darTZeel Audio NHB-108 B version - Manual (Page 21)

darTZeel NHB-108 model one
User Manual, version B 1.0 Page 21 of 35
T4.5. TIO, Totally Identified Object
It is however the final touch that makes this
darTZeel
machine, now installed in your listening
room, your darTZeel NHB-108 model one:
We refer to the identification plate, fully described
in the first part of this manual.
Made from 24k gold plated brass, it is a unique
handmade piece, just like the machine on to which
it is affixed.
Your name is engraved in gold letters, thus amal-
gamating the destiny of the darTZeel NHB-108
model one
with your future unforgettable musical
moments.
We proudly congratulate you!
T5. The audio electronics
Simplicity.
The whole NHB-108 model one electronic con-
cept could come down to this single word.
Simplicity does not mean simple, however.
Purity
Total cancellation or absence of harmonic distortion
does not mean "purity", alas.
You certainly know that most musical instruments
are very rich, harmonically speaking. Thanks to
these harmonics, we can distinguish between a
saxophone and a flute.
Did you know, though, that the level of these natu-
ral harmonics can easily reach 20 to 40% of the
fundamental note, depending on the instrument
played? But do we say that an instrument distorts?
T5.1. What is distortion?
In the audio world, any signal change is called "dis-
tortion". Many different kinds of distortion exist,
but we mostly speak about "Total Harmonic Distor-
tion", or THD. THD is so well known that we more
than often forget that other ones do exist.
Negative Feed-Back, NFB, is a smart electronic
trick used for diminishing or even eliminating all
type of distortions, and can be roughly described as
follows:
At the amplifier input we put a signal having an
inverse deformation from the one it naturally pro-
duces at its output. So, the new output signal will be
"purified" since the 2 inverse deformations will
cancel each other.
This is what the theory says.
Now let us see what actually happens in practice.
We will discuss only the best-known distortions,
given that their behaviour is simpler to explain.
T5.1.1. Keeping in harmony
Let us take an amplifier especially designed to pro-
duce exactly 1% of THD. Then let us feed it with a
recorded musical instrument. We shall suppose that
this instrument is moderately rich harmonically, say
around 20%.
Now, let’s be a bit optimistic and suppose that the
speakers we will use are truly perfect, without a
single trace of any distortion.
Well, now, let us try figure the THD we will have
at the output of the amplifier. We could be tempted
to say "21%, since 20 plus 1 makes 21, no?"
Okay… So then, which "golden ears" could notice
the THD difference between 20 and 21%? Who
could swear that the amplifier does add distortion?
In fact the distortion change is even less than this.
THD, like most other non-correlated physical phe-
nomena, does not increase in a linear fashion. The
"total" THD is equal to the square root of the sum
of the squared individual THDs.
A little equation is even better than a less-than-clear
definition:
( ) ( ) ( )
2 2
2
2
1
....
n
HD HD HD THD
+ + + =
In our particular case, we only have 2 terms, so the
equation becomes:
% 025 . 20
100
1
100
20
100 [%]
2 2
= ⎟
⎠
⎞
⎜
⎝
⎛
+ ⎟
⎠
⎞
⎜
⎝
⎛
=
THD
And now? Who could distinguish between a
20.000% harmonically rich musical instrument, and
another one producing 20.025%? Not us for sure.
And the very next note, how rich is it? And the next
one? Oh! The song has already finished? What sort
of music was it?...
Even though in reality THD is a bit more compli-
cated than this, we can still see that a posteriori, it
does not have the importance that was attached to it
for decades – quite the contrary.
If at darTZeel we could completely eliminate THD
while maintaining our 3 main criteria, then maybe
we would do so. Maybe. Just for the beauty of the
gesture.
Some amplifiers available on the market claim ex-
tremely low THD figures, at the very limit of in-