(Open Box) ZÄHL - HM1, Reference Headphone Mixing Amplifier

REFERENCE HEADPHONES MIXING AMPLIFIER Zahl’s HM1 is an audiophile-grade, fully analogue, Class A reference headphones mixing amplifier designed with zero compromise to deliver a wholly unprecedented degree of transparency and detail which delight even the most discerning professional.

Zahl’s HM1 also boasts two differing stereo source inputs too, which includes a cross-fade, accurate two-band EQ, alongside a stereo base control. This design results in the most true-to-life reproduction imaginable.

Two Different Power Stages The HM1 features two main modes of operation, Class A and Class A + Servo. The first offers the purest and most organic sound with zero crossover distortion and no artifacts resulting in negative and unwanted feedback.

The HM1’s alternate and second mode utilises the same Class A circuitry, but also adds negative feedback as to correct errors which arise between the power amp and headphones. Whilst both modes certainly offer technically greater performance, each mode will hold different appeal to different users.

at a glance • Pure analogue design
• Consistent dual-mono layout
• Logic circuits without clock generators
• Straight linear power supply with power transformer in external housing
• No-compromise interior and exterior construction
• No-compromise selection of components
• Perfect impulse reproduction

twin input sourcesThe HM1 includes two input sources which can be used for critical A/B comparison of different DA converters, cartridges or comparing different mixes or effects. Each input has a dedicated volume control for precise level matching. Each input can be hard switched or gently cross-faded.

The two sources can also be used to be mixed together. The new mix is fed to the headphones as well as the line outputs which can be used to connect to a recording system or active speakers.

Sound processingThe HM1 includes a subtle two band EQ with fixed frequencies and gentle boost or cut. Unlike traditional tone controls found on amplifiers, it uses proven circuits used in studios to make subtle tonal accent changes rather than affecting the sound character.

The HM1 also includes a Stereo Base control akin to the circuit used in their IM1 module or AM1 console which lets you widen the stereo field without losing information in the Mid channels. This processor is useful to check the spatiality of a mix ranging from mono (fully left) to really wide. The Stereo base stage can be completely switched out of the signal to maintain the signal as pure as possible.

A Balance control also lets you compensate for any balance discrepancy whether in the mix, the headphones or the user’s hearing. The 21-position detent allows compensating for volumes up to 2.5dB on either side.

individual power supply for both power-amp and pre-ampThe HM1 uses a dual mono design strictly separating left and right channels, avoiding any interference between channels. Each channel has its own power supply for both the preamplifier and power amplifier stage. Furthermore, the Mains transformer includes independent and completely potential-separated windings for each channel while filtering, voltage regulation and rectification are individual to each channel.

The headphone amplifier includes a 6.5mm Jack output and an XLR 4-pin connector. Using the latter ensures the perfect maintenance of the dual mono principle with no interference occurring at any point.

The Power supply uses a purely linear design and includes a wide range input. Using one of the best interference filters available, the mains input can be set to operate at the following voltages: 100V, 110V, 120V, 220V, 230V, 240V.