What Is Class A Headphone Amplifier?
Did you just buy a pair of headphones for some studio or DJ work, and you discovered that the music volume isn’t as loud and crisp as you’d like?
If you did, then you should consider getting yourself an amplifier (or preamp).
There are different types of amps, but the one that seems to be sparking many debates is the class A headphone amplifier.
If you’d like to know what a class A headphone amplifier is, then you’ve come to the right place!
Class A Headphone Amplifier Explained
A power amplifier is denoted by letter symbols used to specify each type. Users can quickly identify the particular amplifier’s features and sound output performance by looking at the class name.
Each is related to the time frame by which the amp is passing current, and this is shown as a fraction of the period of a specific signal waveform applied to the amp input. That being said, a class A amp is an excellent low-noise solution for you.
Other classes such as the B amp represent just one-half of the input period, while C represents a lot less than half the input period.
As for the D, the amp uses its output device in a switching form – that’s when the fraction of the time the device uses to conduct is adjusted to allow a pulse width modulation output to be obtained from the stage.
There are other letter classes for amps that are denoted for particular purpose amps. They feature extra active elements, a well as a few improvements in power supply.
In some cases, amp manufacturers use new letter symbols for the sake of promoting their unique designs.
Power Amp Classes
Power amp circuits (or output stages) are classed as A, B, AB, and C (mainly linear designs).
We also have classes D and E, which represent the linear switching designs.
Each is based on the proportion per cycle (the conduction angle) when the amplifier is passing the current.
The image of the conduction angle is gotten when the sinusoidal signal is amplified.
If the amp is always on, then the conducting angle is 360°. But when it’s on for just half of each cycle, the conducting angle will be 180°.
The amp power efficiency mostly determines the angle of flow.
Characteristics Of Class A Amplifiers
100% of the audio signal is expended (conduction angle Θ = 360°). Here, the active element keeps conducting all through.
An amp that operates under A conducts over the total range of the audio cycle. You can distinguish the class A amplifier by the output stage devices specifically built for class A operations.
There is a sub-class of the class A amplifier known as the A2.
It denotes the vacuum tube class A stages, which slightly drives the grid positively on audio signal peaks that produce more power than the regular class-A headphone amplifier.
However, this will lead to much higher signal distortion.
What Are The Advantages Of A Class A Headphone Amplifier?
Class A headphone amplifiers have several advantages for studio engineers, DJs, and sound technicians as far as audio is concerned.
Let’s take a look at some of them below.
1. They have a simple design
One of the best characteristics of a class A headphone amp is that its designs are usually simple.
The same cannot be said of other classes like the B or AB, which need two connected devices in the push/pull output (the circuit). Here, each of the connected devices is tasked with handling one-half of the waveform.
A class A headphone amplifier holds the advantage over the rest, being that it can use just a single-ended device.
2. It is always conducting
Since the amp element of class A is biased, it means it is always conducting. Hence, the small-signal collector current for the transistor is near the most linear part of its transconductance curve.
3. No issues with charge storage
Since the device is never “off,” it means the “turn off” time has been eliminated. This also means you wouldn’t have any issues with charge storage, and you’ll have an improved high-frequency response.
To add to that, a class A headphone amplifier also offers better audio feedback loop stability and much less high-order harmonics.
4. No problems with crossover noise
With a class A headphone amp, the point where the machine comes nearest to being “off” isn’t the “zero signal,” which means you can avoid any issues with crossover noise in your audio, as it will always produce an excellent sound.
5. If it is ideal for radio receivers
Since the class A headphone amplifier produces very low noise, it can work well for low signal levels of radio receivers.
6. Good tone quality
Besides producing little to no noise, class-A headphone amps can also be used for guitars due to their impressive quality in tone and vintage sounds.
It is safe to say that musical purists will prefer this to other classes of headphone power amps.
What Are The Disadvantages Of Class A Headphone Amplifiers?
Let’s take a look at some of the significant disadvantages of the class A headphone amplifier.
1. They can be inefficient
With an A amp, you can get maximum theoretical efficiency of around 25% when using regular configuration. The most you can get out of it is 50% with an inductively coupled configuration.
Its inefficiency stems from the standing current, which has to be around half of the maximum output current.
Keep in mind that a significant portion of power supply voltage is evident across the output device at low signal levels. So if the high output power is required from a class A circuit, then the power supply becomes an issue.
2. It consumes plenty of power
Since its maximum efficiency on a typical configuration setting is at 25%, there will be much power usage during operation. There will also be limited operation when being used with batteries.
It is worth mentioning that the amp itself will consume an extra watt for every watt sent to the load.
This ultimately means an increase in power bills and the need for higher-rated power devices.
3. It produces extra heat
When a class A headphone amplifier produces an extra watt over the one added to the load, it will consume more power and generate more heat during operation.
4. It will not last as long as other amplifier classes
Since the Class A amp’s output devices are always in operation (on), they are usually overworked and will not have the kind of lifespan a B or AB amp.
To be fair, though, a few manufacturers of newer models have taken this problem into account and have made modifications for this reason. But this still implies additional costs on maintenance and design.
5. It doesn’t have the best design
The design of the class A headphone amplifier is pretty simple, which is why it is a hobbyist’s favorite. However, it has been overtaken by more efficient and functional designs.
But in all honesty, there is still a market for more expensive, high fidelity class A amplifiers, all thanks to the fact that it offers minimal crossover distortion and minimal high-order harmonic distortion.
Single-ended And Triode Class-A Amplifier
Many hobbyists in love with class-A amplifiers usually prefer to use thermionic valve designs rather than transistors.
One of the main reasons for this is that the single-ended output stages feature asymmetrical transferability. This means that even-order harmonics in any created distortion will not cancel out like in cases of push-pull output stages.
As for tubes and FETs, most distortion is second-order harmonics, stemming from the square-law transfer feature. To some users, this produces a smoother, more refreshing sound.
As for those who prefer the low distortion figures, using tubes alongside a class A and symmetrical circuits like balanced output stages and push-pull output stages will eliminate a lot of even distortion harmonics. This, in turn, will cause the elimination of most of the distortion.
Traditionally, a valve amp was used as a class-A power amp. Valves are typically big and pricey (most class A amplifiers use only a single device).
As for transistors, they cost significantly lower than tubes, which allows for more elaboration in their designs during the manufacturing stage.
One of the most notable uses of a pair of class A devices is the famous long-tailed pair. This is linear, and it creates the foundation for many other units that followed (including several audio amplifiers and pretty much every other op-amp).
Class A amplifiers can be applied in the output stages of op-amps. However, the accuracy of the bias in low-priced amplifiers could lead to a variation in performance by the device in areas of power consumption and temperature.
These are used sometimes as low-efficiency, medium-powered, and high-cost audio amplifiers. However, the power consumption is not related to the output power.
Power consumption is the same with high output volume at the idle state (with no input). This would result in low efficiency and the production of too much heat.
Do All Headphone Amps Sound The Same?
When buying a pair of headphones (either for show or desktop use), the sound production of the headphone amp you plan to use with it should satisfy your sonic needs to a great extent.
Without an amp, you will find that the volume of your headphones is on the low side, which can be a problem if you’re using the headphones at live shows or for more professional purposes like audio mixing and mastering.
In the hunt for the right amp, you will come across several amps classes, which could leave you at a crossroads trying to figure out which produces the better sound.
This begs the question – Do all amps sound the same, or are there classes that sound better than the other?
The straightforward answer to this question is simple – No, all amps do not sound the same.
According to specific purposes, they are built differently and cannot produce the same frequency, quality, or sound volume.
Assuming all classes of amps were built to meet the exact requirements, one will sound just like the other.
To get a more precise answer to this question, you must understand what a headphone amp does.
What Does A Headphone Amp Do?
As far as the word “amplify” goes, headphone amps are built to perform one primary task, and that is to help your headphones sound much better when used on a desktop or at an event.
The world has evolved to the point where almost every piece of content we listen to is distributed in one of these formats –
• MP3 (the most popular of them all)
The file mentioned above formats is significantly smaller than an analog file, making them easier to store and share on several devices (like a desktop) and clouds. While this is great, there is a minor issue to deal with – The speakers responsible for playing out the sound are powered by analog signals.
With this in mind, the digital signals derived from the audio files must be converted to analog signals and use analog inputs before they can be played out of a speaker. And this is where the DAC comes in.
The DAC, also known as Digital Analog Converter) is tasked with converting digital signals to analog. The new analog signal becomes a low-voltage signal during the conversion process, which needs to be amplified before working with a speaker.
In case you didn’t know, DACs and amps aren’t always large boxy devices, as they can also come in smaller forms. Take your iPod, desktop, or smartphone as examples – They both have built-in DACs and amplifiers which allow you to listen to your music and enjoy it without noise.
So what exactly is the function of the headphone amp, since the DAC seems to do a lot of work in this regard?
As you already know, most headphones being made in modern times can be powered with small devices like your tablet, smartphone, and laptop. Headphones are high-sensitivity and low-impedance, so they do not need a lot of voltage before being powered.
Let me quickly define what output impedance is (for those who don’t know) — it is simply the resistance to current flow. With this in mind, you should remember that the lower the output impedance, the lower the voltage you will need to overcome the resistance, and the higher the impedance, the higher the voltage you will need to conquer the resistance.
Unfortunately, there is hardly a high-powered model that is low impedance. Headphones like these are built with more coil windings, which provide more dynamic low noise sounds. And this is precisely why they are high impedance and why small devices like tablets and smartphones can hardly power them.
So you now see why an amp is needed, right?
When you pass the audio output from the source of your audio (let’s say your phone) to an amp, the voltage of the audio signal is amplified well enough to power a high impedance headphone.
This will make the headset sound at its loudest level, just as it was designed to sound. Depending on how well the manufacturer built the particular headphones you are using, it will also sound with minimal distortion (or no distortion at all).
When Should You Use A Headphone Amp?
Most modern headphones are built to be low impedance with a high sensitivity feature. Therefore they do not require the use of an amplifier to boost their sound.
Using an amp alongside it would be a total waste of time with such low impedance headphones, as you will not notice any significant difference in sound volume or quality.
If you use an amp with low impedance headphones, you could end up with distortions in the original sound.
The same goes for Bluetooth headphones, as you also do not need an amp to use them. The first issue here is connecting the Bluetooth headphones to the amp, but there is also the fact that these types of headphones usually have a built-in power source and amp that does the same job.
That being said, you will only require an amp when using high impedance headphones, as they will not be able to produce the best sounds when being used with smaller devices like your smartphone, tablet, or laptop.
Identifying a high impedance headphone isn’t difficult; all you have to do is look at the specifications on the store where you’re buying it from. The specs will also be on the package of the goods.
A high impedance headphone generally has impedances of 100 ohms to 300 ohms.
Another instance where you may need a headphone amp is connecting more than one headphone to a single source.
Is There Any Difference In Sound Quality With Different Amps?
As you would expect, hobbyists are pretty familiar with this question, as it keeps popping up on forums and relevant platforms when any hobbyist wants to buy a new headphone amplifier.
As we have discussed earlier, the primary function of a headphone amplifier is to boost the voltage from a sound source, hence making it louder and clearer.
Briefly put, headphone amplifiers are designed to do the following –
• Reduce noise
• Reduce distortion
• Reduce headphone impedance at all frequencies
• Generate enough voltage to power headphones to a reasonable volume level
Other areas where headphone amplifiers are relevant include –
• Inaudible low channel imbalance
• Flat frequency response
• Good phase response
If all the headphone amplifiers meet these standards, they would all sound the same when using the same set of headphones.
But as we all know, not all headphones are built with these specifications in mind. Some are built cheaply, and these amplifiers will have lower quality than the more costly ones.
And while low-quality amplifiers do exist, there are too many high-quality models in the market. This is because headphone amplifiers are very easy to design and produce.
Some amplifiers have output impedances that are more than 1/8 of the headphones that are connected to them. This will, in turn, reduce damping and cause distortions in the audio output.
When the topic of headphone amplifiers arises, most people refer to solid-state amplifiers, while others refer to the tube amplifier.
Tube amplifiers are those that function with the use of vacuum tubes to amplify voltage. Tube amps could be said to be the main reason why people assume amplifiers sound different.
Tube amplifiers are known to add distortion to the audio signals being received. This may sound like a problem. However, these distortions usually cause the audio from the headphones to be euphonic. This gives the audio sound a warm and smooth feel.
In summary, there will be a difference in sound quality among different amplifiers. Still, it is only usually noticeable if tube amplifiers are used.
That aside, most users only notice a difference in amplifiers strictly due to a placebo effect. It could be that someone had told them that a particular type of amplifier sounds a lot better than the one they are currently using.
This may also be based on perception, where they assume an expensive amplifier sounds better than a cheaper one. But in reality, it’s all in mind.
Are Headphone Amps Class A?
No, not all headphone amps are class A.
As we have already discussed, there are several other classes of headphone amplifiers.
These include –
• Class B
• Class AB
• Class C
• Class D
Are Class A Amplifiers Better?
An amplifier’s class is clearly defined by how it combines power output and signal as for which class is better. Well, that all depends on precisely what you desire from an amplifier.
Take a look and see which is best for your specific needs.
• The class A amplifier is the least efficient of all the classes, but it has the best sound fidelity
• The class B amplifier is slightly more efficient than the class A, but it produces a lot of distortion
• The class AB has excellent power efficiency, as well as a good sound output
• The class D amplifier is the most efficient of them all, but it isn’t high fidelity
Amplifiers are built to give out less power than they consume. And an amplifier’s efficiency is simply the ratio of the power it gives out against the power that it consumes from the source of electricity.
There is no such thing as a 100% efficient amplifier, as none of them can give out precisely the same power that it draws. Any electrical power that doesn’t reach the output terminal is a waste and converted into heat.
Excessive heat will damage the amplifier’s output signal and some of its inner components.
As you may have already figured out, different classes of amplifiers will produce different levels of heat.
Class A Amplifiers: High-fidelity Heat Source
With a class A amplifier, the output transistors work with regular “bias.” This means they operate at full power every time, regardless of the presence or absence of an input signal.
In a case where there is no signal, the transistor power is converted into heat. But this is different when there is a signal present. In this case, the power escapes through the speaker terminal, and there will be no excessive heat.
To add to that, every class A output transistor amplifies the negative voltage and positive voltage sections of the signal’s AC waveform. This will increase the workload and produce more heat.
A class A amplifier typically runs around a 25% efficiency level. What this implies is that the remaining 75% of its power is converted into heat.
Highest Fidelity Amplifier Class
Since each output stage transistor is always on, it means there is an absence of a turn-on and turn-off warning. There are also no cooling or warming cycles that affect the signal flow.
The transistors function in their most linear fashion, which is free of distortion in these conditions. And since there is no switching required, there will be no induced high-frequency interference.
A pure class A amplifier is usually hard to find. It is also worth mentioning that it isn’t used in-car audio.
Class B Amplifiers: The two-transistor solution
One of the main advantages of a class B amplifier is that it eases the workload of each output stage. It performs this function by replacing the single transistor present with two transistors set up in a push-pull design.
Here, one of the transistors amplifies the negative voltage parts of the signal’s AC waveform, while the second handles the positive voltage.
When the two are combined, they create a total unified output. In this case, one transistor is on 50% of the time and the remaining 50%.
Class B Amps: More efficient with lower fidelity than class A
Class B amplifiers are much more efficient than class A amplifiers (about 50% more efficient). However, they give off more distortion because the two transistors are constantly turning on and off.
The crossover distortion produced is so bad that many manufacturers are reluctant to produce pure class B amps.
Class AB amplifiers: Higher fidelity and efficiency than class A amps
The push-pull duo of output transistors in a class AB amplifier is both on more than 50% of the time. To add to that, they don’t suddenly turn on and off either.
This gives the class AB amplifier the features of both the class A amplifier when the signal is low and that of a class B amplifier when the power is high.
There is a maximum bias for each amplifier (the period when the two transistors deliver current), reducing the crossover distortion of a class B amplifier.
Thanks to this incredible design, the class AB amplifier has significantly greater efficiency than the class A amps. This efficiency level is as high as 60%, with less distortion than the class B amps.
It would interest you to know that a lot of stereo amplifiers and home theaters are class AB.
Using a class AB amplifier was the only feasible choice for getting high fidelity and full range until recent times. Now class D amps are being produced, which are just as accurate as of the class AB amplifiers.
However, the class A amplifier remains the most accurate of all the classes.
Class D amplifiers: An excellent alternative to class A amplifiers in terms of efficiency
The way the class D amplifiers operate is unique. It features onboard circuitry, which produces a very high frequency. This frequency is usually greater than 100K Hz pulses worth of DC.
The width of each pulse becomes modified via the input signal. This modification is known as pulse width modulation (PWM).
These DC pulses are then pushed through the amplifying output transistors, producing the high power output.
Since they receive DC pulses and not analog signals, the transistors are either “off” without or on full power.
With this in mind, it is safe to say that this is arguably the most efficient way of running transistors. In some class D amplifiers, the efficiency is as high as 90%.
It is common for many people to assume that the “D” in class D stands for digital. But even though making signals by quickly switching transistors on and off looks like digital processing that uses zeros and ones, the class D amplifier doesn’t offer digital service.
Some of these amps could have digital control switches, but that doesn’t change that amplifier circuits are exclusively analog.
Class D Fidelity Not A High As Class A
The low pass filter of the class D amplifier smoothens the output signal after amplification. Due to this, the amplifier won’t release pulses of power. Instead, it will be a constant analog power output.
It also eliminates the unnecessary interferences produced by the high-frequency DC pulses.
As a result, many audiophiles will not make use of class D amplifiers in their systems.
Why Class D Has Become The Preferred Choice Over Class A
As far as car audio and public address system are concerned (where perfect fidelity is not a must), class D amps have gained more popularity among users.
This is for many good reasons.
• They are smaller
• They are lighter
• They have a significantly cooler operation than other amplifier classes with the same power levels
When considered, you will agree that those mentioned above are considerable advantages in cases where you have to fit an amplifier in a car or use it in shows and parties.
Why Do Class A Amplifiers Sound Better?
With all the advantages that other headphone amplifiers have (especially class D), you would still wonder – why the class A headphone amplifier sounds better?
One of the most significant advantages of a class A amplifier is that the manufacturers can produce more simplistic circuits which are pretty linear with low distortion when on low power.
On the flip side, the manufacturers of class AB amps must design more complex circuits that use feedbacks to obtain deficient levels of distortion. However, they can make a more powerful amp without having to contend with the complications associated with other amps.
As far as the sonic difference between class A and class AB amps is concerned, it lies in the fact that the former has a better power supply and regulation.
How To Choose The Right Headphone Amp
Now that you know what class A headphone amps are, as well as their alternatives (being B, AB, C, and D), you can go to the market in search of a headphone amplifier that meets your specific audio output needs.
But how do you make that choice, knowing fully well that there are several variations to choose from?
The best way to make the right choice is by first considering some critical factors.
Here’s what you should put into consideration.
1. Be sure you need an amplifier in the first place
Before spending your hard-earned money on a headphone amplifier, you need to ask yourself if you even need one at all.
You may assume that by getting an amplifier, the sound coming out of your headphones will be a hundred times better, right?
Unfortunately, this may not necessarily be the case.
Some factors come into play regarding whether you need a headphone amplifier or not. And one of such essential factors is impendence.
Why does impendence matter?
If you recall, I already mentioned that impendence measures the amount of power your headphones require. This power is measured in ohms.
Some headphones require more power than your smartphone or laptop can offer. With devices like these, getting an amplifier will help boost the sound.
On the flip side, some headphones could enjoy the benefits of the extra power coming from an amplifier, but their impendence is so low that they wouldn’t need an amplifier to function.
If your headphones aren’t being supplied adequate power, they will sound low, and you will find that some sounds are even absent.
If your headphones have an impendence of about 80 ohms and above, they will most likely need an amplifier.
If the impendence is greater than 32 ohms, your headphones could produce the sound level the manufacturer originally intended. In such a case, you wouldn’t need an amplifier for your headphones to function correctly.
2. The level of improvement you need in your sound
When buying a headphone amplifier, the second thing you need to consider is the level of improvement you want in your sound.
When the power of the amplifier is increased, it means you will be able to hear some sounds that were absent when using a low-powered amplifier.
With a high-powered amplifier, all the bottlenecks holding back the true power of the headphones will be eliminated, allowing the headphones to sound just as the manufacturers planned.
3. The price range
When it comes to buying high-quality headphone amplifiers, one of the biggest concerns is price range.
On average, a decent headphone amplifier with good build quality will go for a price of about $100, but that’s on the low end. Nonetheless, a headphone amp within this price range isn’t bad for a start, especially if you’re on a low budget.
If your headphones don’t draw too much power and you’re not interested in an integrated DAC, buying an amp for $200 and above would be overkill.
As long as the headphone amp you’re buying has all the features you’re looking for, just make sure it is within the same price range as other similar products, so you won’t be paying more than you have to for the same quality.
Portable vs. Desktop Headphone Amplifiers
As you would’ve guessed, portable headphone amplifiers are built to be used with small devices like tablets and smartphones. These types of amps are equally small, which is why they can be used when on the move.
Portable amps are battery-powered, and some of them can even support Bluetooth.
As for desktop amplifiers, they are more extensive than portable amplifiers, and they possess many more features like volume control knobs and an extra headphone jack.
I really can’t say that one is better than the other because they can both be helpful in different types of applications.
Cheap Vs. Expensive Headphone Amps
Price differences among headphone amps do not necessarily define how good or bad the amps are in basic functionality. However, the amps with a high price are usually packed with extra features like build quality and power.
But even though the more pricey amps will deliver extra power, you may not need it (depending on the kind of headphones you are using).
Compared to the cheaper amplifiers, the more expensive amplifiers usually feature more outputs, screens, internal DAC, extra volume control options, extra headphone jack, and surround sound support.
In addition, the more expensive amplifiers will have fancier knobs and switches, smoother dials, and high-quality metal materials.
Expensive amplifiers may be a good bargain for some users, thanks to their more beautiful build. But looks don’t mean it performs better than the cheaper ones (at least in terms of basic functionality).
Good looks only make you feel better about the amplifier and psychologically change the way you hear the sound it produces. It’s more of a psychological experience than a functional one.
Speaking of psychology, here are a few aspects that can make you feel good.
• Better packaging
• Better unboxing experience
• Fancily designed volume control knobs and switches
• Better colors
While all these are great, the most important thing is getting good value for your money (according to what you need from a headphone amplifier).
These amplifiers are designed mainly for gamers who want to enjoy the whole audio experience of their favorite games.
Like amps for music, gaming amplifiers also have a headphone jack and microphone inputs, while some offer 7.1 virtual surround sound support.
The mic input support is necessary for gamers who use headphones, as they will need to plug the input alongside their headphones into the amplifier.
Like amplifiers for music, a gaming amplifier also boosts sound quality, but in this case, video games.
Since gaming amps also improve the microphone sound, it means you’re not only boosting your sound experience but the overall sound of those around you.
A 7.1 surround sound amplifier can significantly contribute to the immersion of a game, most especially if it is a more open map.
For competitive shooters, they don’t need to make use of surround sound. Most professionals make use of stereo.
Gaming headphone amplifiers are great because of their overall clarity and surround sound stereo, as it allows you hear sounds from in-game rooms and floors.
Gaming amplifiers can serve a 2-in-1 purpose, as they are ideal for videogame stereo and listening to music.
Do You Need A DAC?
Smartphones and desktops are designed with a built-in DAC to play music. However, a dedicated DAC can function much better and help produce a far more superior sound.
With an amplifier, you can connect directly to your laptop or phone and use the DAC that has already been built-in.
Gaming amplifiers also have a DAC in their design, which controls directional processing such as virtual surround sound.
There are several reasons why having a DAC is a good idea. Two of the main reasons include –
• A DAC can process directional audio
• It can process ample information for high fidelity audio tracks
If you want to process high-resolution audio, you will require a DAC (either built-in to a device or dedicated).
Class A amplifiers have a straightforward design, produce low noise when playing music, have decent frequency response, and produce good audio quality with little to no distortion. However, it has a maximum efficiency of just 25%, which causes it to consume too much power.
For this reason, the class D amp has gradually become the more popular alternative to class A in recent times since it offers as high as 90% efficiency when running transistors.
Nonetheless, the headphone amplifier class you choose should be strictly based on the levels you expect your headphones to perform. Because in some cases, you don’t even need headphone amps at all.
Thanks for reading!