Zahl HM1 User manual

ZÄHL HM1
Manual V 1.0

HM1 Reference headphones mixing amplier
Reference Amplier with unprecedented transparency and precision,
attention to detail and massive power performance.
Rich feature set for both high-end enthusiasts and professional users.
• perfect impulse reproduction
• ultra wide frequency response
• extremly low impedance output precisely controls complex loads
• pure analogue design
• consistent dual-mono layout
• logic circuits without clock generators
• straight linear power supply with power transformer in external housing
• no-compromise selection of components
• no-compromise interior and exterior construction
Designed and manufactured in Germany.

CONTENTS | P.3
CONTENTS
NOTES, SAFETY INSTRUCTIONS, WARRANTY ....................................................................... 04
SCOPE OF DELIVERY ............................................................................................... 05
SET UP ............................................................................................................. 05
LEGEND ............................................................................................................06
APPLICATION EXAMPLES...........................................................................................08
SPECIAL FEATURES ................................................................................................09
DETAILS.............................................................................................................10
Power Stage.........................................................................................................10
Class A - HM1 realisation......................................................................................... 10
Class A & Servo - HM1 realisation .................................................................................10
Why Class A and Class A & Servo? ...............................................................................10
A little theory.......................................................................................................11
Class A............................................................................................................11
Class AB with negative feedback ..................................................................................11
Mixing Stage..........................................................................................................11
A/B comparison ..................................................................................................11
A/B switching logic ...............................................................................................11
Cross-fade.......................................................................................................12
Mixing two sources...............................................................................................12
Note .............................................................................................................12
Sound Adjustment ..................................................................................................12
Low and high frequency adjustment .............................................................................12
Stereo Base control, a little theory...................................................................................13
Stereo Base control, what it does .................................................................................13
Balance .............................................................................................................13
Headphones Outputs / Balanced Connection........................................................................13
Dual Mono vs. Balanced amplier design .........................................................................14
Line Outputs ........................................................................................................14
Connect active speakers, power amps or other gear ..............................................................14
„A Thru“ Output ..................................................................................................14
Setup your own test bench / experimental bench ................................................................14
Output Select .......................................................................................................14
Line Inputs ..........................................................................................................15
Dual Mono Design ...................................................................................................15
The idea .........................................................................................................15
Realisation inside the HM1 ........................................................................................15
Optimal output connection .......................................................................................15
Power Supply .......................................................................................................16
Worldwide operation .............................................................................................16
Variable cable length .............................................................................................16
TECHNICAL DATA....................................................................................................17
TROUBLESHOOTING .................................................................................................18
CONTACT............................................................................................................18

ZÄHL HM1 MANUAL V 1.0
P.4|NOTES, SAFETY INSTRUCTIONS, WARRANTY
NOTES, SAFETY INSTRUCTIONS, WARRANTY
1. The equipment must only be used for the purpose described in this manual.
2. Keep the manual for further reference. When passing the equipment on, enclose the manual.
3. Do not operate the equipment at
- very high air humidity (>85% relative humidity)
- high ambient temperature (>40°C) or in the vicinity of heat radiating equipment or objects
- places which are exposed to solar radiation
- very low temperatures (<5°C)
4. Ensure appropriate air ventilation.
5. Do not store the equipment at temperatures below -20°C or above +50°C.
6. Do never expose the equipment to environmental conditions which can lead to the incidence of
condensation water.
7. Do not expose the equipment to mechanical stress or shock.
8. Ensure that liquids cannot get into the equipment.
9. Ensure that foreign objects cannot get into the equipment.
10. Only operate the equipment on a safe, legally approved, mains power supply
11. Only clean the equipment with smooth cleaning tissues and soft detergents.
12. Never open the equipment.
13. In case the equipment has been dropped or there is any external or functional damage, do not
continue to operate the equipment. Have the equipment checked at your dealer’s workshop or a
person who is qualied to do such checks.
14. When shipping, use a package which protects the equipment from environmental impact such as
mechanical shock or humidity.
15. Manufacturer’s warranty covers the equipment to be free from defects of quality at the time of
delivery for a period of 36 month presumed that
- the equipment was treated properly according to its intended use
- all information and safety instructions given in this manual have been followed
- the equipment shows no external damage
- the equipment is shipped to the manufacturer or to an authorised repair-shop free of charge
- a proof of purchase is supplied
- a detailed failure description is supplied
The manufacturer takes over cost of parts and labour incurred by repair. Unless otherwise
agreed any other costs including shipping and packaging will be charged.
16. We expressly exclude any liability for incidental or consequential damages which might arise from
operating the equipment, including failure of the equipment.
17. All information in this manual has been carefully reviewed. It has been updated at the time of pas-
sing for press. Nevertheless we do not take over any liability for sufciency or errors.
18. EEC Declaration of Conformity: The equipment applies to applicable EMC rules 2014/30/EU

SCOPE OF DELIVERY & SET-UP |P.5
SCOPE OF DELIVERY
• HM1 Main Unit
• HMP1 Mains Adapter
• HMP1 Connection Cable
• Mains Cable
• Spare Fuses
• Manual
SET-UP
• First read the chapter NOTES, SAFETY INSTRUCTIONS; WARRANTY in this manual.
• Remove the HM1 from its packaging: insert your hands into the foam recesses on the front and back of the unit, reach
your ngers slightly under the unit and then lift it upwards. Do not lift the unit by the knobs or the connectors.
• Remove the HMP1 from the packaging: insert your hands into the foam recesses on the sides of the unit, reach your
ngers slightly under the unit and then lift it out upwards. Do not lift the unit by the connectors.
• Remove the HMP1 connection cable from the packaging. It is equipped with 12-pin connectors on the ends.
• Plug the end with the female connector into the socket on the rear panel or the HM1.
Make sure that the locating peg shows upwards.
• Turn the strain relief nut clockwise. Push the connector slightly after a few turns.
The connector is seated correctly when the rubber seal on the socket is no longer visible.
• Plug the end with the male connector into the socket on the rear panel or the HMP1 Mains Adapter.
Make sure that the locating peg shows upwards.
• Turn the strain relief nut clockwise. Push the connector slightly after a few turns.
The connector is seated correctly when the rubber seal on the socket is no longer visible.
• Check whether the mains voltage setting on the HMP1 Mains Adapter front panel complies to your local mains voltage. If
not, set the voltage selector to the correct voltage. Use a coin or something similar to operate the mains voltage selector.
• Make sure that the mains switch on the rear panel of the HMP1 is in the off position.
• Insert the mains cable.
• Turn the mains switch to the on position.
• On your HM1 unit, press the power on/off button, the power button will illuminate.
• After several seconds the operating indicator (logo sign) right to the power button with illuminate.
Now your HM1 is ready for operation.
Note: The surface of front and rear panel is black anodized with a special matt nish, the lettering is lasered.
All this makes it very durable. Fingernails or other abrasive objects can leave marks on the matt surface.
These can be wiped off very easily with microbre cloth or similar lint-free cloth.
IMPORTANT! Always follow this order when connecting, otherwise damage may occur!
1. Install HMP1 connection cable
2. Install mains cable
3. Switch on, any order: power switch on HMP1 rear panel and power button on HM1 front panel.

ZÄHL HM1 MANUAL V 1.0
P.6|LEGEND
LEGEND

LEGEND | P.7

ZÄHL HM1 MANUAL V 1.0
P.8|APPLICATION EXAMPLES
APPLICATION EXAMPLES
Conventional
Preamplier in minimalist system
Precision comparison
2-Channel Mixing Console
Effect/Test
Example for a conventional setup as headphones amplier:
Your reference DAC at Input A and an analogue source at Input B
Headphones connected to amplier output, speaker amps or active speakers
to the Line Output. Toggle between headphones and speakers. Example of a
minimalist setup: Streamer to HM1 Input A, analogue source to Input B, active
speakers to Line Out.
Two sources connected to Inputs A and B, precision level meter connected to Line
Output. Source levels can be exactly matched using the level meter and the volume
controls. Activate the sources alternately by the Chan on/off switches.
As a mixer, the HM1 can merge any two sources at Inputs A and B to create
a new music programme - or simply cross-fade from one source to the other.
A device is fed from output „A Thru“ and its output is applied to Input B.
The ratio between the original and the „looped-in“ signal is set at the
A/B volume controls. Or switch between the two.

SPECIAL FEATURES | P.9
SPECIAL FEATURES
UNIQUE: CLASS A POWER
AND A STEP BEYOND
CROSS-FADE, COMPARE
OR MIX TWO STEREO SOURCES
SOUND ADJUSTMENT
AND STEREO BASE CONTROL
• Class A power amplier in its purest form
• switchable negative feedback („servo“) while
maintaining Class A operation
Precise, nely tuned tools for sound adjustment.
Stereo base control for adjusting the stereo
image (spatiality).
• Cross-fade or switch between two stereo sources
(channel A /channel B)
• perform a precise, critical A/B comparison with
independent volume compensation
• create a mix from two audio sources

ZÄHL HM1 MANUAL V 1.0
P.10 |DETAILS
Power Stage
Class A - HM1 realisation
The HM1 power stage provides massive power reserves, which is already evident from the fact that it consumes
almost 40W in idle mode. The output power is more than sufcient for any application, and in the millisecond
range it is increased substantially. The output resistance is remarkably low. The optimum operating point of the
power stage was rst specied by theory, then by measurements on the sample units and nally ne-tuned during
numerous listening tests with experts, especially mastering engineers. The same applies to the selection of
components. This meticulous way of design largely compensates for the possible disadvantages of Class A
described in the theory paragraph below.
Class A & Servo - HM1 realisation
To take Class A one step further, we implement an idea which is as simple as it is ingenious: We take the best of Class A
and the best of negative feedback ampliers and put it together: Class A operation is supplemented by negative feedback
("Servo"). Since there is no crossover distortion, there is nothing for the feedback circuitry to correct. Rather, it only corrects
the errors which result from the interaction between the power amplier and the headphones. The feedback path is
designed in such a way that no artefacts are created by the correction. The output resistance drops to a value which is
smaller than the sum of headphones cables and connectors. In this way, headphone systems can be controlled precisely.
One can say that with the HM1, any headphones sound as they should.
Why Class A and Class A & Servo?
The previous paragraph may lead to the conclusion that the optimum is achieved with Class A & Servo operation So why do
we still have the switching option? Quite simply because we judge our circuits by ear. Our Class A amplier was developed
with the highest musical demands in mind. We experienced that is does not sound the same as the servo version, but it
sounds equally outstanding. Depending on headphones, music and personal preference, the user can make his choice.
Even we were surprised to nd that despite clearly different characteristics and measurement results, the hearing
difference is rather subtle.
DETAILS