1. Introduction
  2. Slider of FFT
  3. Brief description of three things



This section will be interesting for fans of tube sound, who do not believe in their sensory perception of the world (their ears and eyes) but want documentary proof of the existence of tube sound.

There is an easy way to evaluate the parameters of a amplifier with acoustic system: send a test signal (perfect sine) to the amplifier and see what the speaker is reproducing. Now it's very easy to see and determine the difference in sound between solid state and tube amplifiers.

Measurements are something that is independent of our ears and preferences. Measurements are incompatible with the profane trash about tube sound. For this reason, shameless sellers inform a buyer of a special gentlemanly set of parameters that are not relevant to high sound quality. 

Here you have the chance to see the difference between the signal from a tube and a transistor amplifier. And here you can hear what this difference sounds like ...

FFT (fast Fourier transform) Spectral Analysis of an Audio Signal

Y axis: dBu (0 ....   - 140),  X axis: lg Hz (17 Hz .... 21 000 Hz)

Mode pure direct: No amplifier in the signal path.
7tubes amplifier
7tubes amplifier
Mode clean: The second harmonic is minimal.
Mode smooth: The vacuum triode works in standard mode.
7tubes amplifier
7tubes amplifier
Mode smooth: This level of harmonics is typical for a conventional tube amplifier.
Mode warm: The triode is switched to the second harmonic enrichment mode.
7tubes amplifier
7tubes amplifier
Mode warm: The second harmonic is emphasized a modest.

 click to expand

 click to expand

Harmotronix, 7tubes

7tubes headphones amp: spectral analysis of an output, Level 0.5

Here you can see that the disturbance remains at roughly the same low level.

However, there is an significant, beautiful 2nd harmonic that is very low in level.

This sound is similar to a solid state amp.


Measurements at a load of 270 ohms

2nd:  -72 dBu
3rd:   -76 dBu

In fact, almost all of our knowledge is something that has been read somewhere or has come straight to our ears. We are a marketing victim from a young age, also from many professional and well-paid "gurus".

Everything around us is from Gossip, myths about the intricacies of a cable, about musical NOS tubes also about paper, oil capacitors from the good old days, pure copper, silver wires etc., overflowing. And also succinctly: the tube amplifier works with any high-quality speaker system.

From my many years of experience: it is not the minimum harmonic values in the signal or the high volume that is decisive for your hearing.

For example, the IC TPA6120A2 headphones amplifier has exceptional parameters: ultra low THD + Noise (better than -100 dBu), high speed front slew  (better than 1000 V/us). This amplifier gives very accurate reproduction of sound. 

High Fidelity Stereo Headphones Amplifier TPA6120A2

Texas Instruments: web datasheet

Texas Instruments: pdf datasheet

However, if you add to this signal in strictly dosed proportions of harmonics of different orders, the sound becomes also pleasant for our hearing. This is alike to how a chef in a restaurant adds specific spices in fixed proportions to a gastronomic food to make us very tasty.

For our ears at medium volume with classical chamber music, jazz compositions this arrangement of harmonics (overtones) are pleasant:

2nd harmonic: - 30 dBu ...... - 35 dBu,

3rd harmonic: - 45 dBu ... - 48 dBu

Higher order harmonics: lower - 60 dBu, with each subsequent harmonic being about 6 dBu ... 10 dBu lower than the previous one.

Of course, the amplifier does not have to prove its own noise no greater than: - 80 dBu.

Remark: The listed values refer to acoustic measurements with a special microphone.

It tinkle so simple, but it is very difficult to reach these values: the amplifier does not sound by itself, it controls the speaker system (headphones).

Tube amplifiers require specific loudspeakers. And this is the most important condition for sound quality. But this is another story from the field of acoustics. 

SoundBar MR got it done for this problem.

It is simple and reliable,

economical: 50 watts of power consumption from the network,

is designed for many years of continuous operation,

Good value for money: modern tubes of new production.

Harmotronix has another concept: here the signal is prepared for on-line listening via headphones or a conventional transistor equipment. Permanent music in the background does not tire out our hearing anymore. Read more here.....

7tubes will be of interest to purists. Only vacuum triodes and SRPP circuits are used here, a classic from the good old days on modern components. But the making of the Machine 7tubes in the specified quality requires some experience.

This case is not trivial.