Halcro DM8 User manual

Preamplifier with remote control
Owner’s Manual
www.halcro.com
dm8

1
Contents
Introduction................................................2
Important Safety Information...................3
Electrical safety............................................. 3
Protection from fluids .................................. 3
Service warnings .......................................... 3
Product Design..........................................4
Electronic design.......................................... 4
Industrial design............................................ 6
Mechanical design ........................................7
Installation...................................................8
Unpacking ..................................................... 8
Storing packaging ........................................ 8
Positioning..................................................... 8
Controls and Connections.......................9
Front panel .................................................... 9
Rear panel ....................................................12
Remote control ...........................................14
dm8 outputs ................................................15
Connecting signal sources ........................ 15
Connecting home theater processor......15
Connecting to a power amplifier ..............16
Connect the mains supply cable.............. 17
Bridging......................................................... 17
Break-in period............................................ 17
Programmable input selections................ 17
Operation..................................................18
Start up .........................................................18
Source setup ...............................................18
De-allocating program buttons ................18
Display...........................................................18
Volume..........................................................19
Electronic Protection and Reliability..... 22
Components............................................... 22
Mains transient overload protection ....... 22
dm8 Specifications................................. 23
Care and Maintenance.......................... 26
Cleaning....................................................... 26
Troubleshooting...................................... 27
Service and Warranty Information ....... 28
Overview ..................................................... 28
Product warranty ....................................... 28
Exclusions to the warranty ....................... 28
Transferability.............................................. 29
Warranty verification .................................. 29
Warranty registration ................................. 29
If service is required ................................... 29
Transportation of products....................... 30
Freight damage claims.............................. 30
If you have moved ..................................... 30
Thank you for choosing Halcro!............... 30

2
Introduction
Congratulations on purchasing the Halcro
dm8 preamplifier.
It has taken two years and the generous
contributions of leading reviewers, distributors
and dealers from around the world to design,
then create, the Halcro preamplifiers. We are
confident that this combination of expertise,
along with the know-how of the high-end
audio industry’s leading Research and
Development team will ensure the success of
the Halcro preamplifiers.
The brief given to our R&D team, headed by
Bruce Candy, was to produce two models of
preamplifier to satisfy the needs of every
audio connoisseur:
•lowest distortion specifications of any
preamplifier in the world
•physical dimensions to suit a standard
domestic equipment rack, while retaining
the stunning Halcro industrial design
signature
•tractable controls
•superior reliability
•innovation in design
The Halcro dm8 preamplifiers will add no
colorations to the music. When used in
conjunction with Halcro power amplifiers, all
you will hear is the original recording
reproduced the way the artist intended it to
sound. No transistor or valve-added sounds
are present, just a level of musical purity that
was thought impossible until now.
Please enjoy the Halcro audio experience.
Halcro has enjoyed creating perfect audio
reproduction for the world's music
connoisseurs.
If you desire to contact Halcro to give us
feedback on your purchase or for general
enquiries, please feel free to:
E-mail us at: [email protected]om
or phone: + 61 8 8238 0807
or fax: + 61 8 8238 0852

3
Important Safety Information
Electrical safety
Only suitable approved MAINS cords, as per
European individual country requirements in
the CE Low Voltage Directive Scheme, shall
be used with this unit.
Do not use extension cords: To avoid safety
hazards, use only the power cord supplied
with your unit.
No naked flame sources, such as lighted
candles, should be placed on the unit.
The dm8 is designed to operate on any mains
supply in the range of 90 to 240 V, 50 to
60 Hz, without any internal or external
switches.
Protection from fluids
This device is designed for indoor use only
and is not protected against liquids. It must not
be exposed to dripping or splashing, and no
objects filled with liquids, such as vases,
should be placed on it.
IMPORTANT - This product must
always be connected to an
earthed voltage supply.
Service warnings
This product contains no user serviceable
parts.
WARNING: do not use any
cables longer than three meters.
All compartments are sealed at the factory. If
the seals are broken, the warranty will be void
and all service costs will be charged to the
owner.
DANGER: Contains no user
serviceable parts. Do not
attempt to open any of the
amplifier compartments, as
this may expose you to
dangerous voltages and will
void the warranty.
W
ARNING: Weighs 2
3
kg (50 lb)
per unit. Shipping weight is 36 kg
(79 lb). Never lift the amplifier by
yoursel .f
Requires F2AL 250 V fuse for continued
protection against the risk of fire. Never
bypass or use any other type of fuse. The fuse
is located on the rear panel in the main switch.

4
Product Design
Electronic design
by Bruce Candy
In keeping with my philosophy of design, my
basic aim was to produce a preamplifier with
which I, personally, am quite satisfied. I
sincerely hope that others will share my
satisfaction with these products.
As I saw it, the major issues were:
•zero compromise on Transparency
•flexibility
•ease of use
•progressive design concepts
In order to meet this challenge, the resulting
circuits have particular characteristics:
First, all circuits in the preamplifier have
distortion so low that it is immeasurable,
whether THD, IM and so on.
Second, all circuits in the preamplifier exhibit
exceptionally low noise (see specifications).
Third, there is no compromise whatever with
the choice of components (Vishay resistors,
FKP1 capacitors and so on).
Fourth, the circuits are highly immune to
electromagnetic interference. Some inputs
and outputs include both first order filters and
common mode chokes.
Fifth, the power supply and microprocessor
circuits are designed for minimal
electromagnetic emissions (extensive 2nd to
6th order filters).
Sixth, the power supply switching frequency
was chosen to be much higher than the audio
band (>200 kHz).
Seventh, the power supply rails are
exceptionally well regulated, double regulation
in fact (switch-mode and linear servo loops).
Eighth, components and design are selected
for high reliability.
The volume control is implemented so as to
include two identical stages in series. This
minimizes output noise.
The dm8 and dm10 preamplifiers feature
balanced, unbalanced, current mode and
bridged current mode outputs. The latter
consists of a non-inverted and inverted
current output. There is also an unbalanced
output for tape and headphones.

5
Audible relay noise
The dm8 and dm10 use mechanical relays in
all switching including the volume control
because they exhibit the following ideal
characteristics:
•zero ON resistance
•infinite OFF impedance
•very low OFF capacitance
•zero distortion
In contrast, the now universally popular solid-
state relays/switches exhibit none of these
ideal properties and detract from
performance. Hence, sonically, Halcro feels
that it is worth the side effect of mechanical
clicking sounds when parameters are
changed.
Microprocessor control
The excellent audio electronics are
complemented and controlled by a number of
highly integrated micro-controllers located
close to the electronics they serve. Being as
near as possible to the controlled electronics
allows short control paths and virtually
eliminates internal connectors, thereby greatly
increasing system reliability.
Each amplifier channel has its own micro-
controller; the front panel display and user
interface has another. A fourth micro-
controller, located on the rear connector
panel, co-ordinates the activity of the others.
The four micro-controllers are linked via only
four interconnections each.
A unique programming feature of the
microprocessor has been developed which
allows the user to dedicate a particular pair of
input sockets to a specific input device. This
feature provides the user with great flexibility
for connecting input devices to the
preamplifier.
On the rear panel there are one pair of current
inputs, three pairs of balanced inputs and
three pairs of unbalanced inputs.

6
Industrial design
Product form
The aim when designing the dm8 and dm10
was to create a preamplifier that was
unmistakably part of the Halcro product family,
but at the same time a component that would
complement any high-end audio system.
The preamplifier had to sit comfortably within a
contemporary domestic environment, retain
the visual signature of the Halcro family of
products, which differentiates them from
other high-end audio products, and have an
appearance that reflected the high level of
technical innovation. As with other Halcro
products, softer forms and textures are used,
all fasteners are concealed and the heat sinks
are integrated into the external form to
maintain simple, clean lines.
While the unique pillar forms of the power
amplifiers have been carried through to the
preamplifier, proportions have been reworked
to allow this component to be either
freestanding or housed within a standard 19”
shelving system.
Control interface
Knobs and buttons
The volume and input selector knobs use a
unique magnetic incremental indexing
mechanism developed to provide a very
subtle and reliable indexing action. The knobs
and buttons are finished in the same soft
textural finish as the pillars.
Control interface
Knobs and buttons
The volume and input selector knobs use a
unique magnetic incremental indexing
mechanism developed to provide a very
subtle and reliable indexing action. The knobs
and buttons are finished in the same soft
textural finish as the pillars.

7
t
Display
A high-resolution display was chosen in order
to provide clean simple graphics without the
rough edges associated with displays of
lesser quality. The graphic layout of the display
has been optimized to give prominence to the
functions that are viewed most often. These
include volume levels, balance and input
selection. Functions that are accessed less
often are displayed in smaller type along the
bottom of the screen. These include
stereo/mono and in or out-of-phase. The
volume levels for each channel are displayed
side-by-side so that when the levels are not
equalized the user will easily notice it.
Remote con rol
When designing the Halcro Remote Control,
we aimed to reflect the quality and forms of
the Halcro preamplifiers. Machined from a
solid aluminum extrusion, the remote rests
comfortably in the right hand with its minimalist
array of buttons falling within the natural
sweep of the thumb. Simple and logical to
operate, every effort has been made to keep
this product free of unnecessary complexity.
Mechanical design
The Halcro dm8 and dm10 can boast their
spectacularly low noise and distortion
specifications while their cases contain
inherently noisy digital circuitry, including a
switch-mode power supply, partly due to the
mechanical design of their circuit boards and
the boxes that contain them. Supports of
folded aluminum serve not only as bases to
which the electronics are anchored, but also
to shield different sections of the circuitry from
one another.
Each of the audio, panel and display, and
power supply sections is contained within its
own internal aluminum enclosure. Cables
connecting the separate sections are few and
short, minimizing both radiation and reception
of unwanted signals.

8
Installation
Ensure you have read the Important Safety
Information on page 3, before installing your
Halcro preamplifier.
If you require assistance in the unpacking and
installation of your Halcro preamplifier, please
contact your dealer.
Unpacking
oUnscrew the four knurled knobs at the
base of the container, and then remove
the upper part of the container by lifting
directly upwards, until it clears the top of
the preamplifier.
oRemove the plastic wrapping and foam
pieces, then lift the preamplifier from the
base of the container and remove the
plastic covering from the unit.
Please save all packaging material for
later use.
oRemove the centerpiece of foam in base
of transit case, to locate the remote
control and power cable.
oWearing the white cotton gloves
provided (to prevent marking the
preamplifier while moving it in to position),
move the unit to its final location (see
Positioning).
Storing packaging
The packaging is custom designed to prevent
damage from occurring during transport.
Store the packaging in a dry location.
Positioning
The Halcro dm8 preamplifier can be placed
anywhere indoors. There is no need to leave
room around the unit to allow for ventilation as
the dm8 does not generate significant
amounts of heat.
To ensure ultimate performance and to avoid
potential safety hazards, place the unit on a
firm, level surface. When placing the unit on a
shelf, be certain that the shelf and mounting
hardware can support the weight of the
product.
Do not connect to mains power
until all the connections are
made and checked.

9
Controls and Connections
Front panel
Figure 1
1. LCD information display
2. Balance control left
3. Standby/On button
4. Mute button
5. Balance control right
6. Input select control
7. Volume control
8. Phase button
9. Remote sensor window

10
1. LCD information display: This display
delivers messages and system status to assist
you in operating the unit. See page 11 for a
complete breakdown on the display.
2. Balance control left: Use this button in
conjunction with Balance Control Right (Fig 1,
5), to change the relative volume for the left
and right channels. Pressing the Left button
increases the volume on the left hand channel
and decreases the volume on the right.
3. Standby/On button: The Halcro dm8 is
designed to remain in Standby mode when
not in use. This button will toggle the unit
between Standby and On.
To turn the unit off completely, use the Main
Power Switch on the rear panel.
4. Mute button: Depressing this button mutes
the output to the speakers but not the
headphones.
5. Balance control right: Use this button in
conjunction with Balance Control Left (Fig 1,
2), to change the relative volume for the left
and right channels. Pressing the Right button
increases the volume on the right hand
channel and decreases the volume on the left.
6. Input select control: Turning this knob, the
preamplifier scrolls through all programmed
input devices (CD player, Tuner, DVD, and so
on) attached to the unit. The corresponding
selected input is displayed.
7 Volume control: Turn this knob clockwise to
increase the volume and counter-clockwise to
decrease the volume. To mute the system,
when the speakers are balanced, continue to
turn the knob counter-clockwise until the
word MUTE appears on the display, or press
the MUTE button.
8. Phase button: Depressing this button
toggles the unit between in-phase and out-of-
phase mode.
9. Remote sensor window: Behind this
window is a sensor that receives infrared
signals from the remote control. Aim the
remote at this area and do not block or cover
this sensor window.

11
Front panel display
Figure 2
A
B
C
1. Main information display: The information
provided on this display changes depending
on the function that is currently being
processed.
In normal use it will display the volume of both
the left and right of the system (Fig 2, C).
When a different signal source is selected it
will appear on the main display for a few
seconds. (Fig 2, B).
2. Signal source indicator: Displays the signal
source, which is currently selected.
3. Signal source location indicator: Displays
the input to which the signal source has been
connected.
4. Phase indicator: Displays whether the unit
is in- or out-of-phase.

12
Rear panel
Figure 3
1. Programmable inputs
2. Program buttons
3. Tape monitor output
4. Output sockets
5. Remote sensor window
6. Main power switch, mains socket and
fuse holder
7. Remote power amplifier output
8. Output selector switch

13
1. Programmable inputs: Provides connection
to your signal sources. It does not matter
which input each source is connected to, as
these inputs are allocated using remote
control.
2. Program buttons: Allows the inputs to be
programmed by the remote control. They will
remain illuminated once they have been
allocated – see
Connecting signal sources on
page 15.
3. Tape monitor output: For recording direct
to tape.
4. Output sockets: Used to connect the
preamplifier to Power amplifier(s).
5. Remote sensor window: Behind this
window is a sensor that receives infrared
signals from the remote control. Aim the
remote at this area and do not block or cover
this sensor window.
6. Main power switch, socket and fuse holder:
Once the dm8 has been programmed, the
main power switch can be left on and the dm8
left in Standby when not in use. If the main
power switch is turned off, all programming is
stored in memory.
7. Remote power amplifier control output:
Connect a cable from this output to the power
amplifier(s) and the dm8 will switch the power
amplifier(s) between Standby and On.
8. Output selector switch: Allows the user to
select the type of output required, Balanced,
Unbalanced or Current. See
dm8 Outputs on
page 15
.

14
Remote control
Figure 4
1. Volume buttons
2. Mute button
3. Standby/On button
4. Signal source buttons
5. Function button
1. Volume buttons: For volume control and
also used in conjunction with the function
button for various function selections.
2. Mute button: Press to mute sound to the
loudspeakers, press again to reactivate the
sound.
3. Standby/On button: Press to switch the
system between Standby and On.
4. Signal source buttons: Press to select any
one of six signal sources on the dm8.
5. Function button: Press to choose the
following functions: balance between the
speakers, in-phase and out-of-phase and
stereo/ mono. See relevant operating
instructions for full details.
Remote control batteries
To replace the batteries, remove the battery
cover from the rear of the remote control, and
insert the three supplied AAA batteries into the
unit (ensure that the polarity is correct). Refit
the battery cover.
If the remote control will not be used for a
period longer than one month, remove the
batteries.

15
dm8 outputs
The balanced voltage outputs or current-
mode outputs are most desirable for
minimizing earth loop generated mains hum
and ripple, or high frequency interference if
these are a problem.
Power Amplifiers with current-mode inputs
are rare and are most likely to have an RCA
input socket. The advantages of this are:
•earth loop generated mains hum and
ripple are minimized
•cable, plug and socket-generated
interference are minimized (from poor
connections which may be affected by
sound vibration for example)
The unbalanced voltage output is quite
satisfactory as long as earth loop generated
mains hum and ripple are not a problem. (This
should not be a problem unless the source
equipment is poorly designed.)
Connecting signal sources
As a safety precaution please ensure that the
unit is not connected to the mains power
while connecting signal sources.
When you initially receive your preamplifier all
the inputs are de-allocated.
If you are changing your signal source units,
de-allocate the input source first – see
De-
allocating Program buttons
on page 18.
Connect all signal source units (such as CD
player) to the terminals (Fig 3, 1) at the rear of
the preamplifier, make note of which input
each signal source unit is connected to.
Connecting home theater
processor
As a safety precaution please ensure that the
unit is not connected to the mains power
while connecting a Home Theater Processor
(HTP).
Connect your HTP to any of the
programmable inputs at the rear of the
preamplifier.
Program the preamplifier to the unit, referring
to
Source setup on page 18. (We recommend
you use the DVD function.)
To set the preamplifier to operate with zero
gain, adjust both volume channels to 0.0db.
The preamplifier will then have no effect on
the volume. You will now be able to control
the volume of your system by using your HTP
volume control.

16
Connecting to a power
amplifier
Each dm8 has:
•two pairs of unbalanced current outputs
(use one pair for un-bridged power
amplifiers; use both for driving bridged
amplifiers)
•two pairs of unbalanced voltage outputs
•two pairs of balanced voltage outputs for
power amplifiers.
Select the method you wish to run your power
amplifiers in, and connect the units using high
quality cables.
Outputs are color-coded:
•Positive + right channel (red bezel)
•Negative - left channel (white bezel)
The dm8 will control power amplifiers from
balanced and unbalanced voltage sources, as
well as an unbalanced current source. The
dm8 will also control power amplifiers in
bridged pair configuration. Custom-made
cables are required to run bridged power
amplifiers from the balanced Voltage Output
Remote power amplifier control
output
The dm8 has a remote power amplifier control
output (Fig 3, 7), which will remotely switch the
Halcro amplifiers from Standby to On. Cables
can be purchased through Halcro for details
please E-mail us at:
[e-mail]

17
Connect the mains supply
cable
Plug the main power cable into the main
power socket on the rear of the dm8. (Fig
3, 6.)
Bridging
The dm8 will control bridged power amplifiers.
A bridging kit can be purchased through
Halcro, for details please E-mail us at
[e-mail]
Break-in period
The dm8 electronic break-in period is
completed at the factory. A further break-in
period is not required.
Programmable input
selections
The dm8 has seven available pairs of
programmable input connectors:
•three unbalanced voltage inputs
•three balanced voltage inputs
•one unbalanced current input
All inputs that have a signal source connected
must be programmed by the remote control.
Any input can be programmed to connect any
source and each button on the remote
control can have only one signal source
programmed to it at any time.
Input modes Required output source
impedance Input socket Input impedance
Balanced voltage input XLR: Low source impedance XLR 10 kohms + 10 kohms
Unbalanced voltage
input
RCA: Low source impedance RCA 10 kohms
Unbalanced current
input
RCA: Infinite source impedance RCA 50 ohms

18
Operation
Start up
Switch the main power switch to On.
When the unit is switched on at the main
power switch (Fig 3, 6) the preamplifier will go
into Standby mode.
Switch the unit on by pressing the Standby/On
button on the unit or the remote control. To
return the unit to Standby mode, press the
Standby/On button again.
Source setup
All inputs must be allocated using the remote
control (Fig 4).
Once the signal source units (such as CD
player) have been connected to the input
connector terminals (Fig 3, 1), ensure that the
preamplifier is On, not in Standby mode.
Depress the applicable program button (Fig 3,
2) then simultaneously point the remote
control to a remote sensor window (Fig 1, 9
OR Fig 3, 5) and press the button on the
remote control which corresponds to the
signal source unit you have connected.
The program button will flash twice and
remain illuminated, indicating that the pair of
input connectors are now allocated to the
selected signal source unit. Repeat this
process for all signal source units.
De-allocating program
buttons
To de-allocate program buttons, press and
hold the applicable program button and
simultaneously point the remote control to a
remote sensor window and press the Mute
button. The Program button will flash twice
and then remain off. This input has now been
de-allocated and can be used for another
signal source unit.
NOTE: To continue the setup
process, the unit must be On,
not in Standby
NOTE: Ensure the location being de-allocated
is not the currently selected input; the
currently selected input cannot be de-
allocated.
Display
Displayed information
In normal use the center of the display will
display the volume of both the left and right of
the system. When a different signal source is
selected, it will appear in the center of the
display for a few seconds (Fig 2).
Display contrast
To adjust the display contrast, press and hold
any of the Program buttons on the rear panel
(Fig 3, 2) and turn the Volume control on the
front panel until the desired contrast is
achieved.

19
Back light
The backlight can be turned on and off by
using the remote control. Press the function
button once (Fig 4, 5) then the Mute button
(Fig 4, 2) to toggle the back light on and off.
Volume
Front panel
To change the overall volume of the unit, use
the Volume control knob (Fig 1, 7). Turn the
knob clockwise to increase the volume (the
maximum volume is +20 db) and counter-
clockwise to decrease the volume (the
minimum volume is –60 db).
To mute the system, continue to turn the
knob counter-clockwise until the word MUTE
appears on the display, or press the Mute
button (Fig 1, 4).
Remote control
To change the overall volume of the unit, use
the Volume buttons on the remote control (Fig
4,1).
To mute the loudspeakers, press the Mute
button (Fig 4,2). To un-mute the loudspeakers
press the Mute button again.
Stored volumes
The dm8 memorizes the volume levels.
A volume setting for each programmed input
source is memorized on either power off or on
selection of a different input. On re-selection
of the input or on power up, the previously
memorized volume is returned.
This accommodates differing source outputs.
For example, a modern CD player may have
an output up to a few volts, whereas an older
type of analog tape recorder may only output
a few hundred millivolts. This feature will
return the volume setting to the previous
value.
After power up and switching from Standby to
On the preamplifier will enter the mode it was
last in when the power was turned off.
NOTE: If the mode is such that the
preamplifier output is directed to the amplifiers
outputs, the power amplifier set of volumes
are used and displayed.
Mute
When the Mute button is pressed, the output
to the power amplifier is disabled, the db
symbol on the display is replaced by a symbol
that looks like a speaker with a line through it
and the headphone volumes are used and
displayed.
If the Mute button is pressed again the
preamplifier output to the power amplifiers is
enabled, the power amplifier volumes are
used, displayed and the db symbol returns.