Bass Amp Basics: A Buying Guide

By Jim Roberts

Whether you're looking for your first amp or getting ready to upgrade to a massive rack system, it's important to take the time to carefully assess your needs, consider your budget, and shop around. Don't be swayed by clever salespeople or your friends, no matter how convincing they may be. Your amp is a vital element of your sound, and if you rush into an unwise purchase, you'll be shopping again soon (and trying to unload a used amp). With that in mind, here are a few things you should know before you spend any of your hard-earned dollars.

An amplification system has four main components: preamplifier, signal processor, power amplifier, and speaker cabinets. The preamplifier has an input jack, where you plug in your instrument cable. The preamp's main job is to prepare the signal coming from your bass to be amplified, primarily by boosting its amplitude (voltage). Most preamps have a signal processor section, which may be as simple as bass and treble tone-control knobs. In most modern amps, this section includes an equalizer, and it may also have built-in effects units, such as a compressor and/or chorus.

After the signal has been adjusted by the preamp and modified by the signal processor, it's passed along to the power amplifier. This is where it's increased to the voltage level required to be loud. Because a low-frequency sound is harder to produce than a higher-pitched sound, bass amps must have lots of output power. Today, even small amps often produce 100 watts RMS or more, and large power amps rated at 600-800 watts RMS are becoming more common. The last step in the signal chain is the speaker cabinet, where electrical energy is converted into mechanical energy by the speakers. To do this, the electrical signal is passed through a voice coil attached to a flexible cone; as this cone moves in and out, it produces sound waves in the air.

There are three types of bass amps. The simplest is a combo amp, which has all of the components in a single unit. Your first amp is likely to be a combo amp, and you'll probably have one throughout your career, for practicing and rehearsing. Combo amps typically have one or two speakers mounted in an enclosure that also includes the preamp, signal processor, and power amp. The most common configurations are 2x10 (two 10" speakers), 1x12 (one 12" speaker), and 1x15 (one 15" speaker), although many other combinations exist. Generally speaking, combo amps are the least expensive type, with list prices beginning around $200.

For most club gigs, you'll use a stack or piggyback system consisting of a "head" (sometimes called a "brain") and one or more speaker cabinets. In this type of system, the preamp, signal processor, and power amp are all contained in the head enclosure. A stack is quite flexible; speaker cabinets can be added or changed easily, and the head can be replaced by a different unit. Typical two-piece systems for club gigs start at around $700 and prices range well into the thousands.

Today, more and more professional bassists rely on a rack system. This is a more sophisticated version of a stack, with separate preamp, signal processing, and power amp components mounted in a roadcase. Because a rack system is modular, it's easy to upgrade one component while keeping everything else the same, and various signal-processing units can be added over time. Many rack systems are either stereo (with separate power amps for left and right channels) or bi-amp (with separate power amps for high and low frequencies). While a rack is by far the most flexible type of rig, it's also the most expensive. If you want to put together even a fairly simple rack, the cost will probably begin around $1,000--and that's before you buy the speaker cabinets.

Now that you know the basics, here are five essential questions to ask yourself before you go amp shopping:

Where will I use this amp?

If most of your gigs are in tiny clubs, don't buy a system that won't even fit onstage. And don't forget to consider how you'll be transporting it: Can you get it into your car?

How loud do I play?

As a general rule, if you have to turn your amp up more than halfway to get sufficient volume, you need more power. Clean bass requires lots of headroom, so make sure you've got enough power to handle the gigs you play.

Is it reliable?

Most modern gear is built to stand up to years of on-the-road abuse, but it can't hurt to ask around. If there's a good electronics-repair shop in your town, check with the technician to see which bass amps are on his bench too often.

Can I try it out?

A music store is not a real-world sonic environment. If the dealer won't let you test the amp on a gig, try another dealer. You may have to make a deposit or provide some other form of security, but that's a small price to pay when you're pondering a major purchase.

Can I afford it?

There are two sides to this question. Obviously, you can't buy an amp if you don't have the money (and beware of time-payment deals--they're usually a ripoff). On the other hand, you shouldn't buy a "bargain" amp that's underpowered or unreliable. In the long run, it will turn out to be more expensive. Balance the cost of the amp against your real needs and consider all the alternatives. Look at used amps, too; although they must be checked carefully, they often represent outstanding value.

A final point to consider is whether you prefer the sound of tube or solid-state circuits. For bass players, this isn't quite as volatile an issue as it is with guitarists, many of whom would rather eat ground glass than plug into a solid-state amp. With regard to circuit design, modern bass amps are available in three "flavors": all-tube, all-solid-state, and hybrid. All-tube amps, which are available from Ampeg, MESA/Boogie, Trace Elliot, and other companies, have tubes in both the preamp and power amp. (Even these amps, it should be noted, usually have some solid-state circuitry in the signal-processing section.) Many bassists swear by this design, insisting that nothing sounds as warm as an all-tube amp; others are turned off by the heavy weight and maintenance requirements of tube amps, especially since good replacement tubes are becoming more difficult to find. Not surprisingly, all-solid-state amps are now far more common, and they are offered by many manufacturers, including Carvin, Fender, Gallien-Krueger, Peavey, and Randall. Loud, reliable, and lightweight, these amps feature much more sophisticated circuitry than the early "transistor amps," which were noted for their sterile sound and frequent meltdowns. Hybrid amps combine both types of circuits, using tube preamps and solid-state power amps. Made by ADA, Hartke, Hughes & Kettner, SWR, and others, these systems are growing rapidly in popularity. Which type sounds best? That's up to you.