Many beginning electric guitarists think guitar amps are boring and not as exciting, inspirational and important as their guitar. However, nothing could be further from the truth. In fact, it might be said that the right amp can even make a cheap guitar sound good!
However, there are so many guitar amp options, for example: size, sound, configuration, technology and price, that spending a little time to learn about amps is a good idea. So, let’s take a quick tour to discover a few fundamental and subtle differences between your many choices.
Types Of Amplifiers
Simply stated, there are four types of guitar amplifiers: Tube, Solid-state, Modeling and Hybrids.
Tube amps are preferred by many guitarists for their warm, fat tone and smooth distortion. 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. Most tube amps have separate channels that can switch from clean to distorted tones instantly. A vacuum tube performance can deteriorate over time, so tubes need to be changed periodically.
Solid-state amps are called solid-state because they use transistors for their preamp and power sections instead of tubes. They are very reliable and seldom need repairs. They often have a very “clean” tone, although most come with “distortion” channels. Solid-state amps are popular with players looking for a sturdy, low maintenance, reliable amp.
Modeling amps use digital processors to simulate the sound of old-fashioned tube technology. Using software that “models” the sound of tube amplifiers and cabinets, these amps put the sound of numerous amp configurations in one box. Modeling amps are programmable, and often have built-in digital effects such as delay, chorus, etc.
Hybrid Amps combine the best of each type of amp into one package. These amps use actual vacuum tubes in the preamp section and solid state circuitry in the power section to create a tube tone without requiring the use of power tubes.
The following section is a bit technical, but it needs to be presented never-the-less.
Class A: When an amplifier’s stage devices, whether single ended or push-pull, are passing current at all times the amplifier is said to be biased in Class A. Because the current is flowing at all times, an input signal causes the current to be immediately diverted to the speakers, and therefore, the sound is very “fast”. In the case of a push-pull amplifier, there is also less crossover distortion since each side of the push-pull section is already “on”. Class A designs are expensive to build and are usually only found in high-end amps.
Class B: Differs from Class A in that there is no current flowing when the output devices are at idle, and as a result, they have to turn on from a zero current state when signal is present. In a push-pull Class B design the output devices would each produce half of the audio waveform and would not have any 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 power than Class A.
Class AB: As its name implies, this is sort of a combination of Class A and Class B operation. If an amplifier operates in Class A mode for only a portion of its output, and has to turn on additional current in the devices for the remainder of its output, it is said to operate in Class AB. 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 input signal and when the devices are turned on to produce a flow of current to the speakers. Class AB amps are also efficient than Class A and do not require large power supplies.
Class D: The Class D amplifier is one in which the output transistors are operated as switches. When a transistor is off, the current through it is zero. When it is on, the voltage across it is small, approaching zero which increases it’s efficiency, thus requiring less power than Class A, B or AB. These become important advantages in portable battery-powered amps. Class D does not stand for digital as they are based on analog principles, there is no digital encoding of the signal.
Class H: If an amplifier has more than one voltage rail (DC voltage delivered by the power supply), then it is designated Class H. This is a very efficient type of amplification. The output transistors of an amplifier has to dissipate heat (watts), so, when there is a low rail voltage during periods of low volume, and a high rail voltage for use during loud volume, the output transistors don’t have to dissipate as much power when the volume is low. This causes less drain on the power supply and makes it possible to build a very lightweight design. The drawback is distortion at mid-volume when the amplifier has to go back and forth between the two (or more) rail voltages.
Combos Amps, short for combinations, are self-contained units containing the amplifier and the speaker(s) in one cabinet.
Head and Speaker Cabinets are amps that come in two separate sections, the amp and a separate speaker cabinet. These type of amps allow you to use any amp head with virtually any speaker cabinet. Also, by separating the amp and speaker cabinet into two units, each unit is lighter and easier to carry than a single combo. Combining two cabinets and a head is called a “stack.”
For this simple overview, we’ll turn our attention to elementary physics. Smaller speakers can produce higher frequencies than larger speakers, which is why a tweeter is small and a woofer is large. So in the real world, a 10-inch speaker will generally produce a better “top end” than a 15-inch speaker. There is also a sound difference between an open-backed cabinet and a closed-cabinet design.
Many blues players favor 4×10 open-backed amps, as they can produce a range of tones from smooth to searing. Others like the sound of a dual 4×12 cabinet design. While some preferred four 4×12 cabinets. And while it’s true that 16 12-inch speakers will definitely play loud, the overall frequency response, if charted using sensitive laboratory gear, will be totally different than that of our 4×10 example. Today manufacturers custom tweak their amps by combining a certain size cabinet with a certain size set of speakers.
Power and Speaker Size
The power rating and size of the speaker(s) you choose will depend to some degree on application and price. Practice amps are usually solid state or modeling combo units featuring low power, 10-30 watts, and small, 8” or 10”, speakers, although there are a few small tube amps to be found. For rehearsal or for playing smaller venues, tube and modeling combo amps with power ratings averaging about 50 watts with 12” speakers for “bigger” sound are generally used. For larger venues or for performing loud, power ratings averaging of 100 watts and up are the norm. Combo amps that have pairs of 12” speakers, “twins,” are also used as they can get quite loud.
The thickness of wood used to construct the cabinet is a major factor in determining the quality of sound. A thickness of at least 1/2’’ will achieve a strong sound and keep the speaker from rattling loose. Another factor determining sound quality is whether the amp has an open or closed back. Closed-back guitar amps produce better bass response from the speaker. When moving an amp from gig to gig, it’s quite common for them to get banged up a bit. Good corner protectors will add to the life of the amp.
Other Options and Additional Features
Reverb Units: Some amps use spring reverbs, which can sound very natural, while others use digital reverb.
Effects Loops: These input and output jacks allow you to add stomp boxes or rack units after the preamp section of the amp to avoid amplifying any effect noise.
Channel Switching: These amps allow you to switch between different preamp channels, usually from a clean tone to a distorted one. Digital amps often require an additional MIDI foot switch to change tones remotely.
Built-in Effects: Some amps have built-in effects, such as: stereo chorus and vibrato. Tremolo is another effect many amps feature. Modeling amps usually contain many built-in digital effects. Tone and Volume Controls: Some amps have a built-in equalizer (EQ) that enables you to “cut” (de-emphasize), or “boost” (emphasize), particular frequencies to alter the tone of your guitar. A presence, master and gain switch may also be included.
Tube or Solid-State?
The traditional thinking is that solid state circuitry can produce superior clean power at a much more affordable price than vacuum tube-based amps which are much more expensive in a comparably powered amplifier. This has led to hybrids in which the basic tone is produced by a tube-driven preamp, while the power amp is solid state. The majority of vintage players will almost always lean towards a tube amp, though the attitude is changing as manufacturers turn out amazing new amps that are based on cutting-edge technology.
Combo Amp or Separate Head and Cabinet?
The answer to this question really depends on how big a venue you are planning to play. For example, for club dates and even small halls, today’s combos are well-equipped with enough power to deliver sound that will be heard all the way in the back of the room. However, if your goal is to have enough sonic power to fill a giant auditorium or even an open arena, you will want a high-powered stack with at least a 4 x 12 cabinet. It should be noted that, some players still prefer a smaller amp for its specific tone, and then simply mic the amp and run it into the PA system to achieve greater volume.
Modeling amps are like “sonic chameleons” that offer the best of all worlds. You can buy a basic “practice” amp that will deliver almost any tone or effect you might need or want, and it will also serve as a great studio amp. These budget-friendly modeling amps provide everything from clean rhythm tones to full-out overdrive lead tones. They also include an extensive library of effects like reverb, chorus, phase, flange and delay. Back in the 1960s and early ‘70s, guitarists needed multiple outboard stomp boxes to produce distortion, chorusing, flanging or wah-wah sounds. All of those connected boxes added up to one thing: Noise! But today, thanks to modeling, all effects, even multi-effects like chorus plus delay plus reverb, are designed to be amazingly quiet. There is no longer any need to compromise your sound just because you’re choosing an entry-level amp.
Amps for Practice, Studio and Live
This distinction has become less significant with the advent of the modern modeling amp, as they can serve as a practice amp, studio amp, and live amp. There are also modeling modules for home, studio and live applications. These provide an amazing array of amp models, as well as terrific digital effects thanks to sophisticated Digital Signal Processing, DSP.
Of course, the ideal situation is to have one setup specifically for home, one for studio work, and another for those gigs that take place in larger venues. But that’s really an economic fantasy. Fortunately, like all areas of music technology, you have a surprisingly amount of value today, with the exception of the so-called “boutique” amps and vintage reissues that still command premium prices.
Computer Software Amp Plug-Ins
Just like with analog amps, the tone you get from connecting your guitar into your computer depends greatly on the digital amplifier software that you use to model the amp. There are a wide variety of applications available for computer-based musicians playing guitar, here are a few brand names…
AmpliTube 2 allows you to choose between seven high gain amps, 16 cabinets, and six microphones. You can also add 19 effects like Chorus and Flanger to the effects chain to mold your tone just the way you want it. AmpliTube also allows you to configure two separate guitar chains in one preset. This means that you can configure a distorted sound, a clean sound, and then play them separately or at the same time.
Eleven is an amp modeling-only plug-in with no effects included. In other words, this amp is focused on the tone you get from the amp instead of trying to hide defects in the modeling by adding effects over the tone. Effects can be added separately through the digital audio workstation software.
Gearbox is a versatile piece of software that allows you to access 72 guitar amp models, 24 guitar cab models with four mic options each. It also has 28 bass amp models, 22 bass cab models with four mic options each. It also includes over 90 stompbox and studio effects, and six mic preamp models.
Guitar Rig is without a doubt one of the premiere pieces of software for amp modeling on the computer. It has a user interface that is split vertically between your presets on the left and your rig components on the right. It has 44 classic and modern guitar effects, 12 tube amps, and 12 matched cabinets.
Guitar Combos is a small collection of quality virtual amps without any included effects that will give you the ease of configuring your tone quickly. This is perfect for someone who is just looking for the amp sound. There are 100 included presets in the combo package and you can adjust the Volume, Presence, Bass, and other knobs the same way you would with a real combo amp. A Tuner is also included.
ReValver Mk II is a valve modeling package with amps and stomp boxes, but this software goes a step further than the others. In addition to changing amps and adding effects, it allows you to access the power amp rectifiers and output transformers. No other software package lets you do that.
Now, with the valuable knowledge you have gained, you will be able to amp-up a vast array of sounds which you can put to use with maximum effect, no matter what genre of music you play. And perhaps more importantly, you’ll be able to “tone-tweak” like a pro at your local music store as you soar through the complex maze of amp selection.
‘Til next time, have fun and remember: if you want to get your guitar sounding just right, make sure you have the right amp… I’ll be listening!