darTZeel Audio NHB-108 B version - Manual (Page 18)

darTZeel NHB-108 model one
User Manual, version B 1.0 Page 18 of 35
darTZeel NHB-108 model one
Technical Section
T1. Introduction
Thank you for studying this technical section de-
voted to true audiophiles, demonstrating proof of
your interest in the darTZeel NHB-108 model one.
First of all, please do not think for a minute that we
consider audiophiles differently from music lovers.
We know perfectly well that audiophiles love music
too, and we are very happy with this.
It is however true that music lovers are generally
less inclined to enjoy the technical and performance
side of the music, hence the existence of the Music
lover's manual.
In the light of what follows, you will better under-
stand why our technical choices during the design
of the NHB-108 model one led to what one could
call a truly exceptional machine.
We trust that you will derive great pleasure from
reading this manual, and that we succeed in com-
municating some of the burning passion that has
been boiling inside us for more than 30 years.
Enjoy your reading!
T2. Genesis of NHB-108
The NHB ("Never Heard Before") project began in
summer 1984.
Crazy about audio since childhood, we gradually
developed the idea of designing a power amplifier.
Even though the original NHB-108 model one is
the fruit of a single man, the moral, financial and
professional support from family and friends over
all these years has played a huge part in this en-
deavor.
At the time it was only a dream, and we are grateful
to every gal and pal who has been involved in it and
contributed to its achievement.
In the '70s and ‘80s, here in Europe, Japanese elec-
tronics were queens and kings of the market. Very
rare, and above all virtually unknown, was the real
high-end audio gear coming from USA or else-
where. The finish was already very good, but the
sound quality did not come up to scratch, simply
because it was not one of the original design goals!
Only a few companies were able to offer real break-
through products. Not all of them are still in busi-
ness, Alas!
The more the years passed, the more our desire for
designing a new machine became tangible. In mid
spring 1984, we produced a first digital power am-
plifier in a school lab, as a diploma project.
Paradoxically, the innovation here was not the fact
that the amp was digital, but that no feedback what-
soever was used. The output stage was totally open-
loop.
The sonic result was so astounding that we immedi-
ately started the NHB project, although its code
name did not come until later.
The initial idea was to design a new very powerful
digital amplifier, totally open loop if possible, with
the purest sound reproduction we could attain,
without any other consideration, especially the price
factor.
The main problem at the time was that the technol-
ogy did not yet offer the monochip solution, so we
had to build the circuit entirely in hybrid technol-
ogy, using mainly discrete devices. The odd thing is
that even in this early 21
st century, we have still not
surpassed the speed of those old circuits.
Another problem then arose. Our circuits were
much more complex than a single modern IC, and
of course they were not very reliable either. We
especially encountered several performance consis-
tency problems from sample to sample, and we
gave up for a time. Some years later, new ICs al-
lowed further investigation, and we built several
prototypes. We quickly noted, however, that digital
had some limits when pushed hard.
We used a sample frequency of 500 kHz at the
time, corresponding to a theoretical bandwidth
close to 250 kHz, far higher than all competitors,
even in the analog domain. But – alas – even with
such a high sample frequency, the actual measured
bandwidth was strongly dependant on the loud-
speaker impedance.
Another problem, jitter, already well known in labs
at the time, was difficult to cure, to say the least.
The signal to noise ratio was just above our mini-
mum criterion.
Since pure sound was the only goal, then noise, if at
acceptable level, could have been tolerated by us.
On the other hand, interdependence between load
impedance and frequency response was not our cup
of tea. Not by a long chalk.