Pass Labs HPA-1 Headphone Amp Review

[Robbo99999]

He sold it before I did the review. Indeed that was the reason I tested it now as the buyer has been waiting for it.

lol!

 

[Addicted to music]

I’ve had a listen to a number of Pass Lab power amps, the ones I had in the house I’m sure had similar distortion figures, but some people like that!

 

[BeeKay]

Appears stereophile’s JA measured a different device

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

 

[Purité Audio]

Yes you would imagine two completely different amps,

Pass Labs HPA-1 headphone amplifier Measurements

Sidebar 3: Measurements I measured the Pass Labs HPA-1's electrical performance with my Audio Precision SYS2722 system (see the January 2008 "As We See It"). I performed a full set of measurements from both the HPA-1's preamplifier and headphone outputs. The graphs all refer to the headphone...

www.stereophile.com

Thanks Amir.

 

[xnor]

This happens when design/engineering is put above the actual outcome. Such dogmatic approaches usually lead to glaring deficiencies in the final, usually overpriced as well, product.

 

[Geert]

The amp under test reportedly was not designed by Nelson Pass but rather by another Pass Labs employee, as mentioned earlier in the thread

Correct, but it's under the Pass Labs umbrella that products with relatively high distortion are being designed and appreciated.

There are multiple Pass Lab amplifier reviews on Stereophile.com and there's always something going on with distortion. Like distortion rising with frequency, output level or low speaker impedance.

Take the INT-25 class A amplifier for example: "its intolerance in the treble for loads of 4 ohms and below means it will work best with loudspeakers whose impedance doesn't drop below 8 ohms at high frequencies". For a 10k amp... (The INT-150 has the same issue). Or the XA30.5 amp: "the XA30.5's decreasing linearity in the top octaves led to a somewhat disappointing result on the high-power, high-frequency intermodulation test".

Often the artifacts or on the edge of audibility, but it must be that their customers believe they get some benefits in return.

 

[DSJR]

Correct, but it's under the Pass Labs umbrella that products with relatively high distortion are being designed and appreciated.

There are multiple Pass Lab amplifier reviews on Stereophile.com and there's always something going on with distortion. Like distortion rising with frequency, output level or low speaker impedance.

Take the INT-25 class A amplifier for example: "its intolerance in the treble for loads of 4 ohms and below means it will work best with loudspeakers whose impedance doesn't drop below 8 ohms at high frequencies". For a 10k amp... (The INT-150 has the same issue). Or the XA30.5 amp: "the XA30.5's decreasing linearity in the top octaves led to a somewhat disappointing result on the high-power, high-frequency intermodulation test".

Often the artifacts or on the edge of audibility, but it must be that their customers believe they get some benefits in return.

Is this where the comments in earlier posts regarding feedback use *and application* could solve this?

 

[Blumlein 88]

Appears stereophile’s JA measured a different device

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

Yes, and yet most of his measurements are not too different than Amir's. A couple of them are more different than they should be. When you tell people THD was .005% it sounds pretty good and meets spec more or less. OTOH, that is about -86 db which compared to $300 devices running about -120 db for that same number it no longer is impressive. .005% vs .0001% you see or 50 times more distortion in the expensive device versus the $300 device it sounds a lot different.

 

[anchan]

With respect to the mains noise, it’s really hard to get lower than -100 dB/V with a normal linear power supply. I’ve built a few power and preamps with both linear and smps, and smps is always way quieter. This despite all the praise/scorn of linear/smps.

 

[BeeKay]

Yes, and yet most of his measurements are not too different than Amir's. A couple of them are more different than they should be. When you tell people THD was .005% it sounds pretty good and meets spec more or less. OTOH, that is about -86 db which compared to $300 devices running about -120 db for that same number it no longer is impressive. .005% vs .0001% you see or 50 times more distortion in the expensive device versus the $300 device it sounds a lot different.

Dunno. It must be these guys feel about getting extinct. That business model reached its endgame. JA for sure is one of a few with credibility. Herb is for the fun of reading, Fremer - I won't even begin re him.

 

[vkvedam]

High end

 

[Geert]

Is this where the comments in earlier posts regarding feedback use *and application* could solve this?

Sure, that's the purpose of negative feedback. But Pass deliberately chooses to use low feedback. His argument: "Negative loop feedback creates higher order distortion harmonics. So it's pretty clear that while lowering the total amount of distortion, negative feedback does increase the distortion complexity". In practise that distortion is taken care of successfully, as proven by measurements, but Pass thinks his approach sounds better.

(Quotes from a interesting interview https://6moons.com/industryfeatures/distortion/distortion.html).

Since some of the measurements of Stereophile.com show better results I wonder if this also can be related to the low feedback design, in the sense that it's less efficient in tackling drifting operating setting when an amp gets older.

 

[AudioSceptic]

stop it... that is like pouring salt into a wound or thumbing an eye!
I know what it feels like dumping $$ and the subsequent grinch-news delivery!

You are right, but what can we possibly say?

 

[AudioSceptic]

The owner is downsizing his audio system and sent this to be tested before he sells it. So it is not an issue for him although you could say it is fortuitous that it is not a loss anyway.

It's a loss if the value plummets, but I suspect the market for this mostly ignores measurements anyway. Apart from the headphone socket, which clearly is a functional component not meant to be on display, the item looks pretty good.

 

[Sokel]

With respect to the mains noise, it’s really hard to get lower than -100 dB/V with a normal linear power supply. I’ve built a few power and preamps with both linear and smps, and smps is always way quieter. This despite all the praise/scorn of linear/smps.

That's the most simple 15-0-15V PS one can imagine,not even LM7815-7915 but double LM7815 the old DIY way.
Not so hard with a little care.
(don't mind the spikes,is lot better after a little extra care)

Cheap analog electronic crossover

I've been playing lately with a very cheap analog 2-in/4-out analog crossover. Is somehow DIY but very easy to fix. To my surprise it measures very decently! (note that has been measured with the worst possible conditions,long cables soldered just to see,adapters,noisy PSU and by someone totally...

www.audiosciencereview.com

 

[AudioSceptic]

The amp under test reportedly was not designed by Nelson Pass but rather by another Pass Labs employee, as mentioned earlier in the thread

Doesn't matter. Whose (company) name is on the thing? Whose reputation is at stake?

 

[AudioSceptic]

If tests like this had been available for a long time a lot of people would have saved a lot of money.

I doubt that the majority of the market for this ever reads objective reviews, just as is the case for the other "high end" stuff that gets rave reviews in the reality-denying audio press/web.

 

[AudioSceptic]

I would really like Amirm to try the Riviera which in my parts is considered a must. https://www.rivieralabs.com/prodotti/elettroniche/
10000 euros would not be enough I think

Not enough for what? You can buy a HP amp with excellent performance for low hundreds of €/$/£, and little more even if you include excellent DAC performance.

 

[Bleib]

I doubt that the majority of the market for this ever reads objective reviews, just as is the case for the other "high end" stuff that gets rave reviews in the reality-denying audio press/web.

Could've been if objective measurements were provided decadas ago. Obviously it will never be purely science based as people like to buy to impress others, lifestyle etc etc
But there's also a part of me that thinks that people don't want to get fooled into giving cash for things that aren't really that great.

 

[solderdude]

Appears stereophile’s JA measured a different device

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

The measurements are actually quite similar when viewed at 1V out (JA measures at 1V out, Amir at 2V)
Except frequency response and PS noise that is...
For some reason (maybe the volpot position) JA measured 60kHz -0.5dB in 100kΩ load, where Amir measured 40kHz @ -0.5dB in 600Ω load (which also isn't bad)
Amir measured 120Hz hum at -100dB, JA at -110dB
No idea why, did NP alter the circuit a bit ? or is there another reason ?