Well, the short answer is “it depends”. Over numerous years performing in every conceivable situation, I can broadly summarise as follows:
We have the gig where you have a large front of house PA system, and the venue where the PA system is only amplifying the vocals (and possibly keyboards and acoustic guitars).
Now, in the latter performance, you will need sufficient power from your amplifier (or backline, as it is known) to project the sound of your instrument to the back of the room. You will need the power to compete with a full drum kit (if the band is using one), all the other instruments, and still remain clear to all the listeners. Now, such a set up is only really applicable in small to medium sized venues (pubs, small rooms etc), as in larger halls, the band will need a PA capable of amplifying the whole band. However, you still need sufficient power to be self sufficient n terms of amplification.
My recommendations are that on guitar you will need at least 40 watts (for a valve amp) or 100 watts (for a solid state amp – this is a whole other story). On bass, minimum 300 watts is really what is needed if your backline is the only source of your sound.
The other scenario is where there is a large PA providing sound reinforcment for the whole band. Every instrument is fed into the PA mixer via a microphone or direct connection, and the PA system project the sound around the venue. Now, in this case, your on stage backline amplifier is simply there so that you can be heard on stage. This is slightly counter intuitive, but it is usually at larger venues and gigs where the PA will be doing all the work, and thus at a larger gig you will be able to use a smaller amplifier! Remember that in these instances your backline is only there to enable you to hear yourself, since the PA is there for your audience. Furthermore, there will often be onstage PA speakers (called monitors) through which you can hear yourself too, and in some instances this negates the need for an amplifier at all!
OK, so in writing this, I have had to exclude some information and detail simply for the sake of brevity. This is a huge subject, and I will be returning to it in future blogs. For now, suffice to say that many bands out there use on stage amplifiers that are too large. The goal shoudl always be clarity of sound, and not outright volume. AH, but what about those walls of amps you see on stages at festivals etc – why are they needed if the PA is amplifying every instrument? Well, they are not needed, and usually most of them are not even switched on – they are just there for show.
Finally, what do I use? Well, on bass, I use Markbass amps. I use a 300 watt 12″ combo for large gigs (remember, the PA is doing al the work), and for smaller gigs where my backine is doing all the work I boost it to 500 watts by adding another speaker cabinet (traveller 210 in case you are insterested). For electric guitar, I use a Fender hot Rod Deluxe 40 watt valve amplifer in all instances, but simply play it quieter at bigger gigs where the PA is doing the work – remember I said it was counter-intuitive?
Please don’t hesitate to contact me for more info on any of the above – as I say, it is a simplisitc guide, and I will look at some of this in more detail in future blogs.