A customer called and asked if I could improve the headroom on his Deluxe Reverb reissue. He liked the Fender clean sound and had bought the amp to provide it, but he found that on stage he couldn’t get a sound that wasn’t distorted.

…and if you already know the reason why, no need to read on.

In conversation with another caller, it emerged that he had bought his 100 watt Marshall head to get ‘more gain’, and was disappointed to find that on stage it actually gave him a less distorted sound than his old 50 watter.

Both these people had a similar misconception about wattage. Let me explain.

Amps have a preamp and a power amp. The tone is shaped in the preamp. The watts are made in the power amp, and as everyone knows they give you the loudness. Preamp – tone; power amp – volume. Or anyway that’s the intention, though with guitar amps there’s a complication, which is that if you turn the thing right up, the power amp starts to make tonal contributions too.

Preamps do not need to be different in amps of different wattages. Preamps do the same job in any amp – they shape tone via volume and tone controls and other tonal components, give you control over your sound, and they churn out a signal of a few volts AC, big enough to drive a power amp. You could take the output of a 100 watt Marshall TSL preamp and feed it into a Fender Champ power amp, no problem. And vice versa. In high-gain amps with master volume controls the preamp makes distortion sounds too.

At a certain level of preamp output (as set by the volume or master volume control), the power amp will start to distort. This is usually a nice kind of distortion. It is however only available at a certain volume level. You can’t put a volume control on power amp signals, they would fry your pots. Hence attenuators.

OK so here we are on stage with our noisy drummer, doing a sound check. We turn up the preamp volume control until it is driving the power amp hard enough to keep up with Animal. If we have a power amp capable of 100 watts then it is unlikely we will overdrive it. If we have one capable of 12 watts then it is very likely we will overdrive it. Thus at stage volume levels the Deluxe Reverb (18 watts at most) power amp will be overdriven, and the 100 watt Marshall power amp won’t.

So the Fender Deluxe Reverb will not give you the option of a clean sound on stage because it will inevitably be overdriving its power amp, whilst the 100 watt Marshall will not give you the option of power amp overdrive until everyone is weeping blood.

A 50 watt Marshall in a loud band on stage may be beginning to offer power amp overdrive; a 100 watt Marshall won’t. So if you want a great overdrive sound live, go for a lower wattage amp. If you want a good clean sound you will need relatively more watts.

Here then is a brief guide to what levels of wattage will give you what kinds of result on stage in terms of headroom and power amp overdrive.

Amps below 10 watts, usually ‘single-ended’ ie one power valve only, eg Fender Champ. Not enough volume for stage work in any but the quietest band, but lots of lovely power amp overdrive. Single-ended amps are renowned for good power amp overdrive. Not totally sure I agree with this orthodoxy actually, as I like the sound of an overdriven push-pull power amp, though an overdriven Champ does sound lovely. However you can mic up an amp like this, see below.

12-20 watt amps, usually 2 x EL84, 2 x 6V6. Examples would be the Orange Tiny Terror, the classic Fender Deluxe and Princeton, the Marshall 18 watt, the Mesa Studio and Subway models, the Vox AC15. These amps will give enough volume to keep up with a subtle drummer. They will be on the edge of overdrive if the drummer gets energetic, or if there are other lead instruments. They will not give you a good clean sound on stage unless the band knows how to play quietly, or unless you mic up.

30-60 watt amps, usually 2 x EL34, 2 x 6L6, or 4 x EL84. Including 50 watt Marshalls, many Fenders including the modern Deluxe and Deville series, Vox AC30s and the majority of gigging amps. These will give you enough volume to keep up with a drummer and a few other electric instruments. You will almost certainly be able to keep the sound clean if you want to, and also in a loud band you may well be able to push some nice distortion out of the power amp. 50 watts is LOUD however.

80-120 watt amps, usually 4 x EL34 or 4 x 6L6. 100 watt Marshalls, Fender Twins, etc. These amps have lots of volume on tap. The important difference between a 50 watt and a 100 watt amp is that the 100 watt amp absolutely guarantees that you will be able to keep your sound clean even at earsplitting volume. As you experience the volume levels a 50 watt and a 100 watt amp are not that different in fact – the difference will be that at a given setting on the volume control the 100 watt amp will be cleaner, and the higher up the volume range you go the more noticeable this will be.

You will have realised by now that choice of wattage in an amp is also choice of live tone, and that the higher the wattage the more reliably available are the clean tones. On stage, more watts simply allows you to play cleaner should you wish to. Lower wattages make power amp distortion more likely. A 100 watt Marshall can be clean on stage with a loud band, but not so a Deluxe Reverb.

There is a certain inflexibility written into all this. The way around that is to use a small amp, set it to the tone you want, and mic it through the PA to get the volume you want. Or get someone like me to fit a line-out, if it doesn’t have one; we can put a line out on any amp you like.

And if you then decided that you wanted some nice big empty Marshall boxes to hide your mic’d-up Champ behind… well you would not be the first.