Everything you need to know about power amp types (2024)

By Dan Coggins

( Guitarist )

published

Guest writer Dan Coggins joins us to explain the differences in tube amp class and types

Everything you need to know about power amp types (1)

Guest writer Dan Coggins brings us up to speed on some of the fundamental differences between guitar amp class types.

An electronics engineer by profession, Dan Coggins began his career in the music industry during the mid-90s as the circuit designer for stompbox legends Lovetone, before branching out independently with Dinosaural in the early 2000s.

Now collaborating with ThorpyFX, Dan continues to push the envelope and explore new sonic territory, with several different designs having emerged in recent years.

And so, over to you, Dan...

Fixed-bias Class AB valve designs such as most Marshalls, Hiwatts and black-panel Fenders generally have a tauter, wider bandwidth and a more controlled sound

“If you have a valve amp, your preamp valves will almost certainly be operating in Class A mode, which means they are running at their optimum ‘mid-point’ current without any nasty-sounding ‘crossover distortion’ being produced.

“As the rule rather than the exception in most guitar preamp designs, this relatively simple and cost-effective configuration will likely produce some pleasant-sounding harmonics/distortion – an effect that is regularly exploited in the extreme (think Mesa/Boogies and latter-day Marshalls).

“At the power stage of the amplifier, the output valves, configured in a particular ‘class’ of operation such as Class A, AB, D, and so on, interact with the ‘load’, namely the loudspeaker(s), to chiefly determine the amplifier’s signature sound – along with the speakers’ inherent tone and response.

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Everything you need to know about power amp types (2)

“Most high-wattage guitar amplifiers utilise the Class AB mode of operation, whereas the least powerful amplifiers tend to operate in Class A, although a mixture of both of these modes of operation is common within the medium power range. There are other classes of amplifier operation, such as Class B, C and D, although Class A and Class AB are by far the most widespread in guitar valve amp applications.

“Class AB operation is where two valves (or multiple pairs) share the signal in overlapping fractions of more than a half-cycle each. This is to reduce heat wastage and optimise power efficiency – hence why this configuration is almost always used in the higher-power designs.

A well-known example of a small Class A amp is the Fender Champ, which uses just one output valve

“The degree to which the two halves of the signal overlap and the resulting tonal variation is determined by the amp’s ‘fine’ bias setting. Fixed-bias Class AB valve designs such as most Marshalls, Hiwatts and black-panel Fenders generally have a tauter, wider bandwidth and a more controlled sound.

“A well-known example of a small Class A amp is the Fender Champ, which uses just one output valve (known as single-ended operation) and is, by definition, Class A because the output valve must conduct for the whole signal cycle.

“It also operates in what is commonly known as ‘auto bias’ or, more precisely, ‘cathode bias’. Such biasing often uses a large capacitor to smooth out the variations in current, giving a ‘spongey’ attack response, which imparts a dynamic, compressor-like character to the sonic envelope.

“This feature produces the characteristic ‘chime’ of a Fender Tweed Deluxe or a Vox AC30, both of which run in (or very close to!) Class A operation.

Everything you need to know about power amp types (3)

“These classic amps use pairs of output valves where each half of the signal cycle is handled by different/opposing complementary valves in a ‘push-pull’ operation for greater efficiency and less even-harmonic distortion.

“Crucially, however, neither of the two designs use negative feedback around the output stage, and therefore the remaining harmonics generated in the output valves are not as suppressed. In designs with feedback, say, black-panel and silver-panel Fenders and Marshalls, a more audible colouration is apparent.

“Presence controls, when fitted, usually ‘burn off’ some of this feedback in the high mid-treble frequencies only to add sparkle (and sometimes a bit of noise and hiss) while maintaining a controlled lower midrange and relatively firm bass response.

“When pushed far enough, the feedback mechanism rapidly gives way and the resulting breakup becomes a defining factor in the sound as it begins to dominate.

“This creates a ‘dynamic equilibrium’ with the output valves, meaning the speakers and the output valves interact to a far greater degree than if feedback were employed. The net result is a complex and intriguing tone that has both a rich harmonic content and an ability to project sound with great immediacy."

Dan Coggins’ top tube pedal recommendations

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Everything you need to know about power amp types (4)

Effectrode Blackbird – $469 / £369

This compact, all-tube, switchable, two-channel guitar preamp is designed for use on stage or, with its low impedance, transformer-balanced output, in the studio. The clean channel replicates a black-panel Fender design, while the overdrive channel is based on the tube circuitry of Dumble amps.

Everything you need to know about power amp types (5)

Audio Kitchen The Small Trees – $479 / £321.6

Audio Kitchen’s The Small Trees is an all-valve Class A clean boost, providing up to 16dB of full-range clean boost with a Class A valve line driver buffer at the output. Based upon their classic The Big Trees 2.5W-amp clean front-end, the tonal signature is transparent yet distinctively ‘tube-y’.

Everything you need to know about power amp types (6)

Kingsley Page DS V2 – $280 / £225

The Kingsley Page DS V2 pedal is a Dumble ODS-style preamp designed for real tube overdrive tones that will increase in sustain when pushed in level by a clean preamp. This latest version features enhanced EQ options, including three-way Lows and Mode switches in addition to the Tone control.

Everything you need to know about power amp types (7)

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Everything you need to know about power amp types (2024)

FAQs

Everything you need to know about power amp types? ›

What are the types of power amplifier? Power amplifiers are divided into classes based on the amplifier's characteristics. Classes A, AB, B, and C depend on their conduction angle, which is the number of degrees in a cycle during which the amplifying device conducts. Classes D and E are switching amplifiers.

How do I know what kind of amp I need? ›

As mentioned earlier, it's recommended that you choose an amplifier that offers about twice the RMS or continuous power rating of your speaker. This extra power, known as headroom, helps prevent distortion and clipping, especially during peaks in the audio signal.

What are the 3 types of amps? ›

  • Amplifier is an electronic device which amplifies the input power of the signal.
  • The types of the amplifier are: 2.1 Voltage amplifier: The voltage amplifier increase the input voltage. 2.2 Current amplifier: Current amplifier increase the input current. 2.3 Power amplifier: A power amplifier increase the input power.

How do I choose a power amplifier? ›

My recommendation is to choose an amplifier that is capable of providing about twice the continuous power rating of the speaker. Remember, a doubling of power is only a three decibel change.

Which class of power amplifier is best? ›

Class A design is the least efficient but has the highest sound fidelity. Class B design is a little more efficient, but full of distortion. Class AB design offers power efficiency and good sound. Class D design has the highest efficiency and smallest footprint.

What is the difference between Class A and Class B power amps? ›

Unlike a Class A amplifier, a Class B amplifier does not produce a good signal reproduction. It uses complementary pairs of transistors that conducts the half cycles of the input signal. The positive biased transistor will conduct the positive signal while the other transistor is off.

What are the golden rules of amps? ›

Op-amp Golden Rules

1. An op-amp draws no current into either input. 2. An op-amp will do anything it can to its output to ensure that its two inputs have the same voltage.

Are class D amplifiers any good? ›

Class D is not bad, it's very useful, like plastic, but there are simply better choices when it comes to serious high-end gear. A class D amplifier may be the best amplifier you've heard though, and if so, great. Just be sure you listen to a range of class A/AB/D products before finalising your opinion.

What is a class D power amplifier? ›

Class D amplifiers are those that output a switching waveform, at a frequency far higher than the highest audio signal that needs to be reproduced. The low-pass filtered, average value of this waveform corresponds to the actual required audio waveform.

What amplifier do I need for 1000 watt speakers? ›

A speaker's peak power handling is typically 4 times its continuous power handling. So the speaker can probably handle 1000 watts peak. That means you can use a 1000 watt amplifier to drive that speaker -- as long as you use that power for peaks, and do not drive the speaker continuously with 1000 watts.

Which of the power amplifier is most preferred? ›

Class A Power Amplifier

In this class of amplifiers, the entire input waveform is used in the amplification process. A single transistor is used to amplify both the positive and negative halves of the waveform. This makes their design simple and makes class A amplifiers the most commonly used type of power amplifiers.

How many watts is a good amplifier? ›

If you play with a drummer, for live gigs in small to mid-size venues, you should aim for a 20W to 60W tube amp or a 40W to 60W+ watt solid state. For larger venues aim for a 20W to 100W+ tube amplifier, or 50W to 100W+ solid-state especially if you're playing big stages and outdoor festivals.

How many power amplifiers are there? ›

Power amplifiers are divided into classes based on the amplifier's characteristics. Classes A, AB, B, and C depend on their conduction angle, which is the number of degrees in a cycle during which the amplifying device conducts. Classes D and E are switching amplifiers.

What is the difference between Class G and Class H amps? ›

Class H improves on class G by continually varying the supply voltage when the audio signal exceeds a particular threshold level. The power supply voltage tracks the signal's peak level to be only slightly higher than the instantaneous value of the audio wave.

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