Zähl HM1 - Reference Headphone Amplifier - Official Thread

This is the official thread to discuss the Zaehl HM1 Reference Headphone Amplifier.

From the Zaehl website.

" Reference Amplifier with unprecedented transparency and precision, attention to detail and massive power performance. Rich feature set for both high-end enthusiasts and professional users. Designed and manufactured in Germany."

Tech Specs


Line Inputs balanced – Impedance 20KΩ – max. level +23dBu
Line Outputs balanced – Impedance 47Ω – max. level +23dBu
transformer-like behaviour: hot or cold may be connected to ground without loss
Line Inputs unbalanced – Impedance 20KΩ – max. level +23dBu
Line Outputs unbalanced – Impedance 47Ω – max. level +23dBu

Headphones Output

Impedance Class A 0,8Ω, Class A & Servo 0,045Ω
max. level +23,5dBu (+/-16,5V)

Output Power per Side

RMS 4W/30Ω; 7W/15Ω
Peak 7,6W/30Ω; 11W/15Ω; 12W/10Ω (18W for 1,5ms)

Frequency Response

10Hz … 30kHz -/+0,05dB
1Hz … 500kHz better than -3dB at Headphones Output @ +6dBu


Line/Line – 0dB – +15dB switchable on rear panel
Line/Headphones – +6dB – +15dB switchable on rear panel


20Hz … 20kHz flat RMS / A or B active
XLR/RCA Output -102dBu
Headphones Output -97dBu

Headphones Output THD (Total Harmonic Distortion)

Class A 0,07% – Class A & Servo 0,0005%
(typ. @ +20dBu/7,75Veff / 30Ω load / 2W RMS)

Power Supply

Mains Voltage – AC 50-60Hz, switchable 100V / 110V / 120V / 220V / 230V / 240V
Power Consumption – typ. 40W, max. 60W

Measures and Weights

HM1: WxHxD approx. 225 x 90 x 300mm, approx. 5kg
HMP1 (Mains Adapter): WxHxC approx. 170 x 60 x 185mm, approx. 1,2kg


I was fortunate enough to hear the amp with several headphones, and also got the chance to chat with Michael Zähl at length. I got the feeling we could talk for hours about the science and engineering aspects of the audio world, and even though I know much of it would’ve gone over my head, he was super friendly, and it was great to get his insight. You got the feeling he takes this stuff very seriously, and that an extreme amount of thought and careful consideration goes into his designs.

For the HM1 it felt like his focus was to achieve the best possible sound in a device, along with features that would be actually used and valued by the community. I think for all the devices that have features like widening effects they often come off as gimmicks - even on otherwise excellent devices. That was not the case here.

To give a bit of context, many will know that I’m someone who really doesn’t get that much into the whole source equipment world, as I’m much more focused on the headphones and I find that in the majority of cases, it’s all fairly similar. While I do find there to be differences, I usually don’t find them significant enough to mention, and there’s already lots of great sounding inexpensive equipment out there with enough power to drive the majority of headphones. So, why comment on this one?

There’s a reason why every person I talked to at the show confidently referenced the Zähl HM1 as the best headphone amplifier they’d heard - at least for the solid state stuff - and it’s because it actually was a step above, and made the headphones I listened to off of it meaningfully better sounding than I was used to. If anyone has watched my live streams on the subject of source equipment, those are not comments I’m going to make lightly.

Of course, I’d need to spend more time with it, do ABX comparisons and all of those things to get a more comprehensive understanding of the device, but strictly for what I listened to, over the course of that particular session, it was the best I’d heard the following headphones sound:

  • DCA Stealth
  • DCA Aeon 2 Noire
  • Abyss Diana TC

Now I’d only heard the Diana TC off of some of the Feliks Audio gear across the floor, but I did also prefer it off the HM1. But with that said, I’ve spent quite a bit of time with the two other headphones previously and am well acquainted with how they sound off of a wide variety of equipment. Notably these are all planars, so it would be interesting to try some dynamic driver headphones as well.

In any case, with the two DCAs, they mainly sounded like they had more depth to them - like in a kind of sense where in a subjective assessment I’d find them to be more ‘detailed’ sounding - but also that the sounds had an extra kind of structure to them, for whatever that means. So, overall just more engaging than what I was used to with them.

A number of other listeners who I was with also commented on those headphones sounding more punchy, impactful and ‘dynamic’ as well, although I wasn’t specifically indexing for this quality during that session. Those who didn’t like the Stealth, for example, liked it a lot better off the HM1, and the same goes for the Noire. So let’s just say the ‘technicalities’ of each headphone shone through on another level.

Then there are the functions, the most interesting of which is the widening effect. In other devices, like the Pro iCAN there are functions with similar intentions. While these types of functions in other devices can be useful to a certain degree, the HM1’s implementation felt more nuanced and calculated.

Importantly it felt more realistic than any other I’ve heard for that effect. It was subtle - not like changing a DAC filter subtle, more like 20% widening effect to the whole presentation if I had to put a number on it. So still significant enough to where you could easily tell.

Lastly, there’s also the mains adapter power unit. Michael discussed this briefly in an interview we did with him so make sure to check that out when we release it in the coming days to get more info on the intention behind that design, as well as its functions.

In any case, this is truly an endgame piece of equipment, and I need to get one into the studio and do a lot more testing and listening to it to get the full picture before giving a verdict or anything like that. But I am going to say that if you don’t think amps make a difference… (which is something that would be understandable given that many of them don’t really sound all that much different) you need to listen to this, and take any opportunity to hear one if you can.


Hey Resolve, thanks for the great write-up.

It seems to confirm the impressions Golden and Skedra both seem to have after listening to the HM1 in Munich.
Their experience with the amp and also their commitment to sell some of their reference stuff to get one of these in their setup shows me that the HM1 seems to have some very special tricks up its sleeve.

I myself wasn’t really on the lookout for a new amp for my setup but their impressions and finding out more about the company and the people behind it (not far from where I grew up) I suddenly found myself to be interested in the amp although I’d normally never consider something in this price range.
But the features it brings to the table with the soundstage knob and EQ all done analog by such a legendary designer in pure class A plus the optional servo are so unique that I look at it differently than other high end amps somehow.

I feel like this is an amp I’d get for the rest of my life and since analog specialist like Michael Zähl are probably also getting more scarce in the future I feel like this might be one of the amps one will look back at in the future in admiration.

That’s why I got in contact with the distributor today and hopefully sometime this summer I’ll be able to call an HM1 my own :smiley:

I think over the years with incremental upgrades I probably would have spent a similar amount. So why not go all in directly if you have the chance. :stuck_out_tongue_closed_eyes:


I really cannot wait to get more listening time with this amp. It was certainly a standout piece of the show and whilst it’s of course always a bit tough to make solid judgements in a short time (and at a show), it was very clear that this amp was truly something special.

The sound alone was so dynamic and authoritative without at all feeling strained. It was effortless, like it just had infinite drive and power available at all times. Not to mention the fact that you can choose between a neutral and accurate presentation with servo on, or a sweeter/warmer presentation with it off, is very welcome indeed. It’s like having two amps in one!

And the staging adjustment was fantastic.
Other devices with crossfeed, be it digital or analog, can certainly be helpful and quite pleasant, especially for hard-panned tracks. But I’ve always found that they tend to just put things a bit more out in front of you rather than really improving stage. A sort of speaker-simulation.

But this…this was different. It was so much more convincing and was as if you were turning up or down a ‘zoom’ function on the soundstage. Everything expanded or contracted, rather than being shifted into a speaker-like presentation in front of you.
It felt exactly as you said, nuanced and calculated. I loved it.

What a fantastic device this is!


What is the output impedance of the amp? Could dampening factor be coming into play like it does with high ohm dynamic drivers and tubes? I tried looking it up but couldn’t find it.

1 Like

0.8Ω In class A
0.045Ω In class A + Servo

So you’re not going to encounter any issues at all with any headphone or IEM.

Tube amps typically have very high output impedances. They’re a bit of a different story to (most) solid state gear. Though it’s also part of why people like the tube amp sound. They do change the FR of your headphones/speakers (unless it’s a planar in which case FR will be unaffected)


Same here, it’s been a while since an amp literally sounded better than every other amp I’ve heard.

Listening to the servo mode, it was the “right” kind of neutral, not dry, not boring, just not coloured. Dynamics were excellent, transients fast and precise, bass had authority etc etc… Basically what you’d want from a good neutral amp.

And then you realise it’s so much more. The class A mode was just perfectly executed, it was sweeter yet still kept the precision and most of the technical performance. The soundstage change was mind-blowing to me, usually those things seem more like a gimmick, here it felt… Nearly natural? I can see myself using this quite a bit either on recordings that seem too crowded or gear that seems too narrow.

All in all, definitely the best solid state amp I’ve ever heard and I’m hoping to have it on my desk in the near future :smiley:


You, uh, want to send me a quote for one of these?


I’m curious, what digital source was used when y’all listened to it or rather, whatever the whole chain was?


It was being run through the HiFi Rose streamer.


Oh so it was using its internal DAC? Interesting…


The Streamer was actually all over the show floor being used as a streamer /DAC. Was quite surprised to see them all over the place as I felt the brand was relatively obscure.


Is this going to be available via headphones.com
Any idea about pricing?

Yes pre-orders are live now. Price is $7999 USD.


Will this run the Susvara well?

1 Like

Check out this review. He’s using the HM1 and Susvara to compare the Chord Dave and TT2: HM1-Review-Musicalhead.pdf (zaehl.com)


Is the volume remotely adjustable and did anyone listen to it through the unbalanced connector?

the refrence point of dave and tt2 for sus seems a bit suspect to me tbh. Its a shame I have yet to talk to anyone who tried sus on it at the show.

I did try sus on it at canjam socal back in september but something sounded outright broken with that one (and IIRC I was later told it was possibly damaged in shipping) so cant comment on how it handles sus. I also had only owned sus for like 24 hours at that point too so I wasnt even sure what all it was capable of :sweat_smile:

Yeah that’s a valid point. It’s also not specified if it was driven via the headphone output or directly from the real XLR outputs in amp mode from the TT2 which seems to make quite a big difference as well. I’ve no experience with it myself but I know someone who’s using the TT2 for 1266 and he said that there is a noticeable difference for hard to drive stuff between TT2’s headphone out and the XLR outputs in amp mode.

In general it’s obvious that not much information is available on the amp yet concerning pairings etc. I have the impression that it didn’t get through to the audiophile community yet and was mostly bought by people with studios that don’t write a lot about it online.
This will only get better as soon as the people at headphones.com, Golden, Skedra and other people in the community will get their hands on one in their own setup.
I jumped on it already because power isn’t really a concern for the headphones I’m going to use with it. It’s more about the other features + true class A that convinced me to take the risk. Will the synergy with my ZMF be good? No one can really tell. But I’m pretty optimistic.

1 Like

So TT2 is a pretty weird one because there is a quite distinct flavor difference between the rear XLRs and the front jack that is far more than just a power thing. The rear XLRs have a fair bit more warmth and body to them than the front jack but maybe slightly less sharp stage placement. This stayed true for every can I tried on them be it SUS, Soli P, Utopia, VC, and even HD580.

That said, IMO, the rear taps of TT2 still don’t have quite enough juice to really run sus properly. The dynamic impact ends ups a bit stunted with the leading edge of bass notes being fairly rounded off and soft unfortunately. This part is actually why I called out the TT2 as the reference as even on the rear XLRs if that’s what you are use to SUS sounding like it may not be apparent when the can is being underdriven

Yup. I am sure plenty more info will come out as time goes by. Everyone else I know buying one uses SUS so im sure we will get more info on that part as time goes by. Im sure @resolve can hunt down a sus to borrow when he reviews the amp as well.

Yah, the features here seem awesome. TBH I wouldn’t realy use anything aside from the AB tester (a large part of the reason I haven’t ordered one) but if you would this seems like an incredible piece of kit. I totally understand why a reviewer like @GoldenSound would purchase one even if it didn’t run sus just as a very good piece of test equipment. TBH Ill be quite curious how it handles an estat transformer. Being able to throw this behind a set of stats like x9000 would be pretty cool for dac testing IMO