User Manual

darTZeel NHB-108 model one Audiophile's technical manual Page 13 of 28
circuitry to make the best of their possi-
bilities, and that means a longer and
more complex signal path, and hence a
reduced resolution.
MOSFETs are also slower, in absolute
terms, than bipolars, and are much
harder to drive in pulse mode.
Reproducing very fast transients requires
a lot of instantaneous current drive, not
easy for the power supply to properly
feed, so temporal integrity could suffer.
5.2.3. Bipolars
These have been in existence for more
than fifty years. The industry knows
them very well. Today's bipolars are bet-
ter than ever. Ultra linear and extremely
fast, they are perfectly suited for very
high-end audio applications.
Their excellent linearity makes it possible
to minimize the number of peripheral
components, thus obtaining a straight-
forward signal path, with many less su-
perfluous correction circuits.
In the darTZeel NHB-108 model one, the
audio signal travels through only 6
transistors, from input to output,
maintaining low T HD and IMD levels, an d
without using any global NFB, the output
stage even operating in a totally open
loop! The slowest transistors used have a
bandwidth of more than 30 MHz, much
higher than for a MOSFET. This extreme
intrinsic speed allows a total phase re-
spect across the whole audio range,
without any static or dynamic deforma-
tion. In brief, no Temporal Distortion.
In terms of music, these breakthrough
advantages bring you closer to the musi-
cians. Now you can share the emotion of
the violinist, the fire of the conductor or
the sweetness of the flutist.
Words are however not enough to de-
scribe what a single bipolar transistor
pair is capable of. The best is still to in-
vite your friends home, making them
understand, share and believe your ears.
5.3. The circuit of darTZeel
5.3.1. Criteria of choice
Simplicity.
The audio circuit of the darTZeel NHB-108
model one uses only 14 transistors in all,
including current sources.
Only three different bipolar transistor
devices are used, all of the same brand.
Purity.
The version A of the darTZeel NHB-108
model one takes unprecedented care of
the precious musical signal:
No connector, switch, relay or fuse what-
soever is located in the signal path. Even
better, we did not use any of these de-
vices except in the AC mains input.
No current limitation, allowing unbeat-
able dynamic range when in cooperation
with the single output pair devices.
No output DC voltage drift compensa-
tion, offering a truly breathtaking sound,
from whispers to loud shouts.
Only a single, small, local symmetrical
DC NBF, leading to extremely wide
bandwidth, included in the very low fre-
quencies, without addition of any multi
polar phase shift.
The use of a very compact printed circuit
board (PCB) reduces track lengths to the
strict minimum.
Reliability.
The darTZeel NHB-108 model one does not
use any "exotic" or "esoteric" compo-
nent. Each element was chosen for its
intrinsic sound qualities, its long-term
availability, and for its long life. No com-
promise was conceded as to the build
quality of any part or component. Some
of them were tested for 15 years in our
lab before being selected.
5.3.2. darTZeel schematics
For the most curious readers, we give
hereunder the functional diagram of the
darTZeel NHB-108 model one.
Connoisseurs will appreciate how simple
it is, so different f rom the common belief
of "bigger is better".