If you’re an active guitar player, you’ve certainly noticed the continuing trend towards smaller, lower powered amplifiers. This has occurred for a number of reasons: Popularity of boutique clones of early amplifier designs, older players downsizing to focus on playing at home rather than performing, and the advent of very good affordable sound reinforcement systems.
Historically, the first guitar amplifiers were pretty small because the guitar was not necessarily the lead instrument of the band, and in many cases the band itself was not amplified. Plus the technology of the time – tubes – dictated smaller low power systems.
As rock music and the electric guitar became more popular, both the volume levels and the size of the venues increased. But true high quality “house” sound systems like today did not exist. So the guitar amplifier was not for “tone”, but was also the primary vehicle for what the audience heard. Amplifiers also did double or triple duty: Check out the input panel of many early amplifiers and you’ll see input jacks for multiple guitars and microphones. Adjusted for today’s dollars, pro gear back in the day was vastly more expensive than now, and sharing was a practical necessity.
So like the Space Race, the power race was on, and by the end of the 50’s the larger guitar amplifiers were pushing 50 watts or more. Fender’s introduction of the blackface amps in the early 60’s addressed the need for louder, cleaner sound. The blackface amps differed from their tweed predecessors in a number of ways, but features such as fixed bias design, higher plate voltages, and solid-state rectification had more to do with volume and headroom than tone. The largest amps topped out at 100 watts, which is really the practical limit of four 6L6 or EL-34 power tubes. This is pretty much true today for tube amps, and anything more than that gets very heavy and hot (bass players had it tough then). Today a bass player can get a 500-watt Class D solid-state amplifier that’s the size of a phone book.
But back then if you were going to play an arena, you needed stacks of amplifiers because they were doing a lot of the heavy lifting. Plus it’s kind a macho thing and looks really cool too. Today, you can play an arena with a 15-watt amplifier, and some performers do. While there is a certain visceral sensation to the sound of a 4×12, the need for a row of Marshall stacks is essentially visual. And unless you’re Yngwie Malmsteen, many of those cabs on stage aren’t even on.
So how much power do you actually need? Unless you require extremely high levels of clean volume without the assist of a PA, 50 watts is the most you’ll ever need. How much volume an amplifier produces is a function of its design: Fixed versus cathode bias, amount of negative feedback, plate voltage, rectifier type, etc. It’s hard to generalize, but a 15-watt amplifier with no negative feedback and a solid-state rectifier can be very loud and clean. My main amp head has (4) 6V6 tubes, solid state rectifier and a 20/40-watt switch. The only time it’s on 40 watts is when the band is playing outside.
If you are playing clubs and typically put the guitars through the PA, 15-30 watts will likely do it. While early amplifier designs were guided by power output, choosing an amplifier today is more about how you want it to sound, rather than how loud it will go. If you play mostly at home or jam with friends, 10-30 watts is where a lot of the amplifier market is targeted these days. Finding the right amount clean headroom – which is important if you use pedals – is an important selection criteria. If you regularly jam with a drummer, 30 watts is probably a better choice than 10. Five-watt amplifiers can be fun, if all you want is loose, old school grind. But with a humbucker-equipped guitar, there will be little in the way of decent clean volume.
Many modern amp designs have the ability to vary total amplifier output. Some do this by actually dropping out power tubes (4-to-2 for example) while others vary the amount of voltage to the power tubes or phase inverter. These features cut volume as well as headroom, allowing the ability to clip the power tubes at reasonable volumes. The Traynor Ironhorse amplifier has a fixed/cathode bias switch that changes the output of the amp from 37 to 17 watts, respectively. This not only affects total volume and headroom, but also the feel (I like the softer nature of cathode bias).
If you have a large amp that you don’t want to part with, there are of course power attenuators, which are available as an add-on accessory. These work by absorbing some of the energy that would normally go to your speakers. In effect, you can crank the amplifier but the attenuator “soaks up” some of the energy (volume). Attenuators work by placing some type of resistance/inductance network in the signal path to the speakers. Without getting technical, even the best ones mess with the feel of the amp, and how the guitar interacts with the amplifier. It’s hard to explain but it’s a disconnected feeling. They sound good on YouTube, but so does everything. My suggestion is to buy a smaller amplifier.
The trend towards lower stage volumes, and the affordability of good sound reinforcement and monitoring systems has been a boon to amateur and pro players alike. Using a guitar amp as the sole amplification source is very rare, and your band will actually sound better if you turn down and let the PA and the monitors do their job. And your band mates will appreciate it. Which brings us to the guitar player’s favorite lament of “I can’t hear myself.” Which is a topic we’ll address shortly.