Zähl HM1

Michael Zähl has long been one of the top names in the studio world when it comes to high-quality analog electronics. Now, he has turned his attention to building a headphone amplifier as a new hobby, and placed this device right at the top of the list of absolute reference units with unmatched transparency: the HM1.

Thanks to manually selected components and a maximally shielded design, it not only delivers top-tier sound quality – but also includes a few tricks from studio technology that are absolutely unique in the hi-fi world:

4 inputs, 2 of them usable simultaneously

Here you can see the 2 input blocks, which accept signals either via RCA or XLR – since connecting sources is a relatively rare task, you'll also find a selector switch on the rear panel to choose which input is active and whether to optionally apply 15dB of gain. But on the front panel...

You'll see something found nowhere else: the inputs can be individually activated and smoothly blended together.

Tasteful EQ

2 knobs, one for bass and one for treble, to subtly tailor the music to your personal taste – if they are not in use, the signal completely bypasses this circuit and remains entirely unaffected.

The third knob, however, is the absolute highlight:

Adjust stereo width without altering the frequency domain – no crossfeed!

Perhaps you've tried crossfeed before and realized it's not for you. That’s often because the signal is processed as left and right, with parts of the left also played on the right and vice versa. This results in unpleasant frequency overlaps, and it's usually the bass that gets weakened – unfortunately along with the soundstage, since nothing remains where it was originally intended.

This stereo width circuit works differently: Imagine the signal split into "mid" and "side" – the mid is everything played equally on both channels, which our brain perceives as coming from the center.

The side is everything that is louder on one channel, perceived as coming from that side – turning the knob to the left reduces the sides and makes the center more present.

Turning the knob to the right increases the sides, creating a wider soundstage – even when you understand how it works and adjust it yourself, the effect still tricks you into perceiving a larger stage – completely without affecting the frequency response.

Aside from that, the HM1 offers two sound modes: a pure Class A amplifier circuit and a Class A with feedback – a complete package unlike anything else out there.

Availability

All this technology comes at a price – not just financially, but also in terms of the time investment by Michael Zähl himself. As he hand-builds every unit, only 50 are made per year worldwide – so if you're interested, please inquire and I’ll get back to you.