Amp Output Ratings: Sizing The Amp To The Job

Written by
Dave Hunter
Published on
January 21, 2021 11:47:13 AM PST January 21, 2021 11:47:13 AM PSTst, January 21, 2021 11:47:13 AM PST

Who doesn’t enjoy the sensation of standing in front of a 100-watt full stack -- your gut thumping and pant legs flapping as you crunch away at decibel levels which threaten the structural integrity of the venue? There’s nothing else quite like the feeling of unleashing an evil riff through all that raging firepower and grooving on the hovering edge-of-feedback immediacy and totally-alive playing feel of it. 

It’s fun to contemplate the occasions when we might justify such hefty wattage these days, but let’s apply a gigging scenario that’s more common to most performers; one probably not unlike something you encounter when you get out there yourself…

The average venue is a compact 80 to 120-seater club, in which—for example—your 20-watt 1x12" tube combo not only does just fine, but the house sound engineer even asks you to turn it down most nights. Then every once in a while, a slightly larger booking in a 250-capacity room turns up, when you briefly consider bringing your 100-watt amp, but wisely conclude, “Nah, let’s just crank the little fella’.” Does it suffice? Yeah, in spades—and as if on cue, the sound guy still insists mid-sound check that you turn it down a little, because he’s getting more than enough of it through the front-of-house PA system anyway. 

Given the capabilities of modern sound reinforcement systems, with good mixes running both in the mains and the monitors, you really don’t need any more volume than you could comfortably tolerate in a space the size of the average rehearsal room.  And when the aforementioned monitors are done right, you can get away with even less. In many cases (although there are exceptions, which we’ll check out below), the oversized amp just leads to the heartbreak of unsatisfactory tone. 

It’s not just that everyone else in the room will be your friend if you use a lower-power amp, but you’ll also enjoy your own playing experience a lot more, because you’ll be able to hit that sweet spot where shimmering clean segues over into succulent distorted at the thwack of a pick. Err on the side of too large, on the other hand, and the powers that be—which usually means the sound engineer, or your lead singer—will just force you to turn down anyway, stranding you short of the golden tone zone. And if they don’t, you’ll most likely just obliterate the room with excessive volume anyway, and that’s another surefire show-spoiler. (Note that all of these considerations go double in the studio.)

Stack Attack

But none of this sounds quite… rock ‘n’ roll, does it? That 100-watt double stack is out there, calling to you, begging you to caress its glowing tubes with your hot riffs, and it’s hard to feel like you’re really rocking if you plug into anything less. Or is that just an outdated mindset? 

From the early ’60s to the early ’70s, when rock was on the way to becoming the monster it is today, bands found themselves moving from basement clubs, to dance halls, to theaters, to stadiums; and because the PA systems of the day weren’t up to the task, they needed progressively bigger guitar amps to get themselves heard. Leo Fender and co., designed the Showman for Dick Dale; Dick Denney and co., designed the Vox AC50 and AC100 for The Beatles; and Jim Marshall and co., sealed the deal by designing the JTM45/100 for Pete Townshend, and soon sold 100-watt Plexi Super Leads to just about every other rocker in the UK and beyond. Sure, this was all relevant 50 years ago, but if you grew up with the sound of Eric Clapton, Jimmy Page, Jimi Hendrix, or Paul Kossoff through a Marshall stack, it’s hard to get that tone—and that image—out of your head. 

Which is to say, it’s hard not to lust after the rig of doom, even if the world won’t let you play it. Today, the gig more often follows one of these two scenarios: you go to the trouble of hauling your 100-watter, setting it up, and finding your sonic sweet spot, only to be told you must turn it down to frustratingly emasculating and tonally uninspiring levels; or you bring a smaller amp with an edge-of-breakup (or full-on overdriven) volume level that’s suited to the space, and have at it with a smile on your face.

Power Ratings, Overdrive, and Headroom

In order to work towards weaning ourselves off excessive amplification, let’s take a look at how power ratings actually equate to volume. The peculiarities of the human ear and the logarithmic nature of our perceptions of volume mean that output ratings don’t correspond directly to volume levels. While a 100-watt amp might be five times the power of a 20-watter, its perceived volume is really only around twice that of the smaller amp (this is an imprecise science, since it involves so many variables and considerations of frequency perception, but this gets us into the ballpark without going into all the numbers). 

What does increase more dramatically with the higher-wattage amp, is its headroom and the ceiling for the onset of breakup; meaning, you have to push it hard to get into the “juice” if you’re a player who uses amp distortion as part of your tonal palette. Note, though, that many high-power amps do generate the majority of their overdriven tones from the preamp, and these days they can be good at reproducing those at just about any desired volume level, from basement to hockey rink.

Before moving on, let’s examine another scenario:

Ever wondered why your bass player with the 200-watt head and 4x10" cab is always grumbling that your 15-watt 1x12" combo is too loud? For one thing, it takes a lot of wattage—that is, more tubes and a bigger output transformer—to adequately reproduce the low frequencies that the bass guitar requires. For another, human hearing is more sensitive to midrange and high frequency sounds than it is to lows, and the nature of these phenomena changes as an amp segues into distortion. Therefore, the frequency range and distortion content of any given amp will also skew our perception of apparent volume. Stand your 15-watter and his 200-watter side by side on stage, set his volume at noon and yours at 10 o’clock, and chances are you’re still cutting through just fine. All of which, of course, brings us to the issues of speaker type and efficiency, and cab design and speaker complement… which are matters for a future article. 

Power Play

Certain scenarios that allow, or even encourage, the use of a big amp do still exist. If you’re touring with a signed act that plays archetypal rock on big stages, and have got someone to carry the road cases for you, you can probably still get away with the stack (although even many large, professional acts—Nashville and pop artists in particular—are moving away from massive stage volume levels; running amps behind plexiglass shields or even under the stage; and monitoring everything with in-ear units to maintain startlingly low on-stage volumes). 

Here’s another totally legit big-amp scenario:

Many people just prefer the sound of a higher-powered 50- or 100-watt amp, whatever model it might be, for its own inherent tonal characteristics. It might be that they like the sonic girth and bandwidth—including full lows and articulate highs—that big tubes and a big output transformer can more easily and consistently deliver (even when they’re keeping such amps at relatively low volumes). Or it might be that they require the punch and tightness of these amps’ output stages (again, even when at low volumes) to power through with the high-gain tones they’re generating in the preamp or via overdrive and distortion pedals. Or if their playing is always super-clean, articulate and defined, they don’t need to hit that edge-of-breakup sweet spot anyway, so the 100-watt amp delivers.

Or, if you’re a country or jazz player who needs 100 watts in order to obtain the clean headroom that 30% of its potential provides you, or a 7-string metal thumper who wants to project pure punch and crunch with a lot of low-end rumble, you might very well need the power. Also, the player who uses a lot of pedals to achieve overdrive and distortion, or who uses a channel-switching amp’s high-gain lead channel coupled with appropriate master volume levels to rein in output, might find a 50-watter is appropriate, and even necessary.

Many higher-powered amps today have superb master-volume controls, while also relying on distortion generated at the preamp stage more than at the output stage. If you want cranked-up rock tones from a 50- or 100-watt amp in a small club, studio, or rehearsal setting, you’ll almost certainly have to dial down your master volume pretty low (or use an output attenuator or other decibel-reduction method to get there). But if your amp still sounds great at that restrained volume, all is well. That’s what matters most at the end of the day. 

In such circumstances, it’s still worth considering this: If you never get to use anything close to the full bluster of that bigger amp, perhaps A/B it against a smaller, lower-powered amp which otherwise delivers similar tones, gain levels, and features to see if you can achieve the same performance without the same weight, investment, and power (or tube) consumption rate. If you still prefer your big-amp-set-low regardless -- fine. If not, maybe you’ve learned you can lighten your load. 

And then there’s the matter of output attenuators, cab emulators, and other solutions for making powerful amps work at any desired volume level. If you’re attached to your big amp, and use one of these solutions to make it work in venues of any size, have at it—and that’s another subject for future discussion.