Saturday, October 22, 2016

The difference between tube and solid state amps

Hello and welcome to this week's article!
Today we are going to take a look at the difference between tube watts and solid state, why does everyone say that there is a big difference?
Why does a 100w tube amp overshadows a 100w solid state one in a live environment?
I am no engineer, but we will try today to make a little clarity and to separate the facts from the myth.

Note: this article is an addition to our articles about, speakers and tubes.

Fact: 100w tube = 100w solid state.
The main difference is that a tube amp uses one or more vacuum tubes to amplify the signal while a solid state one relies only on diodes, transistors etc (for the sake of simplicity we won't talk about the many hybrids that uses a solid state power amp adding a tube just to add some harmonic warmth or those who uses digital emulation of tube response).
Then why in a live environment the tube amp usually sounds much more powerful than a solid state amp? For a serie of reasons, which involves the fact that tubes can increase certain harmonics (therefore push a little more the sound on frequences that appear to cut throught the mix better) and the break up limit.

What is the break up threshold?
When playing at a low volume with both a solid state and a tube amp we will notice that the difference between the two amps is not that noticeable, both amps have a certain amount of headroom (the space in which the volume can be increased without causing distortion), but then when we will turn up the volume we will notice that we will reach a level in which the headroom will finish and the amp will start distorting.
It's at this point that a solid state amp will start sounding really bad, therefore the volume excursion ends at the break up limit or a little over, while a tube amp can easily surpass it, since after the breakup the tubes really starts warming up adding a sligh compression and harmonic warmth that actually makes the sound even more pleasant.

What is a workaround that amp manufacturers usually choose to make solid state amps to sound comparable to tube amps? Easy: they add more watts, to let the preamp do his job with no interference.
Examples: the Marshall Mode Four head, which has 350 watt, which is used for example by the Testament guitarist Alex Skolnick, or the Fender Metalhead, which produces 400w, starting from the assumption that usually in order to match a tube amp at full volume a solid state one should usually have the triple of the wattage.

So far we have only talked about guitar amps, but with bass amps the wattages are even more extreme, because it takes even more power to deliver bass frequences with the right clarity, so the same rule applies to bass amplifiers too, and the wattages are even higher.

Myth: tube power amps sounds better than solid state power amps.
This assumption is true as long as you want/need the sound effect of tubes, which is, as we have said, a harmonic enhancement especially in the mid and high frequences and a sligh compression that influences the dynamic range. This is an effect that is often desired in rock, blues and other genres, while many jazz or funk players prefer solid state amps because they sounds usually more "clean", like the Roland Jazz Chorus, which is in production by 40 years and it is still considered an industry standard for the genre. The final word is that you should really try both solutions and find the right one for your music genre, keeping in mind that it's not mandatory to use the power amp type that everyone uses in a certain genre: heavy metal is a genre typically dominated by tube amps, but some of the most influential icons actually have shaped their tone with solid state amps (for example Dimebag Darrell of Pantera or Chuck Schuldiner of Death).

Difference between Peak and Rms wattage: some amps have the wattage calculated in rms (root mean square, which put in simple words is the average volume actually perceived by our ears), and often tube amps have their wattage reported in rms, which means that if they are 100w rms, they can play at 100w for hours, while other amps (often solid state ones) have their wattage expresses in peak: this means that if an amp is 100w peak, it can sound 100w for one fraction of a second, for example, while for most of the time it will play at around 50w rms. This is more of a marketing gimmick, and we should really be careful when reading the specifics of two amps when comparing them, or when choosing which one to buy.
This is another of the most common reasons why tube amps usually seems to sound much louder than solid state ones: the wattage is reported in a different way.

Click here for a Follow-up article about the differences between class A, B, AB and D power amps!

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