Zähl HM1 - Reference Headphone Amplifier - Official Thread

Personally, for me the HM1 is the best SS amp I’ve heard. The features are a (very big) cherry ontop, but even without them the sound is truly spectacular.

The amp that comes closest to it for me (and does indeed get really close) is the Holo Bliss. Which is just over $3000

Bliss is 12W, full discrete class A, and shares a lot in common with the HM1 in terms of how well it powers stuff like Susvara, the holography etc, and also backs it up with top tier objective performance.

But also for IEMs is as quiet as something like a Topping L70 (93dB SNR @ 50mV).

The main issue is that it’s pretty big, and won’t fit on the desk for many people. Especially as given the heat it outputs (It pulls and dissipates about 50 watts), you can’t really stack stuff with it.

Bonus for being one of the most gorgeous amps internally though…


There isn’t one, that I’m aware of.

The HM1 is the best, and most enjoyable, solid-state amplifier I’ve heard.

Benchmark’s HPA4 might beat it on measured performance, but I’ve never particularly enjoyed listening to music through it. While it is highly resolving, entirely neutral, and has good power output, I just find it dry, sterile, and it gets fatiguing very quickly.

Not that there aren’t other solid-state amp I’ve enjoyed … and maybe even didn’t think could be improved upon at the time … but the HM1 shows all of those a clean pair of heels.


Thank you both, what about tube amplifiers?

Well, on purely technical grounds … again … none.

In terms of simple listening enjoyment, however, tubes remain my preference. But, at least for me, you’re playing in a realm where the amps are the same price, or more, and then you have to add tubes on top of that - which can be a substantial fraction of the cost of the amp itself*.

WA234MKII Mono (my preference, and what I use/own), DNA Stellaris, Bottlehead Neothoriator**, Viva Egoista 845, WA23, EC Studio, WA33 (maybe), DNA Stratus, DecWare Taboo MK IV … pretty much in that order.

I say “maybe” on the WA33 (and to a certain extent on the EC Studio), due to the balanced configurations eliminating a good chunk of what tube amps are, for me, about. Makes the more accurate, but I like the sound less … though they’re both excellent regardless.

But, still, the comparison is really apples and oranges, unless we’re purely considering subjective listening enjoyment.

*I have a couple of sets of pre-war NOS WE300Bs that cost more, per pair, than my WA234MKII Mono.
**Essentially unobtanium - only two exist, and only one was for sale; don’t know if it still is.


Roon → Linn Klimax DSM (Organik) → HM1 (Class A) → ZMF Atrium, playing David Fesliyan’s “Drum Warfare” …

No words.


Even substituting an RME ADI-2 Pro FS R BE for the Linn … still … just … damn …

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The EC studio isn’t balanced, it’s SE, runs the output tubes in parallel, not push pull. Hence the input transformers on balanced input.
Though it is very much on the dryer side of tubes, more so the Tribute than the Monolith.

I’m a big WA33 fan, but mid range richness isn’t my thing and it’s not for everyone.

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I think the WA33 is an excellent amplifier (oddly more so the standard version, than the elite, though it’s been a while …). It just wasn’t what I wanted from a tube amplifier. It’s probably the most technically accurate amp Woo makes.

On the EC Studio … I think it’s been about 4.5 years since I spent any real time with one, so god knows what I’m remembering at this point … :wink:


Torq and GoldenSound thanks so much for the work which probably feels more like play. My HM1 came Monday morning and because of my usual end of the year crunches out of Asia markets I still haven’t even plugged in my Susvara or AB 1266. Just reading your findings while staring at it is maddening but I anticipate great joy for Christmas. Thanks again for all the hard work.


@GoldenSound. How hot is the HM1 main unit and the power supply as well, in comparison to the Bliss you mentioned?

In terms of how much heat they’re actually dissipating into the room they’re quite similar.

Bliss is about 50W, HM1 is about 40W.

The tops of each unit are about 37C here right now, though the room is a little cold.
Measuring the hottest parts of each though (inbetween fins of HM1 and on the bottom of Bliss), Bliss is 46C and HM1 is 39C


Sounds like a good excuse to break out the absurdly long XLR cable for D8000 Pro LE. :smile:

GSX Mini is a very nice amp, but I find it tends to slightly color the chain with a bit of extra warmth. Going back to it now, I hear maybe a slight veil in the treble. To be fair, these are nitpicks by any reasonable measure. If I weren’t critically listening I’m sure I’d acclimate and those attributes wouldn’t stand out to me; I’d be lost in the music.

The Mini has been mostly retired since I got Ferrum Hypsos + Oor, which delivers a cleaner / more neutral sound with authority. Oor still lives on my desk as a daily driver. It’s the first amp I own that I feel can drive anything (from IEMs to Susvara) without compromise.

Sound wise, HM1 has more in common with Oor than the Mini. Both deliver clean, neutral sound with great detail and dynamics. The surprising thing is how much better HM1 does that. Until I heard it, I never would have guessed that Oor “left so much room for improvement.”

That said, it’s hard to convey the magnitude of these differences, which are simultaneously minute and game-changing. Objectively, the sound is very close. Subjectively, HM1 is crossing an uncanny valley of realism that is immediately apparent.

It comes across in little details, like how clearly multiple reflected decays fade even while the rest of the music marches on. Or how dynamics range from the edge of audible to authoritative punch. Low level sounds simply fade into and out of existence with perfect clarity. Louder sounds have intensity without ever coming across as forced. These characteristics are undeniably closer to live listening, but at a macro level all of these amps deliver every feature of the music with superb clarity, excellent detail and separation, etc.


OK. Thanks for that info.

So they double as nice space heaters! :grinning:

Thanks for the detailed response!

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When did you get this racks? They look amazing!

Imo, for raw Sq, wa33 elite and aic are similar general tiers but each with different focuses

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makes sense, though much cheaper than the aic and simpler to own then the wa33 with the cost of tube rolling etc so more plus points for the zahl

Good to know. I had assumed the “lack of tubiness” from wa33 was due to being PP after hearing the wa23 have all the tube magic but was second guessing myself after reading that post for a second

Oh yah. Aic before price hikes was similar but not even close now. I don’t have any desire to own hm1 since I have aic but I suspect hm1 is a pretty solid value proposition after hearing it a few times now

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Thanks! Have had those for a few years, since I upgraded my theater components. Link:

They’ve got good weight rating (obviously–they’re supporting Nautilus, McInstuff, Furman Reference 20i), but they’re not break-the-bank expensive like a lot of audio furniture.

I over-bought rack parts so that as equipment changes I can alter the stacks as needed. I added another short shelf over the Mapletree XLR switch to make room for HM-1 and get it on the same level as Nautilus. Looks like it was planned all along. :smiley: