Buying an Amplifier- read this first!!!

Which is best, Solid-state or Tube?
Here the traditional thinking is that solid state circuitry can produce superior clean power at a much more affordable price, while the scarcity of vacuum tube manufacturers today tends to make tube-based amps more expensive in a comparably powered amplifier. This has led to some interesting hybrids in which the basic tone is produced by a tube-driven preamp, while the power amp is solid state. Still, the majority of “serious” 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.

Amplifier classes explained (A,AB,B,D,H)
Class A – When an amplifier’s stage devices are passing current at all times, including when the amplifier is at idle (no music playing), whether the amplifier is single ended or push-pull, 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 when the signal passes from the positive to the negative or negative to positive, since each side of the push-pull section is already “on”. 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 B – 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 (one set for the positive half, and another for the negative half) 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 robust power supplies.

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 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 efficient than Class A and do not require such large power supplies.

Class D – A 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, ideally zero. In each case, the power dissipation is very low. This increases the efficiency, thus requiring less power from the power supply and smaller heat sinks for the amplifier. These are important advantages in portable and battery-powered equipment.
The “D” in class-D is sometimes incorrectly said to stand for “digital.” The Class D amplifier is based on analog principles; there is no digital coding 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 have to dissipate, in heat (watts), the difference between the rail voltage and the voltage across the speaker terminals, multiplied by the current (as stated in Ohm’s law). So, when there is a low rail voltage for use during periods of low volume, and a high rail voltage for use during loud volume, the output transistors don’t have to dissipate very 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.

Speakers: Does size matter?
For this discussion, we turn our attention to simple 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 difference between an open-backed cabinet and a closed-cabinet design. Which is why certain amps, like a 4×10 Bassman with an open back will sound different than a 2×12 Bassman with a closed cabinet.
Many blues players swear by those old open-backed 4×10 Fender amps, as they can produce a range of tones from smooth to searing. If you want to sound like Jimi, you’ll likely want to plug your Strat into a Marshall with a dual 4×12 cabinet design. One well-known guitarist preferred four 4×12 cabinets, which may explain his current hearing problems – yikes, 16 12-inch speakers will definitely play loud, but the overall frequency response, if charted using sensitive laboratory gear, will be totally different than that of our 4×10 example. Today manufacturers can custom tweak their amps by combining a certain size cabinet with a certain size set of speakers.
Some Vox and Marshall amps use Celestion speakers

Guitar amps for live, studio & practice
This topic has become less significant with the advent of the modern modeling amp, as these can serve as a practice amp, studio amp, and live amp. There are also interesting modeling modules for studio applications, like the Line 6 POD HD series. These provide an amazing array of amp models, as well as terrific digital effects thanks to sophisticated DSP processing.
Naturally, the ideal situation is to have one setup specifically for studio work or at-home use and another for those gigs that take place in larger venues. Like all areas of music technology, you have a surprising amount of bang-for-the-buck today, with the exception of the so-called “boutique” amps and vintage reissues that still command premium prices. Fortunately, Sweetwater carries amps from your basic (yet still very powerful) beginner’s amp all the way up to those drool-worthy Fender, Vox, and Marshall reissues.

Guitar Amps 

Now that you’ve selected your dream guitar, we need to find an amp to go with it. There are numerous options depending on size, sound, amplifier technology, and configuration. Below, you find a friendly guide to steer you through the maze.
Types Of Amplifiers
There are four types of guitar amplifiers: Solid-state (analog), Tube, Modeling (digital), and Hybrids.

Solid-state Amps: These 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 many come with “distortion” channels also. These amps are popular with players looking for a sturdy, reliable touring amp.
Tube Amps: Tube amps preferred by many guitarists for their warm, fat tone and “organic” 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. Tube performance can deteriorate over time, so tubes need changing occasionally.

Modeling Amps (Digital Amps): 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 amps in one box. Modeling amps are programmable, and often have built-in digital effects such as delay, chorus, etc. Some include digital or analog outputs with speaker simulation for going direct into a recording interface or PA system.
Hybrid Amps: Combining the best of each type of amp into one package, these amps use an actual tube in conjunction with the solid state power section of their amps. Marshall Valvestate amps use 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.

Configurations
In addition to types of amplification, amps come in different configurations. Combos (short for combinations) are self-contained units containing the amplifier and speaker in one cabinet. Amps also come in separate Head and Speaker Cabinets. These allow you to use any amp head with virtually any speaker cabinet. They also break the amp into two units, making each unit lighter and easier to carry than a single combo. Combining two cabinets and a head is called a “stack.”
Construction
The thickness of wood used to construct the cabinet is a major factor in determining the quality of sound. The thinner the wood used, the more likely the speaker will vibrate itself loose. A thickness of at least 1/2” will achieve a strong sound and keep the speaker in place. Another factor determining sound quality is whether the amp has an open or closed back. Closed- back guitar amps produce a 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 guitar amp.

Power and Speaker Size
The power rating and size of speaker you choose for your amp 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 some small tube amps to be found. For rehearsal and playing smaller venues, consider tube and modeling combo amps with power ratings averaging about 50 watts and 12″ speakers for fuller sound. For larger venues or for performing loud, expect power to average at 100 watts and up. You can use “twins,” or combo amps that have pairs of 12″ speakers, but this is where a separate head and speaker cabinets (a “stack”) are most effective.
Other Options
Other additional features you might encounter include:

Reverb Units: Some amps use spring reverbs, which can be very natural sounding, while others use digital reverb.

Effects Loops: These 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 going from a clean tone to a distorted one. Check to see if a footswitch is included. Digital amps often require the purchase of an additional MIDI footswitch to change tones remotely.

Built-in Effects: Roland Jazz Chorus amps are famous for their built-in stereo chorus. Tremolo is another effect many amps feature (great for surf guitar.) Modeling amps usually contain multiple built-in digital effects.

Hopefully this will give you enough knowledge to purchase the AMP you need!!

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