This is why you’ll usually find a selection in any recording studio. A good studio engineer will know the intricacies of each at their disposal, each one will have a slightly different tone and add a different level of ‘coloration’ to the sound.
A Brief History
Nowadays we are used to using electrical items day in day out, most of which use transistors (i.e. solid state) and are small, compact and often portable.
The earlier incarnation and uses of tubes are understandably more primitive than what we have today but the way they are used largely remains the same.
The original invention of tubes came from a phenomenon known as thermionic emission.
What Is Thermionic Emission?
In a nutshell, this is the process whereby a heated piece of releases electrons. If a cathode (a device which current will flow out from) is heated it will give off electrons through thermionic emission. If an anode (a device that will receive current, sometimes called a plate) has a positive voltage applied it will attract these electrons.
By placing these inside a vacuum tube the electrons can flow freely as there is no air resistance.
How This Applies To Preamps
Up until the 1940’s, most amplifiers used tubes in this way. Around this time however transistors were invented which became much more affordable, and were much less fragile than tubes.
A transistor itself becomes an amplifier by helping to raise the strength of a weak signal. Unsurprisingly one of the first uses of a transistor was in hearing aids, amplifying the incoming signal by this method to produce a much larger signal for the user to hear.
The idea of a transistor is arguably more complex than that of a tube, but in very brief terms a transistor works by taking a small current at one end (the input) and producing a much larger current (the output).
The transistor works as a current booster, hence the term ‘amplifier’. One of the great things about transistors is they require much less power because of this than a tube.
Transistors themselves are much smaller and less fragile than a tube, so it is easy to see why they are now more common in electrical items than tubes. Can you imagine having to run your computer at home with a set of tubes?!
Tube vs Solid State: Tonal Differences
We know, in music, that even subtle differences can cause big changes whether that be the angle of a microphone’s placement through to the type of wood a guitar is made from. So naturally, a tube preamp will have different qualities to a solid-state amp with transistors.
A tube preamp tends to have warmth and smoothness that a solid-state often lacks.
Because of the way they work, driving the tubes creates a subtle but smooth distortion adding a pleasing character to the tone. This doesn’t necessarily constitute distortion in the sense of ‘overdrive’ but rather more color or character.
In fact, there is a more scientific explanation as to why a driven tube preamp is more pleasing than the sound of solid state transistors.
As a tube creates distortion it produces harmonics which are known as ‘even harmonics’. Essentially these are tones which are the same note but are produced higher in octaves. This is why typically a tube amplifier is said to sound better, because the harmonics it produces are much more pleasing to the user’s ear.
Now if we’re talking about mic pre-amps, it can often be the case that the difference is subtle but nonetheless will add character to the recording that when placed with other instruments causes it to sound better and balanced with other instruments.
If we take a look at high-gain guitar amps, ‘driving’ (or increasing the input to) the tubes creates a lush distortion that many regard as superior due to the way the tubes behave.
The downside of this however is that tube amps don’t respond or perform as well at lower volumes, meaning for the bedroom guitarist they may not be the most suitable option if you’re looking for tonal quality.
The characteristics of tubes will also change depending on their temperature, with tube pre-amps generally sounding a little better when they have been left on to warm up.
In contradiction, a solid-state pre-amp tends to create odd harmonics, which in themselves can create a sense of dissonance which are less pleasing to the ear.
That said, solid state pre-amps tend to have a more ‘transparent’ sound in general, so whilst there may be some odd harmonics present, the sound will generally have less colouration that a tube pre-amp and will be able to handle higher levels of gain without being pushed to distortion.
So, what does this all mean? Well, a solid state preamp could be a great choice if you want to capture the natural sound of your source.
Tube vs Solid State: Pros and Cons
As with most musical equipment, there is no right or wrong. Both tube and solid state offer different characteristics. If you’re thinking about investing in a good quality pre-amp, weigh up the pros and cons first:
Warm tonal quality
Creates a lush distorted sound that adds character
Emphasizes even harmonics which are pleasing to the ear
Tubes require more maintenance and will eventually need replacing
Tubes may not be as suitable as a solid state pre-amp for instruments such as drums that have powerful transients and quick attack
Tube tone changes over time and use
Clean sounding with very little distortion
Ability to handle higher gain signals
More suited to instruments such as drums and often acoustic guitar
Tend to be cheaper than tube pre-amps
Can produce odd harmonics which aren’t as pleasing as tubes to the ear
Can sound harsh on certain instruments
Cheaper pre-amps often don’t sound great, you may need to invest to get a quality sound
If you’re still unsure on the tonal characteristics of the two, you’ll find plenty of comparisons online or on Youtube. We’d recommend checking out the Universal Audio Solo/610 for a classic tube sound or the Neve Portico 5012 for solid state.