Luxman P-750u User manual

Owner`s Manual
HEADPHONE AMPLIFIER
P-750u

HEADPHONE AMPLIFIER P-750u
Contents
Precautions ············································································································· 1
Features of This Unit································································································ 3
Names and Functions······························································································ 5
Connections ············································································································ 9
Block Diagram······································································································· 11
Specifications ········································································································ 12
Before Asking for Repair Service············································································ 13

1
Precautions
Installation place
Install this unit in a location where good ventilation and heat
radiation are assured. Especially, the installation of this unit
where the direct sunlight is present, where the temperature
rises excessively high such as close to a heater, or where it
is humid or dusty may cause a malfunction even if heat is
efficiently released. Therefore, do not install this unit in such
places.
Note:
For heat dispersal, do not install this equipment in a confined
space such as a book case or similar unit.
* Note
Wall
*
*
*
Precautions in connecting with input
devices
When connecting this product to input devices such as a CD
player, be sure to turn off the operation switches of this prod-
uct and all other connected devices. Failure to observe this
may generate a large noise and accordingly cause hearing
impairment. The RCA plugs connecting input devices should
be firmly pushed into the input terminals. Likewise, firmly push
connectors into the output terminals of any input device, such
as a CD player. Inadequately connections may compromise
grounding and lead to noise and hum and seriously affect the
S/N ratio.
Protection circuit
This product is equipped with a protection circuit that is ac-
tivated upon the detection of overcurrent, abnormally high
temperature, and DC output to protect the amplifier and
headphones. When the protection circuit is activated, the
output to the headphones is shut off and the operation indi-
cator blinks to show that this unit is in the muting state. When
the cause to activate the protection circuit is eliminated, the
blue operation indicator light comes back on and the operat-
ing state resumes. If the protection circuit is frequently acti-
vated after a lapse of a certain time and turning on the power
again, please consult your dealer.
Timed mute circuit
This product is equipped with a timed mute circuit to delay
the output to connected headphones. No sound will be gen-
erated immediately after turning on the power.
ATTENTION: increasing the output volume or input volume
from a connected device while the unit is muted may result
in damage to headphones. With the output level set to a low
level, wait a short time for mute cancelation and then increase
the output level slowly to the desired listening volume.
Connecting / Disconnecting headphones
Connecting or disconnecting an unbalanced headphone jack
causes a brief short circuit between the left and right chan-
nels. This is due to the structure of the unbalanced head-
phone socket. If the volume of this unit is turned up at this
time, a short circuit will be detected and the over-current de-
tection circuit in the headphone amplifier output stage will be
activated, causing the unit to go into a muted state or may
even lead to a malfunction.
ATTENTION: plugging or unplugging headphones should be
done with the output volume set to zero and when there is no
input signal from connected input devices.

HEADPHONE AMPLIFIER P-750u
2
Repair and adjustment
When repairs or adjustments are needed, please ask the
dealer where you bought the unit.
Cleaning
For cleaning, use a piece of soft cloth to wipe the unit such as
cleaning cloth. When the dirt is hard to remove, use a small
amount of neutral detergent to wipe, and then wipe the unit
with dry cloth. Do not use a solvent like benzine or thinner
because such a substance can damage the exterior.
Caution when using headphones
If the headphones are used for a long time at a high sound
volume level, your hearing may be damaged.

3
Features of This Unit
3-stage Darlington output configuration
This product has 3-stage Darlington structure with bipolar
transistor. Rated output: balanced; 8 W + 8 W (16Ω), unbal-
anced; 4 W + 4 W (8Ω)
High grade headphone amplifier,
supporting balanced and unbalanced
headphones
This product is equipped with four independent identical
quality, discrete amplifier channels, which support balanced
headphones via the connection. There is also a balanced in-
put/output straight transmission feature. Two paralleled am-
plifier channels support the left and right of the unbalanced
headphone connection and allows for straight transmission
and develop powerful driving ability. The following conver-
sions are also supported: balanced input→unbalanced head-
phones, unbalanced input→balanced headphones.
LECUA equipped volume control
This product features LECUA, which stands for LUXMAN
Electronically Controlled Ultimate Attenuator. This is a com-
puterized combined resistance attenuator which offers fine,
accurate volume adjustment from –87dB to 0dB with no de-
terioration of the sound quality. LECUA also allows accurate
left/right balance control and reduces the tracking errors of
normal phase/reversed phase operation.
ODNF – Only Distortion Negative Feedback –
The output section features LUXMAN's original distortion-on-
ly negative feedback system which allows for a high speed
primary slew rate and ultra-wide audio bandwidth. Only dis-
tortion generated in the amplification process is fed back for
cancellation. This maintains pure, high quality sound repro-
duction in the main amplifier section.
The latest version, ODNF 4.0 has achieved low impedance
and a high signal to noise ratio for the transmission circuits
thanks to the paralleled first stage and Darlington equipped
second stage amplification circuits. Also the input stage error
detection circuits are triple-paralleled to moderate frequency
characteristics and noise.
Highly stable power supply
This unit features a highly enhanced and stable power sup-
ply featuring a large capacity OI core power transformer, two
custom 10,000μF blocking capacitors for the amplifier stage
and two 3,000μF capacitors for the driver stage.
Parallel speaker relays
This product is equipped with two large, low resistance par-
alleled speaker relays which are also used in our integrated
amplifiers. These help to reduce the impedance of the head-
phone output stages.
Beeline construction
LUXMAN's "Beeline" construction ensures that the audio
signal path takes the optimum shortest route from input to
headphone output.
Selector relay
A high sound quality selector relay is used to enhance
separation and crosstalk performance, a key point of any
LUXMAN amplifier.
Schottky barrier diodes
By using Schottky barrier diodes, manufactured by Nihon
Inter Electronics Corporation, this unit achieves higher DC
conversion efficiency in the rectifier circuit and much less
switching noise.
Original LUXMAN's OFC wiring
Our original un-plated OFC wiring with spirally wrapped shield-
ing is used for all internal connections to ensure smooth, pure
signal transmission.

HEADPHONE AMPLIFIER P-750u
4
Non-angled circuitry
After careful consideration of the delicate nature of audio sig-
nal flow, non-angled circuit board tracking has been adopted
to achieve smooth signal transmission.
Sensitivity selector
A HIGH/MID/LOW sensitivity selector has been provided for
adjustment according to the efficiency of your headphones.
Through output switch
This control allows the line input to be fed directly to the out-
put terminals and can be set to on or off.
Loopless chassis structure
This unit features a loop-less chassis, independently con-
structed to eliminate increases in ground impedance caused
by chassis current.
18 mm RCA terminal
We have used 18mm pitch RCA terminals to facilitate the use
of high grade signal cables with large connectors.
Balanced headphone output
High quality, non-locking XLR sockets have been utilized for
safety and reliability. Three XLR outputs are located on the
front panel, two separated L/R 3-pin XLR terminals and an
integrated L/R 4-pin XLR terminal.
Unbalanced headphone output
The unit is equipped with LUXMAN's standard high grade
headphone jack output socket.
Cast-iron insulator
For stability and support, this product features cast iron feet
with vibration reducing density gradient.
* About balanced headphone connections
• Balanced headphones are driven by the amplifier output section with normal phase (HOT) and reversed phase (COLD) and support 4-core
connections where the left and right ground wire (COLD side) is separated. Generally 3-pin XLR, with left and right channels separated,
or 4-pin XLR, with left and right channels integrated, are used. In the case of 4-pin XLR connections, there is no ground wire for left and
right channels and the cold signals are separated. There is no influence from the grounding of connected input devices and playback with
excellent separation is achieved.
• LUXMAN's approach to balanced headphone operation is to drive normal phase (HOT) and reversed phase (COLD) with independent
amplifier circuits for each of the left and right channels. Small, low level signals up to high, large level signals are driven powerfully without
current flowing into the ground wire. The pin assignment for these two types of connection are as follows:
3-pin XLR (PHONES-3) 4-pin XLR (PHONES-2)
qGROUND qLch HOT (positive phase)
wHOT (positive phase) wLch COLD (reverse phase)
eCOLD (reverse phase) eRch HOT (positive phase)
rRch COLD (reverse phase)

5
Names and Functions
1. Operation indicator (OPERATION)
This blue indicator blinks for a short time to show that the
system is in preparation immediately after the operation
switch is turned on. No sound will be generated during this
period. The indicator will light up steadily when the timed
mute mode is cancelled and operation mode is activated.
If a short circuit or over-current is detected, DC voltage is
generated or the unit experiences an abnormally high op-
erating temperature, the indicator will blink to indicate that
mute mode has been activated. After resolving the cause
of the fault, the blue indicator should light up steadily, in-
dicating normal operation mode has been activated again.
If this indicator continues to blink after resolving the fault,
please contact your country's official LUXMAN distributor
for a repair or service.
2. Operation switch (OPERATION)
This switch turns on and off the power.
ATTENTION: when connecting input devices or connecting
the output to other audio equipment ensure that the power
is switched off.
ON: Turns on this unit's power. The blue operation in-
dicator light will blink and then light up steadily.
OFF: Turns this unit's power off.
3. Input selection switch (INPUT)
This switch toggles between the unbalanced line input
(LINE), balanced line 1 input (BAL LINE-1), and balanced
line 2 input (BAL LINE-2) which are located on the rear panel
of the unit.
4. Through output switch
(THROUGH OUT)
This switch enables the user connect the line input of the
unit directly to the through output terminals, for example a
CD player connected to the line input may be directly con-
nected to an output destination device such as an amplifi-
er. Set to on, this switch enables the direct through output
connection and the orange indicator will light up. Selecting
off disconnects the signal to the through output.
When the power to this unit is switched off, the line in-
put signal IS ALWAYS connected to the through output
terminals, regardless of this switch setting. Signals from
devices connected to the balanced line inputs are not
outputted from the through output terminals.
1 2 11853 4 6 9 107
Front panel

HEADPHONE AMPLIFIER P-750u
6
5. Unbalanced headphone jack socket
(PHONES-1)
This socket accepts a standard 1/4 inch stereo headphone
jack plug. Use headphones with an impedance of 8Ω or
more.
6. 4-pin balanced headphone output
terminal (PHONES-2)
This connection accepts a 4-pin XLR connector for bal-
anced type headphones. Use headphones with an imped-
ance of 16Ω or more. The pin assignment for this 4-pin XLR
output is as follows:
qLch HOT
wLch COLD
eRch HOT
rRch COLD
7. 3-pin balanced headphone output
terminals (PHONES-3)
These connections accept 3-pin XLR connectors for bal-
anced type headphones with separate left (L) and right (R)
connectors. Use headphones with an impedance of 16Ω or
more. The pin assignment for each of the left and right 3-pin
XLR outputs are as follows:
qGROUND
wHOT
eCOLD
8. Headphone output selector switch
(OUTPUT)
This switch is an output selector which toggles between
the three available headphone outputs, unbalanced output
(PHONES-1), balanced 4-pin XLR output (PHONES-2) and
balanced 3-pin XLR outputs (PHONES-3). Each time this
button is pressed, the output selection changes and the
corresponding output will be identified by an orange indi-
cator light.
9. Sensitivity selector switch
(SENSITIVITY)
This control can select between HIGH, MID and LOW in ac-
cordance with the efficiency of the headphones being used.
If low efficiency headphones are used and the volume is
insufficient, even after turning up the volume control, se-
lect HIGH . If high efficiency headphones are used and the
volume is hardly controllable, select LOW. The sensitivity of
this unit is set to the following:
HIGH : 0 dB
MID : –6 dB
LOW : –12 dB
10. Balance control (BALANCE)
This control allows the listener to adjust the relative volume
level of the left and right channels.
Rotating the control counter-clockwise gradually cuts the
volume of the right channel, rotating the control clockwise
gradually cuts the volume of the left channel.
Under normal conditions, this control should be set to
the center position and then adjusted as necessary. The
maximum adjustable value for left/right balance is down
to –12dB.
11. Volume control (VOLUME)
This control adjusts the headphone output level. At first, the
volume control should be rotated fully counter-clockwise,
setting the level to zero. Gradually rotate the control clock-
wise to adjust the volume of the headphone output to the
desired level.
ATTENTION: connecting or disconecting headphones
should only be done with the volume control set fully count-
er-clockwise, with the output level set to zero.

7
Names and Functions
12. Balanced input connections - INPUTS
(BAL LINE-1, BAL LINE-2)
These four XLR input terminals are for two line level bal-
anced stereo inputs. Connect these inputs to the balanced
XLR outputs of any input device, such as a CD player, using
balanced XLR cables.
13. Balanced input phase selector switches
(PHASE)
Use these switches to reverse the phase of the balanced
input signals by 180 degrees. In the normal position, input
signals will be normal and in phase, with these switches
set to the invert position, the input signals will be phase
reversed as shown in the table below.
normal position ......... qGROUND
wCOLD
eHOT
invert position............ qGROUND
wHOT
eCOLD
14. Unbalanced line input connections-
INPUTS (LINE)
These two RCA line input terminals are for an unbalanced
stereo line input. Connect these inputs to the unbalanced
outputs of any input device, such as a CD player, using
RCA cables.
15. Through output connections
(THROUGH OUT)
These RCA output terminals are for connection to another
audio device, such as an amplifier, and allow the user to
directly connect the line input to an external device using
the through output.
Audio signals fed to the through output are not affected
by the volume control of this unit.
16. AC power inlet (AC IN)
Connect the supplied AC power cable to this socket to
power the unit from a household AC power socket.
Rear panel
161412 15
13

HEADPHONE AMPLIFIER P-750u
8
Memory
This unit stores the following items when the power is off:
Item Default
THROUGH OUT on/off
OUTPUT PHONES-1/-2/-3
Memory reset procedure
The following operations restore all the settings to the
factory defaults.
(1) Turn off the power of this unit. (Wait for 5 seconds or
more.)
(2) Press the OPERATION switch while holding down the
headphone output selector button (OUTPUT) to pow-
er on the unit.
(3) All of the headphone output indicator lights for
PHONES-1, PHONES-2 and PHONES-3 will light up
in 5 seconds.
(4) Immediately after these indicator lights come on as
described above, press the through output switch
(THROUGH OUT) once, while still holding down the
headphone output selector button (OUTPUT), and
the through output indicator will light up.
(5) Release the headphone output selector button
(OUTPUT).
(6) The power is turned on and the unit will go into nor-
mal operation mode with all settings restored to the
factory defaults.
The memory reset procedure is complete.
If any abnormality is detected by this unit upon powering
up, all of the indicators will blink. If such a condition is
encountered, turn off the power to the unit at once. Turn
the power back on and wait to see if normal operation
mode is activated. If the system is normal, the memory is
reset and the system will be activated in a factory default
state. If the abnormality persists, power off the unit and
please contact your country's official LUXMAN distribu-
tor for a repair or service.
Factory default
Item Default
THROUGH OUT off
OUTPUT PHONES-1

9
Connections
HEADPHONE (UNBAL) HEADPHONE (BAL)
CONTROL AMP
USB D/A
CONVERTER
CONTROL AMP POWER AMP
SPEAKER
SYSTEM
CD PLAYER
SACD PLAYER
L
R
L
R
L
R
L
L
R
R
L
R
PC / Mac
L R
3-pin XLR type
4-pin XLR type
L R

HEADPHONE AMPLIFIER P-750u
10
Before connecting
Before connecting this unit to any other input/output devic-
es, ensure that the IEC connector of the supplied AC power
cable is firmly connected to the AC power inlet on the back
of the unit.
Before making any connections, turn off the operation
switch to power off the unit and ensure all other input and
output devices are also powered off to avoid any unexpect-
ed accidents or problems resulting from noise.
How to connect the AC power supply
Use the supplied AC power cable to connect the AC power
inlet to an AC power socket on the wall of your listening area.
How to connect input devices
Connect the input terminals of this unit to the output terminals
of input devices such as a CD player, SACD player or the
record output of a control amplifier. Connect the RCA unbal-
anced line inputs of this product to the RCA output terminals
of an input device using RCA cables. Connect the balanced
XLR input terminals of this device to the balanced XLR output
terminals of input devices using XLR cables.
Use the input selector switch to select an input device, set
to LINE to select input devices connected to the unbalanced
line input (LINE) or set to BAL LINE-1 or BAL LINE-2 to select
input devices connected to the two balanced line inputs.
How to connect balanced headphones
With the volume control turned fully counter-clockwise to set
the volume level to zero, insert the XLR connector(s) of your
balanced headphones into the terminals on the front panel
of the unit. If the connector is a 4-pin XLR, connect it to the
PHONES-2 terminal, if your headphones have two 3-pin XLR
connectors, connect them to the PHONES-3 terminals, pay-
ing attention to the left (L) and right (R) configuration. You may
now adjust the volume control to the desired level.
The applicable impedance range of this unit is 16Ω to 600Ω
for balanced headphones.
How to connect unbalanced headphones
With the volume control turned fully counter-clockwise to set
the volume level to zero, insert the 1/4 inch stereo jack plug
of your unbalanced headphones into the stereo jack socket
PHONES-1 on the front panel of this unit. You may now ad-
just the volume control to the desired level.
The applicable impedance range of this unit is 8Ω to 600Ω
for unbalanced headphones.
CAUTION: Attention must be paid to the volume level be-
cause this product is is capable of high powered output
levels. Be sure to rotate the volume control fully count-
er-clockwise to reduce the volume to zero before turning
the power on or off or before connecting or disconnecting
headphone connector(s) to prevent any damage to head-
phones or hearing.
How to connect the through output
The through output (THROUTH OUT) on the rear panel of
this product may be used when an input device connect-
ed to the line inputs (LINE) of this unit only has one stereo
pair of outputs. It is possible to connect the through output
of this unit to the input of a control amplifier or integrated
amplifier. To enjoy listening on headphones, set the through
output to off. When not using headphones, turn the volume
control fully counter-clockwise to set the volume to zero and
set the through output to on. The signal from an input device
connected to the line inputs will be directly connected to the
through output and can be reproduced via a connected am-
plifier and speakers.
When this unit is powered off, the line input is automatically
connected to the through output regardless of the through
output selector switch position (on or off).
In a situation where the output impedance of an input de-
vice is high and the input impedance of a device connected
to the through output is low, this product's headphone out-
put level will be reduced
CAUTION: Whenever the power to this unit is switched on
or off, ensure that the volume control of the amplifier con-
nected to the through output of this unit is set to zero. Fail-
ure to observe this may generate unwanted noise and lead
to possible damage of the output amplifier and speakers.
It is recommended that you set the through output control
switch to off when listening using headphones.

11
Block Diagram
BAL LINE-1 BAL LINE-2 LINE
BAL
→
UNBAL
Lch HOT
THROUGH OUT
BAL-1
→
BAL
PHONES-2 OUT (4P XLR) PHONES-3 L OUT (3P XLR) PHONES-3 R OUT (3P XLR) PHONES-1 OUT (UNBAL HP)
OPERATION FUSE
Power Transformer
−B2
OUTPUT /MUTE
REG. B2
+B2
−B1L
+B1L
+B2' +B1L −B1L
−B2'
For μ-Com./Acc.
For Main Amp For Driver
For AC SENSOR
μ-Computer
Key
LED
ODNF Ver.4.0
LECUA
Protector
DC./OC.
TEMP.
RECTIFIER
REG.
off
on
off
Volume/Balance
PHASE INVERT
INV.
PHASE INVERT
INV.
−1
Buffer
−B2'
+B1R
−B1R
1
2
3
+B2 −B2 −B2'
REG. B2
Input/Sensitivity
REG. REG.
Rch HOT Lch COLD
Rch COLD
MUTE
THROUGH
on
1
2
3
1
2
4
3
12
3
12
3
BAL-1
→
UNBAL
BAL-2
→
UNBAL
LINE
→
BAL
LINE
→
UNBAL
BAL-2
→
BAL
PHONES-1 PHONES-2 PHONES-3
+−
+B2'
+B2' −B2'
−B2'
Volume/Balance
/Sensitivity
+B1R −B1R
BAL
→
UNBAL
For Pre Amp
+B2 −B2 −B2'
REG. B2
+B2' −B2'
+B2 −B2 −B2'
REG. B2
+B2' −B2'

HEADPHONE AMPLIFIER P-750u
12
Specifications
Rated output UNBAL : 4 W + 4 W (8 Ω), 1 W + 1 W (32 Ω)
BAL : 8 W + 8 W (16 Ω), 4 W + 4 W (32 Ω)
[UNBAL: PHONES-1 output, BAL: PHONES-2 output, PHONES-3 output,]
Input sensitivity LINE →UNBAL : 1 V (SENSITIVITY HIGH)
BAL LINE →BAL : 2 V (SENSITIVITY HIGH)
LINE →BAL : 2 V (SENSITIVITY HIGH)
BAL LINE →UNBAL : 1 V (SENSITIVITY HIGH)
Input impedance LINE : 15 kΩ (THROUGH OUT OFF)
BAL LINE : 40 kΩ
Total harmonic distortion LINE →UNBAL : 0.003 % (8 Ω, 1 kHz, 1 W, both CHs simultaneous drive)
BAL LINE →BAL : 0.002 % (16 Ω, 1 kHz, 1 W, both CHs simultaneous drive)
S/N ratio LINE →UNBAL : 113 dB or more (IHF-A weighted, input short)
BAL LINE →BAL : 116 dB or more (IHF-A weighted, input short)
Frequency response LINE →UNBAL : 20 Hz to 20,000 Hz (+0, –0.1dB)
10 Hz to 170,000 Hz (+0, within –3 dB)
BAL LINE →BAL : 20 Hz to 20,000 Hz (+0, –0.1dB)
10 Hz to 170,000 Hz (+0, within –3 dB)
Supplied functions • Balance control • Sensitivity selection
• Headphone output selection • Through output selection
• Input selection
• Unbalanced headphone jack (PHONES-1) ×1 line
• 4-pin XLR balanced headphone output (PHONES-2) ×1 line
• 3-pin XLR balanced headphone output (PHONES-3) ×1 line
Accessories • Owner’s Manual (This document) • Power cable
• Safety cautions
Power supply 230 V 〜(50 Hz)
Power consumption 40 W
27 W (at no input)
Max. external dimensions 440 (W) × 92 (H) × 400 (D) mm
(front side knob of 14 mm and rear side terminal of 6 mm included in depth)
Weight 13.3 kg(main unit)
* Specifications and appearance are subject to change without notice.

13
Before Asking for Repair Service
While in use, this unit may display phenomena which may be confused as malfunctions. Before contacting your country's official
LUXMAN distributor for repair services, please read the operating instructions and operating instructions for any connected input and
through output devices and check the troubleshooting table below. If the cause of the malfunction cannot be identified, please con-
tact your dealer. After LUXMAN's representatives have accepted your request for repair services, inspection fees and transportation
expenses may be claimed, even though the unit may be found to be operating normally.
Problem Cause Solution
No power is supplied even
though the operation switch is
pressed.
• The AC plug is disconnected from the wall
outlet, or it is not completely inserted.
• Insert the AC plug in the wall outlet com-
pletely.
• The power cable is disconnected from the
AC inlet, or it is not inserted completely.
• Securely insert the power cable in the AC
inlet completely.
No sound is generated. • The volume control is set to the minimum
level.
• Adjust the volume control.
• Connection is not securely made. • Make cable connections securely.
• RCA cables and balanced cables are incor-
rectly matched.
• Match the cable type to be used with the
setting of the input selector switch.
• The selected item of the input selection
switch of the control amplifier is not appro-
priate.
• Properly adjust the input selector of the
control amplifier.
• The volume control of the input device such
as a control amplifier is set to a lower level.
• Adjust the volume control of the input de-
vice such as a control amplifier.
• The REC OUT output of the input device
such as a control amplifier is set to off.
• Set the REC OUT output to on.
No sound comes out from one
side.
• The balance volume of the input device
leans to one side, right or left.
• Set the balance volume to the center or
your favorite balance.
• The connecting cable is not connected on
one side only.
• Connect the cable correctly.
No signal comes from the
through output.
• The through switch is set to off. • Set the through switch to on.
Protection mode is activated
when connecting or discon-
necting headphones.
• The volume control is largely rotated clock-
wise.
• Rotate the volume control fully count-
er-clockwise, setting the volume level to
zero when connecting ot disconnecting
headphones.
Humming sound (boon or zzz
noise) is generated.
• The grounding side of the connection cable
has no contact with the terminal.
• Make cable connections securely.
• Induction noise is picked up from a power
transformer of another device.
• Install the unit away from other devices and
sources of induction.
• The headphone cable is too close to the
power cable.
• Keep the headphone cable away from the
power cable.

HEADPHONE AMPLIFIER P-750u
14
MEMO

15
MEMO

LUXMAN CORPORATION, JAPAN
1-3-1 Shinyokohama, Kouhoku-ku, Yokohama-shi, Kanagawa 222-0033, Japan AG00987E68A
Printed in Japan