Lehmannaudio Black Cube Linear User manual

Black Cube Linear
Headphone amplifier / Single Source Preamp
User manual

Lehmannaudio Manual Black Cube Linear - page 2 -
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Dear customer,
congratulations for buying the Lehmannaudio Black Cube Linear You will be
rewarded with the best possible sound from your headphones You can use
practically all dynamic headphones on the market Carefully selected components
and a highly sophisticated circuit design guarantee a very high level of audio
reproduction
Please read this manual carefully and keep it nearby the unit for future reference
even if you have experiences with other headphone amplifiers
Precautions
Please read the following before operating your Black Cube Linear.
While installing the Black Cube Linear
- Be careful to use an apropriate cable for the connection between your power outlet and the
Black Cube Linear Make sure that you have the appropriate version for your mains voltage
- Be careful to prevent Black Cube Linear from getting wet; do not allow water to enter the
unit, especially when raining or snowing, or near a body of water Otherwise fire or electrical
shock may result
- Do not place heavy objects on the power cord If the cord is damaged, fire or electrical
shock may result In particular, it is possible that one might accidantally place a heavy object
on a carpet that covers the cord; definitely avoid these situations!
- Do not install the Black Cube Linear in a place where it might be exposed to oil, smoke or
steam (for example, near a cooking table or humidifier) Otherwise, fire or electrical shock
may result
- Do not place the Black Cube Linear on an unstable surface, such as an unstable bench or
slanted surface Otherwise, the device may fall or drop, resulting in an injury
- Do not place the power cord near a heating device Otherwise, the cord sheath may melt,
resulting in fire or electrical shock
- Do not locate the Black Cube Linear in a place subject to excessive heat, such as inside a
car with all the windows closed, or in direct sunlight Otherwise, fire may result
- Do not handle the power plug with wet hands Otherwise you may receive an electrical
shock
- When you remove the power plug, be sure to hold the plug Never pull on the cord
Otherwise, the power cord may become damaged, resulting in fire or electrical shock
- The Black Cube Linear offers superb sonic quality To ensure best possible results, you
should use the best quality connecting cables that you can afford Regular maintenance
involves keeping all connections clean using a quality contact cleaner

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Using the Black Cube Linear
Do not touch the Black Cube Linear under the following circumstances:
- If you hear thunder, remove the power plug from the AC outlet as soon as possible If you
fear a lightning hit and the Black Cube Linear has been connected to an AC outlet, do not
touch the power plug Otherwise you may receive an electrical shock
- Do not attempt to modify this equipment Otherwise, fire or electrical shock may result
Warranty is void on modified devices
- If you think the Black Cube Linear needs to be checked for maintenance or repair, consult
your dealer
- Do not place a container of water or any small metal object on top of the Black Cube
Linear If water is spilled or if the metal object gets inside, fire or electrical shock may
result This applies to vases, pottet plants, glasses, cosmetic bottles, medicine, etc
- Do not damage, process, bend, twist, stretch or heat the power cord If the cord is
damaged, fire or electrical shock may result
- When you are connecting other audio devices to the Black Cube Linear make sure that you
first turn off the power to all devices to be connected Refer to the user´s guide for each
device and use the specific cable for connection
- Set the volume levels of all devices (including that of the Black Cube Linear) to minimum
before connecting the Black Cube Linear to your actual setup and to the AC outlet
Otherwise, an extremely loud noise could damage your loudspeakers or even your hearing
- If you plan not to use the Black Cube Linear for a long period of time (such as when you
are on vacation), remove the power plug from the AC outlet Otherwise, a fire could possibly
result
If any abnormality occurs while using the Black Cube Linear, remove the plug from
the AC outlet. In this case first shut off the power amplifiers or turn down the
volume controls and so on to avoid possibly damaging transients
- If you notice any abnormality - such as smoke, smell, noise, etc - remove the plug from
the AC outlet Confirm that the abnormality is no longer present, then consult your dealer for
repair If you continue using the Black Cube Linear under abnormal conditions, fire or
electrical shock may result
- If a foreign object or water enters inside the equipment, remove the Plug from the AC
outlet and consult your dealer for repair If you continue using the Black Cube Linear under
this condition, fire or electrical shock may result
- If the power cord is damaged (for example if it is cut or if the core wire is exposed), ask
your dealer for a replacement If you continue using the Black Cube Linear under this
conditions, fire or electrical shock may result
- If the Black Cube Linear is dropped, or if the case is damaged, remove the plug from the
AC outlet and consult your dealer If you continue using the Black Cube under abnormal
conditions, fire or electrical shock may result
Maintenance
- Before cleaning the Black Cube Linear remove the power plug from the AC outlet for safety
Otherwise, an electrical shock may result
- Do not open the Black Cube Linear There are hazardous voltages inside that might result
in an injury or an electrical shock

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Why headphones?
When you use headphones you can reach a very high level of sound reproduction at
a fraction of the price you would have to spend for a regular hfi setup with high
quality loudspeakers Detail resolution and dynamics of even the best loudspeakers
can easily be reached with the best headphones In most cases headphones will be
used to enjoy music either to acoustically disclose a noisy environment to just to be
able to listen to louder levels without disturbing other people
What makes headphones different?
There is a number of parallels between (dynamic) headphones and loudspeakers
Technically they are complex loads for the amplifiers driving them and should
therefore be used with stable outputs There are headphones with higher
impedance that need a higher signal voltage and low impedance types which need
more current for optimal sonic results Just connecting a headphone to any given
headphone output without considering the headphone’s electrical characteristics will
most likely yield dissatisfactory results
Impedances of dynamic headphones can vary from 30 Ohms to 600 Ohms
Transferred to loudspeakers this would result in impedances from 4 Ohms to 80
Ohms The same signal amplitude results in a power consumption difference of
factor 20!
Loudspeakers and headphones are manufactured in a dazzling variety Irrespective
of their impedance headphones and loudspeakers can have very different
effectivities which means that the electrical signal is converted more or less
effective to acoustic anergy When comparing loudspeakers the dimension used is
the sound pressure level (SPL) reached at a given power of 1W (at 1m distance)
There is a similar parameter for the effectivity of headphones except for the fact
that the standard power is 1mw (=1/1000W) The figure is given as dB/mw which
means the resulting sound pressure level at 1mW (not per 1mW)

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If the power is doubled then the resulting sound pressure level is 3dB higher If this
is calculated the other way round it means that only half of the power is needed
when using a headphone with 3dB more effectivity to reach the same sound
pressure level The 3dB formula is valid for headphones and for loudspeakers
From the given effectivity the power needed for a certain sound pressure level can
be derived The power for the same sound pressure level can differ up to a factor of
500 for the different headphones on the market In the end what counts when
selecting a headphone or a headphone amplifier is if the desired volume can be
reached without distortion At least equally important is to avoid damage for the
headphone and – most important – to avoid damage for your hearing The
maximum power rating is a figure that can be found in the data sheet of the
headphone From this power rating the maximum voltage can be derived If the
voltage will be higher then the voice coils of the headphones will be destroyed
Today most headphones allow hearing levels well above a secure level for the
listener This means that a standard pair of cans might survive extremely high
levels without any degradation of long term performance but the hearing of the
listener might be seriously damaged Especially interesting are the standards of
different regions Taking a look at laws in the US and in Europe reveals tremendous
differences in what is thought to be suitable for the listener:
Taking a look at laws in the US and in Europe reveals substantial differences in
what is thought to be suitable sound pressure levels for the listener:
Permissible noise exposures in Germany (dBA)1
SPL /dBA
Duration
85 88 91 94 97 100 103 106 109 112 115 118 121
hours per day 8 4 2 1
minutes per day 30 15 7,5
seconds per day 225 112 56 28 14 7
Permissible noise exposures in the USA (dBA)2
SPL /dBA
Duration
90 92 95 97 100 102 105 110 115
hours per day 8 6 4 3 2 1,5 1
minutes per day 30 15
1 Roughly harmonized throughout Europe
2 Figures taken from US department of labour noise regulations

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Overview of power consumption of different headphones at
different signal levels:
level
(veff)
Headphone impedances
32 Ohms 60 Ohms 120 Ohms 300 Ohms 600 Ohms
0 1V 0,31mW 0,16mW 0,08mW 0,033mW 0,016mV
0 5V 7,8mW 4,2mW 2,1mW 0,83mW 0,42mW
1V 31,3mW 16,7mW 8,3mW 3,3mW 1,7mW
2V 125mW 66,7mW 33,3mW 13,3mW 6,7mW
3V 281mW 150mW 75mW 30mW 15mW
4V 500mW 267mW 133mW 53mW 27mW
5V 781mW 420mW 210mW 83mW 42mW
6V 1,13W 600mW 300mW 120mW 60mW
7V 1,53W 817mW 408mW 163mW 82mW
8V 2W 1,06W 533mW 213mW 107mW
9V 2,53W 1,35W 680mW 270mW 135mW
Voltage needed for 1mW power
units Headphone impedances
32 Ohms 60 Ohms 120 Ohms 300 Ohms 600 Ohms
Volts 179mV 245mV 347mV 550mV 775mV
dBu
(0dB = 775mV)
-12,7 -10 -7 -3 0
dBV
(0dB = 1V)
-14,9 -12,2 -9,2 -5,2 -2,2

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Table of effectivity of common headphones3
Type Impedance
/Ohms
Effektivity
dB/1mW
Voltage for
100dB SPL
Power for
100dB SPL
AKG
K141Studio 55 101 209mV 0,8mW
K240DF 600 88 3,1V 16mW
K501 120 94 694mV 4mW
K1000 120 74 6,93V 400mW
Beyerdynami
c
DT660 32 97 253mV 2mW
DT770, DT880,
DT990
250 96 800mV 2,6mW
Grado
All 32 98 225mV 1,6mW
Koss
Portapro 60 101 218mV 0,8mW
Sennheiser
HD500 32 97 253mV 2mW
HD555 120 94 694mV 4mW
HD650 300 97 775mV 2mW
Ultrasone
HFI-15G 32 94 716mV 4mW
HFI-550 64 100 252mV 1mW
HFI-700 75 94 548mV 4mW
It can easily be seen that even among the products of one manufacturer there can
be huge differences as far as impedance and/or effectivity are concerned This
makes it very important that you either choose headphone and headphone
amplifier as a matching combination or go for a headphone amplifier with
switchable gain that can be used with a wide variety of headphones Purchasing the
Black Cube Linear was a perfect stepp in the right direction
3 All figures were taken from freely available data sheets of different manufacturers and have been partly recalculated
from other dimensions. Voltage and power are referring to effective values and not to peak values. All figures are given
without any guarantee.

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Elements at the front section
1. Power LED
When this LED lits the Black Cube Linear is connected to mains voltage
switched on and ready for being used
2. Headphone output 1
6,3mm headphone jack for common headphones When a headphone is
connected to this headphone output the line output at the rear side of the
unit will be muted Warning: when you are also using the line output please
make sure that the volume knob is turned to minimum position (counter
clockwise) to avoid sudden signal peaks Please have in mind that the same
signal amplitudes can result in very different volume levels connected to
power amps or to headphones
3. Headphone output 2
6,3mm headphone jack for common headphones When a headphone is
connected to this headphone output the line output will not be muted This
enables you to listen to headphones and your loudspeakers at the same time
You can connect to headphones of the same type at the same time to the
Black Cube Linear Please avoid using two different headphones This may
result in very different levels
4. Volume knob
Here you can adjust the desired output level Turn clockwise to get a higher
volume and counter clockwise to lower the volume
W A R N I N G :
While using headphones you can easily reach volume levels that can seriously
damage your hearing. Every time before you put on a pair of headphones you must
make sure that the volume is set to an appropriate level

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Elements at the rear side
1. Line input (Stereo)
RCA connectors for the source you want to hear with the Black Cube Linear
2. Line output (Stereo)
RCA connectors for the connection of your power amplifier or active
loudspeakers Depending on which headphone output you are using on the
front side of the unit the signal is either fed through the Black Cube Linear to
the line output or muted The RCA jacks are connected in parallel to the
Black Cube Linear’s output stage and not just passively connected to the
input connectors so that you benefit greatly when you use the unit as single
source preamp
3. Power switch
This switch separates the primary coil of the power supply transformer from
the mains voltage There is no stand by mode
4. Fuse holder
Fuse holder for the primary fuse In case of replacement you must use the
same type (100V – 120V AC: 630mA slow or T; 200V – 240V AC 315mA
slow or T) If there is a mechanical noise (rattle) when you move the unit
the Black Cube Linear is equipped with a spare fuse which is also placed in
the fuse holder
5. Mains connector
IEC receptable for the connection to mains voltage Please connect the
power cord here You must make sure that you connect the Black Cube
Linear to the appropriate mains voltage The mains voltage and fuse type
needed are both printed on a sticker underneath the unit

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Adjustment of maximum gain
You can easily adjust the maximum gain of the Black Cube Linear to use any
available headphone with best results independent from effectivity or impedance
The gain setting has direct effect on the active gain of the input stage which is
placed after the volume potentiometer It is recommended that you choose a
setting which, at the maximum potentiometer position (turned clockwise), results in
a volume level that is slightly higher than your normal listening habit so that you
have a bit of reserve with lower level signals You also make sure that
extraordinary high levels can be avoided much easier
Gain with volume
turned to maximum:
Switch 1 Switch 2
0dB Off Off
10dB On Off
18dB Off On
20dB On On
The gain setting is done for each channel separately Please make sure that both
channels show the same setting Otherwise you will hear an abnormally twisted
stereo panarama
Warning: Do not change the gain setting while listening to avoid suden
peaks that might damage your loudspeakers or even your hearing