Bass Amp - Bass Combo Amp - Bass Amp Head - Tube Bass Amp
Bass Speaker - Bass Cabinet - Bass Stack - Settings - Reviews

Also called bass guitar amplifier or simply bass amp, performs a bass guitar sound amplification. Bass amps are available either as a combo, the most common type, also called bass combo amp with amplifier and speaker(s) in one unit. Or, they are available as a bass amp head which is just the amplifier, supposed to be used with one or two separate speaker cabinets. Instead of a bass head, a separate bass pre-amp and bass power amp can be used too.
Since a bass amp has an extended bass frequency response, the speakers are usually larger. The tone controls are also optimized for bass guitars, typically ranging down to 40Hz.
Below on this page, there are some words about the various bass amp/speaker arrangements and its terms.

All bass amps, combo amps or amp heads, have at least volume and tone controls. Some have two channels. As an example, the first channel with bass, midrange and treble and the second channel with bass and treble. Or one of the channels has a parametric eq tone control too. Better bass amps, may also have a pre-amp input gain, graphic and/or parametric equalizer, compression/limiter or more. Some other amps, not necessarily better overall, have built-in digital effects and modeling.
The above mentioned controls and functions are also available as separate units. Pre-amp, tone controls, graphic equalizer, parametric equalizer, compressor/limiter.

Like all other electronics in the late 40s and early 50s, the first bass amps only used vacuum tubes. Fender and Ampeg were some of the first manufacturers. Transistor (solid state) bass amps became more popular in the early 70s. The transistor amps did not color the guitar sound as the tube amps. In that way it sounded different, cleaner. On the other hand, if overloaded it usually didn't sound good.
Transistor amps had higher dynamics without any soft overdrive like tube amps, so distortion in the final amplifier would sound more raw and unpleasant. People learned how to master the "solid state" sound and other ways of overdrive and distortion were used, with overdrive/distortion pedals in particular.
Eventually, at the time when pedals with tube emulation had become more popular, tubes were getting in the light again. The "tube sound" again regained more popularity, and old tube amps where put in production, including vintage reissues of old classic and trustworthy models. There are also hybrid amplifiers with tubes only in the pre-amps, usually 12AX7, and transistors in the power section. Some users prefer tube amps but transistor amps are the most common.
Worth mentioning is that some guitar players may prefer bass amps because they provide more of the low frequency range.

Bass Pre-Amp

Bass combos and heads have a bass pre-amp inside. A dedicated bass pre-amp and power amp combination can be used instead of a bass amp head. There are many bass pre-amps on the market but not as many dedicated bass power amps so if a certain pre-amp is to be used, most users would use it together with an amp head, or combo.
And if someone likes the preamp of an amp head, and wants to upgrade in regards of power, he or she might take the pre-amp out on the amp head and put in into a power amp, or another amp head with more power. So, there are different ways to go, of course.
Below, there is a more bass pre-amp info.

Bass Power Amp

Again, bass combos and heads also have a bass power amp inside. Bass power amps only make the final amplification so they have no instrument level insputs. A pre-amp or other device with a line level out has to be used in front of it.
There not many bass power amps but two can be mentioned, the Ampeg SVP-1600 and Fender the MB-1200.

Also called bass combo. With a built-in speaker and sometimes two speakers, as in the Fender Rumble 100 to the right.
Common driver sizes are 8, 10 or 12". There are some models that may have two 10" LF drivers, or one 15" LF driver, and also an HF driver/HF tweeter/horn in order to keep a good sound in the entire frequency range.

A bass amp with no speaker is a bass amp head or just bass head. Since they are smaller than a usual combo they can be put near to the bass player. It is then easier to reach the controls, while the speaker/cabinet can be put on another location.

The term tube bass combo amp is too long and not used and for some unknown reason, not even the shorter name tube bass combo is used more than very rarely.
Next, tube bass amp head is used and we find more results with the shorter tube bass head.

When a bass is played through a tube amp, the harmonics that can be created in the (tube) sound will be perceived relatively more, because of the less sensitivity at low frequencies related to human hearing. [Image below right].
The harmonics, second most, will be heard relatively stronger. That's why using a tube bass amp can make such a difference.
Yes, in average a tube bass amp cost somewhat more. Many bass amps are solid state, transistorized, some are hybrid which usually is that the amplifier has a tube pre-amp and the rest is transistor. Those who look for an all tube amp usually believe that a "real" tube sound can only come from from a final power amp where there are tubes, triode tubes in particular. Infact, the pre-amp does not have to be a tube pre-amp in order to get a good tube sound from the power tubes. But since most serious tube amp users know this, it is better to inform about that when the pre-amp is discussed.
Tubes are often easily replacable if needed. However, sometimes it can take some time to find the same or equivalent tubes for older products. A semiconductor/transistor amplifier though, needs more service to be repaired.

Look of tube amps

Common for tube amps, combos and heads, is that they look older, although mixed with a more modern design and aesthetics, if compared to (newer) transistor amps. Simply because manufacturers use their old design on the reissues and on newer models but also, that other new manufacturers just use old design and in that way, look "older" and hence, more "reliable" etc.

Tube amp sound

It refers to a class A power tube amplifier. There are class B tube amps as well. These do not have the typical tube sound because of only odd order harmonic distortion.
Class A tube sound is reviewed as more "warm", "musical" etc. The transfer function graphs of an class A amplifier gets non-linear towards the signal peaks in a way that the gain get lower towards signal peaks. This causes a compression at higher levels. This compression of the signal waveform creates harmonic distortion. Because the non-linearities at min and max levels are asymmetric, an even order overdrive distortion is created. It means that the first harmonic of each of all frequencies in the signal, is one octave above the fundamental frequencies.
A tube amp generally distorts smoother, has a smoother overdrive, since the distortion increases more gradually towards higher volume. Conventional transistors or diodes tend to be less rounded at the bottom and the top. However FET/MOSFET transistor circuits can also create a distortion somewhat like tubes and it is possible to simulate asymmetric and smooth overdrive circuits even with bipolar junction transistors.
Class A has the lowest power efficiency so these amplifiers run warmer. Class A tube amps have current constantly flowing through the output tubes (or transistors) even if there is no incoming signal, so the output devices are always on. The class A amplifier is dissipating ca 80% of its power in heat with an efficiency of only 20%.
Tube emulation can sound quite well, but it cannot sound as a tube amp. Tube simulation fails to sufficiently capture the nuances with the different origins of the bass, tube amp, output transformer and speaker(s). That is why tube emulation cannot match up to the "real" tube sound.

In a tube amp there is an output transformer between the power tube(s) and the speaker, that matches the impedance and voltage. Depending on the size, it will affect the sound too.

Output transformer saturation

When the ferromagnetic core of an output transformer, becomes electromagnetically saturated due to overload, the signal becomes compressed, and smooth clipping occurs. It is called output transformer core saturation. This distortion is added to the tube distortion. The transformer also affects the levels of low and high frequencies, rounding them a bit.

Microphonic tubes

One less mentioned reason, nevertheless claimed to be impossible to disregard, is that vacuum tubes may have, or get a microphonic effect as they get older. Therefore, speakers might cause a mechanical feedback which can become a part of the sound if the volume is high and feedback close, as in a combo or stack. This mechanical interaction is probably not thought of by the tube emulation designers.
A microphonic tube will feedback like a microphone though not as flat. No tube is free from microphonics because of its electromechanical construction. Microphonics are increased as a tube gets more worn out, and less steady in the internal parts.
If there is a sound as of a telephone when a tube rings, then there is a filament rattle, and it has to be replaced with a new tube.
If there is microphonics only, the tube could be replaced maybe somewhat later. If you tap very gently on the tubes to hear which one, when they are not too hot, you may find out which tube or tubes that may be microphonic.

The settings of a bass amp include several parts, the pre-amp gain, tone controls with additional tone switches, compressor/limiter levels, graphic and/or parametric equalizer and volume control. Above that, various filter switches might be used, often hi and lo and these switches may be used more to protect the sound or output from getting overloaded

Bass amp combos and heads, except bass power amps, have a pre-amp inside. But not all of them a a gain control. A set of tone controls or more filters are standard. Separate bass pre-amp units often have more controls.
Bass amps with a pre-amp gain control, can be set for overdrive/distortion independently of the output volume and some of these have a pre-amp output.
A pre-amp may be "solid state" ie semiconductors only, which may provide a more authentic sound. Many pre-amps use a tube in the gain section.

Bass tube pre-amp

It has been wrongly believed by some, that a good tube pre-amp would give the "real" tube sound. It's not that simple. The classic tube amp sound comes mainly from loaded final power tubes, and somewhat from the saturation in the output transformers. So, an amplifier with tubes only in the final power amplifier, should be able to achieve a good "tube sound" with a clean gaining solid state pre-amp.
A solid state amplifier with a tube pre-amp will most likely provide a better sound than a solid state amplifier. However, not all bass guitarists favor a tube sound, if clarity is considered more appropriate.

Tube overdrive / distortion

Usually, vacuum tubes are noted for a smoother overdrive distortion and transistors/diodes for a harder distortion. It doesn't have to be that way. Tubes are typically providing a smooth distortion but it can also be with an symmetrical odd order distortion unless it works in class A (unsymmetrical peak transfer characteristics) where both odd and even order distortion occurs, which is regarded as more "musical".
Pre-amps using transistors or diodes are generally considered as hard and cold sounding although it really does not always have to be so. A solid state pre-amp in a bass amp can be designed to give even smooth even order distortion. So read the reviews!
There are also separate bass pre-amps as pedals, rackmount units or in other sizes.

Bass overdrive / distortion

Here are some good tips on how to control bass overdrive/distortion with the use of an equalizer before the pre-amp:
If you set the pre-amp gain to overdrive or distort, you can use an equalizer before the pre-amp, in order to change the tone before the overdrive/distortion. The standard tone controls on the amp can then set the tone on the amplified sound.
Here are some examples;
1. To increase the lowest frequencies before the pre-amp, you will get a more "growling", bassy overdrive which you may lower with the amplifier bass control.
2. If you decrease the lowest frequencies before the pre-amp, you will get an overdrive with cleaner low frequencies.
3. If you increase the treble before the pre-amp, you will get a thinner or sharper overdrive which you may soften with the amplifier's treble control down.
4. If you decrease the treble before the pre-amp, you will get an overdrive with cleaner high frequencies.

Bass amp compressor/limiter

There are two purposes of a compressor/limiter:
A compressor differs from a limiter in that the dynamics of the signal becomes gradually compressed as it gets stronger, above a certain threshold. As the signal gets close to this threshold, its dynamics becomes compressed, and above the threshold, even more compressed. As an example, 10 dB signal variation can be "compressed" to a 3dB variation, making the sound more flat.
A compressor, is used to improve the bass sound either by flatten out the dynamics and/or the attack of the sound (shorter attack time), or to make the attack stronger (longer attack time). A compressor may also limit the dynamics more near clipping, so that both compression and limiting is accomplished. In its simplest form, bass amps just have a compressor switch and on the better, the compression can be adjusted in terms of attack time and/or intensity.

On larger bass amps, a dedicated limiter may be available. A limiter is like a compressor but it acts only above a certain threshold with a higher compression ratio which means that even if the imput signal gets stronger above the threshold, the output is the same. This is done to protect the final amplifier from being overloaded which might be not well for the speakers and of course, the audio.
A limiter is a compressor with a higher compession ratio so most limiters are designed to compress more just before clipping occurs, and to protect the output from getting too high.

A bass compressor pedal, or another compressor, can be used if the amp doesn't have a compressor, like older bass amps. Other reasons to use an external compressor can be to use a favored compressor, and/or because more parameters is wanted, attack and release time, ratio and threshold.
Most bass amps with a compressor do not have these controls so it is worth giving some info about the very good advantage of having a separate bass compressor, which is even designed for bass. Take a look at this Bass Compressor site.

Bass tone control settings

Tone controls as on the Ampeg bass amp SVT-CL

Except for the usual tone controls, like bass, treble and mid/midrange, some models have more controls, lo mid, hi mid, contour etc and separate tone switches (bright/presence low etc) that enable further tone settings to be done. Other models can instead have a volume and/or tone control, where there is a "bright" tone switch, if pulled. Mesa/Boogie, as one example, has this.
A bass tone, meaning bass guitar sound, has a range up to 5 - 10khz. Detailed tone control settings are done with an equalizer or at least, an external or built-in bass equalizer (ie designed for bass).

Bass amp eq settings

A bass amp can have a graphic and/or parametric equalizer. It enables a wide tone control over the sound. A parametric equalizer can also be used for feedback control, which may be of concern for acoustic bass amps.

Graphic Eq on Hartke "Kilo" bass amp

Parametric Eq on the Fender Bassman 150 Bass Combo Amp

Graphic Equalizer

These often have 7 or 9 bands, but the better have 10 or even 12 bands. The frequency range is between ca 30/50 to 5-9kHz, or higher, with +/- 12 or 15dB gain for each band.
The dramatic advantage of using a graphic equalizer on a bass amp's sound, will be more obvious in situations where the bass sound interacts with other instruments and vocals. A bass amp does not only provide bass frequencies, the range is nearly as high as the audible spectrum. In certain live environments, there may be reflections, or lack of reflections, that affect especially the low frequencies. Because the entire spectrum of the bass sound is important to be balanced, changes can be made for conditions in each situation.

Parametric Equalizer

On a parametric equalizer, the center frequency can be varied and boost or cut (notch) can be set, hence making more detailed settings of the tone.
If the Q-value (bandwidth) can also be adjusted on a parametric equalizer (then "true" parametric), it can then be used to somewhat control feedback. On some models there are, for feedback control, "notch"-filters (=parametric equalizer where the Q is high and the gain is set down) where a feedback frequency can be tuned-in.

Bass amp effects

Settings on the Roland bass amp Cube-100 with digital effects.

Most bass amps are not equipped with digital effects but some examples are:
Roland Cube-100 - 5 digital effects, chorus/flanger/t-wah and independent delay/reverb. -->
Ampeg BA210SP - 16 digital effects presets.
Having effects in the bass amp is easier, but if a bass amp is chosen for its sound, bass effects pedals can be chosen, to combine the best of both.

Here some words about speakers for bass amps, and what common terms mean.

Also called bass stack, is a bass amp head stacked on top of usually two speaker cabinets since most amps have two parallell speaker outputs.

Bass half stack

The term half stack means an amp head on only one cabinet. Later on, the user can get another cabinet, the same or another one, larger or smaller.

Mostly referred to as bass speaker or bass guitar speaker. A bass speaker is a speaker in a bass combo amp, or in a bass amp cabinet when used together with a bass amp head.
The speakers have to be able to provide higher levels in accordance to the human hearing sensivity which is lower at bass frequencies.
Sizes are typically 8", 10", 12" and 15". If five- or six-string bass guitars are used, even 18" speakers can be used to cover the lower notes. When using that large drivers, horns or tweeters are sometimes combined with speakers to keep a good sound for higher frequencies.

Bass Amp Speaker Frequency Response

The bass speaker frequency response goes lower because four-string bass guitars go one octave below standard guitars. Furthermore, because the human hearing frequency range is unlinear, the hearing sensitivity falls off rapidly at the lower frequencies.
Therefore, a bass speaker size has to be somewhat larger in order to compensate for that circumstance as well.
If we look at the low part of the human hearing range diagram, comparing at the lowest frequency for a four-string bass guitar (40Hz) and an electric guitar (80Hz), we see at lower levels the difference is ca 10dB and at the lowest bass frequencies around 15dB. This means an effect difference between ca 10 and up to 30 times at the low end!

Mostly referred to as bass cabinet but also bass speaker cabinet or bass guitar cabinet. It is an enclosure that houses the speaker(s) and sometimes also horns/tweeters. Construction is generally more rigid than cabinets for other amplification of other instruments.
Bass speaker cabinets usually include vents or tuned bass reflex ports that are cut into the cabinets.

A PA amplifier can also be used to amplify a bass guitar, when it is put directly into a PA system.
Because a bass sound is quite dark, it can be handled quite well in a PA system, which wide frequency response have developed over the last decades.
A bass guitar does not have the same amount of certain nuances and harmonic overtones like electric guitars have. Putting an electric guitar into a PA is rarely done but with a bass guitar it is common practice.
A bass player can use a bass pre-amp and/or more effects, into the PA. But a modern bass amp can also be used, that has a pre-amp out or line out. This way, the bass player can still use his or her own bass amp with its tone controls, equalizer, compressor etc, while keeping the sound settings into the PA system. Then, the bass player can use his or her bass amp as a monitor. Otherwise the bass player's monitor speaker is fed by the PA.
However some serious bass players who favor the subtle nuances in his/her sound strive to have own tuned-in amplification equipment, just like guitar players.