A combo amplifier contains both the amplifier head and speaker cabinet in one intergrated unit.

Guitar amps are specifically voiced to make a guitar sound good, and Amp heads come in different power ranges and sizes. Some are very plain, some have bells and whistles, but they all must be paired with the correct 'Ohm-age' of cabinet.

Guitars require a specially voiced amplifier and cabinet in order to sound good. That's why just putting an electric guitar through a PA doesn' work. The cabinets can be different combinations of speakers and speaker sizes and most importantly will have a specific 'Ohm-age' that must be adhered to when connecting the amplifier head.

When it comes to Amplifiers, it's all about the voicing. Guitar amps are voiced especially for Guitars, which is why an Electric guitar just DI'd into a PA doesn't sound so good. Keyboards, need a specially voiced amplifier too,as they emit a much broader spectrum of frequencies. Here are the amplifiers specially designed to sound great when used with keyboards or synths.