Pass Labs HPA-1 Headphone Amp Review

[fpitas]

Some of the planar headphones gobble power, even though they do sound nice.

 

[Drakkar Noir]

And I thoroughly enjoyed rock music in the late 1970's played through my pair of big custom JBL bass reflex speakers (from Hank Hong of Honker's Sound Company in Berkeley, CA). The drivers were the famous JBL S8 drivers with 15" woofer, and powered by a McIntosh receiver. This speakers below are JBL C50's - with the same S8 drivers and crossovers.

View attachment 246884​

Hank was a friend and business associate of Nelson Pass ( who had started Threshold Audio two years earlier, shortly after getting his degree in physics at the University of California, Davis.) Technically, Nelson Pass knows physics and electronics, and is far more qualified than characters like Danny Ritchie (business degree) or Paul McGowan ("self-taught", no degree). On a related note, there is lots of interesting discussion about the evolution of the audio scene and businesses in California at the Audiokarma.org thread on Pacific Stereo stores history HERE. Nelson Pass was - and is - an integral figure in the California audio scene, and has designed a number of excellent components that are now considered classics- including the excellent classic Adcom GFA555 power amplifier.

I also owned, in the early 2000's, and enjoyed very much a pair of very efficient Klipsch Forte II's powered by a flea-power custom 2A3 single-ended amplifier with NOS Marconi tubes from Italy's Attilio Caccamo of Tektron.

I am sure that neither of those systems would measure well, but they both brought me great pleasure. It is always good to frame comments about one's own personal; experiences and pleasures in the first person, and not as generalities. I am very aware that the sound waves that strike my tympanic membranes do not get passed accurately to my consciousness - the brain "converts and interprets" those sound waves in ways of which I am not aware, and cannot objectively evaluate. However, well-designed and implemented double blind ASX testing can remove some of the most obvious influences that alter my perception of the sounds I think that I "hear" - and can allow me to know if I really do hear "differences".

If someone thinks that $3.7k is a fair price for a headphone amplifier sans DAC without balanced input and output, and not enough juice for "power hungry" headphones, go for it. As for me, I'll stick with My $350 Topping DX7s DAC/headphone amp which doesn't have those limitations, and spend the $3.3k I saved elsewhere.

Sir love the pic!

My system before I loaned the HPA-1 to Amir:

I am selling the amp and most of what you see in the pic. Probably just sticking with the DNA and MAYBE the Mjolinr and gonna upgrade the record player.
As to the price paid for the Pass as a headphone amp, wont defend or trash it based on that. It brought me a lot of joy and now the time has come to part ways with it.

Wish I had the money and/or space to have a speaker system like the one in your pic. My audio rack space is all I have available for me and my toys. The rest is controlled by my wife and daughters.

 

[Drakkar Noir]

Alright, I bought the "Silent Shout" album on Bandcamp and downloaded it as FLAC (16 bit, 44.1 kHz). "Like a Pen" is a fun track!

I wanted something to compare the HPA-1 to since I never know whether distortion is part of the recording, the compression or something in the chain. I figured I'll compare the HPA-1 to the Schiit Ragnarok 2 for this (original version, before the production change to a toroidal transformer). Given its spec of 2x 24 W RMS into 32 Ohms lack of power should not be an issue here.
Due to its position in the room (requiring long cables) and balanced topology there are noteworthy differences in the setup (see below). I also haven't used it much as a headphone amp since it's my speaker amp.

Setup:
1) Schiit Yggdrasil OG > RCA out > 1m Wireworld Equinox 8 > Pass Labs HPA-1 > ZMF 2K Copper 6.35mm TRS to 4-pin XLR adapter
2) Schiit Yggdrasil OG > XLR out > 25 ft WBC Mogami 2549 & Neutrik > Schiit Ragnarok 2 (low gain) > 4-pin XLR out > 15 ft Blue Jeans Cable Canare L-4E6S & Neutrik extension
For both I then used the DCA Stealth via a 6 ft ZMF 2K Copper 4-pin XLR headphone cable.

Round 1: LOUD
I briefly listened via the HPA-1 and set it to a very high volume for my standards, about as high as I occasionally go (about 1:30 o'clock if I look closely).
I then level matched it with the Ragnarok 2 (~3 o'clock, low gain) with a BAFX3370 held in place by the earpads, playing a 440 Hz sine wave via onlinetonegenerator.com.

The Knife - Like a Pen (FLAC 16/44.1):
I like this track, and listened to it several times in a row with both amps to get more acquainted. I agree that with the HPA-1 the section starting at around 3:12 is grating (harsh, unpleasant glare) to the point that I didn't look forward to it on repeat listening. It is noticeably more bearable with the Ragnarok 2, albeit not entirely clean, either. At the same time, especially the beginning sounds better to me with the HPA-1, the recorded part (reminiscent of Yosi Horikawa's Bubbles) sounds real and three dimensional on the HPA-1 and flat on the Ragnarok 2. The beat is also a bit more fun and engaging while the pops have a bit more snap on the Ragnarok 2 (i.e. feel sharper, more sudden).
I gave my ears some rest and then continued with Marble House at the same volume.

The Knife - Marble House (FLAC 16/44.1):
Ragnarok 2 first this time. Someone recorded a ground loop. Hummmmm. Bit of a harsh mess from the get go... the high hats are quite good. Then the bass sets in nice and tight at the same time as the harsh highs continue. The bit at 2:12 is extra unpleasant, same thing a minute later. Wow, this is hard to bear throughout at this volume. Only the bass and drum sound clean. Finally relief when it fades out at the end. Yikes. I won't listen to this a dozen times like I did with Like a Pen, that's for sure.
Okay, HPA-1 next. The same three dimensionality and realness as with the other track is immediately apparent, that quality of the HPA-1 is remarkable. On the Ragnarok 2 you can of course hear the room echo, it just doesn't translate to an intuitive sense of depth. I expected the rest of the highs to be as grating as with the Ragnarok 2, but it's not too bad. The bass seemed a bit firmer on the Ragnarok 2, a little grainy on the HPA-1. The male voice sounds decent, didn't notice that with the Ragnarok 2 (unfamiliar track, though). The bits at 2:12 and 3:12 aren't quite as bad here, but 3:40 gets awful, sibilant. The bass line stood out more on the Ragnarok 2.
Alright, one more round, for science... back to the Ragnarok 2. The hi hat and bass/drums are definitely more composed here. Wincing again at 2:12. The male voice is cleaner than the female voice, but was more intriguing on the HPA-1. The part at 3:40 is also sibilant here, but slightly more bearable. Neither sounds good, this track at this volume is pretty torturous.
Back to the HPA-1. That hi hat setting in at 0:27 is definitely cleaner on the Ragnarok 2... is what I wanted to say, but going back and forth it seems more like the synths have more glare with the HPA-1, masking the hi hats somewhat and making it harder to focus on them.

Okay, enough, this is not fun.

I'm going to throw in some tracks I'm more familiar with before I mess with volume levels, etc.

Christophe Beck - The Pink Panther (2014): Main Titles (FLAC 16/44.1):
HPA-1 first. Normally I perceive this to be a fantastic recording (though I mainly use it as a test track), but the bass sounds distorted as do the horns. The triangle (I think) sounds nice, though. Good timbre. There's a reason I don't normally listen this loud...
Anyway, Ragnarok 2 next. Wow. Considerably more composed. Much easier to listen to and focus on the instruments. I noticed the triangle much sooner this time, before it was almost the only instrument playing at ~2:40. It's still all very loud, but fun. Nice dynamics.
HPA-1 again. Okay, the triangle thing was a fluke, it's clearly discernible here as well, just didn't grab my attention the first time. Overall this is still enjoyable, but shouty and less clean compared to the Ragnarok 2's presentation, at this high volume.

Doug MacLeod - Black Nights (Spotify Premium):
From the album "There's a Time", a remarkable recording. I first heard this song with the HPA-1/Stealth combo and immediately loved it. Very groovy. I always tend to crank up the volume a bit for this one (higher than usual dynamic range, I think), but definitely not this much. Alright, let's listen.
HPA-1: Sounds quite nice indeed. Noticing some light bass distortion. The vocals occasionally get shouty. Certainly not as flawless as I normally perceive it to be (at lower volumes). Still want to keep listening, though.
Ragnarok 2 time. Wow again. Significantly cleaner and more refined. Easier to notice fine details. What isn't completely smooth about the bass I perceive as texture / natural resonance of the instrument, not distortion. The voice can still get a bit shouty, but less often. This was good and perfectly bearable, even at this volume, except for the occasional vocal shoutiness. The guitar transients also stand out here as extra crisp.

Round 2: Reasonable volume
I gave my ears another break, also helpful to not perceive the lower volume as quiet. I set the volume by ear on the Ragnarok 2, came out as 10.4 dBA less loud at 440 Hz, whatever that's worth. I level matched the HPA-1 to it again and started listening. Still sounded loud to me after this break. ~11:30 o'clock on the HPA-1, ~1:30 o'clock on the Ragnarok 2.

The Knife - Like a Pen (FLAC 16/44.1):
First up: Ragnarok 2. Sounds kind of boring this time. Nothing objectionable to point out, but nothing intriguing either. Some songs work better loud, I guess? The part that fades out at the end has noticeable glare.
HPA-1: Oh, there's that sound bubble again, and that sumptuous bass. Head bobbing commences. Is this really the same track? So much more engaging. Not because the bass is particularly hard hitting or anything, though. This was fun throughout, didn't notice anything objectionable. Let's try again and listen more attentively.
Ragnarok 2 once more. Not as dull as earlier, maybe I needed some time to adjust. Still just alright, am tempted to skip to the next track, which wasn't the case with the HPA-1. It's missing a sensation of something interesting happening. The recorded bubbly sounds do that much better with the HPA-1 at this volume.
HPA-1 again. It's a sighted test, sure, but this track is immediately more of an event than with the Ragnarok 2, and I'm making silly dance moves on my office chair. Good thing I live alone. Again thoroughly enjoyable, no eagerness to skip on my part. Totally missed for the second time that I'm past the nasty section that irked me at high volume. Let's skip back to that... nah. All good, no issues at this volume. Same with the Ragnarok 2 for that section, no problem at this volume.

The Knife - Marble House (FLAC 16/44.1):
Alright. Deep breath... maybe this time this isn't torture...
Ragnarok 2: Hi hats a bit tizzy, bass & drum impactful and fun as before. I can hear that all those highs aren't exactly smooth, but it's listenable at this volume. I blame this on the recording, but I could be wrong. That part at 3:12 is still a bit nastier than would be good. The part at 3:41 is still sibilant.
HPA-1. Noticing that glare on the background synths more, hi hats are also quite tizzy here. Despite the lower volume the bass is again less composed than with the Ragnarok 2. The sound is overall harsher and still a bit unpleasant, makes me want to skip ahead, which I didn't want to do with the Ragnarok 2. The sibilance is also more noticeable. Do not like. If you want to hate the HPA-1, this is a great track to play on it.
Ragnarok 2. Less enjoyable than earlier, I think I'm fatigued. This song is really a bit much. Still, the Ragnarok 2 really does a good job with the bass and drum here.

Enough, though. Glare galore with this track.

Christophe Beck - The Pink Panther (2014): Main Titles (FLAC 16/44.1):
I needed a break first.
Sounded decent, but not super clean. I actually thought I was listening to the HPA-1 (not based on the sound, I just lost track of what I last used) and when the track was over I saw that I was still plugged into the Ragnarok 2.
HPA-1. Ah, refinement! Also more engaging. This is more how I know this track to be. So weird that this time the HPA-1 seems to do it more justice.
Back to Ragnarok 2. Better than before again, cleaner.
And HPA-1 yet again... still beats it. More refined, more fun. No complaints.

Doug MacLeod - Black Nights (Spotify Premium):
Ragnarok 2 first this time. Mmmh. Really, really good. Especially guitar and bass. Articulate, nuanced, snappy but not aggressive at all.
HPA-1. Hard to believe, but it's even more satisfying. Acoustic music can sound so banal, but when it's well reproduced it's like the musicians are speaking to you coherently through their instruments. Sorry, getting carried away here. I'm just really digging what I'm hearing right now. This is why I love this hobby. This kind of experience. Just from carefully stimulated gases. In addition to the excellent guitar and bass I like Doug's voice a little better with the HPA-1.
Ragnarok 2 again. Still very very good.
And HPA-1. Well, see above. Glorius.

Conclusion
Amir is right. When you really want to crank it with the DCA Stealth, the HPA-1 loses its composure noticeably. I am willing to pay a high price for excellence, but it's not excellent at this volume. Fully agree. If that were my typical listening volume I wouldn't have kept it.
However, I've had mine since September 2021 and this hasn't been an issue for me. Because at more reasonable (to me) volumes, it often sounds magnificent. Instead of distortion ruining the party, it gives me a finely crafted three dimensional space that I'm eager to stick my head in (no, not the chassis). It does that better than anything else I've tried.
But I haven't heard all the amps out there, including the many moderately priced measurement marvels. Maybe there's one out there that works even better in my situation., or just as well for much less money. Still, as the Ragnarok 2 shows, power isn't everything. Past a certain threshold other things matter more. Depending on your personal circumstances this amp may well work for you, but so may others.

This was educational. I was baffled when I saw Amir's extra poor subjective impressions, but they make sense to me now. HPA-1 + Marble House = torture. Yuck. Whether it sounds good to me with any amp remains to be seen, though.

Thanks for engaging, Amir

Great counter argument @Alcophone
Others like HiFiBob should take note.

 

[Peternz]

I always thought the goal of equipment was to get it out of the way; create transparency. Get the DAC out of the way. 0.000X,; get the amp out of the way, 0.000X. Isn't that providing the best way to get source material to the ear unmolested whether with speakers or headphones? To use the stupid cliche, "listen to it as the artist intends it"? Anything else adds coloration or distortion? With that said, I enjoy my crystal clean transparency with certain genres of music, but admit to also enjoying tube listening with certain genres and especially with vinyl. Undisputedly, Amir provides us with information that is invaluable, love it or hate it. There is no malice here, just hard cold facts.

I think you are wrong. Transparency is not really the "goal". The goal is to reproduce music in a way that sounds enjoyable to you. You paid for it so it should serve you. If you like certain types of distortion and noise I can understand why you will want to buy equipment that provides that. I have gone through enough equipment in my life to know that it can be very pleasing. I can see why people like listening to tube amps. The problem with such equipment as far as I am concerned is that the novelty value gradually wears off and it ends up sounding annoying because the equipment draws attention to itself and distracts from the music. In my experience reasonably priced, well made, well designed and well measuring equipment is what gives me the most pleasure, so to me, yes, transparency is best. There are however good reasons why transparency is not best for everyone. It is a matter of taste.

And while I am here, I am the one who pays for the equipment and the music, not "the artist". I will gravitate to what I like, whether or not that is exactly as the artist intended. I don't really have a clue what the artist intended anyway, they may have intended that I listen through an old AM radio or their intention may have been that I use huge speakers with 15 inch woofers and 1000 watt amps, I have no clue.

So, in regard to the Pass amp being discussed it may very well be something that provides someone with more pleasure than a better measuring amp. There may even have been a time that I would have considered buying one but that time has long gone. Good luck to anyone trying to sell theirs.

 

[GPJ]

I don't think I'm wrong. Thanks though.

Whether it's the gear or the ear that's not getting it done, tweaking it by adding coloration or distortion is in disagreement with the producer.

As I mentioned earlier, I listen to tubes amps with vinyl and enjoy it very much regardless of all the errant stuffs happening. But, I also listen to ultra clean DAC's and amps that I do not tweak at all and find it flat out incredible.

 

[amirm]

I think you are wrong. Transparency is not really the "goal". The goal is to reproduce music in a way that sounds enjoyable to you.

In formal tests, audiophiles gravitate toward neutrality. That uniqueness of 'what sounds good to them' disappears in controlled testing. So what you say is right, but it has to be based on reality, and not imagination. To think you like a tube amp because it "sounds warm" is very different than what it is actually producing.

When an amplifier clips, it sounds horrid to everyone. There is no differing opinion. And when its distortion is very low, it has no sound for anyone to have a preference for it, on sound alone. Measurements show both of these factors.

 

[Extreme_Boky]

To grok this amplifier you have to be ready for it to go into clipping with insensitive headphones. And have noise with every sensitive IEMs/headphones.

Transparency is not really the "goal". The goal is to reproduce music in a way that sounds enjoyable to you.

The headphone amplifier should be well-engineered to accomplish what Amir wrote above... with a negated logic structure... if I may:

It should not go into clipping with insensitive headphones. And it should have very little noise/hiss with very sensitive IEMs/headphones.

If it does (and that's where this site comes into play), a listening session is in order to make sure it suits your individual taste and your headphones.

 

[ctbarker32]

The DC Hi-Fi Group had a special virtual meeting with Nelson Pass yesterday.

One of the best comments from Nelson was "It's entertainment, not Dialysis"

Lots of good discussion about the art and science of designing audio from a true legend of the industry.

 

[Ken1951]

Wonder what the average upper frequency limit is by the dudes in that group?

 

[Doodski]

My favorite comment so far from Nelson @ is, Dropped a lot of energy." In reference to a absurd and cool tube amp design of his.

 

[Tom C]

The DC Hi-Fi Group had a special virtual meeting with Nelson Pass yesterday.

One of the best comments from Nelson was "It's entertainment, not Dialysis"

Lots of good discussion about the art and science of designing audio from a true legend of the industry.

Well, it’s not dialysis, but it’s priced like dialysis

 

[danielsmi]

On the Pass Labs website it says that the HPA-1's power supply comes with a "faraday shield" but I didn't see a faraday cage in the internal pic amirm posted. Is the black cover on the toroid the faraday shield?

Headphone Amp Archives - Pass Labs

Headphone Amp

www.passlabs.com

 

[Extreme_Boky]

I do not see anything inside that amp that could be called a faraday shield. I see a fully enclosed aluminium box and a toroid transformer that, by close inspection, may have internal shielding sheets (but no ground-connected drain leads coming from that transformer). I might be missing something there that is not obvious to the naked eye...???

 

[WayneC]

I do not see anything inside that amp that could be called a faraday shield. I see a fully enclosed aluminium box and a toroid transformer that, by close inspection, may have internal shielding sheets (but no ground-connected drain leads coming from that transformer). I might be missing something there that is not obvious to the naked eye...???

The transformer has a mu metal shield and an electrostatic shield with a ground wire on the connecto.

 

[Extreme_Boky]

Thanks Wayne.

 

[GXAlan]

Sony TA-ZH1ES: A DAC/Headphone Amp with a Sonic Signature?

Sony TA-ZH1ES: A DAC/Headphone Amp with a Sonic Signature? Stop. やめる. Halt. Arrêt. You probably shouldn’t read the rest of this post, it's triggering. There's a lot of speculation even though there are a good amount of measurements too. If you're looking for a transparent DAC/headphone...

www.audiosciencereview.com

Posted a zero negative feedback headphone amp from Sony. Super high distortion like this Pass Labs but ultra clean power supply in comparison.