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Pass Labs HPA-1 Headphone Amp Review

Rate this headphone amplifier:

  • 1. Poor (headless panther)

    Votes: 312 91.0%
  • 2. Not terrible (postman panther)

    Votes: 17 5.0%
  • 3. Fine (happy panther)

    Votes: 6 1.7%
  • 4. Great (golfing panther)

    Votes: 8 2.3%

  • Total voters
    343
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amirm

amirm

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I wish Amir had arranged to have the amp inspected at the factory before publishing such a scathing review.
If the company had supplied me with the unit, I would have done exactly that. But when members send something to be tested, I do that and post the results. You need to be pushing companies to publish comprehensive measurements like I do so there is no doubt as to validity of the testing. Until they do, this situation will remain.
 

Xulonn

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NO. I'm saying I find rock n roll very pleasing and exiting with this setup. Very simple.
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.

JBL C50 S8-075.jpg

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.
 

GPJ

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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.
 
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HiFiBob

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Amir:

Per JA's distortion graph in Stereophile, the HPA-1 clips at about 8.5VRMS out into 30 Ohms. The amp has a robust output stage and power supply, so should produce sufficient current and voltage to meet its claimed power output of 3500mW into 20 Ohms.

With a gain of 8dB (x2.5), you cannot actually "push the product to its limit" with the 2VRMS output of your analyzer. Your readers may not understand that and might draw the wrong conclusion about the amplifier's power rating.

To grok this amplifier, you need to prepare yourself psychologically for the concept of 0.1% distortion. The ear is remarkably insensitive to 2nd harmonic distortion in real-world signals. Nelson Pass has written plenty about this. You just don't need ultra-low distortion for audible transparency.

The claim is that sighted listening tests are worthless. So I choose to ignore your subjective evaluation. I do wonder if your impressions of the amplifier's sound were colored by knowledge of the measurements.

About made-in-China versus made-in-USA, it doesn't seem appropriate to discuss that topic here. The issues are obvious to anyone who reads the news.

I don't feel the need to address your other comments. I'm satisfied with everything I've posted here. Thank you for giving me the opportunity to respond to your review of the HPA-1.
 

Alcophone

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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.
The DCA Stealth is a power hungry headphone. It sounds beautiful out of the HPA-1. It's plenty loud with the volume level at noon. With some songs I get so into it, I turn it to 2 or 3pm, but very rarely because that's hearing damage territory.
More than enough power for this application, it would seem. But there's a graph on the internet says it doesn't have enough power, so what do I know.

I had the DX7s. I didn't enjoy it very much and sold it long before I got the Stealth. Glad it works for you. Did they fix the issue were it stops working at some point until you disconnect power for long enough?

I also got the SparkoS Aries ($3000) around the time I got the Stealth and HPA-1 because the SparkoS opamps let me enjoy the Burson Fun and Gustard H20. The Aries is well respected among audiophiles. Someone preferred it over the Benchmark HPA4.
The Aries is also a single ended amplifier with balanced inputs for convenience, and strangely it needed them to sound just okay to me with the Yggdrasil, while the HPA-1 sounds much more pleasant with just the single ended output of the balanced Yggdrasil. I tried my best to like the Aries, trying most of the headphones in my inventory, but it wasn't happening. I returned the Aries and kept the HPA-1, which reliably provides a beautiful sound bubble to stick my head in and relax.
But sure, it must have been the $500 price difference that convinced me.

Would I prefer to spend 10% or less and get something I enjoy as much? Yes. Sadly, even Amir hasn't cracked the code yet of posting a number that correlates with "sounds good to me". The latter is the performance I care about. I don't worry about the AAF (Analyzer Acceptance Factor).

But I'm always curious and open minded. If someone is crazy enough to send me an amp that will certainly trump the HPA-1, or a DAC to trump the Yggdrasil OG, I'll happily try it out. Unfortunately my cat isn't qualified to facilitate blind testing, so my feedback can be all too easily discarded.

If only we could measure brain states while listening to gear and post screenshots of those.
 

Xulonn

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The claim is that sighted listening tests are worthless.

Objection.jpg

That is one of the lamest strawman fallacies that infects ASR. No one who understands science and agrees with the fundamental principles that guide ASR says that.

Amir and most, if not all, of the rest of the rational objectivists here at ASR know that there are real, easily to moderately difficult to distinguish audible differences in reproduced music and other sounds. With good electronics and proper component matching, differences exist mostly with respect to transducers and environments, and for audiophiles, that means speakers and listening rooms. Sonic anomalies related to speakers and their interaction with rooms are not just common, but ubiquitous on the world of audio.

We also know that there are human limits on audibility, and that scientific instruments can be far more sensitive with respect to sound than human hearing. Intelligent, aware audiophiles and audio professionals are aware of both the limits of human hearing, and where and when double blind ABX testing is the only way to verify claimed audible differences.

To claim that objectivists say that "sighted listening tests are worthless" is simply a strawman based on ignorance or denial.
 
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amirm

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With a gain of 8dB (x2.5), you cannot actually "push the product to its limit" with the 2VRMS output of your analyzer.
2 volts is the maximum DAC RCA output of almost all the DACs I test. It is not material what the product does beyond that level of input. You are not likely to have that kind of source. Heck, a lot of mass consumer products don't even do 2 volts out (think many AVRs).

The competitors to this product have 2 or 3 gain settings and hence, are able to deal with this or other output levels from source components.
To grok this amplifier, you need to prepare yourself psychologically for the concept of 0.1% distortion.
Nope. 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.
 

HiFiBob

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You're just wrong Amir. It's not a good review. But the thing is, nothing good ever comes from arguing with a narcissist holding a ban hammer.

LOL, I've said what I came to say. See ya.
 
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amirm

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The claim is that sighted listening tests are worthless. So I choose to ignore your subjective evaluation. I do wonder if your impressions of the amplifier's sound were colored by knowledge of the measurements.
They are only worthless if they go against all objective data and engineering knowledge. In this case, the amplifier is extremely weak by desktop standards and readily will go into clipping region. You don't need a blind test to know that the sound is severely distorting then. Measurements back the same.

Now, if we are talking about that second harmonic adding something to the sound of the unit, then you would be absolutely right. We would need blind tests to know what this euphonic effect is.
 
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amirm

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You're just wrong Amir. It's not a good review. But the thing is, nothing good ever comes from arguing with a narcissist holding a ban hammer.

LOL, I've said what I came to say. See ya.
You were allowed to say what you wanted despite creating a duplicate login after being banned before. So don't use that card. Like your arguments about this product, you speak without correct knowledge.
 
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amirm

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The DCA Stealth is a power hungry headphone. It sounds beautiful out of the HPA-1. It's plenty loud with the volume level at noon. With some songs I get so into it, I turn it to 2 or 3pm, but very rarely because that's hearing damage territory.
More than enough power for this application, it would seem. But there's a graph on the internet says it doesn't have enough power, so what do I know.
You have to use critical content and listen for the distortion. Otherwise it may be very difficult to hear it. In addition, some clips sound a lot less loud than others due to their spectrum but nevertheless stress the amp (low frequencies do this). Here are my goto test tracks:



Let them play out until you get a mix of bass notes and the highs. Then listen to how clean the highs are are you turn up the volume. Tolerate it for a few seconds if it is too loud. The idea is to get used to hearing the distortion and what it sounds like. Then you can turn the volume back down and see where the distortion disappears.

And oh, please stream the original versions. Youtube clips likely have lossy compression artifacts of their own so may not be revealing.
 
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amirm

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By original you mean lossless or would you say Spotify Premium is good enough?
Lossless for this kind of testing although you could try spotify (I don't have it to test). High frequencies is where loss compression gets in trouble and hence my comment here.
 

Extreme_Boky

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Nope. 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.

It is hard to say anything when presented with the above. I think I forgot there for a moment that what you stated is what defines an amp as a headphone amp - specifically.
 

solderdude

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The ear is remarkably insensitive to 2nd harmonic distortion in real-world signals. Nelson Pass has written plenty about this. You just don't need ultra-low distortion for audible transparency.

Correct for 2nd harmonics BUT with 2nd harmonics there are also IM products which may not be masked depending on the actual music and IM is generally not 'pleasant' (euphonic) when reaching audible levels.
While I agree that we don't really need anything better than 0.01% for audible transparency that doesn't mean amps with 0.1% or even 1% are audible transparent and that a design that has this amount of distortion is 'good enough'.
That said, those that like a 'distortion generator' applied to an entire recording are free to do so. There are plenty of amps around with even more distortion (and less) and would recommend to just enjoy it if you have one.

There is no harm in measuring and posting technical performance of audio equipment.

I wish Amir had arranged to have the amp inspected at the factory before publishing such a scathing review.

There is nothing technically wrong with this amp (aside from the loose connector which was fixed) so even if it were inspected it would have changed nothing in the results.

And yes, the subjective review from Amir is 100% sighted but people ask for his opinion.
When Amir does not say anything about how it sounds he is attacked on this, when he does vent his opinion it also isn't good. No win situation.
 

Alcophone

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You have to use critical content and listen for the distortion. Otherwise it may be very difficult to hear it. In addition, some clips sound a lot less loud than others due to their spectrum but nevertheless stress the amp (low frequencies do this). Here are my goto test tracks:



Let them play out until you get a mix of bass notes and the highs. Then listen to how clean the highs are are you turn up the volume. Tolerate it for a few seconds if it is too loud. The idea is to get used to hearing the distortion and what it sounds like. Then you can turn the volume back down and see where the distortion disappears.

And oh, please stream the original versions. Youtube clips likely have lossy compression artifacts of their own so may not be revealing.
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!
 
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DrowningNotWaving

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You are confusing constant average A-weighted SPL (as shown in the linked safety regulations) with unweighted peak SPL in the bass and the desire to have distortion free audio reproduction where distortion is not allowed. This has been discussed a number of times. Most people will not listen to more than a few mW on average. It is not about those people. It is about having the ability to drive a headphone to 120dB SPL peaks when someone cranks a song up to uncomfortable loud levels and wants to do that without running into distortion. I am not advertising to listen to those average levels all day long. How much voltage/power is needed (if one has a couple of headphones) depends on the efficiency and impedance of them. Some may never need more than 50mW, others may want several Watts.

Besides, this isn't about the HD650 it is about the input voltage needed to reach clipping levels. The HD650 is actually quite efficient but there are other headphones that aren't.
Like the well known DT880/DT990 600ohm for instance.


Well, each to their own I guess. If your notional human that likes to crank it up to 120dB does so on a regular basis their hearing won’t last long.

My 2 cents, ymmv etc etc
 

solderdude

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Well, each to their own I guess. If your notional human that likes to crank it up to 120dB does so on a regular basis their hearing won’t last long.

My 2 cents, ymmv etc etc

No one is advocating people should listen to music with 120dB peaks on a regular basis or even at all.

It has do with amplifiers being capable of reaching 120dB peak SPL in different headphones when someone has them and on a rare occasion wants to listen to a song at impressive levels with some low bass boost without any distortion.
0.1W is overkill for an IEM, 1W may not be enough for some inefficient headphone.
1V is enough for a lot of ear/headphones but some insensitive headphones simply require 10V or more to reach comfortable loud levels.
 
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