Valve Amp Head to Cab Wattage

eoin5

I've read some conflicting views on head to cab wattage relationships. Some people say its ok to match watt for watt while others will say that the cab should have much more capacity. I think it makes more sense to have more wattage in your cab and many of the manufacturer pairings tend to favour that idea. Any thoughts peoples?

Paolo_M

eoin5 wrote: »

I've read some conflicting views on head to cab wattage relationships. Some people say its ok to match watt for watt while others will say that the cab should have much more capacity. I think it makes more sense to have more wattage in your cab and many of the manufacturer pairings tend to favour that idea. Any thoughts peoples?

All guitar amplifiers benefit from additional speaker capacity, anyone who says otherwise doesn't know what their talking about.

As usual though, it's not quite that simple.

Firstly speaker manufacturers realised that guitar amps are heavy duty pieces of kit a long time ago, and they routinely under rate their gear as a result. For example a Celestion speaker rated at 60 watts could probably take 75 watts without much problem. However there is no under-rating rule that all manufacturer comply to so DO NOT rely on this.

The power amplifier in solid state amplifiers are not designed to distort. Therefore, in theory, they never exceed their stated power output. A 100 Watt SS amp will usually only reach 100 Watts on 10. Therefore a 100 Watt speaker should be enough. However just because they are designed not to distort doesn't mean that they don't at least a little bit at full volume.

The power amplifier in valve amplifiers do distort routinely. A distorted power amplifier is putting out more power than expected.
Old Marshalls 100 watters will put out around 175 watts when turned up fully, they regularily blew up speaker cabs.
A good rule of thumb for most valve amps is to exceed the state amp power output by at least 1.5.

It is this fact that people come out with this utter bull-sh*t that "a valve watt is louder than a SS watt."
A cranked 100 Watt Marshall is putting out 175 watts, of course it's louder than a 100 Watt SS that's putting out 100 Watts.


In addition to all of this you, the guitar player, own the volume knob. An amplifier that is turned down to roughly half it's full volume is putting out around a tenth of the power.
This doesn't apply to vintage Marshalls, but most other valve or SS amps will be putting a tenth of their rated output power at just below half volume.
Therefore you could get away with under rated speakers quite easily, but this is not advised and very much buyer be ware. What happens when you daugher/brother/whoever turns the dial on your amp without you noticing and you tun it on?


Notice that this discussion has nothing to do with preamps what-so-ever. I'm fully aware that an SS amp can have distortion, just not from it's power amp. Valve amps get distortion from both the pre and power amp invarying degrees.



Hope that answers your question.