Amp wattage query ?

[dmccombe7]

I'm curious how bass amp wattage is calculated.

For years i've never understood how all-valve amp wattage is far lower than SS or even Class D.

100W valve appears to be as loud as a 600W Class D. 

 

Anyone offer anything ?

 

Dave

[Bolo]

Rule of thumb is that the wattage is calculated to the power output before distortion. Valve amps for electric instruments are designed to operate beyond the point where distortion occurs. For bass, 300 watt valve amps are not uncommon because of the vastly increased headroom (how long it sounds clean Vs power output).

Increasing the amplification beyond the maximum undistorted signal is Overdriving and will alter the nature of the signal. 

The area where this sounds pleasing in some way gives a lot of extra loudness output so the amplification and power usage if measured at the wall are actually way higher than the rated wattage.

[Dad3353]

33 minutes ago, dmccombe7 said:

...Anyone offer anything ?...

 

It's not calculated, it's measured. Watts is simply the current drawn multiplieed by the tension, or voltage. 1 amp at 9 volts is 9 watts. For amps, there is no fixed tension (voltage...), as sound waves vary in intensity. It's become convention, then, to do the power (watts...) measurement at one frequency: 1 kHz. The power stated for that frequency is therefore nominal, and may be different at other frequencies. It is also useful to understand that the power output of an amp varies a lot if one takes distortion into account. It is a Good Idea to state at what level of distortion the power has been measured. For HiFi amps, 0.1% distortion might be quoted, for music amps it might be 1%, and some quote power ratings at 10% distortion. There are other factors in play when thinking about sonic output to a cab, though, apart from just power output. It becomes a bit arbitrary to try comparing simply power outputs from differing technologies. Notions such as the 'class' of amp will affect the audible perception of the amp (a Class A doesn't sound like a Class A/B at the same power level, for example...).
In theory, all the power rating should give identical audible results; it's just not the case. The technologies aren't directly comparable, that's all.
Hope this helps, even if only a little. 

Edited July 18, 2022 by Dad3353

[Downunderwonder]

There's a whole lot of questioning going on there.

 

'Wattage' from an amp assumes a load so as to calculate power from the known amp voltage output.

 

Class D amps come with varying levels of claim about their wattage.

 

Agedhorse can fill you in on the detail but the more reputable claims are based on a 'duty cycle' that acknowledges the lack of noise required most of the time and  leverages that to increase the peak power that can be had without anything blowing up.

 

Less than reputable schemes shrink the duty cycle to claim stupendous power output that fails the thumping 8ths test.

 

This contrasts with old school Trace Elliot solid state rating which was the continuous rated output. Play whatever you like and it can come out with the peak clean voltage every time.

 

Tube amps still sound good with quite a bit of distortion going on. That raises the power level without raising the peak voltage.

[Reggaebass]

It’s easy, the valves are magical 🧙‍♀️ 😁

[dmccombe7]

I'm learning a lot on this thread so far and obviously @Reggaebass has explained it best 

Dave

[BigRedX]

Tube amps also introduce a fair amount of compression as you reach maximum power output so they tend to sound louder even the the peaks in the signal are no greater than a solid state amp the average signal level is.

[Dubs]

2 hours ago, dmccombe7 said:

100W valve appears to be as loud as a 600W Class D. 

Cos it goes to 11...

[dmccombe7]

1 hour ago, Dubs said:

Cos it goes to 11...

The Marshall amps in the rehearsal studios can go up to 21. Cant remember the model of amp but it is a full valve amp, now that is loud. 

Dave

[Lord Sausage]

Many years ago I disappeared down a wattage rabbit hole in the Amps and cab section. It was very enlightening. The main thing I learned I wattage doesn't mean volume.

 

Learned all sorts about ohm's, matching cabs, speaker sizes, dispersion etc. 

 

It's worth a go

[Burns-bass]

It’s like the air we breath, or gravity, or why some people find Rod Stewart attractive: it’s better not to question why.

[Balcro]

On 18/07/2022 at 09:03, dmccombe7 said:

I'm curious how bass amp wattage is calculated.

For years i've never understood how all-valve amp wattage is far lower than SS or even Class D.

100W valve appears to be as loud as a 600W Class D. 

 

Anyone offer anything ?

 

Dave

 

For general reference, see here in the "Amps & Cabs" forum.
An Uncontroversial Way to Compare the Output of Class D Amps.
By Stub Mandrel, Monday at 22:34

 

For a very concise answer to your original post, BigRedX's Monday post fits the bill. It sounds to me that with a valve amp, once the peak is reached there's increasing compression (at the peak) but the other parts of the sound spectrum continue to rise, so the overall sound seems louder.