Tubes Sound Good – Why?

“In electronics, a vacuum tube, an electron tube, or just a tube (North America), or valve (Britain and some other regions), is a device that controls electric current between electrodes in an evacuated container.” Wikipedia.

Electrons are emitted and are then absorbed causing the device to heat up.

In musical terms tubes sound “warm” and “musical.”

In marketing terms they are “Old Skool” and “cool, creamy, dark, magical, coloured” ….etc……..

What does it all mean?

Tubes are simply devices for controlling electricity flowing through a curcuit.

Like a water tap, the more you turn it on the more water flows.

This ability can be used for all sorts of applications from computers to audio gear.

When operated in its optimal range a tube will give as much power as supplied by the power supply in a linear fashion.

So what?

Isn’t that what transistors and IC’s do?


So what’s all the fuss about?

Tubes handle electricity in a different way than silicon based transistors etc. Circuits that use tubes are also different due to the properties of tubes. Tubes are very stable and the circuits can be very simple. Lots of famous old gear is still going, highly prized and costs a fortune. Newer silicon based audio circuits can replicate some of the basic characteristics of tube circuits like CLASS A amplification.

Class A amplification circuits produce no crossover distortion- the great Rupert Neve made this a foundation for many of his famous transistor and IC audio designs.

Everything has limitations and transistors are unstable and their function fluctuates with heat and capacitance changes. To overcome these limitations circuit designers must include ways of keeping these devices stable to deliver a desirable outcome within very specific parameters or they will oscillate, overheat and fail. These circuits can get very complex and can produce audible artifacts that our ears may not appreciate.

Odd order harmonics……..

Imagine one out of tune violin in an huge Orchestra. Our ears are so sensitive they will hear that out of context violin!

“In power systems, Harmonics are multiples of the fundamental wavelength. Thus, the third order harmonic is the third multiple of the fundamental wavelength. This type of harmonics is generated in non-linear loads. Examples of nonlinear loads include transistors, electrical motors, and the non-ideal transformer. Nonlinear loads create disturbances in the fundamental harmonic, which produce all types of harmonics. However, in this section we focus on the 3rd order harmonic due to its certain special characteristics in the context of powers systems. ……….For many purposes different types of harmonics are not equivalent. For instance, crossover distortion at a given THD is much more audible than clipping distortion at the same THD, since the harmonics produced are at higher frequencies, which are not as easily masked by the fundamental.” Wikipedia

It only takes a tiny amount of Third Order Harmonic Distortion for the sound to become objectionable, 0.001% as opposed to a figure of 1% Total Harmonic Distortion that could still sound pleasing. The numbers are a bit misleading but the point is that the ratio of ODD to EVEN order harmonics in an audio signal seems to be important to produce pleasing audio.

The effects of higher level odd order Harmonic distortion are clearly heard in an annoying and piercing rather than smooth upper frequency range. Sounds become overly hard or bright and unrealistic because they are distorted! EQ doesn’t help much as it just makes a distorted harmonic content quieter but the annoying distorted signal is still present to the ear and most likely conflicting with other important high frequency information.

The kicker with crossover distortion and the associated third order distortion is that it increases when the signal levels drop.

Which critical part of the audio signal is low level and further decreases over time? Spacial information, reverb tails and the upper harmonics of instruments. So these vital quality signals get more distorted the quieter they become.

These are the expensive sounds of high quality recording.

So back to tubes-

Tube gear operating in its optimal range can produce crystal clear sound with miles of top and bottom end, with realistic powerful mids.

It’s when a tube goes beyond its optimal operating range where things become really interesting.

The tube starts to reduce output power as the input voltage continues to rise.

Depending upon how far you continue to drive the input, you can get lovely, fuzzy, warm, smoothed out, coloured creamy goodness with splashes of euphoric energy.

Keep pushing it and you get the simply horrible!

A tubes performance characteristic is based upon its fundamental design. When operated under optimal conditions, the dynamic range, frequency response and harmonic content of the audio signal can reproduce a simply stunning amplification of the original source signal.

To our ears this is perceived as realism, openness and definition or signs of “life.” Of course it’s only an impression but speakers and our ears like it this way. This is as true for acoustically captured signals as well as electronic and digitally generated sound signals when processed with tube equipment.

When you push a tube beyond its optimal range and get creative, something else starts to happen…..

Depending on the tube type in a corresponding circuit, sound source and the many operational factors involved, the effects of tubes become more obvious and maybe desirable as compared to solid state and digital gear which produces different results.

With most good tube gear there seems to be large operational “sweet spot” to get things “right” and “wrong” which gives a great variety of effects with lots of creative room to experiment. It’s a 15- 20dB “sweet spot.”

This is different to solid state and digital gear which seems to have a narrower “sweet spot” with less variation of sounds when operated outside of their optimal parameters.

Transistors have about 5db of sweet spot before the onset of ugly distortion, 10db for opamps and digital 0db or no sweet spot at all.

Tubes do different things differently……

Tubes are amazing for their clarity and realism. They are even more exceptional when using this built in sweet spot compression/ limiting feature which is pleasing to the ear being perceived as being big and loud!

Tube based devices are so easily used to create a very realistic “alive” sound or very interesting and engaging sounds with lots of “energy” because of this one simple feature.

There are many limitations with tubes and tube based circuits.

Most tube based devices have very limited functionality, so a tube based iPhone is not going to happen!

Tube gear has to be designed to work in a certain way that produces very good results. It’s either going to do what you want or it won’t.

The main functions available on tube gear are amplification, compression and filtering. There are basic EQs or parametrics and there are also some complex multiband compressors, all made with tubes!

So why use tube based equipment?

The fact is that what they do they do it really very very well and everything sounds good through a tube-right!

No, this is simply not the case!

Things sound good through tube gear, yes, but you can also make things sound very, very bad and the cheaper tube gear is just horrible as is some newer tube gear manufactured which was never very good to begin with. And there’s lots about!

Everything has it’s place…..

An optimally operated, overdriven or current starved tube may end up producing the exact thing that gets our ears excited but may not be the right choice for many applications where other qualities are required.

Sometimes you need to work on a sound to add a bit of euphoric overemphasised harmonic distortion, just ask a guitarist about tube amps. Sometimes you want the compression artefacts of a vari mu but sometimes you need flexibility, portability, precision or hard and fast control.

The sound produced by audio gear is determined by the sound source, components, circuits and how it’s being used. If you know how you want something to sound then try and get your audio gear make it sound that way. Sometimes a piece of gear connot do what you want it to.

Each brand and product has it’s own characteristics and when it comes to good audio gear you get what you pay for.

And that’s certainly the case with tube gear!

What are some of the limitations of a tube device that contribute to the way tube gear sounds?

1. Tubes need high voltages and alot of power- so the power supplies of tube gear need to be very good. At its most basic level when working with audio we are simply shaping the power that’s been delivered by the powersupply. So fundamentally power supplies are critical for quality audio.

2. Simple features mean designers of tube gear focus on sound quality and reliability rather than a big variety of functional options that require complex circuits.

3. With high quality audio less processing is required and therefore less phase shift.

So do tubes really sound good?

According to the conclusions of the very knowledgable audio engineers, electronics engineers and scientists at the Audio Engineers Society in May 1973-

“Vacuum-tube amplifiers differ from transistor and operational amplifiers because they can be operated in the overload region without adding objectionable distortion. The combination of the slow rising edge and the open harmonic structure of the overload characteristics form an almost ideal sound- recording compressor. Within the 15-20 dB “safe” overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level, which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective headroom that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass response is directly related to the strong second and third harmonic components, which reinforce the “natural” bass with “synthetic” bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube preamplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.”

So it looks like there is something to the “tubes sound better” story…

But guitarists already knew that.

You be the judge….answer the question based on your own experiences.


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