Why Do Tube Amps Sound Better… or Do They?

Many guitarists, especially those that play rock, blues, or country music, seem to agree that “tube amps sound better”.  Almost all guitarists would agree that given the same rated output power, that “tube amps sound louder”.  A 30W amp tends to sound louder than a 65W solid state amp.  Of course, for some types of music, solid state is the preferred amp, and it’s for very reasons that tube and solid state amps sound different.   A jazz guitarist who is not going to overdrive his amp may like the cleans that solid state amps offers.  A metal guitarist or “shredder” may like the very overdriven tones that solid state amps produce that make them so very different than tube amps.

Why do so many think tubes sound better?  I am one of them.

Here’s why:

Guitar amplifiers are often severely overloaded by signal transients, (THD 30%), especially in today’s world of high output pickups and pedals. Under this condition there is a major difference in the harmonic distortion components of the amplified signal, with tubes, transistors, and op-amps separating in distinct groups.

Op-amps produce strong third, fifth, and seventh harmonics when driven only a few dB into overload.  The resulting sound is metallic with a very harsh edge, which the ear hears as strong distortion. Because the sound may be objectionable, op-amps are rarely operated in their saturated region.  This results in a very clean amplified sound with little coloration and true dynamic range (within the limits of the amp).  This dynamic range is not necessarily a good thing, because of the limits of the rest of the system.  The top end of the dynamic range contains transients, but lacks solid pitch information.  The result?  Clean, but perhaps sibilant and cymbally.  Colorless.  Dull.  Perhaps you don’t want your amp to “color” your sound.

Transistors produce buzz or white noise when severely overloaded, caused by the edge produced by overloading on transients, mostly seventh and ninth harmonics. The ears hear this dissonance as noise. Another factor is a lack of “punch” due to strong third harmonics, a kind of blanketing of the sound. Transistor amps exhibit a strong third harmonic when driven to overload, producing that blanketed sound.  This sound, compressed lack of punch, and strong odd order harmonics, may be what some guitarists are looking for.

Tubes generate a whole spectrum of harmonics when overloaded, particularly the second, third, fourth, and fifth, to give a very full bodied sound.  Tubes also differ from op-amps and transistors in that they can be operated in the overload region without adding objectionable distortion.  A slow rising edge and open harmonics combine to create an ideal sound.  Within the 15-20 dB overload range, the electrical output of the tube increases only 2-4 dB, creating a natural compression.  Since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear.  It is this effect cause tube amps to have a higher apparent volume level not indicated on a volume (VU) meter.

Tubes sound louder and have a better signal-to-noise ratio because of the extra subjective headroom that transistor amplifiers do not have.  Tubes get their punch from their natural overload characteristics.  Since loud signals can be reproduced at higher levels, the softer signals are also louder.  This is the famous “sweet spot” that tube amps exhibit.  Strong second and third harmonics give a feeling of a more natural bass response.

The sweet spot will sound loud clean and full, and exhibit wonderful touch sensitive dynamics that follow the guitarist’s playing dynamics.  Roll back the volume control on the guitar or play softer, and you get the full, rich tone at a quieter level.  Dig in, or roll up the volume control, and now you have that natural, sweet, singing tube overdrive that we love so much as guitarists.  This is why we love tube amps!

Notes on harmonics. The primary color characteristics of an instrument are determined by the strength of the first few harmonics.

  • Odd harmonics (3rd and 5th) produce a stopped or covered sound.
  • Even harmonics (2nd, 4th, & 6th) produce choral or singing sounds.

The second and third harmonics are the most important.  The second, an octave above the fundamental, adds body and makes the note sound fuller.  The third harmonic is a musical 12th.  Instead of making the sound fuller, it blankets the sound and makes it sound softer.  Adding a fifth harmonic to a strong third gives the sound a metallic quality that gets increasingly annoying as the volume increases.  A strong second with a strong fifth tends to open up the covered effect that the third induces (this is usually what we want).  Adding fourth and fifth to this will change the sound to an open horn like sound.

Higher harmonics, above the seventh, give edge or bite to the sound.  As long as this edge is balanced, it will reinforce the fundamental and give a sharper attack quality.  Too much of the higher harmonics- seventh, ninth, eleventh – will give that raspy, dissonant kind of sound.  The human ear is sensitive to the edge harmonics.

The major characteristic of tube amps is the presence of strong second and third harmonics, sometimes in concert with the fourth and fifth.  Remember, a strong second with a strong fifth tends to open up the covered effect that the third induces, and strong second and fourth harmonics help create that singing sound we all love so much in our tube amps.

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