Amplifiers Types And Classifications

This article offers a basic outline of the types and classifications of amplifiers.

0

Types Of Amplifiers

In addition to the different classes of amplifiers, there are four types of guitar amplifiers: tube, solid-state, digital, and hybrids thereof. Tube Amps: Tube amps are preferred by many guitarists for their great tones and very organic-sounding distortions. Tube amps usually sound louder than solid-state amps of the same wattage and have a definite "feel" that you don't get from solid-state amps. Tube amps require more upkeep and are definitely more delicate than other kinds of amps, but the sounds they get are completely worth it. Solid-state Amps: Sold-state amps use transistors for their preamp and power sections instead of tubes. They are less expensive, very reliable, and seldom need repairs. They often have pleasing clean tones, but their distortions sound much thinner. These amps are the sound of many genres, and are recommended to anyone looking for a reliable touring amp that needs little upkeep. Digital Amps: These amps use digital processors to simulate the sound of many different kinds of amps: tube and solid-state. Using software that models the sound of various amplifiers, cabinets, and sometimes even mics and micing positions these amps put the sound of many variables in one box and allow for some amazing experimentation. Modeling amps are programmable, and often have built-in digital signal processing such as delay, chorus, etc. Some include digital or analog outputs with speaker simulation for going direct into a recording interface or to house. Hybrid Amps: These amps use a tube preamp section in conjunction with a solid state power section. These amps generally use the combination of tube and solid-state technology to create a tube tone without requiring the use of power tubes.

Classifications of Amplifiers

There are three main classes of operation for a guitar amplifier. These are: A, AB, and B. Each class of operation has certain applications and characteristics. Likewise, each class has its advantages and disadvantages. Guitar amplifier classifications are determined by the amount of time, in relation to the input signal, that current flows in the output circuit. This is a function of the operating point of the amplifying device. The operating point of an amplifier is determined by how it is biased. Class A Class A amplifiers are generally known to have good fidelity and low efficiency. Fidelity means that the output signal is analogous to the input signal in every way, save for amplitude. 100% (360 degrees) of the signal is used throughout the entire circuit. There is a 1:1 ratio regarding energy used to energy lost, as Class A amplifiers are not efficient in the power department since the circuitry is designed for quality of fidelity. Since the output signal is a 100% (or 360) representation of the input signal, current in the output circuit must flow for 100% of the input signal time. This is the definition of a class A amplifier: amplifier current flows for 100% of the input signal. Since every device takes power to operate, if the amplifier operates constantly when powered on, it uses more power than if it was only on when signal is present. If the amplifier uses more power for the input, less power is available for the output signal and efficiency is lower. Since class A amplifiers operate for 360 of input signal, they are low in efficiency. This low efficiency is acceptable in class A amplifiers because they are used where efficiency is not as important as fidelity. In some cases, there may be a phase difference between the input and output signal (usually 180), but the signals are still considered to be in phase. Efficiency refers to the amount of power delivered to the output compared to the amount of power that is supplied to the circuit at the input. If all stages of the amplifier are biased in Class A, and the amplifier operates in Class A to full output (enough current flowing at idle that could be required for full output), it is said to be a "Pure Class A" amplifier. Pure Class A designs are understandably expensive to build and are usually only found in high-end boutique amps. Class AB Class AB is, as the name suggests, a hybrid of Class A and B operation. AB amplifiers remedy cross-over distortion (cross-over distortion is a type of distortion that occurs when one side of the output stage shuts off and another turns on) to a great degree by combining the best features of both classes. If the amplifier is biased so that the current flows in the device for 51-99% of the input signal, the amp is known to be operating in Class AB. Likewise, if an amplifier operates in Class A mode for only a portion of its output, and has to be supplemented with an additional current in the device for the remainder of its output, it is said to operate in Class AB. Class AB amplifiers are usually defined as amplifiers operating between class A and class B because class A amplifiers operate on 100% of input signal and class B amplifiers operate on 50% of the input signal. Anything between these two limits is operating in class AB. Relying on the use of two Class B units, a Class AB system is a pair of complementary push-pull devices, each amplifying ~55% of the original signal and combining them afterward, resulting in a full signal. The push-pull drivers are carefully biased just above their fully off state so that the transition between drivers is smoother. Therefore, each driver is never completely turned off. This alleviates most of the cross-over distortion at the expense of efficiency. The reason why each device takes more than 50% of the signal is to ensure that the signals crossover and match up, and no device is completely turned off at any time. However, Class AB amplifiers are still extremely efficient. The risk of crossover distortion still exists, where the mismatched signal ends clipped when summed; even at most performance volumes, the distortion is not readily noticeable and the power efficiency of the amplifier is considered to be worth it. These amplifiers have better power efficiency but poorer fidelity than class A amplifiers. Most amplifiers are in this category since they operate in two classes. In class AB and B, the amplifier is slower than in Class A because there is a finite time between the application of the input signal and when the devices are turned on to produce a flow of current to the speakers. However, Class AB and Class B are more energy-efficient than Class A and do not require such large power supplies. Class B Class B amps differ from Class A in their utilization of power. There is no current flowing in a Class B amp when the output devices are idle, and so they must turn on from a zero current state when signal becomes present. In a push-pull Class B design the output devices would each produce half of the audio waveform (one set for the positive half, another for the negative half) and would have no current flow when the other half is operating. Class B designs tend to have a slower slew rate and more crossover distortion but are less expensive and require less-intensive power supplies. The class B amplifier not only reproduces half the input signal, but amplifies it as well. Class B amplifiers are twice as efficient as class A amplifiers since the amplifying device only conducts (and uses power) for half of the input signal. These amplifiers utilize two drive elements operating in a push-pull configuration. On the positive excursion of the signal, the upper element supplies power to the load while the lower is turned off. During negative going signal excursions, the opposite operation occurs. This increases operating efficiency, but suffers from the nonlinear turn-on, turn-off region created where the driver elements switch from their ON state to their OFF state. This switching error creates a condition commonly called cross-over distortion. Total Class B amps are less common among guitarists due to their unusual output signal. Instead, they are usually paired with with a matching push-pull element, resulting in a Class AB system. I truly hope that after reading this article one can understand a little more about how amplifiers get their sound, and how to achieve results in the never-ending search for tone.

23 comments sorted by best / new / date

comments policy
    LivinJoke84
    Nice to see some plus points for solid state amps. Theres too many snobs on here that will have you believe that if you dont have a tube amp then you should just quit and go home
    Raijouta
    These amps are the sound of many genres, and are recommended to anyone looking for a reliable touring amp that needs little upkeep.
    In the article he says that a gigging musician would prefer a solid-state amp to a tube amp because they're supposedly more reliable. There are several falsehoods and fallacies in the early descriptions of amps, such as tube amps being inherently less reliable than solid state amps. For example, a tube amp will survive an electro-magnetic pulse from a nuclear blast, whereas a solid state will not. As well, hybrids are not always tube preamp and solid state power amp. The Vypyr Tube 60 is one example, and so is the Music Man HD130. SSes are not inherently less expensive than tube amps, either. It is true that many companies use SS technology in their cheapo amps, but a good solid state will cost just as much as a tube amp, if not more, eg. Pritchard Amps, Retro Channel Retro Wreck, etc. There are too many generalizations and stereotypes in the article and glossings-over of vital information for me to really state that this is something truly helpful for a beginner, or at least, helpful for someone who isn't willing to spend a lot of time researching the benefits and drawbacks of various kinds of guitar amplifiers.
    mmolteratx
    Mufassa wrote: ohh and whoever said that you can just pop a tube in like a light bulb is misinformed and must of never heard of the word BIAS.. applies to power tubes.. must replace them with the exact same mfg,lot,etc or you might run into issues... Last time I had to get my Randall fixed.. it cost a mere $75 and that was after 15 years of use.. its now 7 more years and all is good... some things I have the skill to do myself like I built a new footswitch and saved a $60.. Looked damn professional too.. 40 bucks in parts and a an hour or so of work.. no way in hell im paying 100 for a footswitch Old SS amps can be fixed even if you dont have the right part the mfg used.. its called a substitute.. Hell.. Just go to a electronic parts website.. used the search engine AND see how many parts have substitutes.. and YES.. electronics techs use substitutes all the time.. They even have a book used for this purpose.. looks like a big phone book.. LOL as for tube amps.. with the proper care.. they will last forever.. BUT they don't like drastic changes in temp and the power tubes have to replaced ever so often.. If you dont let them warm up or cool down properly.. You drastically shorten a tubes life AND Just because you dropped your amp.. DOESNT MEAN its a good idea.. you were lucky.. and that it
    Bro, I'm an engineer who does his own tech work. Bias is blown way out of proportion. Stick any EL34 in any EL34 amp and 99% of the time you won't need any bias adjustment. As long as it isn't dissipating ridiculous amounts of power, you're golden. There's a reason many manufacturers (Peavey, Mesa, etc) don't even bother including bias adjustments. Tube amps don't really give a crap about temperature. Again, they were designed for military use which requires usability from Arctic temps all the way to desert temps. The standby with warm up times is a myth that carries on from the 50s/60s when there would be a surge of current when the tubes weren't warmed up. When that happened, the shit caps that were available at the time would blow. And yes, I know about substitutes. Doesn't always mean one is available. And the shit construction of most SS gear doesn't lend itself to easy repair. It's gotten slightly better in the last few years but it's still easier and more economical to just scrap it and buy a new one in the majority of cases.
    mmolteratx
    thf24 wrote: Raijouta wrote: In the article he says that a gigging musician would prefer a solid-state amp to a tube amp because they're supposedly more reliable. There are several falsehoods and fallacies in the early descriptions of amps, such as tube amps being inherently less reliable than solid state amps. For example, a tube amp will survive an electro-magnetic pulse from a nuclear blast, whereas a solid state will not. Honestly, how likely is it that we're going to get hit with an EMP while you're playing a gig? In practical terms, it's a perfectly valid statement that a solid state is more reliable than a tube amp. If your stack falls over, your tube amp is done for the night, while with a solid state just stand it back up and you're good to go. There isn't reason to compare every scenario in which one amp's survivability is superior to the others; it suffices to say that tube amps are more delicate than solid states, therefore solid states are more reliable.
    http://www.youtube.com/watch?v=Q-z_qNNc Vz8 Add to that the fact that 90% of problems with tube amps can be fixed in minutes if you know what you're doing and I'd take my Diezel over an SS amp for gigging. Tubes were designed for military and aviation use. They're not lightbulbs FFS. Drop one 6 feet onto a hard floor and it'll survive, provided there weren't any structural defects off the line. And it's inside of a wooden box secured to a metal chassis. Dropping it isn't going to do shit to the tubes. I've dropped my Flexi down the stairs and not a single problem, not even a bent chassis. And then there's the fact that the vast majority of SS gear is built as cheaply as possible with no regard for longevity. While the majority of tube gear is built to be pro grade and last a lifetime. Besides, how often are your amps getting knocked over at a gig? Issues with the article: 1. Class B guitar amps don't exist as the crossover distortion renders them useless. 2. If you consider a task as difficult as replacing a lightbulb difficult, sure. Tube amps require more maintenance. 3. Tube amps are just as if not more reliable than solid state amps. 4. While you may rarely need to repair SS gear, those repairs are labor intensive and expensive. Especially when it's older SS gear using discontinued parts. They're just not meant to be serviced. 5. Hybrid amps are a combination of SS and tube technologies, regardless of the location of each. NeXEkho, class D power amps aren't used in any production guitar amps yet AFAIK. They're gaining series traction in the bass world due to light weight and high efficiency though.
    thf24
    Raijouta wrote: In the article he says that a gigging musician would prefer a solid-state amp to a tube amp because they're supposedly more reliable. There are several falsehoods and fallacies in the early descriptions of amps, such as tube amps being inherently less reliable than solid state amps. For example, a tube amp will survive an electro-magnetic pulse from a nuclear blast, whereas a solid state will not.
    Honestly, how likely is it that we're going to get hit with an EMP while you're playing a gig? In practical terms, it's a perfectly valid statement that a solid state is more reliable than a tube amp. If your stack falls over, your tube amp is done for the night, while with a solid state just stand it back up and you're good to go. There isn't reason to compare every scenario in which one amp's survivability is superior to the others; it suffices to say that tube amps are more delicate than solid states, therefore solid states are more reliable.
    NeXEkho
    Nothing about Class D? It's not common but Class D amps do exist.
    sim_1113
    I've played on many horrible tube amps just as I've played on many bad solid states, its all about opinion.. if u want an amazing tube amp tho, go bugera. The stack I got cost about $850 and I used to own a krankenstein that cost $1500 just for the head. Needless to say, I returned the krank. Money isn't everything
    Mufassa
    ohh and whoever said that you can just pop a tube in like a light bulb is misinformed and must of never heard of the word BIAS.. applies to power tubes.. must replace them with the exact same mfg,lot,etc or you might run into issues... Last time I had to get my Randall fixed.. it cost a mere $75 and that was after 15 years of use.. its now 7 more years and all is good... some things I have the skill to do myself like I built a new footswitch and saved a $60.. Looked damn professional too.. 40 bucks in parts and a an hour or so of work.. no way in hell im paying 100 for a footswitch Old SS amps can be fixed even if you dont have the right part the mfg used.. its called a substitute.. Hell.. Just go to a electronic parts website.. used the search engine AND see how many parts have substitutes.. and YES.. electronics techs use substitutes all the time.. They even have a book used for this purpose.. looks like a big phone book.. LOL as for tube amps.. with the proper care.. they will last forever.. BUT they don't like drastic changes in temp and the power tubes have to replaced ever so often.. If you dont let them warm up or cool down properly.. You drastically shorten a tubes life AND Just because you dropped your amp.. DOESNT MEAN its a good idea.. you were lucky.. and that it
    tubetime86
    This is like the book series 'XXXX for dummies.' The difference is this one is 'Amp Classifications by a dummy.'
    Mufassa
    bahh.. need an edit function.. the 1st para I meant to say must replace them with the exact same mfg,lot,etc unless you want to re-bias them.. @ a gig.. this is not very feasible.. will be made easier though with an external way to adjust the bias
    Mufassa
    hmm.. I have a '89 Randall RG 100es and it discounts most of what this article says about SS amps.. but that amp is exception.. not the rule though... IMO.. this amp has the best distortion of any SS amp and even quite a few tube amps.. modellers dont count as their distortions generally suck with a few exceptions AND MUCH tweeking
    Rubixcuba
    311ZOSOVHJH wrote: I would say my Peavey Vypyr 60 is a Hybrid amp and it doesn't have any tubes in the preamp. Also, maybe you could elaborate more on why gigging musicians prefer solid state amps.
    Uhh, you mean tube amps?
    oOJonnyLOo
    311ZOSOVHJH wrote: I would say my Peavey Vypyr 60 is a Hybrid amp and it doesn't have any tubes in the preamp. Also, maybe you could elaborate more on why gigging musicians prefer solid state amps.
    Firstly, you mean tube amps... and because they sound better ... what more do you need? they're also louder.
    DavidChainsaw
    Thanks a lot! Never thought about such specific thing until I got a L6 HD300 and found that is offers some kind of classes....sounds lame =D but that's whatta'ya working with virtual amps =D anyways, this info was helpful.
    fastlanestoner
    If anyone inferred that my stance is "solid state amps are better" then you should learn how to read context better. All I said was that solid-state technology is more reliable than vacuum tube, which is the truth. I was not saying SS amps are better.
    311ZOSOVHJH
    ^ We are happy that you like your Randall. I've read some posts by mmolteratx and I'm pretty sure he knows what amp biasing entails. Also, I have a Blog on how to bias a Class A/B push/pull amp manually. If you know what you are doing it takes about 15 minutes. Not all tube amps need to be biased. Tubes just need to be matched within say 4-5 mAmps. In a gigging situation you could get buy without biasing. Resistors, broken solder joints, etc are relatively easy to fix too. How are you going to troubleshoot and trace out an SS amp? I'm not really knocking SS amps, I've owned my share of those as well. I just think this Article is inaccurate in a number of areas. +1 to mmolteratx, Stratman and Raijouta. That Crate vid is golden.
    oOJonnyLOo wrote: 311ZOSOVHJH wrote: I would say my Peavey Vypyr 60 is a Hybrid amp and it doesn't have any tubes in the preamp. Also, maybe you could elaborate more on why gigging musicians prefer solid state amps. Firstly, you mean tube amps... and because they sound better ... what more do you need? they're also louder.
    No. I was asking fastlanestoner to expound on why SS amps are better for gigging. I didn't say it, he did. I want to learn more...
    311ZOSOVHJH
    I would say my Peavey Vypyr 60 is a Hybrid amp and it doesn't have any tubes in the preamp. Also, maybe you could elaborate more on why gigging musicians prefer solid state amps.
    fastlanestoner
    HeavyMetalSonic wrote: Didn't mention how bad digital and hybrid sound.
    ...didn't think I had to! www.audioecstasyproductions.com