When you’re looking to buy an amplifier, you’ll need to check the specifications, including the letter system used to categorize the products. Letters A, A/B, D, and G are all used for an amp’s class, but they also tell us more about the amplifier in question.
These letters show the topologies, which is how the amplifier actually works and what it does to the audio signals. While all audio amplifiers do the same basic job of boosting the signal level to a higher volume without distorting, there are different methods along the way. Every type of amp has its pros and cons, and in this guide we’re exploring the best things about the Class D amplifier.
Class D Compared - What Do The Types of Amp Mean?
To properly understand the benefits of using a class D amplifier, it is important to get to grips with how all of the different types of amp actually work. What is the difference in topology?
Class A amps have transistors which provide the speaker with the current needed to boost the signal. It provides a great sound quality when used correctly, but because there is a high DC current bias, it doesn’t necessarily all make it to the speakers. The power may dissipate and is often wasted. This is inefficient.
With a Class B amplifier there is less power lost as the transistors work differently. They’re all controlled with a “push-pull” operation. Positive currents are being sent to the speaker while the negative are fading away. This means more efficient use of power when using the amp. Unfortunately, Class B circuits and topology actually produce a fair amount of distortion in the crossover between the types of current. This means a lower sound quality.
As you may have guessed, Class A/B amplifiers combine the two methodologies above. The A/B amp will use DC bias current that is not quite the same as what a Class A topology uses. This means there is not the same level of distortion, and helps to improve the sound quality, preventing degradation in the sound that is being carried.
You may also have some control over the current being supplied to the speaker. Unfortunately, A/B amps are far from perfect. Even if it is made well, and the circuitry is as good as possible, the midrange outputs provide big voltage drops and this leads to power dissipation. Simply put, this type of amp is not efficient.
Class D sometimes gets misinterpreted. Some people think that anything with digital amplification means Class D. This is not correct, it’s just because of the alphabetized system. Class C amps aren’t mentioned in audio as they aren’t used for these types of applications. So, Class D gets its name just from being next on the list!
Class D amps can be either digital or analog.
The analog systems have an analog control and input. This means there’s a bit of correction for feedback error.
A digital system of Class D amp tends to only have digital controls, they don’t always have the same error control for feedback. Some do have the error control inbuilt, and they’re similar to the analog-controlled Class D amp.
The bottom line, and the main thing to understand when it comes to Class D amplification is the fact that the analog controlled models tend to perform far better. As well as having lower impedance they generally struggle far less with distortion, something that the digital alternatives might find to be an issue.
Class D amps have a lot to like for audiophiles and anyone building an audio system. Class D amps happen to be the very best at power dissipation and circuit board design, and they are also the best performing batteries. Even Class A amps, which aren’t too bad for dissipation, are nowhere near as efficient. The output of the Class D model can switch between negative and positive. These pulses mean a zero current when they’re not switched on, and the wave that is made means that there’s less dissipation. This doesn’t just mean more efficiency, it means less heat is produced, and this even provides more of a suitable environment for audio components, which could otherwise get “fried” over time from high heat levels.
The Key Advantages of Class D Amplifiers
Let’s delve more into those key benefits of using a Class D amp in your system.
Class D efficiency rates are typically above 90%. This is far higher than all of the other varieties. Because it uses pulse modulation, the dissipation is lower, and gets closer to 100% efficiency to the other wave forms found in class A, B and A/B.
In an A/B model for instance, the efficiency starts to improve when the max output is reached. With a Class D amp, it doesn’t matter anywhere near as much what sort of range it is operating at. You don’t have to be running it near full output to get an efficient use out of it.
Size and Price
Because Class D amp systems don’t waste as much power, it usually translates to savings for both the price and the space that it takes up. Some amps use things like fans and heatsinks that can cool it down. This isn’t required with every Class D system. A modulator is driving the conversion of the audio to turn it into a pulse. The active components are the modulator and output stage.
There is an LC filter sometimes included in Class D amps. This can add to the cost. Do you need the low-pass filter or not? The filter takes up space on the circuit board, too. Filterless amps are good for low power setups but if you need something like a big booming stereo, don’t go without the low-pass filter.
For most people choosing an amplifier, they will look at the power and clarity first and foremost. There’s no denying that some of the very best models on the market when it comes to clarity are Class D. These tend to be much better at avoiding disturbances in the audio signal as well as hiss in a system.
The SNR or “signal to noise” ratio is used to rate this. This is measured in dB (decibels) If you need relatively low system power then anything above 90 is fine, but for high-power you want something above 100 or even 110dB to ensure that you aren’t hearing these nasty clicks and hiss sounds.
It’s subjective, of course, the design of the amplifier plays a huge part in the tone, and just because an amp is Class D does not mean that it is definitely going to be a superb amp, but in general, Class D amplifiers perform brilliantly.
Historically, some Class D amplifiers have not been so good at higher-power applications. However, technology is improving all the time and people are reaping the benefits of this type of topology.
Better operating efficiency and less heat can only be a good thing, and the fact that the amps don’t require the same level of cooling technology even saves on space. There’s a lot to like about the tech driving Class D, and while the other amps still have their place, it is worth considering.