H1 Reference headphones amplifier.

Reference Amplifier with unprecedented transparency and precision, attention to detail and massive power performance. For both high-end enthusiasts and professional users. Designed and manufactured in Germany.

H1 Reference headphones amplifier

"This is the best possible example of a reference sound. This is the amp that out of everything I have tried is genuinely the most deserving of the description 'transparent'."

Cameron Oatley

Special Features

Unique: Class A power and a step beyond

  • Class A power amplifier in its purest form
  • switchable negative feedback [„servo“] while maintaining Class A operation
Class A power
H1 stereo bass control

Stereo Base Control

Stereo base control for adjusting the sound stage to your preferences. Precision tool for widening or narrowing the stereo image or switching to mono.

Three output connectors

XLR 4-pole - ¼” Jack - Pentaconn

Three output connectors

"The H1 will drive any headphone to its optimal performance. Offering the same core technology as its sister product, the HM1."


H1 overview
  • perfect impulse reproduction
  • ultra wide frequency response
  • extremly low impedance output precisely controls complex loads

Designed and manufactured in Germany.

  • pure analogue design
  • consistent dual-mono layout
  • logic circuits without clock generators
  • integrated toroidal mains transformer with specially designed mumetal housing
  • straight linear power supply
  • no external power adapter needed
  • no-compromise selection of components
  • no-compromise interior and exterior construction
H1 front - details and legend
H1 rear - details and legend
Cameron Oatley Golden Sound

Review

By Cameron Oatley

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Golden Sound Logo

This is the best possible example of a reference sound. This is the amp that out of everything I have tried is genuinely the most deserving of the description 'transparent'.

Watch Camerons review on Youtube
Golden Sound Channel / The Headphone Show

Details H1

Power Stage

Class A - H1 realisation

The H1 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 sufficient 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 first specified by theory, then by measurements on the sample units and finally fine-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 - H1 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 amplifiers 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 amplifier 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 H1, 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 amplifier 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 find that despite clearly different characteristics and measurement results, the hearing difference is rather subtle.

A little theory

Class A

Advantages: no crossover distortion at the output transistors and no artefacts caused by negative feedback.
Disadvantages: The internal resistance of the output transistors and usually also the emitter or collector resistors are in series with the load. Simplified, one can say that the material properties of the output stage components substantially determine the sound. And since both the resulting internal resistance of the output stage and the resistance of the load, i.e. the headphones, are complex items, the result is also complex: it is quite common that certain combinations of even very high-quality amplifiers and headphones do not produce optimal results. Experienced audiophiles know this experience.

Class AB with negative feedback

Advantage: Any error at the output caused by the effects described above is "corrected" by a negative feedback circuit. And furthermore, the output resistance of the power amplifier, as long as there is no overload condition, theoretically approaches zero; practically it is in the 2-digit milli-ohm range. The complex internal resistance of a headphone system is almost equalised by the low impedance output. A headphone system is therefore tightly “guided” by the power amplifier.

Disadvantage: The crossover distortion occurs first, then it is corrected. Thus, negative feedback control (at least theoretically) always runs a little behind the action, which can lead to artefacts in the signal. However, modern negative feedback audio power amplifiers are usually not purely Class AB. Very effective techniques are used to keep crossover distortion low without having to use the costly and power-intensive Class A technique. Certain techniques are used in the negative feedback signal, so that the "lagging" of the correction almost no longer plays a role.

Stereo Base Control

Stereo Base control, a little theory

A special feature is the possibility to adjust the stereo width. The perception of spatiality when listening with headphones differs from listening with loudspeakers. Instead of a cross-feed circuit, we use our stereo base width setting. It is based on the mid/side technique which is commonly used in professional studios. It provides additional benefits.

The stereo signal is converted into a mid signal (in simple terms, what L and R have in common) and a side signal (in simple terms, what distinguishes L and R). Summing mid and side signals in a 1:1 ratio will result in the original stereo signal. However, if you change the ratio between mid and side before summing them, you change the stereo base width. In our circuit, we leave the mid signal as it is. We only adjust the level of the side signal. If we lower the level, the stereo image becomes narrower, if we raise the level, the stereo image becomes wider.

Stereo Base control, what it does

You have direct access to the perception of spatiality. With a music programme which seems too "wide" in the headphones, one will turn the control one or two steps to the left. If you perceive a recording as too "dry" (centred), turn the control one or two steps to the right. The leftmost position is mono. This is the preferred setting for early stereo recordings, when individual instruments have been mixed to the extreme left or right - without spatial reference.

Professional users check the spatiality of their mix with this function and may discover possible problems, especially in the extreme positions.

Also important: With the DIR (Direct) button, this stage can be completely switched out of the signal path. In this way, the purist approach is taken into account.

Balance

A precision potentiometer with 21 detents is available for balance control. The centre position is perfectly calibrated and haptically clearly defined. In fine increments, left/right volume differences of up to about 2.5 dB - caused by music programme, headphones or individual perception - can be compensated.

Headphones Outputs / Balanced Connection

XLR 4-pin, Pentaconn and ¼ inch jack connectors are wired in parallel and are intended for alternative use. Theoretically, you could use them at the same time, the power amplifier is strong enough. However, for a reference quality listening experience, we do not recommend such use.

Ideally, XLR 4-pin and Pentaconn are used in conjunction with balanced wired headphones. In this case, the signal currents of the two power amplifiers are not mixed with each other, mutual interference is impossible. The H1 can unfold its full quality (also refer to chapter "Dual Mono Design").

Dual Mono vs. Balanced amplifier design

With its dual mono design, the H1 features the same advantages as a balanced output stage but avoids the drawbacks.

The drawbacks of a balanced output stage are the significantly increased number of electronic components - a balanced output contains two output stages per channel which work in reverse phase. Two output stages result in doubling the output impedance. More components result in an increased risk of non-linearities.

¼ inch jack compatible

Another advantage of the H1 architecture is that unbalanced headphones with ¼ inch jack plugs can also be operated without any problems.

Line Inputs

INPUT Bal/Unbal

Input can be switched between balanced and unbalanced mode.
• XLR connectors for balanced
• Cinch connectors for unbalanced

Balanced mode behaves transformer-like: hot or cold may be connected to ground without any loss. XLR and Cinch must not be connected at the same time

INPUT Gain

Basic amplification rate input to output: 6dB
3-position gain switch (-10/0/+10) to reduce or increase input gain by +/-10dB allows adjustment to sources with different output levels.
It is also useful for adapting to headphones of varying sensitivity.

Dual Mono Design

The idea

The idea behind strictly separating left and right channels is to keep any interference away from the circuits. A term like “crosstalk” does not get to the core of the matter. Music signals usually have left/right references, so that an extremely low crosstalk value - moreover, usually measured with sine waves - does not mean so much. But with music highly energetic signal pulses occur, and then high currents are individually demanded by the output stages. It is extremely important that in these cases there is no coupling via a common power supply or via ground lines carrying signal current. Only this way an amplifier can produce absolutely undistorted output signals.

Realisation inside the H1

In the H1, the power supplies for left and right channels are separate, for preamplifiers and power amplifiers. The mains transformer has independent, completely potential-separated windings for each channel. Rectification, filtering and voltage regulation for each channel are individual. For logic circuitry and front-panel indicators, there is another winding and separate rectification, filtering and voltage regulation.

The ground potentials of the two channels are connected to each other at one point only, but this is done purely as potential equalisation; it is impossible for signal currents to be mixed.

Optimal output connection

If the XLR 4-pin or the Pentaconn output is used in combination with balanced wired headphones, the dual mono principle is implemented in full consequence.

When using the jack output, the ground wires of both channels are connected in the jack socket and the jack plug of the headphones. The use of headphones with jack plugs therefore is not that ideal. In the H1, however, an optimised ground routing ensures that the disadvantageous effects are as low as possible.

(also refer to chapter: Headphones Outputs / Balanced Connection)

Power Supply

will be updated soon...

Technical Data

Inputs

Line Inputs balanced – Impedance 20KΩ – max. level +23dBu
Line Inputs unbalanced – Impedance 20KΩ – max. level +23dBu

Headphones Output

Impedance Class A 0,8Ω, Class A & Servo 0,045Ω
max. level +23,5dBu (+/-16,5V)

Output Power per Side

RMS 4W/30Ω; 7W/15Ω
Peak 7,6W/30Ω; 11W/15Ω; 12W/10Ω (18W for 1,5ms)

Frequency Response

10Hz ... 30kHz -/+0,05dB
1Hz ... 500kHz better than -3dB at Headphones Output @ +6dBu

Gain

will be updated soon...

Noise

same or better than HM1
will be updated soon...

Headphones Output THD (Total Harmonic Distortion)

same or better than HM1
will be updated soon...

Power Supply

will be updated soon...

Measures and Weights

will be updated soon...

Story

Why H1?

Headphones in the professional field

Today, top-quality products allow applications in the professional field which were inconceivable before. While in the past headphones were mainly used during recording, today they are also used by sound engineers for reference monitoring during the final mix. It is essential that the reproduction is pure and does not mask or brighten up anything.

Headphones in the high-end range

Demanding high-end enthusiasts - in general - primarily have in mind to enjoy the music. So why shouldn‘t their headphones or amplifiers shape the sound a little more pleasingly than the recording actually is? Unfortunately, such „sweetening“ cannot be relied upon. What is advantageous for one recording can be disadvantageous for the next, which can also apply to instruments within a recording. If a recording is really good, true-to-life reproduction is always the best option.

That’s why H1

At this point, professional users and high-end enthusiasts come to a common conclusion. The power amplifier of the H1 is extremely powerful and incorruptible in terms of sound.

The H1 offers all the core features of its sister product, the HM1: the power supply design, the power amp stage with its unique option to switch between amp architectures and its stereo base control circuitry. Its sound characteristic and reproduction quality are identical.

So for users, who do not need the HM1’s mixing or A/B comparison function, who do not need the high & low frequency equalizer and who do not need the pre-amplifier functionality, the H1 is a perfect choice.

By dispensing with the equalizer and mixing stage, both being highly sensitive to magnetic and electric interference, the mains transformer (after packing in an elaborately designed mumetal housing) could be integrated. This benefits handling.

Michael Zähl and Mark Ernestus

About Zähl - The man and the company behind H1

Zähl Elektronik-Tontechnik has been a manufacturer of analogue studio technology for more than 35 years. The current range of products stands for top technology. Present flagship is the AM1 analogue mixing console, which has no equal anywhere in the world. Its users include numerous internationally renowned music makers and producers.

History

Michael Zaehl started his professional career in 1978 as a sound engineer's assistant in Conny Plank's studio, where legendary recordings were made (e.g. by Kraftwerk, Brian Eno, DAF, Ultravox, Gianna Nannini, Eurythmics and many more). Michael Zaehl gained experience working in the studio, but then turned to technology. During his time in Conny's studio, he created his first custom-made mixing desks, e.g. for Conny’s recording truck and for CAN studio. Michael Zaehl went into business for himself in 1982. In 1985, he custom-built the large 56-channel mixing console, which remained in service at Conny's Studio until the end. Zaehl’s focus always remained on analogue technology, mostly custom-made or small series. Over the years, numerous mixing consoles and other products for music production studios or mastering studios, for public and private broadcasting stations and many more were created. Later, the portfolio also included a product line for pure broadcast applications.

Work Setup

Zähl is a relatively small size, personally run company. Circuit development is Michael Zaehl’s domain, as well as bringing product to series production, whereby the ideas and experience of committed and qualified employees flow in. Production steps where the use of large production machinery make sense, such as SMT PCB assembly, front panel and mechanical manufacturing, are carried out by selected external partners. In-house, all individual parts are tested, sensitive components are added, the internal wiring is prepared and finally all components are carefully assembled into the final product. Before delivery, each product undergoes an elaborate 100% single-unit inspection. This method of working combines the advantages of modern, effective production techniques and careful, qualified manual work.

Concept - Design

Due to the numerous custom-made products, it has always been a matter of course for Michael Zaehl to develop products very close to the respective application. For about 12 years now, this claim has become even more solidified. The Berlin musician and music producer Mark Ernestus supports the conceptual development work. He brings in his experience and contributes a bundle of creative ideas.

Analogue vs. digital?

Zähl was founded when digital audio technology was still in its infancy. High-grade studio technology was analogue. As the quality increased, digital technology took over a large part of the applications and many believed that analogue technology would be displaced. Today, it is clear that analogue and digital technology can coexist perfectly, as both have their advantages in terms of sound and functionality. In creative recording studios, they stand side by side, with high-quality analogue technology steadily gaining relevance. In the high-end sector, analogue technology has always maintained its place. However, here too the demands are increasing - to the advantage of the Zaehl brand.

Analogue is not vintage

Zaehl products are purely analogue, but not "vintage". Michael Zaehl stands for the conviction that with today’s means better products can be developed than was the case in the past. Moreover, the applications have changed extremely. A wealth of experience is an excellent basis, but only when openness to new things and an alert eye on the users are added, can really useful products be created.

How to Order your H1

The H1 is manufactured in Germany

Recommended retail price excluding VAT and country-specific import duties: 6,500 €. Final prices may vary depending on the dealer, dealer location, and import conditions.

Our Dealer for Germany, Austria, Switzerland:

audioNEXT GmbH
D-45130 Essen
Germany

Phone   +49(0) 201 - 79939404
Mail   info@audiodomain.de
www.audiodomain.de

Contact for all other countries or other enquieries

To buy the H1 in countries not mentioned above or to ask a question feel free to use our contact form.

Zaehl Elektronik-Tontechnik
Am Stadion 18-24
D-51465 Bergisch Gladbach

Phone   +49(0) 2202 - 863901
Mail   highend@zaehl.com

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