Pass Labs HPA-1 Headphone Amp Review

[DrowningNotWaving]

The only 'poor' performance is lack of gain (needs a source > 3.5V out in RCA) and the (intentional) amount of 2nd (and lower 3rd) harmonics, at least up to 2V out.
We can only guess the harmonic spread above 2V but that might not look great in low impedances.
The hum ... I can't say anything about that.
200mW in 300ohm and 3.5W in 20ohm (>0.1% distortion) could easily be reached in 2000 already.

Most people listen to music with just a few mW average and maybe 10-30mW peaks. (a bit more with insensitive low impedance headphones)

Hi,

My comment is less about the prodcut under discussion, and more about your observation that a headphone amplifier "requires" 3.5V of output to drive a notional HD650 references in an earlier comment.

Frankly, you must listen at very, very high SPL's: the HD650 (a nominal 300ohm headphone, that might be expected to have an actual impedance of about 350 ohms) requires 0.001W (i.e. 1mW) for an SPL of 100dB. The SPL for 1V RMS signal is 105dB. In my world, that is LOUD.

From an industrial safety perspective, if a person is exposed to 85dB for 8 hours, hearing loss will occur. 85dB is also quite loud from an "average SPL" standpoint. My personal "average SPL" listening level is around 75dB. Maybe I'm a wuss, but I can still hear 14kHz and I'm over 55, which is not a bad result for my age.

So, lets say that one wants 30dB head room over a notional threshold of hearing loss SPL of 85dB, this equates for 115dB SPL on peaks. Which equates to 32mW of input power and matches up (3.35V) with your 3.5V requirement V=sqrt (0.032X350).

Another way to look at it is that 2V into the HD650 equates for 108dB (i.e. double the 1V for 105dB spec).

While some folks might siggest that these SPLs are "reasonable real world requirements", one will lose hearing very quickly.....

my 2 cents, ymmv, dyor

 

[DrowningNotWaving]

To highlight my earlier post, the following describes the level of SPL exposure before hearing loss occurs. If one is listening to our notional HD650 with a 1V input (i.e. 105dB SPL, which was indicated by another poster as "normal") you are losing hearing capability after 4 minutes.

Sound Pressure Level	Sound pressure	Permissible Exposure Time
115 dB	11.2 Pa	0.46875 minutes (~30 sec)
112 dB	7.96 Pa	0.9375 minutes (~1 min)
109 dB	5.64 Pa	1.875 minutes (< 2 min)
106 dB	3.99 Pa	3.75 minutes (< 4 min)
103 dB	2.83 Pa	7.5 minutes
100 dB	2.00 Pa	15 minutes
97 dB	1.42 Pa	30 minutes
94 dB − − − − − − − − − −	1.00 Pa − − − − − −	1 hour − − − − − − − − − − − − − −
91 dB	0.71 Pa	2 hours
88 dB	0.50 Pa	4 hours
85 dB	0.36 Pa	8 hours
82 dB	0.25 Pa	16 hours

Guidelines for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH-AINSI and CDC. For every 3 dB sound pressure level (SPL) over 85 dB, the permissible exposure time is cut in half − before damage to our hearing can occur. NIOSH = National Institute for Occupational Safety and Health and CDC = Centers for Disease Control and Prevention. OSHA = Occupational Safety and Health Administration. This may not represent a worldwide view of the subject. Noise is an increasing public health problem and can have the following adverse health effects: hearing loss, sleep disturbances, cardiovascular and psychophysiological problems, performance reduction, annoyance responses, and adverse social behaviour. A person feels and judges sound events by exposure time, spectral composition, temporal structure, sound level, information content and subjective mental attitude.

 

[LazyBear]

Tube amps don't measure that well. Pass actually performs appropriately to its purpose - to sound closer to tubes and not to solid state. Which is why I own it. I am happy to hear that it measures exactly like I expected it to sound Matter of taste. Besides, it depends on the music. Guitar head amps are cranked up to 11 for tube distortions anyway

 

[Ken1951]

I just don't get why people consciously induce distortion into devices designed to reproduce recorded music, or use such devices to listen to music and imparting the same distortion to every type of music. I understand guitarists using distortion - they're creating the flipping music to begin with.

 

[BDWoody]

Guitar head amps are cranked up to 11 for tube distortions anyway

Maybe put a whammy bar in your setup too?

 

[LazyBear]

I just don't get why people consciously induce distortion into devices designed to reproduce recorded music, or use such devices to listen to music and imparting the same distortion to every type of music. I understand guitarists using distortion - they're creating the flipping music to begin with.

I don't think it is intentional. Just an effect of design. Like there is no way one would be able to make tube amp with 0.001% THD. Pass gear is FET, simple schematics Class A with no feedback, so you get what you get. I'd call Pass solid state Audio Note if you know what I mean.

 

[LazyBear]

Neither do I. Do these people also use tinted glasses to improve the visual impressions when watching a film on TV or looking at a van Gogh at the museum?

Same reason we have room correction. Personal taste. My Dirac in my HT setup is set to the sound I like, not to some 'standard committee curve'.

 

[Alcophone]

I just don't get why people consciously induce distortion into devices designed to reproduce recorded music, or use such devices to listen to music and imparting the same distortion to every type of music. I understand guitarists using distortion - they're creating the flipping music to begin with.

Just throwing some thoughts in: When music is recorded and mastered, it's also listened to through gear that may not be free of distortion, so it's possible that the final sound that was approved included some distortion of the reproduction system in the studio (and maybe originally a lot of that was tube gear). When you then use a system with practically no distortion to listen to those productions, it would sound less "like the artist intended".

Presumably in recent decades most pro gear has had less distortion than in decades prior (though the SINAD war is a pretty recent phenomenon). But it still wouldn't be surprising if in the pursuit of achieving known liked sounds some practices carried over. It would also make sense to use more consumer like gear when mastering (at least partially) to judge the sound based on how the vast majority of people will hear it (at least to make sure it doesn't sound horrible with either great or mediocre gear). I've heard that the Yamaha NS-10 can be found in many studios precisely because it's pretty crappy, but I don't have first hand experience with it.

On my end I like the apparently poorly measuring Yggdrasil (Amir had exactly my unit) and I tried the DCA Stealth with about thirty different combinations of gear to get a sense of how hard to drive they truly are (an important caveat because I therefore deliberately included many crappy sources like a cheap small display and a projector) and with the HPA-1 they simply sound better, to me, than with all the other systems.

So maybe I do indeed like (certain forms of) distortion, though I frankly was offended when I first heard that suggestion, leaning more towards me liking something that doesn't show up in the measurements and not hearing the distortion, but that may well be wishful thinking. Still, I'm not going to force myself to listen to ASR approved gear while self flagellating any time I get nostalgic about the gear I simply preferred the sound of. I happily tried the Topping DX7s a while back and happily sold it.

One surprisingly enjoyable source for the Stealth was the Loxjie A30. Didn't like it that much for speakers, but in my brief test it seemed to be a compelling option for the Stealth. And wouldn't you know it, according to ASR it's trash for headphones.

 

[LazyBear]

For sure you can use your room correction to whatever purpose you like, but the intended use is to get rid of room modes and other resonances and reflections. You can also drive with your car in the ocean if you like...

Yep. My music tastes, my ocean to drive my car into You don't like Pass, you don't buy it... I don't need 'revealing' and 'super honest' for often poorly recorded stuff that I like.

 

[okok]

gosh, faulty unit? this is some very good PR

 

[solderdude]

To highlight my earlier post, the following describes the level of SPL exposure before hearing loss occurs. If one is listening to our notional HD650 with a 1V input (i.e. 105dB SPL, which was indicated by another poster as "normal") you are losing hearing capability after 4 minutes.

​

Sound Pressure Level	Sound pressure	Permissible Exposure Time
115 dB	11.2 Pa	0.46875 minutes (~30 sec)
112 dB	7.96 Pa	0.9375 minutes (~1 min)
109 dB	5.64 Pa	1.875 minutes (< 2 min)
106 dB	3.99 Pa	3.75 minutes (< 4 min)
103 dB	2.83 Pa	7.5 minutes
100 dB	2.00 Pa	15 minutes
97 dB	1.42 Pa	30 minutes
94 dB − − − − − − − − − −	1.00 Pa − − − − − −	1 hour − − − − − − − − − − − − − −
91 dB	0.71 Pa	2 hours
88 dB	0.50 Pa	4 hours
85 dB	0.36 Pa	8 hours
82 dB	0.25 Pa	16 hours

​

Guidelines for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH-AINSI and CDC. For every 3 dB sound pressure level (SPL) over 85 dB, the permissible exposure time is cut in half − before damage to our hearing can occur. NIOSH = National Institute for Occupational Safety and Health and CDC = Centers for Disease Control and Prevention. OSHA = Occupational Safety and Health Administration. This may not represent a worldwide view of the subject. Noise is an increasing public health problem and can have the following adverse health effects: hearing loss, sleep disturbances, cardiovascular and psychophysiological problems, performance reduction, annoyance responses, and adverse social behaviour. A person feels and judges sound events by exposure time, spectral composition, temporal structure, sound level, information content and subjective mental attitude.

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.

Music: how loud is loud? (video)

Here is a much needed video on the topic of how loud we really listen to music. And issues related to hearing damage, etc. It is an argument that seems to come up twice a day since I started testing headphones. Here, I review the literature on true dynamic range of music and considerations...

www.audiosciencereview.com

power, efficiency, levels, balanced, impedance

home back to Learn published: Dec-11-2013, last update: Oct-17-2022 Power levels, efficiency, impedance, voltages, current, balanced (bridged) versus single ended (common ground), sound pressure&#8…

diyaudioheaven.wordpress.com

 

[BeeKay]

I just don't get why people consciously induce distortion into devices designed to reproduce recorded music, or use such devices to listen to music and imparting the same distortion to every type of music. I understand guitarists using distortion - they're creating the flipping music to begin with.

Spot on. The hobby I started with is Hi-Fi. Not boutique distorted sound by weird engineering. Everything other than ruler flat frequency response is something to overcome. Not to cherish. Instruments should be recreated with high fidelity not being added as part of the gear. The moment I see a musical (replace by any hardly logical high end attribute) amp or DAC, I start running away. Bruno Putzeys solved the riddle to a high degree. Nearly all is left are speakers.

 

[pma]

This is a Wayne Colburn design btw, not a Nelson Pass (who only does the power amplifiers). But that psu is bad, the rest is what to expect from Pass Labs. High low order harmonic distortion in their amps is their signature, and their selling point. But normally that is in a outside that harmonic distortion, a very low distortion amplifier for it's class. And this is not the case here.

The psu seems to be not really regulated as far as i can see in the picture of the inside (i could have missed something). That should be standard these days, and is something Nelson Pass insist on in every diy design he presents. So it would be strange that it's not done in this one.

And i think it's better to use an wel build SMPS for this, much easier these days to make the noise they make so low it does not matter anymore. And for that pricepoint the cost to do it should not matter.

PSU related hum spectral components are related to both poor PSR and EM coupling from the toroidal transformer.

Engineering and production QC is poor, the high price is not reflected in QC. Interesting and the product to be avoided. Still, it will find its buyers, due to the marketing bubble.

 

[Extreme_Boky]

The mains wiring loom and voltage selection should not be placed on that area of the PCB. It should be on an independent little PCB located in that empty space, away from everything. This would reduce THD + Noise a fair bit.

The IEC filter should have lugs at 90 deg to the right (looking from the top), so that the mains loom is very (extremely) short. Would help with the above distortion & noise reduction.

What is kind of really hard to accept is the fact that the audio signal is sent via a flexible ribbon cable to that volume pot, and then back to the PCB. That volume pot should be placed right where the ribbon cable connector (on the PCB) is located - and then a metal shaft should've been used.

The ribbon cable connectors should have side locks... it is kinda obvious... isn't it.

The distortion harmonic spectre is what Pass Labs does.... like it or hate it. It does not look good when measured, that's for sure.

 

[okok]

The mains wiring loom and voltage selection should not be placed on that area of the PCB. It should be on an independent little PCB located in that empty space, away from everything. This would reduce THD + Noise a fair bit.

The IEC filter should have lugs at 90 deg to the right (looking from the top), so that the mains loom is very (extremely) short. Would help with the above distortion & noise reduction.

What is kind of really hard to accept is the fact that the audio signal is sent via a flexible ribbon cable to that volume pot, and then back to the PCB. That volume pot should be placed right where the ribbon cable connector (on the PCB) is located - and then a metal shaft should've been used.

The ribbon cable connectors should have side locks... it is kinda obvious... isn't it.

The distortion harmonic spectre is what Pass Labs does.... like it or hate it. It does not look good when measured, that's for sure.

thanks for describing the $6600 headphone amp

 

[BDWoody]

Presumably in recent decades most pro gear has had less distortion than in decades prior (though the SINAD war is a pretty recent phenomenon).

Is it?

Seems they were selling high fidelity, not emphasizing it's pleasing distortion characteristics.

 

[xnor]

To highlight my earlier post, the following describes the level of SPL exposure before hearing loss occurs. If one is listening to our notional HD650 with a 1V input (i.e. 105dB SPL, which was indicated by another poster as "normal") you are losing hearing capability after 4 minutes.

It is not that simple and the NIOSH recommendations also are not safe. See the link in my signature. There's also a spreadsheet.

Depending on the program material, a 1V RMS full-scale sine wave at a sensitivity of 105 dB SPL/V may resulting in an integrated listening level ranging from roughly 80 dBA allowing 40 h/week (according to WHO ITU H.870) to 98 dBA allowing only about 38 minutes/week.

If levels were actually boosted to 105 dBA then this would reduce safe listening time to less than 8 minutes/week. It would also require insane peak voltages for uncompressed, high dynamic range content.

 

[Deleted member 21726]

Weird:

Pass Labs HPA-1 headphone amplifier

When Pass Labs is mentioned, it's natural to think of its founder, iconic engineer Nelson Pass. But Nelson heads a team of engineers at the California company: Their XP-30 preamplifier, which I enthusiastically reviewed in April 2013, was designed by Wayne Colburn; and the subject of this...

www.stereophile.com

Pass Labs' HPA-1 offers superb measured performance that reflects equally superb audio engineering.—John Atkinson


Did @amirm listened this amp before or after measurements?

 

[Extreme_Boky]

You don't listen.

You just check the measurements and buy based on that.

Simple.

 

[Deleted member 21726]

^

I assume.