance, you can place an audio processor between the pre and power amps, which isn’t always bad.

Tape loop – Some pre and integrated amplifiers still come with tape-out and tape-in connections. This could be useful if you consider getting a device to record analog signals.

Tone controls were common in transistor amplifiers back in the days of stereos, but many hi-fi purists frowned upon them. They have limited utility and are not often seen in modern amplifiers.

#3 Different Input Signal Connections

Most amplifiers provide multiple input signal connections to accommodate various audio sources and devices. These input terminals can include RCA, XLR, and digital inputs. Find an amplifier that has the type of input signal connection that best suits your audio needs.

#4 Similar Speaker Output Power Ratio

There are different types of amplifiers that cater to different signal connections and speaker output power ratios. Therefore, it is important to choose the right amplifier for your specific needs. Finding the correct output power ratio will ensure that your amplifier can effectively drive your speakers and provide the desired sound quality.

Amplifier FAQs

How much power do I need for the output?

Usually, more power is better, but there’s a catch. You’d have to double the power to notice a slight difference. Increasing power only adds about three decibels, which isn’t much.

So, if you’re choosing between fifty and a hundred watts, go for the higher if everything else is the same. But the power difference barely matters when it’s between 115 and 130 watts – only a 0.5dB change. Focus on other aspects of the devices instead.

What’s the Damping Factor?

Sometimes, amplifiers mention the damping factor, which is a way to measure how well the amplifier controls input impedance from the speakers and matches the amplifier’s output impedance. This factor basically acts as a dampener on the current flowing through the speaker.

Can I stack my pre-amp on top of my power amp?

No, you shouldn’t. I’ve always been puzzled by those images, too. I’ve been to product launches where they do this, and it’s not a good idea. Audio power amplifiers need good airflow to avoid overheating. Preamplifiers don’t need extra heat. So, it’s best not to do it.

What are small signal amplifiers?

A signal amplifier is an amplifying device found on broadcasting and wireless communications audio equipment. These signal amplifiers are capable of taking small electrical signals and amplifying them to a higher level, increasing their strength and quality. A common emitter amplifier uses a transistor to amplify the signal to the final output stage.

Last Updated on: October 17, 2023

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