KVG Laboratories crafts audio and music instrument equipment made with vacuum tube and with solid state electronics. Most use vacuum tube, but not for the reason you may expect.
Critics often assert that tube electronics lack the clarity and low distortion of transistors. This assertion is seemingly verified by the majority of commercially made equipment that you will encounter, but to generalize that a commercial example of tube technology represents the ultimate capability of the technology is erroneous. Our proprietary research into the causes of, and characteristics of, all forms of distortion and quality losses in vacuum tube and solid state audio technology has given us a unique perspective. KVG Laboratories’ design techniques and quality standards for vacuum tube and solid state electronics are based on our research.
Despite the naysayers, vacuum tubes are actually capable of the same level of clarity and low distortion as transistors, albeit with possibly greater cost. Consider that a vacuum tube won't overload with severe clipping, which is an advantage over transistors that clip a signal readily during transient overloads.
One reason KVG Laboratories builds most of our electronics products with vacuum tubes is because we can create any sound the customer requires more quickly and more easily with tubes than we could with transistors. Regardless of whether the customer wants extreme clarity, extreme distortion or anything in-between, KVG Laboratories can almost always satisfy the required sound using vacuum tubes. In those instances where portability or size are important requirements, or where we cannot satisfy sound requirements with vacuum tubes, we use a variety of solid state designs. It’s not a dogmatic issue for us. First and foremost, we want the best sound possible and we’ll use whichever technology achieves that sound.
At first, the vacuum tube was the only way to build audio equipment. The 1950s brought the transistor, which rapidly pushed vacuum tube-based electronics out of the market because advertisers in the late 1960s said that the solid-state electronics was the “wave of the future,” claiming it was always quieter, clearer and more accurate when compared to vacuum tube gear. That told only part of the story.
Transistors are the best technology for many applications (computers being one excellent example), but they are not always the best way to build an audio circuit. Professional recording studios and many audiophiles have always prized vacuum tubes for the tone and the quality of the sound they produce, seeking the very “coloration” that was criticized in Hi-Fi marketing literature. The recent rise of computer-based digital audio has increased the demand for tubes.
Audiophiles, audio engineers and musicians have long debated the question of vacuum tube sound compared to solid state sound. Measurements of the differences assume the tested amplifiers operate perfectly linearly, which in fact is never the case. Conventional methods of frequency response, distortion and noise sometimes show that no significant difference exists between tubes and transistors. Recording engineers often are directly involved with the controversy of tube sound versus solid state sound, especially in pop recording and in audiophile recording projects.
Differences are quite noticeable now that solid-state consoles are commonplace. It's not uncommon during a recording session in studios notorious for bad sound that a visiting engineer will plug the microphones into vacuum tube mixers or preamplifiers instead of the studio’s console. The resulting change in sound quality that is nothing short of incredible.
Those who avidly listen to analog LP disc records can easily discern that vacuum tubes sound different from solid state. Defining the cause of the difference is a complex problem in psychoacoustics, further complicated by a wide variety of subtle phenomena.
Musicians tend to be are more objective listeners than audiophiles or engineers. They don't express their observations in standard measurements, but the musician's "by ear" measuring technique seems quite valid because the human ear's characteristics are quite different than an oscilloscope's.
Common statements by musicians express their observations that:
- Recordings made with solid state electronics tend to emphasize sibilance, especially at low levels.
- Recordings made with solid state electronics tend to over-emphasize emphasize cymbals, especially at low levels.
- Recordings made with solid state electronics are very clean yet lack the "air" of a recording made with vacuum tube electronics.
- Recordings made with vacuum tube electronics have a tightly defined space between the instruments, even when they play loud
- Recordings made with solid state electronics sound restricted, like they're under a blanket.
- Recordings made with vacuum tube electronics "jump out of the speaker at you."
- Recordings made with vacuum tube electronics have more bass.
- Bass sounds like it is an octave lower with vacuum tube electronics.
- The middle range of recordings made with vacuum tube electronics is very clear
- Each instrument has presence with vacuum tube electronics, even at very low playback levels.
- Vacuum tubes do not restrict the music's dynamics because they overload gently.
- Transistors buzz.
- Transistors add musically unrelated harmonics or white noise, especially on attack transients.
- Transistors have a "shattered glass" sound that restricts the music's dynamics.
- Transistors have highs and lows but there is no "punch" to the sound.
- The major distortion characteristics of vacuum tube amplifiers are the presence of strong second and third harmonics, often in concert with, but greater than, the amplitudes of the fourth and fifth harmonics. Harmonics above the fifth harmonic are insignificant until the equipment's overload exceeds 12 deciBels.
Triodes and pentodes differ in the composition of their distortion components. When triode tube amplifiers distort, the second harmonic is dominant, followed closely by the third harmonic; the fourth harmonic's level rises 3 to 4 deciBels later; and the fifth, sixth, and seventh harmonics remain below 5% up to the equipment's 12 deciBel overload point. Clipping is asymmetrical and the waveform's duty cycle shifts prominently. When pentode and cascode amplifiers distort, the third harmonic is dominant and the second harmonic increases about 3 dB later, both the fourth and the fifth harmonics are prominent, the sixth and seventh harmonics remain under 5% up to the equipment's 12 dB overload point. Clipping is asymmetrical and the waveform's duty cycle shifts slightly.
Transistor electronics’ distortion is dominated almost entirely by the third harmonic, with all other harmonics present at a much lower amplitude than the third harmonic. As transistor electronics overload, the amplitudes of all the higher harmonics begin to increase simultaneously within 3 to 6 deciBels of the 1% third harmonic point. Overload waveforms of transistor amplifiers are the distinct square wave shapes, Clipping is symmetrical and the waveform's duty cycle is not altered.
Operational-amplifier, or “opamp,” electronics exhibit distortion similar to that of transistor electronics, of course, but the rate of the increase in the slope of distortion rises steeply because of the extreme amount of inverse feedback inherent to opamp-based circuits. The third harmonic is the dominant distortion component, but its slope increases steeply, increasing very strongly from the same point as the origin of the fifth and seventh harmonics. Opamps, in typical circuits, suppress all even-order harmonics almost completely. The opamp’s CMRR (common mode rejection ratio) measurement indicates the degree to which this occurs. Even slight overloading results in a perfect square wave, limiting the opamp circuit's ability to reproduce transient overloads cleanly.
- The differences between vacuum tube and solid state sound is caused by the relative proportions of the harmonics that comprise the amplifier's distortion during the time the amplifier overloads.
- Transistor amplifier distortion is mainly comprised of the third harmonic, creating a "veiled" sound that gives recordings a restricted quality.
- When a vacuum tube amplifier overloads it generates a spectrum of harmonics comprised of a particularly strong second harmonic, with overtones from the third harmonic, fourth harmonic, and fifth harmonic, creating a full-bodied "brassy" quality to the sound. As the amplifier's overload increases, the magnitude of the seventh harmonic, eighth harmonic, and ninth harmonic greatly increase, adding an edginess to the sound which the human ear interprets and a sign of increasing loudness.
- When an opamp overloads, it produces harmonics with such extremely-fast rising slopes that they quickly become objectionable.
- Transistors extend the overload range, while vacuum tubes provide the greatest extension of overload range. This illustrates why vacuum tube amplifiers are considered excellent for music instrument amplifiers as well as high-end high fidelity amplifiers.
HARMONICS DEFINE TIMBRE
Musicians have determined how various harmonics relate to the timbre of a musical instrument.
- The timbre of an instrument is determined by the magnitude of the first few harmonics.
- Each lower harmonic produces its own effect on timbre when it dominates, and it modifies the effect of another dominant harmonic when it becomes prominent.
- Odd-order harmonics (the third and fifth) produce a "blanketed" or "veiled" sound.
- Even-order harmonics (the second, fourth, and sixth) produce "choral" or "singing" sounds.
- Musically, the second harmonic occurs one octave above the fundamental tone and is therefore imperceptible on its own because of masking. Yet, the second harmonic adds fullness to an instrument's timbre.
- The third harmonic is referred to by musicians as a "quint" or a "musical twelfth." Therefore, the third harmonic produces a softer timbre, creating the sound described by many musicians as "blanketed."
- Adding a fifth harmonic to a strong third harmonic gives the instrument's timbre a metallic quality that becomes annoying or grating as its amplitude increases.
- A strong second combined with a strong third harmonic tends to open the "veiled" sound.
- Adding the fourth harmonic and the fifth harmonic to the combination of second and third harmonics changes an instrument's timbre to an "open horn" like character.
- Higher harmonics, above the seventh, give "edge" or "bite" to an instrument's timbre. If the edge is balanced with the fundamental pitch, it reinforces the fundamental, giving the timbre a sharper attack.
- The seventh harmonic, ninth harmonic, and eleventh harmonic are musically-unrelated.
- The presence of too many "edge" harmonics produces a raspy, dissonant timbre.
- The human ear seems very sensitive to edge harmonics, so minimizing their amplitude is extremely important.
- The effect of "edge" harmonics varies directly with loudness.
- Playing the same note pianissimo or forte creates little difference between the amplitudes of the fundamental tone and its lower harmonics.
- The amplitude of any harmonic above the sixth harmonic varies directly with changes in loudness.
- The relative balance among "edge" harmonics is a critical cue for the ear to perceive changes in loudness.
- As an aside, the second and third harmonics are those used when making electronic distortion measurements, which brings into question the validity of steady-state distortion measurements as a means of predicting the subjective quality of an amplifier.