# Guitar/Buying an Amplifier

Amplifiers come in a wide variety of designs and your choice of
amplifier should be based on the type of music you wish to play. Your
local guitar dealer will let you test the different amplifiers they
stock though they may only offer a limited range due to space
restrictions. Its always a good idea to visit many dealers including
pro-audio outlets to test amplifiers across the entire price range
before committing yourself. This chapter will explain the difference
between a tube amplifier and a solid state amplifier as well as
exploring the variations on these two basic designs.

## Tube, Solid State and Hybrid Amplifiers

### Tube

Tube amplifiers produce a warm and fat tone that is popular with
guitarists. New models are available from Marshall, Fender and Vox as
well as other manufacturers which range in quality and price. Vintage
tube amplifiers from the 1960s and 1970s are available to buy, though
maintaining them can be expensive especially with regards to the cost of
replacement parts. The continuing popularity of vintage amplifiers from
earlier decades has resulted in a market for reissues.

!Mesa Boogie Mark IV Combo tube
amplifier

There are three operating modes for tube technology: Class A, Class B
and Class AB.

-   Pure Class A operates by having a full continuous current flowing
    through the tubes. The tubes are still fully powered even when there
    is no signal to divert to the speaker. This makes Pure Class A tubes
    expensive to run; similar to a car idling in neutral with the
    throttle pedal right down. Pure Class A responds very fast to an
    input signal with a tube saturation (distortion) that many
    guitarists find appealing. Many Pure Class A amplifiers use tubes
    with a low wattage to offset their inefficient operating mode
    thereby increasing the tubes lifespan and reducing running costs.

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-   Class A refers to an output design that doesn\'t use a Pure Class A
    single-ended output stage. Class A uses a pair of tubes or multiples
    terminating in a push-pull output stage.

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-   Class B is rarely used in guitar amplifiers due to crossover
    distortion issues so manufacturers instead use a combination of
    Class A and Class B known as Class AB.

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-   Class AB operates by using a pair of tubes. Whereas Pure Class A
    produces the entire waveform, positive and negative, with a
    single-ended output, Class AB produces the entire waveform using two
    tubes with one handling the positive voltage and the other the
    negative voltage. In comparison to Pure Class A, which uses a full
    continuous current to achieve a three hundred and sixty degree
    waveform and is always on at full power even when there is no signal
    present, Class AB uses a smaller amount of constant current to
    achieve the same always on state for the two tubes. Class AB is
    thereby more efficient with regards to power consumption and heat
    dissipation and the operating life of the tubes are greatly
    extended.

\
Tube amplifiers:

-   A tube is based on vacuum technology and requires more energy than a
    solid state amplifier with the same wattage.
-   Vacuum tubes are expensive and require replacement every one to four
    years depending on use.
-   Amplifiers with tubes are generally heavier than solid state
    amplifiers due to the need for an output transformer.
-   Tube amplifiers are usually more expensive than a solid state
    amplifier.
-   Tubes require a warm-up period before they reach optimum
    performance.
-   Tube amps are more fragile and repair-prone than solid state amps.

### Solid state

!Roland Jazz Chorus JC-120 solid state
amplifier

Solid state amplifiers use transistors instead of tubes. They are
popular with beginners due to their affordability and lower weight.
Solid state amplifiers have a fast attack time and are immediately
available for use when switched on. Solid state circuitry allows more
volume to be applied to the output signal before clipping occurs which
makes the amplifiers appealing to amateur and professional jazz or
acoustic guitarists who may wish to retain a clean sound at high
volumes. A solid state amplifier matched with good quality speakers can
produce a wide frequency response. Some solid state amplifiers use field
effect transistors (FET) on the preamp stage which at high gain produces
a distortion similar to a tube amplifier.

Solid state amplifiers retain a tight low end while producing a full
harmonic distortion at high gain which is desirable for the metal genre.
This has resulted in a range of solid state amplifiers specifically
designed for metal guitarists. Solid state amplifiers tend to be smaller
and lighter than their equivalent tube amplifiers and these design
factors allows manufacturers to build amplifiers weighing less than
10lbs which are capable of 150w clean RMS sound. Root Mean Square refers
to continuous output as opposed to Peak measurement which is the wattage
of an amplifier measured in a short burst.

Solid state amplifiers:

-   A solid state amplifier requires less energy to power than an
    equivalent tube amplifier.
-   Solid state circuitry needs minimum maintenance and there are no
    tubes to replace.
-   Solid state amplifiers are more robust than tube amplifiers.
-   Solid state amplifiers are available in an affordable price range.
-   A solid state amplifier requires no warm-up.

### Hybrid

All amplifiers have a preamp stage which boosts the signal from the
guitar before it is sent to the power amplifier stage. Hybrid amplifiers
are designed to utilize both tube and solid state technology and are
available in the following configurations:

-   tube preamp coupled with a solid state power amplifier
-   solid state preamp coupled with a tube power amplifier

A tube preamp coupled with a solid state power amplifier outputs a tube
tone with a fast attack. A solid state preamp coupled with a tube output
provides solid state high gain with the warmth of tubes.

Design variations may include digital modeling, integrated tube/solid
state stages or further additional tube or solid state stages in the
signal path:

-   The Vox Valvetronix signal path starts with solid state effects and
    preamp which sends the signal to a tube/solid state integrated
    output stage.
-   The Line 6 Spider Valve signal path starts with digital tone
    processing followed by a tube preamp which sends the signal to a
    tube power amplifier.

## Features

### Standard

-   Input - accepts a quarter inch mono jack cable
-   Power - off and on
-   Volume - adjusts the volume
-   Speaker - built-in or separate cabinet

### Additional

-   Gain - the amount of boost applied at the preamp stage
-   Overdrive or distortion
-   Reverb
-   Tone/equalizer - treble and bass tone knobs, sometimes three or more
    (mid, or low mid and high mid may be added), or graphic equalizer
-   Headphone socket - headphones can be used for private practice
-   Channel selection - switch between clean and high gain/overdrive
    (often with a footswitch)

### Extra

-   Additional inputs - high sensitivity input for use with a low-output
    pickup and low sensitivity input for use with a high-output pickup
-   Modeling - digital emulations of popular amplifiers, speakers and
    effects
-   Onboard effects - built in proprietary effects such as chorus,
    delay, echo and compression.
-   Effect loop - external effects can be plugged into the amplifier
-   Line in - the audio signal bypasses the preamp stage and is sent
    directly to the power amplifier
-   Line out - the output from the amplifier can be sent to another
    power amplifier or mixing desk
-   Speaker out - standard on a separate amplifier \"head\" and when
    found on a combo amplifier allows a different speaker to be used, or
    a second speaker. Adding a second speaker can increase the wattage
    output and volume.
-   Foot-switch plug input - an external foot-switch can be plugged in
    to control overdrive, reverb, solo boost, or another feature.
-   Impedance switch (on tube amplifiers only) - change the resistance,
    measured in ohms, of the amplifier to match speaker impedance
-   Standby switch (on tube amplifiers only) - the standby switch has
    exactly the same function as the standby mode of a computer which
    removes the need to cold boot when taking a short break. Any
    technology that requires a time period to reach optimum working
    state benefits from this idea. Components are powered down while
    remaining in a ready state which saves energy and extends their
    operating life.

## Wattage

### Amplifiers

The wattage rating is the maximum volume that an amplifier is designed
to output. A 10 watt amp is typically the first purchase for a beginner.
An amplifier in the 30 to 50 watt range is loud enough for band use and
home band rehearsals and is a common first performing amp. If you are
intending to buy a 100 watt amplifier you will need to consider using a
rehearsal studio for practice, as this will be too loud for a home. The
list below outlines possible uses based on the amplifier\'s wattage
rating.

The ratings below need to be interpreted differently for some genres of
music. A 30W amp that would only suffice for a rehearsal amp in a death
metal band might be entirely appropriate as a large-venue amp in a jazz
quartet, where all the other instrumrnts are acoustic.

Solid state amplifiers:

-   10-30W: home practice
-   30-50W: band practice, small club
-   50-100W: large venue

Tube amplifiers:

-   10-20W: home and band practice
-   20-30W: band practice, small to medium club
-   30-50W: small to medium club
-   50-100W: extremely loud in confined spaces or small clubs, though
    diffuse in large halls

### Speakers

The function of a speaker is to convert an electrical signal into sound
waves. This is achieved using an electromagnet called the voice coil
which is attached to the speaker cone by a spring called the spider. The
vibrations from the voice coil are transferred via the spider to the
speaker cone.

A speaker cabinet will house either a single speaker or multiples. A two
speaker configuration may utilize smaller speakers than a single speaker
model e.g. 2x10″ instead of 1x12″. The main benefit of having multiple
speakers is an increase in volume and bass response without sacrificing
the higher frequencies. By having more speaker cones the speakers will
move more air. For example, two 10″ speakers have a combined surface
area of 157 sq.in. while one 12″ speaker has a surface area of 113
sq.in. A 4x10″ cab is often used for large combo amplifiers as it
provides most of the bass response you would get from a 1x15″, but
retains the high frequency that the 1x15″ cannot produce. Also, it will
have increased power-handling capability, or more precisely, they split
the amplifier output. Thus, given the same amplification head, a two
speaker configuration will have a louder volume but only half the power
to each speaker.

A low power speaker is louder at the same power than a high power
speaker. This is known as speaker efficiency or sensitivity. A 25 watt
speaker with a 10 watt amplifier will generally be louder than a 100
watt speaker with the same 10 watt amplifier. A cabinet with multiple
speakers allows the use of low power speakers with a high power
amplifier.

To avoid damaging speakers it is recommended that the speaker wattage
should exceed the amplifier wattage. Damaging transient peaks or spikes
that are the result of an amplifier outputting more wattage than the
stated rating are negated by the higher headroom. It is not unusual to
find a 150 watt speaker matched to a 100 watt amplifier or a 75 watt
speaker matched to a 50 watt amplifier. Multiple speakers achieve the
same effect by sharing the amplifier load between speakers which allows
low wattage speakers to be used with a high wattage amplifier. If you
are buying a combo amplifier the issue does not arise as the
manufacturer has ensured that the amplifier and speaker are matched.

### Impedance

The speaker-out socket of an amplifier will have an impedance rating.
You should only plug in speakers with the same impedance rating. Some
amplifiers are equipped with a switch or dial which allows the impedance
to be set at 4 ohm, 8 ohm or 16 ohm. Plugging in a speaker with a too
low impedance rating may cause damage to the amplifier.

Tube amplifiers are much more sensitive to speaker impedance. Any
mismatch between the speaker impedance and the impedance set on the
amplifier will cause a strain on the transformer and tubes. Never turn
on a tube amplifier with no speakers connected. This might cause severe
damage to the output transformer. Always turn off your tube amplifier
before disconnecting the speaker. Some amplifiers have shorting jacks,
e.g. Hiwatts, these may allow you to change speakers on the fly, but
always at the amplifier side of the cable, never at the speaker side.

## Types of Unit

!Marshall amplifier without the speaker cabinet plugged in. Commonly
referred to as the
head._1959SLP-01_firmy_Marshall.jpg "Marshall amplifier without the speaker cabinet plugged in. Commonly referred to as the head.")

### Micro/Headphone amplifiers

Micro amplifiers are small portable amplifiers that generally do not
exceed 10 watts. These low wattage solid state amplifiers do not utilize
FET circuitry so they tend to distort very quickly. The Danelectro
Honeytone and Vox amPlug respectively illustrates the differences
between a micro amplifier and a headphone amplifier. The Danelectro
Honeytone has a speaker and pots and resembles a miniature amplifier.
The matchbox shape Vox amPlug is a headphone amplifier with rotary dials
instead of pots and offers four model emulations including the Vox AC30.

### Busking amplifiers

These small portable battery powered amplifiers are designed for outdoor
use where no mains power is available. The battery will normally provide
up to six to ten hours use on one charge though buying a spare battery
or ensuring that the amplifier can also be used with AC power will
offset this limitation. Examples include the Pignose Hog 30 which has an
8″ speaker and a rating of 30 watts and the Vox DA5 which has a 6.5″
speaker and a rating of 5 watts.

### Practice amplifiers

Practice amplifiers are designed to be used at home and are not suitable
for concerts or band rehearsals. The Vox DA5 and Epiphone Valve Junior
are small practice amplifiers designed for home use and are easily
transported and stored.

### Small venue/recording amplifiers

Combo amplifiers are suitable for small venues. The standard combo
consists of a 50 watt amplifier combined with one 12″ speaker with both
components enclosed in a single cabinet. Some manufactures combine a 30
or 40 watt amplifier with two or four speakers. A tube or solid state
amplifier with a minimum of 30 watts and good tone would be acceptable
for professional use. Combo amplifiers are favored by many guitarists
because of their compact form and matched amplifier and speakers. The
Vox AC30 and Fender Twin are examples of combo amplifiers.

These combo amps are also used in the recording studio, as they are
easier to transport and one does not need high volume in a recording
setting. As well, a very loud stack may need too high a volume to get a
guitarist\'s preferred tone, to the point that there may be sound
leakage into other booths or microphones. A smaller combo can reach
desired overdrive levels at lower volumes.

### Large Venue amplifiers

Amplifiers that range from 50 to 100 watts are suitable for a large
venue. A half stack consists of a separate amplifier head connected to
one 4x12″ speaker cabinet and is a very common guitar rig. A full stack
consists of a separate amplifier head with two speaker outs and two
4x12″ cabinets stacked vertically. A Marshall head and full-size cabinet
are bulky and heavy items to transport. A full-sized Marshall cabinet
has two handles, one on either side, and requires two people to lift and
move it safely. Large 8x10\" cabinets are hard to transport, if you are
moving them yourself (touring rock bands have a road crew to move gear
like this from vehicles to the stage). Storage and transportation must
be considered when buying a large guitar rig.

### Heads, cabinets, and stacks

A half-stack consists of two components:

-   head - amplifier
-   cabinet - speakers

When purchasing the two components check that the impedance of the
cabinet matches the impedance of the head. Make sure the cabs RMS rating
is about the same as the head\'s power output at the impedance of the
cab. Generally a single guitar cabinet would have 4x12″ speakers though
1x12″ and 4x10″ cabinets are also available. Some players use 1x12\"
speakers for small clubs or 1x15\" for deeper bass response.

### What format to buy

Most beginners start by buying a small, lightweight practice amp. Then,
when they start jamming, they buy a more powerful, larger amp capable of
being used at a pub or nightclub show. As they progress, an amateur
guitarist may buy a bigger, more powerful stack for large venue shows
and one or more higher-quality, expensive combo amps for recording.
 
