Certainly, one could not have anticipated the impact HM1 has made on the high-end headphone amplifier market. Originally designed as a precision tool equipped with a range of front-panel controls, Zähl was initially conceptualised as an essential instrument for professionals whose livelihoods relied on precise auditory perception.
Featuring controls like A/B input source comparison, crossfeed, mixing sources, EQ, and the option to incorporate optional negative feedback, HM1 adapts to diverse preferences and transducers.
All adjustments are executed in the analog domain, utilising premium components that seamlessly integrate into the signal path. However, a toggle is provided to bypass these components, allowing your music to flow directly to your headphones as a veritable straight-wire-with-gain.
Even when toggled, negative loop feedback enhances measured performance without detrimentally impacting audio quality. At HM1's simplest, most basic circuit level, Zähl takes a unique approach by not attempting to "fix" your headphones but rather syerngise seamlessly with them, flattering their best traits.
Operating in Class A with high operating voltage and bias, the entire circuit of HM1 functions stably, free from feedback. HM1 relies on a full Class A bias and elevated operating voltages to ensure its transistors operate in the most linear regions. This fundamental characteristic starts with HM1 drawing power from its lifeblood – a linear power supply connected to the main enclosure through an umbilical cord.
With the toroidal transformer already dissipating 40 watts of power even without signal playback, Zähl's oversized power supply is capable of meeting HM1's demands at a moment's notice during transient peaks or intense musical passages to fulfil its role as the lifeblood of the system.
It's quite the feat running in the open loop doesn't stop HM1 from producing enormous frequency extension. Touching 500Khz at -3dB is certainly no mean feat without the aid of negative feedback. Its DC-coupled signal path without coupling capacitors reaches 1Hz – truly subterranean levels, for an amplifier of any sort.
Indeed, this champion of frequency response achieves a flat 10Hz to 30Khz, paying off in perfect phase reproduction in the human hearing range for life-like dynamics, fast impactful bass, realistic portrayal of musical images and tremendous air.
HM1 excels in stereo separation, leveraging a fully dual-mono configuration with distinct power supply transformer windings, rectification, and regulation for each channel. This meticulous design extends to HM1's signal path, ensuring no interaction between channels and delivering exceptional crosstalk performance.
Driving the audio microscopes that are today's flagship headphones, Zähl's audio reproduction stands out for its remarkable transparency and naturalness. The signal's transparency, preserved by HM1, is fed to the finest Head-Fi equipment through large output devices with exemplary current-handling, taking advantage of its robust power supply.
Zähl built a brute that functions as a near-perfect voltage source, given the way it almost doubles power output into halving impedances of 30ohms to 15ohm. Dan Clark Audio, HIFIMAN's Susvara and Abyss Headphones all bow before HM1. This isn't a question of using inordinate closed-loop gain to inflate specs, but rather, genuine, raw driving power.
The realism of Zähl's performance through Rosson Audio Designs, Final Audio's D8000 Pro, HEDD Audio's HEDDPhone 2 and the ZMF Headphones Caldera is also haunting – especially when played back with Matrix Audio's Element X2 Pure as a source.
Because HM1 isn't merely a product, but a moment in time – the cumulation of analog technology's feats, brought perfectly into a timeless package that will be the final solid-state headphone amplifier you will ever need. Get in touch to own a piece of audio heritage designed by Michael Zähl now.
Amp Discrete Class A
Output power 7.5 watts @ 30ohms
Frequency response (-3dB) 1Hz to 500Khz