How Many Watts Do You Really Need
The most common mistake I see with amps is buying too many watts. A parent picks up a 100-watt half stack because bigger looks more serious, and it ends up set to 1 on the volume knob for the rest of its life. Watts are not a measure of quality, or even of loudness in any straightforward way.
Watts and loudness are not the same thing
Doubling the wattage of an amp gets you about 3 decibels more volume, which your ear hears as slightly louder. To sound twice as loud, you need roughly ten times the power. So the jump from 15 watts to 30 watts is smaller than people think, and the jump from 50 to 100 is barely noticeable in a band mix.
The speaker matters as much as the amplifier. A 5-watt amp through an efficient 12-inch speaker can hang with a drummer. A 40-watt amp through a small, inefficient 8-inch speaker will struggle. Read the whole package, not just the number on the back panel.
Headroom versus breakup
This is the part that actually matters. Headroom is how loud an amp can get before it starts to distort. A high-wattage amp has lots of headroom: it stays clean at stage volume. A low-wattage amp runs out of headroom sooner and starts to break up, which is the sound many players want in the first place.
If you play clean, funk, jazz, country, worship music, you want headroom, which means more watts or an amp designed to stay clean. If you play blues or rock and you like natural overdrive from the amp itself, fewer watts lets you reach that sweet spot at a volume that will not clear the room.
Tube amps and solid-state amps behave differently here, which the guide on tube, solid-state and modeling amps covers in more detail.
Bedroom and apartment practice
For playing at home, 1 to 15 watts is plenty. Honestly, 1 watt through a 10-inch speaker is louder than a television. If you live with other people, a modeling amp with a headphone jack solves the problem entirely. Several of my students practice on 10-watt combos and only bring out something bigger for band rehearsals.
A 15-watt tube combo can be a wonderful home amp if you keep it on the clean side. Once you crank it for that breakup sound, though, you are into loud territory.
Rehearsal with a drummer
An acoustic drum kit in a garage is around 100 to 110 decibels. To be heard clearly next to that with a clean sound, you want something in the 30 to 50 watt range through at least one 12-inch speaker. If you play overdriven, a 15 to 20 watt tube amp will cut through fine because the compressed, saturated sound sits in the mix better than a clean one.
This is the range where most of my gigging friends live: 15 to 40 watts, one or two 12-inch speakers.
Small clubs and bars
At a bar with a PA system, the sound person will mic your amp or take a line out. Your stage volume just needs to cover the stage, not the room. A 20 to 40 watt amp does that easily. I have played hundreds of bar gigs on a 22-watt combo and never once wished for more power. If there is no PA and you are filling the room from the stage, 40 to 50 watts gives you the headroom to stay clean.
A 100-watt head is for large stages, outdoor shows, and a certain kind of nostalgia. Very few players actually need one.
A quick word on attenuators
An attenuator sits between the amp and the speaker and soaks up some of the power so you can run the amp hard at a lower volume. They work, and the good ones sound fine. They are not free, though, and the cheapest ones can dull the highs. For most home players, a lower-wattage amp or a master volume is the simpler answer.
My rule of thumb
- Home, headphones or low volume: 1 to 15 watts.
- Rehearsal and small gigs with a PA: 15 to 30 watts.
- Rehearsal and gigs without a PA, clean sounds: 30 to 50 watts.
- Anything above that: only if you know exactly why.
Buy the amp that sounds good at the volume you actually play at. That single test tells you more than any wattage rating ever will.