How's this for a topic? Your 100 watt amp is NOT twice as loud as my 50 watt amp!
Ok so we're not going to open a can of worms here. I really want to stress that there are some really fantastic advantages of playing say a 100 watt amp over a 20 or even 50 watt amp, BUT volume is NOT one of them.
As musicians, we each have different playing styles and preferences. While some may prefer lower wattage amps, some may prefer a 50 or even 100. Why is that you ask?
Well first let's discuss the actual differences in volume. I'm going to show an example of the DBW (DBW is decibels relative to one watt. Not to be confused with DBM which is decibels relative to one milliwatt or .001 watt)
*Something to note. These calculations are based upon power amp only. Actual volume is affected by any pre circuitry such as pedals and preamp.
Let's take a 10 watt amplifier. We just did the boring old math and we came up with 10dbw. Cool that's easy to remember. 10 watts is 10dbw. Well shoot. What do you say we double the wattage now and see what happens. So now we have a 20 watt amplifier and we did the boring old math and the dbw came out to.......drum roll please...... TA DA..... 13.01dbw!! Wait a second. That's only 3 DB. Thats hardly noticeable to the human ear. We just doubled the wattage and only a slight change? I'm confused and I'm the one writing the article. Well, that's because the wattage is not directly proportional to the DB. There's a bunch of crappy math involved.
P(dBW) = 10 ⋅ log10( P(W) / 1W)
See, no one has time for that. It is also important to consider that db and dbW are not the same thing. This can be confusing to someone who knows that a whispering human voice is measured at roughly 30db and a 20 watt amplifier is said to be at 13dbw. We all know that if you crank a 20 watt amp to its max, it's quite a bit louder than a whisper, wouldn't you say? To get into that any further would defeat the purpose of this article as well as probably remove your interest from it entirely. So why watts? This is where your personal preference comes into play. First of all, TONE IS SUBJECTIVE! Meaning....whatever sounds good to YOU is good tone. I can't tell you what sounds good any more than you can tell me what sounds good. If you like the sound of some guitar strings on a shoe box plugged into a megaphone....well that's your thing. Ok so the differences. Ah yes....well higher wattage usually means larger output transformers. Larger output transformers mean a bigger bass response. This is a very sought after thing (especially in the 80's) with higher gain amplifiers and the heavy metal tone. This doesn't mean you can't get your favorite 80's tones out of a 20 watt amp. This just means simply what it means......the larger the output transformer.....the bigger the bass. This is something that many people argue with the 50 and 100 watt marshalls. Many say they can't tell the difference between the two. From my experience in building the same preamp topology in a 100 and 50 watt circuit, I have found that the 100 watt has a MUCH thicker sound. The output transformer in my 100 watt circuitry is DOUBLE the physical size as the 50 watt output transformer.
Ok so that's one example. What about tube breakup? A lot of that warm breakup that so many players like to achieve come from pushing the power sections of their amp. If you compare the Fender Twin 85 Watt amp with the Fender Princeton 15 watt, you'll notice that the 85 Watt Twin has much more headroom. For this amp to breakup, you'll REALLY have to push those tubes. In most cases, the volume that you would achieve to do so would be unbearable. Now the Fender Princeton is 15 watts. It can achieve that warm breakup much earlier on and at a much lower volume. Both of these amps have amazing clean tones, but some of the clean can be lost within the breakup at higher volumes in the lower wattage example.
This is all tomatoes potatoes. These differences aren't really pros and cons. They are simply just differences between the higher and lower wattage amplifiers. I always extremely encourage you to go out and see for yourself. Test out different amps. Understand the differences between the amps. Understand their similarities. The point in all this rambling wasn't to really throw a bunch of technical details at you. It is meant to be a starting point to help you know what to look for in finding your tone. Remember.....BE yourself!