The Zähl HM1 is high-quality fully analogue, Class A reference headphones mixing amplifier designed with no compromise to offer an unprecedented level of transparency and detail that will thrill the most discerning professionals and audiophiles alike.

The Zähl HM1 als includes two different stereo source input with a cross-fade, Precise two band EQ and a stereo base control. Its design is meant to offer the most true-to-life reproduction possible.

Two Different Power Stage

The Zähl HM1 features two operation modes Class A and Class A + Servo. The first mode delivers the purest sound with no crossover distortion and no artifacts causing negative feedback. The second mode uses the same Class A circuit but adds negative feedback to correct errors that occur between the power amplifier and headphones. While both modes offer technically superior performance, each mode will appeal to different users.

Mixing Features

The 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 processing

The 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.

Dual Mono Design

The 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.