Pass Labs HPA-1 Headphone Amp Review

[voodooless]

It doesn't perform like it.

Well, they forgot to connect the feedback loop…

 

[Jokerbre]

Idiots from diyaudio.com locked the thread.

 

[Alcophone]

It doesn't perform like it.

Its power consumption doesn't change depending on the volume level or how much bass there is, even with the inefficient DCA Stealth. That's class A like behavior as far as I understand it.

 

[tallbeardedone]

Stereophile measured this and both objectively and subjectively evaluated it as excellent:

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

Thoughts Amir? @amirm

I'm very interested in what you think of the stereophile evaluation.

 

[solderdude]

Stereophile measured this and both objectively and subjectively evaluated it as excellent:

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

Thoughts Amir? @amirm

I'm very interested in what you think of the stereophile evaluation.

see post #160

 

[tallbeardedone]

see post #160

I'd like to hear @amirm 's perspective. It's interesting to me how JA can twist the measurements to make it appear to have "superb measured performance that reflects equally superb audio engineering."

 

[Jimbob54]

Can someone answer the question when would spending over $1000.00 for a headphone amp be a good idea ? I’m seriously asking.

When it is incorporated into an RME ADI 2 DAC. But that is a cheating answer.

 

[amirm]

Stereophile measured this and both objectively and subjectively evaluated it as excellent:

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

Thoughts Amir? @amirm

I'm very interested in what you think of the stereophile evaluation.

It is hard to analyze some of his measurements as they lack clear parameters. Take THD+N vs frequency:

For this type of measurement to make any sense we need to know the bandwidth used. Otherwise we don't know how much of the harmonics of high frequencies are included in there. Compare it to mine:

Notice how I am using 90 kHz bandwidth which allows up to 4th harmonic of 20 kHz to be counted. If you reduce that bandwidth, then the curve flattens just like he is showing.

Take his only FFT measurement:

You see that he is using 50 Hz main tone. This operates the am in its lowest distortion mode per my measurement above. I don't know why JA has picked 50 Hz anyway. Harmonics of that are far, far less audible than 1 kHz.

His power curve into 30 ohm is actually quite similar to mine:

The difference is that I proper stop at 2 volts as hardly any non-pro DAC outputs more voltage than that. It is clear JA drove it harder to get the clipping.

Most importantly, he has no reference to know what is or is not excellent unlike my graphs. That way, he can declare anything excellent and get away with it. I can't when you see the measurements of THX or Benchmark amps.

 

[amirm]

Idiots from diyaudio.com locked the thread.

A shame as I did not see any hostility there. Folks were just talking back and forth. Answering some of their questions, I am driving the amp harder than the 2 volt dashboard. That 1 khz tone also the best case distortion rating for the amp, not the worst which occurs in higher frequencies. And distortion in high frequencies is precisely jumped out at me. Folks said I "hate" pass labs. I am without emotion as I go into every review. I can't afford to act differently as measurements must back what I claim. I am not like a subjectivist reviewer who can say anything and you have no way of disproving it. An amp that runs out of power is going to sound poor into a power hungry headphone. There is no two-ways about it unless you listen at very low levels which I noted.

As to the review not being "scientific," it is not supposed to be. I am doing a review which includes subjective remarks about the look and feel of the unit in addition to fidelity. This is not a white paper. It is not like there is any other review out there more "scientific" than mine. The review creates reliable results which is part and parcel of scientific endeavor but I have never called my reviews science. They are tests of product. No reason to elevate them to that level and then complain. To be sure, some science is thrown in as I comment on measurements but that is it.

 

[voodooless]

As to the review not being "scientific," it is not supposed to be. I am doing a review which includes subjective remarks about the look and feel of the unit in addition to fidelity.

If you don’t do a listening test:

But did you listen to it?

If you do a listening test:

But that’s not science!

You can never win…

 

[confucius_zero]

inb4 somebody claims this amp made their hifiman HE6 or sennheiser hd800 sound glorious

 

[amirm]

The reviews read like this, "it is a Pass Labs so of course it sounds great." What amazing brand he has built. Power of gorilla marketing in forums....

 

[ObjectiveSubjectivist]

inb4 somebody claims this amp made their hifiman HE6 or sennheiser hd800 sound glorious

Oh yes. They say for example that benchmark HPA4 cannot drive susvara but pass hpa1 is very good option.....
Its funny and sad at the same time.

 

[Jimbob54]

The reviews read like this, "it is a Pass Labs so of course it sounds great." What amazing brand he has built. Power of gorilla marketing in forums....

Wrong guerilla bossman.

 

[SKBubba]

I rarely listen to headphones. But if I did, there's no way I'd pay more than the entire cost of my pretty good stereo/AV/speaker setup for inferior performance that only I can listen to.

 

[Geert]

Switching to high impedance Sennheiser HD-650, to my surprise, made it worse. Yes, there was enough volume now but distortion would set in early and keep getting worse. At max volume, the sound was miserable

@amirm , is my assumption correct that for the listening test you were using higher levels than for the measurements? And give the measurements showing rising distortion with higher volumes and lower impedance, the distortion you heard is probably worse than the measurements indicate? (The max output level for the measurements is about 5V if I'm not mistaken while the amp seems to be designed to provide at least 24V, needed for high impedance headphones).

 

[amirm]

@amirm , is my assumption correct that for the listening test you were using higher levels than for the measurements?

I listen to range of volumes from below to above the measurement in the dashboard.

 

[Geert]

I listen to range of volumes from below to above the measurement in the dashboard.

I can imagine, but it's the levels where you heard distortion that are interesting. The reason I ask is some people argued the measurements of the amp are not that bad and distortion levels are below audible threshold. But if you see how they evolve with higher levels and lower impedance I'm not to sure of that.

 

[Deleted member 4708]

Stereophile measured this and both objectively and subjectively evaluated it as excellent:

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

Thoughts Amir? @amirm

I'm very interested in what you think of the stereophile evaluation.

Someone gets a "minus F" for not doing their work:
Pass Labs' HPA-1 offers superb measured performance that reflects equally superb audio engineering.—John Atkinson
vs
I can't express enough how the HPA-1 ruined the sound of the two headphones I tested with it. Had this been my only experience, I would have thought neither headphone is any good! This mirage of more distortion is good for you needs to go go away and commitment to fidelity restored. - Amir

For 3600$ it better measures like a Benchmark HPA4. Or else.

 

[milosz]

The Stereophile review showed better THD results than Amir's test revealed. I wonder if there is a unit-to-unit performance difference here?

The use of a design that allows a little low order THD tends to make things sound more "tubelike" and more like the kind of sound produced by guitar amplifiers.... to some people this is "more musical;" and some research has shown that a little 2nd harmonic makes the stereo image sound "deeper." But this amp doesn't allow "a little" low order THD- it is way worse than "a little." I am surprised by the amount of power supply noise. That is inexcusable unless they are going for the "blues bar" sound here....

These are made in small numbers and built the USA, and as such they will be expensive. Here once again we have proof that "U.S. Made" and EXPENSIVE do not always translate to HIGH QUALITY.