In addition to the ever-popular guitar/bass/drum/vocals format, many modern bands have members that double up on keyboards for a few songs, or who exclusively play the keys. The electronic keyboard is a full-range instrument that can really fill up a lot of space, and in the case of synthesizer keyboard, cover an amazingly wide range of sounds. As such, an amplifier that faithfully reproduces its entire frequency range is essential.
A popular solution is to purchase an amp made specifically for keyboards. These are usually solid state, compact, and portable, and like guitar and bass amplifiers, have equalization controls to help you dial in your sound. If you play live often, be sure to choose a model with an XLR output so you can send it straight to the PA.
On that note, plugging your keyboard directly into a PA system is also a good way to go. If you’re a solo singer/keyboardist act or a small band this is an ideal setup, as you can also plug in your microphones into the PA, but it also has many benefits in other situations. Using a PA system for keys allows you to have a modular setup in the same way many guitarists and bassists do. For smaller gigs, you can bring one speaker; for larger ones, bring two and watch the rest of your band tower in fear at your keyboard rig of doom. While it may seem like using a whole PA system for your keyboard is overkill and the keyboard amp is a more practical option, the advent of portable, battery-powered PA systems like the Carvin Audio S600B make this option a lot more viable. The S600B also comes with an onboard mixer for tone and EQ shaping, similar to what you would find on a keyboard amp.
If you’re a bassist making the switch to keys, your bass combo amp may also suffice for use with a keyboard- just make sure it has sufficient power. This is especially true if you are using heavily modulated synthesizer sounds or doing a lot of left hand chordal work. In their low octaves, keyboards can cover similar frequencies as a bass guitar, and those low frequencies tend to eat up a lot of power. If you’re looking for a bass amp that can pull double duty as a keyboard amp, Carvin Audio’s MB Series bass combos play nicely with keyboards and have the power and tone to keep up. The MB15, for instance, puts out 250W at 4 ohms, which is enough to hang with a moderately loud band.
Unfortunately for all the guitarists out there, it’s not recommended to plug a keyboard into a guitar amp. While it will not spontaneously combust if you do, a guitar amp’s speakers and preamp section just do not tailor to the broad frequency range of the keyboard. There is indeed some overlap between the keyboard and guitar in the upper octaves, but overall you are likely going to be much better off using any of the above options.
Playing the keyboard may not be as glamorous as the guitar or bass (you aren’t going to be standing in front of a half-stack!) but that doesn’t mean you can’t have a killer rig that helps you sound your best.