darTZeel NHB-108 One User manual
NHB-108 model one Version B
User Manual
darTZeel NHB-108 model one User Manual, version B 1.0 Page 2 of 35
darTZeel NHB-108 model one User Manual, version B 1.0 Page 3 of 35
Table of contents
First Section, User Manual
1. Introduction .......................................................................................................5
2. Brief description................................................................................................5
3. The NHB-108 in details......................................................................................6
3.1. Front Panel..................................................................................................................................... 6
3.2. Rear Panel ...................................................................................................................................... 6
3.3. Top View ........................................................................................................................................ 7
4. Who am I? ..........................................................................................................8
5. Connecting and setup.......................................................................................8
5.1. Important prior notice .................................................................................................................... 8
5.2. Location ......................................................................................................................................... 8
5.3. Speaker impedance ........................................................................................................................ 8
5.4. Choice of the input......................................................................................................................... 9
5.5. Powering ON ................................................................................................................................. 9
6. Using the darTZeel ............................................................................................9
6.1 Power cycle.................................................................................................................................... 9
6.2. darTZeel's Eyes.............................................................................................................................. 9
6.3. User parameters ........................................................................................................................... 10
6.4. Jumper settings............................................................................................................................. 11
7. Maintenance.....................................................................................................11
7.1. Fuse(s) replacement ..................................................................................................................... 11
7.2. DC voltage drift ........................................................................................................................... 13
7.3. Cleaning and upkeep.................................................................................................................... 13
8. Some advice and tips......................................................................................13
8.1. What not to do.............................................................................................................................. 13
8.2. Troubleshooting ........................................................................................................................... 14
8.2.1. Eyes Closed.................................................................................................................................. 14
8.2.2. Blinking Eyes............................................................................................................................... 14
8.2.3. Amplifier ON, no sound............................................................................................................... 14
8.2.4. Warped sound .............................................................................................................................. 14
8.2.4. Sensitive fuses.............................................................................................................................. 14
8.2.5. Sound too quiet ............................................................................................................................ 15
8.2.7. Melting Fuse(s) at power ON....................................................................................................... 15
8.2.8. RAS (Regular And Satisfactory).................................................................................................. 15
9. Conditions of warranty ...................................................................................15
9.1. Breakdowns or faulty parts .......................................................................................................... 15
9.2. Conditions of use ......................................................................................................................... 16
10. Assistance .......................................................................................................16
11. Technical data..................................................................................................17
darTZeel NHB-108 model one User Manual, version B 1.0 Page 4 of 35
Technical Section
T1. Introduction .....................................................................................................18
T2. Genesis of NHB-108 ........................................................................................18
T3. Criteria..............................................................................................................19
T4. Structural aspects ...........................................................................................19
T4.1. The case modules......................................................................................................................... 19
T4.2. Divide to conquer......................................................................................................................... 20
T4.3. Eliminating vibrations.................................................................................................................. 20
T4.4. Everything is transparent..................................................................................... 20
T4.5. TIO, Totally Identified Object ..................................................................................................... 21
T5. The audio electronics......................................................................................21
T5.1. What is distortion? ....................................................................................................................... 21
T5.1.1. Keeping in harmony..................................................................................................................... 21
T5.1.2. Inter Modulation Distortion ......................................................................................................... 22
T5.1.3. Temporal Distortion..................................................................................................................... 22
T5.2. What application field? ................................................................................................................ 23
T5.2.1. IGBTs........................................................................................................................................... 23
T5.2.2. FETs............................................................................................................................................. 24
T5.2.3. Bipolars........................................................................................................................................ 24
T5.3. The circuit of darTZeel ................................................................................................................ 24
T5.3.1. Criteria of choice.......................................................................................................................... 24
T5.3.2. darTZeel schematics .................................................................................................................... 25
T5.3.3. Component layout........................................................................................................................ 25
T5.4. Symmetrically balanced? ............................................................................................................. 26
T5.4.1. From the microphone… ............................................................................................................... 26
T5.4.2. To the loudspeakers… ................................................................................................................. 26
T5.4.3. And into the air… ........................................................................................................................ 26
T5.4.4. Via the darTZeel .......................................................................................................................... 27
T5.5. darT to Zeel 50Ω.......................................................................................................................... 28
T6. Onboard safety ................................................................................................29
T6.1. Crowbar circuit ............................................................................................................................ 29
T6.1.1. Crowbar activation....................................................................................................................... 29
T6.1.2. Crowbar cycle .............................................................................................................................. 29
T6.2. Supervision system ...................................................................................................................... 30
T6.2.1. Current sensing ............................................................................................................................ 30
T6.2.2. For its eyes only ........................................................................................................................... 30
T7. Power supplies ................................................................................................30
T7.1. From mains to loudspeakers......................................................................................................... 30
T7.2. Voltage or current?....................................................................................................................... 31
T7.3. Received idea ............................................................................................................................... 32
T8. The sound of darTZeel ....................................................................................32
T9. Reliability .........................................................................................................32
T9.1. Quantified longevity .................................................................................................................... 32
T9.2. Long term availability .................................................................................................................. 33
T9.2.1. Spare parts.................................................................................................................................... 33
T10. The next darTZeel............................................................................................34
T11. Keeping an open door.....................................................................................34
T12. Special adjustments........................................................................................35
T12.1. Output DC voltage drift ............................................................................................................... 35
T12.2. Monitoring circuit ........................................................................................................................ 35
darTZeel NHB-108 model one User Manual, version B 1.0 Page 5 of 35
darTZeel NHB-108 model one
Version B
User Manual
1. Introduction
Congratulations for purchasing a darTZeel NHB-
108 model one.
Our machines are designed and hand built for very
long lasting use and musical pleasure.
The darTZeel NHB-108 model one is a highly
unusual power amplifier, and requires special care.
We strongly recommend you read this manual in its
entirety, in order not to miss any reason for enjoy-
ing your machine at its very best!
When opening the crate, you certainly noticed the
three separate information sheets. They are of pri-
mary importance and you must read them without
fail before continuing.
These documents are:
-The warning notice, printed in red.
-The “3-step-to-go” commissioning leaflet,
printed in blue.
-The packing/unpacking notice, printed in green
While humor is truly part of our philosophy, please
keep in mind that all our warnings must be taken
into account, for the sake of your own safety.
If you carefully follow all the instructions herein,
you will be rewarded by very long, joyful listening
sessions, for years and years to come.
Please carefully keep all documentation and pack-
ing material in a safe place, especially the crate, in
case you have to move house one day.
2. Brief description
The darTZeel NHB-108 model one is the pinna-
cle of more than 16 years of research & develop-
ment, with the first goal in mind being sound repro-
duction, nothing but sound reproduction.
Every basic element of the darTZeel NHB-108
model one was chosen for its high intrinsic sound
qualities. No compromise about the cost price was
even contemplated.
The result is what you can see, touch and hear…
right now.
One of the secrets of the darTZeel NHB-108 model
one can be found in two words:
Passion and Love… The passion for sound, of
course, and love of music, needless to say…
As for the rest, we just put in few electronics, a wee
bit of mechanics, and an awful lot of working
hours.
If you want to know more about the technical side
of the darTZeel NHB-108 model one, we invite
you to read the dedicated section at the end of this
manual, in which you should find much of interest.
darTZeel NHB-108 model one User Manual, version B 1.0 Page 6 of 35
3. The NHB-108 in details
3.1. FRONT PANEL
1. Identification Plate
2. The Eyes
3. The Power Nose
3.2. REAR PANEL
4. 50ΩBNC Zeel Inputs
5. RCA Inputs
6. Speakers Terminals
7. XLR Inputs
8. IEC Power Socket
9. Input Impedance Selector
darTZeel NHB-108 model one User Manual, version B 1.0 Page 7 of 35
3.3. TOP VIEW
10. DC Offset Trimmer
11. Jumpers
12. Speaker Impedance Switch
13. Fuse Holder
14. Operating Voltage Selector
darTZeel NHB-108 model one User Manual, version B 1.0 Page 8 of 35
4. Who am I?
Your darTZeel NHB-108 model one bears, on its
front panel, its Identification Plate (1). On this 24k
gold plated brass plate are engraved your name, and
the serial number. Do not unscrew the plate since it
is the identity card of your machine!
The serial number can be read as follows:
TZ-XY1081.dcbZ
X = Century of making
Y = Batch number
dcb = Identity in the batch number
Z = Version (Aor B)
Example:
The sample bearing the serial number
TZ-UC1081.001B
Is the first machine of the third batch, made in the
21st century, and of version B. This numbering is
thus valid until the end of the 26th century.
From the second batch, we chose to manufacture
only the darTZeel NHB-108s in version B. Actu-
ally this version even offers some slight improve-
ment over the version A. If you want to know how
the version A differs, please visit our website at
www.darTZeel.com, where you can download the
previous manuals.
It is vital to bear in mind all the following notes
and remarks concerning the use of your
darTZeel NHB-108 model one.
Thank you.
5. Connecting and setup
5.1. Important prior notice
In order to protect the loudspeakers, your darTZeel
NHB-108 model one features a special monitor-
ing circuit. If any abnormal situation is detected,
this circuit will intentionally melt the power fuse(s).
This behaviour is not be interpreted as a failure.
The NHB-108 has been designed to behave this
way, in line with our philosophy of not spoiling the
sound by adding any protection circuit in the signal
path. If you want to know more about this specific
circuit, also called Crowbar, please refer to the
technical section, in chapter T6.
5.2. Location
Before making the first connection, you should
think carefully about the location where you are
going to put your gear. If you planned to fit your
darTZeel NHB-108 model one into furniture,
please bear in mind that you must allow at least one
inch of free space all around the unit, for proper
cooling.
If you do not respect this, the darTZeel NHB-108
model one may stop playing if it becomes too hot.
The heat sinks shutdown point is at around 70°C,
and the power supply starts up again when the tem-
perature has dropped to 55 °C.
Please also note that permanent excessive tempera-
ture will reduce the life span of your machine. Read
the technical section at the end of this manual if you
want to learn more about this topic.
Anyway, if possible, always leave enough space
around your darTZeel NHB-108 model one, allow-
ing you to gain easy access to it when making con-
nections.
5.3. Speaker impedance
The darTZeel NHB-108 model one can drive virtu-
ally any loudspeaker, provided its nominal imped-
ance is between 1.5 and 8 ohms. Above 8 ohms,
maximum available power output will be slightly
reduced, but without any sound quality loss.
Nominal standardized impedance can vary by ±
20%, and can thus reach the following critical
minimum values:
6.4Ωin the case of 8Ωspeakers
3.2Ωin the case of 4Ωspeakers
1.6Ωin the case of 2Ωspeakers
If your loudspeakers are between 3Ωand 8Ω,
which is nearly always the case, you can directly
hook them to the Speaker Terminals (6).
Black terminal (upper) = Ground.
Red terminal (lower) = Live signal.
If your loudspeakers impedance is less than this, or
if you want to parallel 2 pairs of 4Ωspeakers, you
must go to chapter 6.3. "User parameters" before
you consider going further.
If you do not respect the above, you may encounter
some blown fuses when playing music at loud lev-
els.
CAUTION: You must connect your loudspeakers to
the Speaker Terminals (6) before powering ON
the darTZeel NHB-108 model one!
darTZeel NHB-108 model one User Manual, version B 1.0 Page 9 of 35
5.4. Choice of the input
Only one input can be used at a time. All inputs are
paralleled, so you cannot select them separately.
If you do not own a darTZeel NHB-18NS pream-
plifier yet, we suggest you use either RCA (5) or
XLR (7) inputs, with the Input Impedance Selector (9)
switched on "RCA Hi Z" (mid position, physically
speaking), or "XLR Bal". (lower position), respectively.
The XLR inputs are truly balanced on the version
B, through floating transformers:
Pin 1 = Ground
Pin 2 = Hot leg
Pin 3 = Cold leg.
If you have already paid us the honour of purchasing
a darTZeel NHB-18NS preamplifier, we strongly
recommend using the 50ΩBNC Zeel Inputs (4),
with the Input Impedance Selector (9) switched on
"Zeel 50Ω"(upper position, physically speaking).
The Zeel input is definitely the one that will bring
you the purest sound ever achievable. Read the
technical section at the end of this manual if you
want to know more about this topic.
5.5. Powering ON
Please do not forget that the darTZeel NHB-108
must have loudspeakers connected before you
power ON.
Your machine has already been factory set in order
to adapt to your mains supply, as confirmed by the
3-Step-To-Go commissioning leaflet. In case of
doubt, please contact us.
Connect the supplied power cable into the IEC
socket (8) and plug the other end into the mains
wall outlet.
You can then power ON the darTZeel NHB-108
model one by pushing the Power Nose (3) button.
If a source is already connected, you should imme-
diately hear the music.
When powering the amplifier OFF by pressing the
Power Nose (3) button, you can still hear the music
for 10 to 30 seconds before the level goes down
dramatically and stabilizes. This behavior is per-
fectly normal, and it is not a failure at all. If you
need more details about this, please refer to the
technical section.
6. Using the darTZeel
6.1 Power cycle
The darTZeel NHB-108 model one has been de-
signed to deliver more than 90% of its magical
sound at cold start.
After 5 minutes, you are very close to the best the
machine can offer. The increasing quality you may
hear as time goes by will be mostly the reflection of
your growing musical pleasure…
No need then to leave your machine powered ON
all the time, except of course if you like paying
bigger electricity bills…
If your present preamplifier produces some clicks
and/or bumps when powering on/off, we suggest
you observe the following sequence:
Powering ON: first the Preamp, then the darTZeel
NHB-108 model one.
Powering OFF: first the darTZeel NHB-108 model
one, then the preamplifier.
If this procedure is not respected, you may encoun-
ter some blown fuses due to Crowbar triggering.
If you still hear some thumping at powering OFF,
you will have to wait around 10 seconds before
switching the preamplifier OFF. This noise, how-
ever, will be inconsequential and harmless.
6.2. darTZeel's Eyes
The 2 giant orange LEDs, called Eyes (2) for obvi-
ous reasons, are fully featured function indicators.
Five different illumination states, for each individ-
ual channel, are described hereunder:
1) Eyes shut (light off). This is of course the
status when the darTZeel NHB-108 model one
is either powered off or not plugged in. If one
Eye only is shut, it means that there is a power
fault or a blown fuse in the channel in question.
In the latter case, please go to chapter
7.1."Fuse(s) replacement".
2) Idle state. 45 to 55 seconds after powering ON,
and with no input signal, the Eyes go into this
barely illuminated state.
3) Signal presence. When an input signal, corre-
sponding to over 10 mW at 8Ωis detected, the
Eyes illuminate fully. You are in "musical
cruise mode". When the input signal disappears
for more than 45 to 55 seconds, the Eyes go
back to idle state. While listening at very low
levels, Eyes could toggle between states 2 and
3; this is normal behaviour.
4) Clipping. When approaching maximum output
power, the corresponding Eye flashes brightly
for about half a second, and then goes back to
the "musical cruise mode".
5) Blinking. Please refer to chapter 8.2.2. "Blinking
Eyes".
darTZeel NHB-108 model one User Manual, version B 1.0 Page 10 of 35
6.3. User parameters
The darTZeel NHB-108 model one must be cor-
rectly set, accordingly to the loudspeakers' nominal
impedance. Your machine is already factory set for
speakers having nominal impedance from 3Ωto
8Ω, as is usually the case.
If your loudspeakers' nominal impedance is be-
tween 1.5Ωand 2.5Ω, or if you connect two paral-
leled 4Ωspeakers, you must adapt your NHB-108
to that load. If you want to know more about this
special mode, please refer to the technical section.
The procedure for the adaptation of the output im-
pedance is described hereunder:
Power the machine OFF.
!!! UNPLUG THE AC CORD FROM THE WALL,
and please wait for 5 minutes !!!
Disconnect all links you may have installed by
removing all cables from inputs (4), (5) or (7), and
from Speakers Terminals (6). Unscrew the single
central cover screw, and remove the smoked glass
using the supplied suction grips, as shown in fig.1
Gently wet them in order to get firm vacuum.
Please be very careful when removing the cover,
since it is real tempered glass, not Plexiglastm.
Fig.1 – Suction grips
The speaker's impedance switch is located at the
upper left of the transformer (upper right for the
right channel),
Fig.2 – Speaker's impedance switch
as shown in Fig.2
When the switch is pointing towards the front plate,
you are in Lo mode, suitable for 1.5Ωto 2.5Ω
speakers. In this mode, you can also parallel 2 pairs
of 4Ωspeakers.
By flicking the switch towards the rear panel direc-
tion, you set the Hi, default mode, for speakers of
3Ωor more. This is the most often used configura-
tion.
The darTZeel NHB-108 model one being a true
dual mono design, you can also use it to biamplify
hybrid loudspeakers (having different technology
and impedance drivers, i.e. an 8Ωwoofer and a 2Ω
tweeter) by switching one channel to Hi and the
other one to Lo, respectively.
Please bear in mind that in this case, you will need
two NHB-108 model one, one for each loudspeaker.
Once you have chosen your configuration, you can
carefully put the glass cover back, and screw it on
again as follows:
Freely hand screw until you feel the thread-end
resistance. Then use the supplied screwdriver and
turn an extra 1/8 turn approximately. The screw
must be sufficiently tightened to prevent the possi-
bility of the glass rotating around the screw axis.
Then reconnect all the wires and cables, paying
special attention to the loudspeaker cables. They
must be hooked to the Speaker Terminals (6) be-
fore powering the amplifier ON.
Now just sit back and relax, and immerse yourself
in pure musical pleasure!
darTZeel NHB-108 model one User Manual, version B 1.0 Page 11 of 35
6.4. Jumper settings
Before making any change in the jumper set-
tings, power off the amplifier, REMOVE the AC
cord, and wait for 5 minutes before removing
the glass cover.
On the inside rear panel (see chapter 3.3. "Top
View", no. 11), where the input circuit boards are
located, you will see 3 jumpers per channel:
Fig.3 – Jumpers
2 jumpers are labeled Ground LIFT and XLR pin
1 FLOAT. They can be changed over in the event
of a hum problem when an XLR input is used, de-
pending on the circuit design of the associated pre-
amplifier. In a lesser extend, these jumpers may
also affect RCA inputs. Their factory default posi-
tion is the most commonly used in order to obtain
best results.
The third jumper, labeled DC Offset COMP is the
most important one since it does affect the sound of
the amplifier.
This jumper is set to ON at the factory, preventing
any problem of DC offset due to AC voltage varia-
tion or too great an ambient temperature change.
If your AC mains voltage is stable, and your listen-
ing room is at standard temperature, we recommend
removing the compensation by putting the jumper
to off.
In doing so, you will fully benefit from the very
philosophy of the NHB-108 model one, which is
to refuse any compensation or global negative feed-
back which could impair the sound. Most users
have reported to us that this setting has the best
sound. Depending on your own audio system, this
result may vary, however, so experiment for your-
self.
7. Maintenance
7.1. Fuse(s) replacement
The following procedure concerns the left channel.
For the right channel, the procedure is the same but
that the fuse is in a mirror image configuration.
If one – or both – fuse(s) has/have blown, first try
to determine the cause.
The Crowbar circuit installed in the darTZeel
NHB-108 model one causes fuses to melt when an
abnormal situation is detected. This is normal be-
haviour.
For more information about this topic, please refer
to the technical section, chapter T6.
If a newly replaced fuse immediately melts when
you power on your NHB-108 model one, even
though your speakers are correctly connected to the
Speakers Terminals (6), unplug the AC mains and
contact us directly:
Hereunder is the procedure:
In order to change a fuse, power off your NHB-108
model one by pressing the Power Nose (3) button.
!!! UNPLUG THE AC CORD FROM MAINS, and
wait for 5 minutes !!!
Remove all the input and output connections.
Remove the single central screw located on the top
smoked glass cover. Take the two supplied suction
grips, slightly wet them in order to provide strong
vacuum, and firmly apply them on the cover glass,
as indicated in Fig.1
Please be careful when removing the top cover,
since it is of real glass, not PlexiglasTM.
Put the amplifier on a carpeted surface, and gently
(but firmly, as it is a heavy, 30kg electronic crea-
ture) pivot it vertically onto its front handles. Use a
protective cloth as indicated in fig.4 in order to
avoid scratching the inside aluminum parts
Fig.4 – Soft cloth
darTZeel NHB-108 model one User Manual, version B 1.0 Page 12 of 35
while using the supplied long nosed pliers (fig. 5),
Fig.5 – Supplied tools
gently turn the fuse holder, as shown in fig.6, 180°
counter clockwise,
Fig.6
and pull it off, as shown in fig. 7
Fig. 7
Then turn again 180° counter clockwise and let the
fuse fall onto the inner side of the front panel, as
shown in fig. 8
Fig. 8
Pick up the fuse with pliers and check that the glass
envelope is dark or black, indicating a blown fuse.
Remove it and simply install a new fuse in the holder.
Once the new fuse is inserted, push back the fuse
holder and turn it 180° clockwise until you feel a
slight click.
You’re back in business!
Fuse ratings are:
110-125vAC: 6.3 amps T type.
220-240vAC: 3.15 amps T type.
T type means “Temporized”. Do NOT use the so-
called "slo-blo" type, especially the kind with coil-
wounded filament. The filament in the fuse glass
envelope must be seen as a thin STRAIGHT wire.
Never use improper fuse ratings. Very great fire
risk!
Now you can restore the amplifier back to its hori-
zontal position and put the glass cover on, as de-
scribed in chapter 6.3. "User parameters".
Connect again all your cables, without omitting the
loudspeakers, and power ON your NHB-108 model
one.
Now you are ready to enjoy some more good mu-
sic, compensating all that tiring physical effort you
have just put in…
Although the above procedure could seem rather
long and complicated, you will see that it is a sim-
pler task to perform than to explain.
Anyhow, if you carefully respect all advice and
warnings, you should never encounter such prob-
lems of blown fuse(s).
darTZeel NHB-108 model one User Manual, version B 1.0 Page 13 of 35
7.2. DC voltage drift
Every single NHB-108 model one is lovingly
checked, tested and listened to before leaving our
workshop.
Output DC voltage drift normally does not need any
further adjustment, provided you use your amplifier
in a room temperature ranging from 59°F to 95°F
(15°C to 35°C).
Furthermore, the version Bnow features a built-in
DC compensation circuit. In order to fully benefit
from total lack of any overall negative feedback,
you can disable this circuit.
Please refer to chapter 6.4. "Jumper settings".
If one – or both – Eye begins to blink, even though
your loudspeakers are properly connected, a read-
justment is recommended.
This tuning procedure is described at the very end
of the technical section.
7.3. Cleaning and upkeep
The darTZeel NHB-108 model one has not only
been designed for providing you intense moments
of musical pleasure; it is also designed to withstand
the rigors of time, especially if you take proper
care.
This is undoubtedly one of the few, if not the only,
amplifier to be virtually dust-proof. The whole case
performs heat exchange, while the two lateral heat
sinks regulate and maintain the correct temperature.
This design avoids the need for any vent slot.
The only visible traces you will see in the long-term
will be located on the inner side of the smoked
glass, and will be due to some natural evaporation
of some plastic packaged components.
We suggest that you remove the cover glass once a
year, and use a soft cloth to gently wipe the glass
with an appropriate cleaning solution. Your NHB-108
model one will then keep its "like-new" aspect for
decades, and as time goes by, the less you will need
to perform this operation.
As for the external parts of your equipment, a soft
cloth or even a dust brush will be completely ade-
quate.
In case of fingerprints, a gentle rub with a cloth
soaked in isopropyl alcohol will be more appropri-
ate.
Just bear in mind, however, that the simplest things
are, more often than not, the most efficient.
We personally found that a spot of soap on a wet
soft cloth is the best method most of the time. Try
for yourself!
As you have certainly guessed, we confirm that it is
strongly recommended to never use acid to clean
your gear. Acid is very corrosive and could react
with the anodized coating. Furthermore, acid is very
corrosive for the skin, too…
If you follow these few elementary rules, you will
be assured of having a very nice looking machine
for decades to come.
8. Some advice and tips
8.1. What not to do
Our advice and recommendations have been volun-
tary placed close to the end of this owner's manual.
This does not mean that they are of only minor
importance - quite the contrary.
We just thought that the following points are not
directly involved in the everyday use of your ampli-
fier.
However, the completely new concept of the NHB-108
model one calls for certain precautions.
These few but important warnings are the follow-
ing:
1) Never, ever attempt to short circuit the
Speaker Terminals (6).
Repetitive shorts could lead to permanent dam-
age to the corresponding output stage.
When bi or tri cabling, be especially careful
when connecting the cables. If you inadver-
tently cross the polarity of one run regarding
the other(s), you will make a perfect short cir-
cuit. This can easily destroy the corresponding
output stage!
The warranty will be partially or totally
void in the event of non-compliance with the
above !
2) Do not power ON the darTZeel NHB-108
model one when no loudspeaker is hooked to
the Speaker Terminals (6).
In such a case the internal fuses could be blown
by the Crowbar circuit, especially if the DC
compensation offset has been disabled.
3) Before connecting or disconnecting the audio
cables to/from the RCA (5) or XLR (7) inputs,
always flip, when possible, the Input Impedance
Selector (9) onto "Zeel 50Ω" position. You will
thus avoid any of the resulting parasitic clicks
and bumps.
darTZeel NHB-108 model one User Manual, version B 1.0 Page 14 of 35
8.2. Troubleshooting
While setting up your NHB-108 model one, it is
possible that you may not obtain the desired results.
Hereunder we list the most frequent problems you
are likely to encounter. If the problem cannot be
solved, please do not hesitate to contact us directly
at:
8.2.1. Eyes Closed
The eyes are closed – I beg your pardon, extin-
guished - while the Power Nose (3) button is ON.
Please check that the AC power cord is correctly
connected at both ends, and that the mains AC volt-
age is present. Just test with a table lamp. If AC is
present, it means that both primary fuses have
melted. Please go to point 7.1. "Fuse(s) replace-
ment".
One Eye only is not lit. This means that you have to
change the corresponding channel fuse.
8.2.2. Blinking Eyes
Blinking Eyes indicate that the output DC offset
value has exceeded the permitted limit. If such an
event occurs, please read the following:
A) Eyes blink at cold power ON. If your listening
room is at a temperature below 65°F (18°C),
this could be considered as normal, provided
that this behaviour disappears in the following 3
to 5 minutes.
In a room at a temperature above 65°F (18°C),
blinking eyes indicate that your NHB-108
model one could do with some tuning. How-
ever, if this behaviour ceases after 3 to 5 minutes,
and especially if you can put up with it, no ad-
justment is mandatory.
B) Eyes blink after several hours, when the ma-
chine is hot, or even very hot. If your room tem-
perature is above 90°F (32°C), this can be con-
sidered as normal behaviour, and normally the
eyes should stop blinking as soon as the ambient
temperature returns to "human being" levels.
Please also check that your darTZeel NHB-108
model one is properly ventilated, as indicated
in chapter 5.2. "Location" and that you are not
using it at quasi-permanent power clipping lev-
els with 3Ωloads.
If the ambient temperature is under 90°F (32°C)
but the Eyes blink, your machine needs some
tuning.
To cut a long explanation short, NHB-108's eyes
should not blink in ambient temperature ranges
from 65°F to 90°F (18°C to 32°C). If they do, the
amplifier needs some adjustment.
In all cases it is important to know the working
environment in which you will use your darTZeel
NHB-108 model one.
If you live at the South Pole or on the Equator, a
slightly different setting could be necessary, espe-
cially when the DC compensation offset is off.
If you need to know more about this topic, can you
guess what? Yes, read the technical section…
8.2.3. Amplifier ON, no sound
Please check first the Eyes’ illumination state, as
described in point 6.2. “darTZeel’s Eyes”.
A) Idle state. No signal is present at the input of
your NHB-108 model one. Be sure that the
source (SACD, CD, Tuner or whatever) is cor-
rectly selected and connected to the preamplifier
feeding your machine.
Please also verify that the Input Impedance
Selector (9) of each channel is not at the upper
position ("Zeel 50Ω") when you are not using a
darTZeel NHB-18NS preamplifier.
B) Signal presence. The input source is correctly
connected and routed, but the loudspeakers are
not hooked to the Speakers Terminals (6)! We
remind you that this is totally forbidden. Okay,
no trouble for this time. You are lucky enough
that the Crowbar circuit did not melt one fuse or
two…
C) No sound when using XLR inputs. Please check
that the Input Impedance Selector (9) of each
channel is at the lower position ("XLR Bal.").
8.2.4. Warped sound
You are using the RCA input (4), but the Input
Impedance Selector (9) of one or both channels is
in the upper position ("Zeel 50Ω").
Your present preamplifier not being a darTZeel
(this will change one day), its outputs cannot drive
50Ωloads.
So please switch the Input Impedance Selector (9)
to "RCA Hi Z" mode (mid position).
8.2.4. Sensitive fuses
Fuses have the bad tendency to melt much too of-
ten. Why, then, not replace them by a higher value
rating?
Please never, ever do such a thing!
Improper fuse ratings could produce a fire! Please
carefully read the technical section at the end of this
darTZeel NHB-108 model one User Manual, version B 1.0 Page 15 of 35
manual in order to better know how the Crowbar
circuit works.
Fuses can blow if the nominal impedance of your
speakers is less than 3 Ωand your NHB-108 model
one has not been set up to drive such a load.
Please refer to chapters 6.3. "User parameters" and
5.1 "Important prior notice". Then again check
your fuses if you are in doubt, by taking a look at
point 7.1. "Fuse(s) replacement". Be sure that you
are using fuses of correct rating and type.
8.2.5. Sound too quiet
A) darTZeel's Eyes are quasi-permanently in the
clipping state, as described in chapter 6.2
"darTZeel's Eyes", point 4.
Your speakers are particularly inefficient! Please
choose loudspeakers of more than 84 dB/w/m …
Alternatively, maybe your room is very big, and
that even with your old 1200 watts per channel
powerhouse amp, there was only just enough
volume?
In such a situation, please do not hesitate to
consult us. We will try to help you find a solu-
tion.
B) The volume setting of your preamplifier is close
to maximum.
This can occur if you use either a passive or a
low gain preamplifier.
8.2.7. Melting Fuse(s) at power ON
The NHB-108 model one features a Crowbar inhib-
iting circuit working at power ON. During the first
20 milliseconds, no Crowbar operation will occur,
avoiding blown fuse(s) if bumps greater than 2
volts are detected.
However, if you power your machine ON again,
immediately after having powered it OFF, it is pos-
sible that it will eventually trigger the Crowbar
circuit, and lead to melted fuse(s). In such a case,
you will have to change the blown fuse(s) as de-
scribed in chapter 7.1. "Fuse(s) replacement".
In order to avoid this situation, we recommend that
you wait around 3 seconds before powering your
NHB-108 model one ON again, when switched
OFF.
8.2.8. RAS (Regular And Satisfactory)
In such a situation, we sadly deplore having no real
cure.
We suggest you display your most charming smile,
relax in your armchair, and enjoy listening to your
favorite tunes.
Symptoms should disappear by themselves within a
few days. If everything continues OK, please invite
some friends!
9. Conditions of warranty
9.1. Breakdowns or faulty parts
The darTZeel NHB-108 model one is guaranteed
for one full year, parts and labor, against any break-
downs or component failure, as is the tradition in
Switzerland for such equipment.
As we see it, any warranty longer than 1 year is the
obvious sign of inferior quality and design, indicat-
ing that a failure could arise anytime.
Any component either will fail within days or will
last "forever" (several decades in practice).
This is the reason why all our machines are thor-
oughly broken in before being lovingly packed and
sent to you.
We are still fully aware that no component is al-
ways flawless, and that a problem could arise any-
time after the warranty period.
In such a case, we will carefully examine every
situation, with the aim of reducing the likely repair
costs to minimum levels. You can always trust us
for customer care, as you already trusted us when
purchasing your NHB-108 model one.
darTZeel NHB-108 model one User Manual, version B 1.0 Page 16 of 35
9.2. Conditions of use
darTZeel Audio SA company disclaims any respon-
sibility in case of damage or injury directly or indi-
rectly due to any misuse, incorrect manipulation, or
simply the non-observance of red warnings, and/or
advice formulated in this entire manual, including
the technical section.
Any non-authorized intervention on or in the darTZeel
NHB-108 model one, or any failure due to one of
the situations described above, or any similar situa-
tion, will render the warranty void.
10. Assistance
If you need any commercial or technical informa-
tion about the darTZeel NHB-108 model one, or
if you have any difficulties or enquiries, please feel
completely free to contact us by email at
You can of course write us at the following address:
darTZeel Audio SA
2, chemin Louis-Hubert
CH-1213 Petit-Lancy
Geneva/Switzerland
We also invite you to visit our website at
www.dartzeel.com
We wish you countless hours of musical delight with your NHB-108 model one and do hope that you will have
no further need to read this manual except for the pleasure…
Musically yours,
Hervé Delétraz
darTZeel NHB-108 model one User Manual, version B 1.0 Page 17 of 35
:
11. Technical data
darTZeel NHB-108 model one, version B
Nominal output power : 100 watts RMS @ 8 (Hi) and 2 (Lo) ohms.
160 watts RMS @ 4 (Hi) ohms.
Gain : 26 dB @ 8 ohms.
Input impedances : RCA: > 30 kohms, 5 Hz to 100 kHz.
BNC: 50 ±1 ohm, 1 Hz to 1 MHz.
XLR: > 15 kohms bet. Pin 1 and 2.
> 15 kohms bet. Pin 1 and 3.
Output impedance : < 0.33 ohms, from 20 Hz to 20 kHz (measured under 8 ohms).
Frequency response : 1 Hz to 1 MHz, +0, -6 dB (depends on measurement method).
10 Hz to 100 kHz, +0, -0.5 dB (depends on measurement method).
20 Hz to 50 kHz, ±0.5 dB (XLR inputs).
Rise time : < 0.8 µs. (depends on measurement method).
Slew rate : > 88 V/µs, peak-peak.
DC voltage output DC comp Off : < ± 590 mV max.
drift DC comp ON : < ± 50 mV max.
Total Harmonic
Distortion (THD) : < 1 % from 7 Hz to 77 kHz
Temporal Distortion : None, at any level and load, as specified above.
Crosstalk : < -90 dB from 20Hz to 20kHz.
Signal to noise ratio : > 112 dB (A) @ nominal power.
Consumption : 150 watts @ idle, 900 watts @ maximum output power.
Size in mm : 440 x 335 x 170 (WxDxH). Total deep with handles: 415 mm.
Net weight : 30 kg.
darTZeel NHB-108 model one amplifiers are made to last forever by
darTZeel Audio SA in Geneva, Switzerland.
darTZeel Audio SA www.dartzeel.com
2, chemin Louis-Hubert
Suisse
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 21st 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.
darTZeel NHB-108 model one User Manual, version B 1.0 Page 19 of 35
End of the digital trip.
It is interesting to note that several manufacturers
offer digital amplifiers, with greater or lesser suc-
cess. The theoretical limits remain the same, even if
better managed than in the '80s. Analog fortunately
does not have to cope with such limitations.
After several months of deep thinking, circuit de-
signing, and circle squaring attempts, the project
was revived (in 1990) on brand new bases. The gear
would be fully analog, moderately powerful, and as
close as possible, philosophically speaking, to the
signal treatment used in its digital ancestor.
Two new prototypes were built on the basis of ex-
isting designs; even though heavily modified to suit
our tastes, they produced unexciting results. Then
we asked ourselves what is the point of producing
nice looking gear if the sonics bring nothing new
under the sun?
In 1992, we decided to develop a revolutionary
design from scratch. This ultimate quest (for ulti-
mate sound) lasted over 5 years, with more disap-
pointment than joy. But the fun was always here.
Countless schematics were studied, scrutinized and
hooked together until we obtained, in mid 1995,
what we could call the first theoretical design corre-
sponding to our aims.
From 1995 to 1999, on that first elementary circuit
basis, dozens of different versions were simulated,
some of them being built and listened to.
By 11 November 1999 the definitive circuit was
built and assembled. This was the very first
darTZeel machine, the NHB-108 model zero.
The results, sonically speaking, were outstandingly
better than expected. It seems that this design was
the right one. So much so that most of our test lis-
teners said that this product must be put into pro-
duction, even on a very small scale.
The darTZeel NHB-108 model one was born.
T3. Criteria
Your NHB-108 model one is not an ordinary ma-
chine and this is no doubt one of the reasons why
you purchased it.
The entire concept is based on just three criteria:
-Simplicity
-Purity
-Reliability
These words can often be deceptive. Easy to pro-
nounce, conjuring up elegance and fascination, they
nevertheless constitute very tough technical chal-
lenges, since their respective meanings are not at all
easy to reconcile.
Nothing is eternal. As for the NHB-108 model
one, not enough time has yet elapsed for us to as-
sert such a claim.
What we do assert is that everything has been taken
into account so that you can benefit from your ma-
chine for a long time. A very long time.
You will discover that more often than not, simplic-
ity means long lasting. Sometimes, it also means
purity, whether of sound or of form.
Welcome to darTZeel.
T4. Structural aspects
It would be all too easy to compare the darTZeel
NHB-108 model one and wristwatches, both be-
ing made in Switzerland. There are no springs,
cogwheels, or hands in a NHB-108 model one.
Here, everything is a tad… bigger.
T4.1. The case modules
The case of your machine is exclusively machined
from AW-5754-ALMG3 alloy aluminum, offering
a remarkably even surface and hardness.
Every item is CNC machined from the billet in
order to ensure a very high density and outstanding
rigidity, thus considerably lowering all unwanted
resonances.
The elements are finished in the three hard ano-
dized darTZeel colors, namely Electric Blue, Blaz-
ing Red, and Gleaming Yellow. This unique finish
gives to the NHB-108 model one its inimitable
appearance.
The three main elementary modules are the mother
plate, the transformer platforms and the heat sinks.
They are tightly assembled together with non-
magnetic, stainless steel screws.
Each basic module is first carefully hand assem-
bled, and individually tested. Only then is it dated
and signed before being fitted.
If you dismantle your darTZeel NHB-108 model
one, you will see that modules are not assembled in
a hurry. Some of them are installed with several
weeks elapsing between construction and assem-
bling.
In line with this non-stress approach, we take all the
time necessary to achieve the best job we can. If our
tests show that a component is out of specification
– this can sometimes occur after its assembling –
the entire module is dismantled, checked, and reas-
sembled before being tested a second time.
The NHB-108 model one housing features a 20mm
thick false bottom machined from the billet, and a
darTZeel NHB-108 model one User Manual, version B 1.0 Page 20 of 35
5mm thick bottom plate, in the form of a sandwich.
All cables and wires are routed in this sandwich,
minimizing the influence of electromagnetic fields.
Furthermore, such an arrangement is of extreme
rigidity ensuring exceptionally good mechanical
coupling between the mother plate and heat sinks
modules.
T4.2. Divide to conquer
The inside of the NHB-108 model one is divided
into four distinct volumes. The left and right chan-
nels are insulated from each other, as are their re-
spective power supplies. This unprecedented con-
struction allows extremely low crosstalk behavior
across the whole audio frequency range. You are
either true dual mono, or you are not. The darTZeel
NHB-108 model one definitely is.
The two front compartments are devoted to the
power supplies, and are themselves divided into a
two-storey structure. The Crowbar elements and the
soft start circuitry are located on the lower level,
while the suspended toroidal transformers are fixed
on the 6mm thick, upper decks.
We insist on the fact that in the final assembly
process, all parts are precisely aligned by means of
cotter pins, like in Swiss precision clockwork
movements, before being tightly screwed together.
This additional precaution adds still more rigidity,
and the entire case then behaves as a single block.
As a free bonus, the case is thus virtually dust
proof.
T4.3. Eliminating vibrations
The fastening of the power supply transformers was
carefully thought out as regards noise reduction and
trouble-free life. A specially developed suspension
ensures that even in case of failure, the transformers
will not fall off.
So, in 40 or 50 years, when the rubber absorbers
have become – perhaps – worn out, they will with-
stand their last trip to the factory for their replace-
ment.
The same is true for the silentblocs used for sus-
pending the lighter audio and monitoring circuits.
These various suspensions, tuned on different reso-
nance frequencies, are coupled quite tightly to the
chassis, absorbing especially the medium and high
frequencies, most important in terms of sound re-
production accuracy.
And while on this subject, have you ever heard an
amplifier singing? This can occur when the transis-
tors of the final stages and/or the power transform-
ers are not properly decoupled.
They start to vibrate at the excitation signal fre-
quency – in this case the music – this vibration
interfering with the electrical origin of the signal.
You can hear it if the amp is hooked to a dummy
load, since in normal use, loudspeakers fortunately
mask this disconcerting internal “singing”.
No such mechanical singing on the NHB-108
model one! The electric signal is transmitted stage
to stage, from input to output, free from any me-
chanical disturbance, internal or external.
The NHB-108 model one stands on 3 pads incor-
porating rubber inserts. Oddly enough, very few
manufacturers rely on 3 legs instead of four. We
can recall that the Lunar Explorer Module (LEM)
also had three legs, but that is another story after
all.
Weighing around 30kg, the darTZeel (not the LEM)
needs to have a good stable base. Those three pads
are evenly located around the horizontal center of
gravity of the amplifier, ensuring excellent stability
on virtually any surface.
The absorbing rubber pads dampen the lower fre-
quencies, thus forming the ideal complement to the
suspensions described earlier. In the case where you
would want to use 2, 3, or even 4 stacked darTZeel
NHB-108 model one units, we can make on spe-
cial request pads of different diameter to maintain
the very same vibrational absorption behaviour.
These pads are easy to install and can be purchased
separately.
T4.4. Everything is transparent
The NHB-108 model one cover is made of 8mm
thick tempered, bronze-smoked glass. It harmonizes
magnificently with the colours of the housing, and
gives an inimitable touch.
The glass is held by a single, central 24k gold
plated screw, and rests on a dedicated, cut-out rub-
ber seal, giving to NHB-108 its dust proof quality.
Your machine will therefore remain as new for
years to come.
The reason why we did not choose a metal cover is
not so obvious as it might appear. It is true that to
look through the glass of the darTZeel NHB-108
model one is a pleasure for the eyes. Look at those
24k gold plated, 5mm thick pure copper Moon-
crescent shaped bar busses, and tell us frankly what
you feel…
There are also a couple of technical advantages that
glass has over metal.
Its crystalline, inert structure, combined with the
rubber foam seal, functions as an internal noise
killer.
And contrary to metal, glass is totally transparent to
magnetic fields, thus avoiding the inherent mag-
netic loop that metal would induce over the power
supply transformers. Last but not least, the internal
housing is much less polluted by magnetic ghosts.
Other manuals for NHB-108 One
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