Benchmark HPA4 headphone amplifier/line preamplifier

I am certain the quality of life I live is determined by two factors: who and what I give my attentions to, and my ability to observe all that I encounter with an open mind. This approach to living has served me well—especially during this review of the Benchmark Media Systems HPA4 headphone amplifier ($2999).

While removing the Benchmark HPA4 headphone amp from its simple-but-effective packaging, I noticed three things. First, I noticed that the amp had shipped from Syracuse, NY, where it was made. Second, one whole side of the box said "Benchmark. . . the measure of excellence!™" As I cut the clear tape with my boxcutter, I noticed the "THX Technology" logo printed on it and wondered why it was there.

After sliding it out of the box, I held the HPA4 in both hands and turned it around, examining all six sides. It was light, weighing only 8lb, and compared to most audiophile-level headphone amplifiers, it was small. According to the HPA4's spiral-bound instruction manual, it is a "half-rack wide" (8.65") and "2 RU" (rack units) high (3.47"), and only 9.33" deep including knobs and connectors. The HPA4 occupies the same stacking-friendly footprint as Benchmark's DAC3, although it's roughly twice as tall.

After admiring the black, 0.5"-thick, brushed-aluminum side panels, I looked at the HPA4's 0.25"-thick brushed aluminum front panel. The first thing I noticed was a 3.5" Color TFT touchscreen and thought, "I hope that screen has a dimmer." (It does.) The manual says the touchscreen is a "Status Display" that uses two bargraphs to indicate volume (separately or together) for headphone and line outputs (footnote 1).

On the left, just under the screen, I noticed a small (0.25") black button that I guessed was the power-on button, but there was no labeling to confirm that it wasn't a wayward faceplate screw. I was right—it was a power button. Next to the power button is the tiny infrared receiver sensor. To the sensor's right is the 0.25" headphone output jack. Next to that is an XLR output jack. Farthest to the right is the big, click-stepped volume control.


Looking at the chassis's back, it finally hit me. This thing is not just a headphone amp; it has four (!) line-level inputs: two unbalanced (RCA) and two balanced (XLR). Then I peeked again at the instruction manual. The HPA4 is not just a "Reference Stereo Headphone Amplifier"; it is also a "Reference Line Amplifier" with "Relay Gain and Input Control." I didn't know what that last thing was, so I checked Benchmark's website and consulted via email with John Siau, Benchmark's vice president and chief engineer.

The attenuator
Siau explained, "The Benchmark attenuator is actually a fully balanced relay-controlled gain stage. It applies up to 15dB of gain or up to 127.5dB of attenuation for a total range of 142.5db. There are 286 volume control steps in precise 0.5dB increments. Of these, 256 are mapped to the user volume control. The remaining 30 steps are reserved for the balance control and for the input boost and cut functions that allow ... level matching of the four analog inputs. When this is set properly, the user can switch between sources without experiencing a change in volume level."

The circuits
The THX-888 headphone amplifier board "is a unity gain (current) amplifier with feedforward error correction." Feedforward error correction is also used in the AHB2 power amplifier. According to Benchmark's website, the HPA4 can deliver up to 11.9V RMS into 300 ohms and 6W into 16 ohms: "The THX-888 headphone amplifier board in the HPA4 is manufactured by Benchmark under license from THX."

Reference line preamplifier
After unpacking, I replaced the hybrid (transformer-tube-JFET) Rogue Audio RP-7 line-level preamplifier ($4999) with the Benchmark HPA4. My plan was to start by auditioning the Benchmark as a line stage in my floor system, which consisted of the Dr. Feickert Blackbird turntable with a 10.5" Schick tonearm, and a Koetsu Rosewood Signature Platinum moving-coil cartridge feeding Sunvalley's SV-EQ1616D phono equalizer. Digital came from my reference HoloAudio May (Level 3) DAC feeding the balanced inputs of the HPA4 via Cardas Clear Cygnus interconnect. The Benchmark's 30 ohm output impedance fed the 33k ohm input impedance (via unbalanced Cardas Clear Cygnus) of a Parasound A21+ stereo amplifier powering Harbeth M30.2 monitors, via the extremely neutral Triode Wire American Series loudspeaker cable.

During my first day of HPA4 listening, I noticed that every digital and analog recording was sounding curiously similar. They all sounded cleaner, better sorted, and more macrodynamic than they had with the Rogue, but strangely, compared to the RP-7, hall resonances and piano note reverb tails seemed shorter to me.

I played Neil Young's soundtrack to Jim Jarmusch's 1996 film Dead Man (16/44.1 FLAC Vapor Records/Tidal), and as always, the illusion of a sound space was enormous, but the HPA4's "enormous" sound space was different: images of performers inside the illusion appeared more distinctly outlined and concrete than I routinely observe with the Rogue. This sense of image concreteness appeared to be caused by, or enhanced by, the fact that the "empty spaces" surrounding these instrument and performer images were now the most air-free, glare-free, nonrefractive environs I have encountered while listening to home audio. In comparison, the RP-7 delivered the same recordings with a subliminal sense of looking through a not-quite-perfectly-clean camera lens (of a certain focal length) onto an illusion with air dense enough to resist the motions of my Japanese paper fan.

This Jim Jarmusch–Neil Young collaboration is a provocative sound collage that relies for its effect on extended actor dialog and a wide range of diverse Foley sounds, including wind, idling cars, and crashing sea waves. Compared to the RP-7, the HPA4 lost some of the wind and ocean sounds, but in so doing, reduced the ambiguity of the other Foley sounds and increased the legibility of Johnny Depp and Gary Farmer's campfire dialogs. With the Benchmark, the total number of identifiable Foley sounds increased.


Working as a line-level preamp, the HPA4 seemed to reduce the levels of reverberant information I routinely enjoy with the Rogue RP-7, but fortunately these reductions were accompanied by a positive effect: They allowed the Benchmark to dramatically enhance something I always crave but rarely get from tube preamps; something which, for now, and for lack of a better a word, I will call aural specificity, which I define as the ability to point at and identify everything I hear. The HPA4's sharp-focus specificity is something I associate with recording studio sound but almost never encounter in home systems.

Driving HiFiMan Susvaras
With most headphone amplifiers, the tires go flat trying to drive HiFiMan's $6k Susvara open-backed planar-magnetic circumaural headphones. The Susvara's low (83dB/mW) sensitivity and flat 60 ohm impedance need at least a few watts, probably a third of an amp, and maybe 7V, plus 15–20dB gain, to play effortlessly and sing with their clearest voice. (I normally drive them with the 25Wpc Pass Labs XA25 power amp.) The HPA4's THX-888TM headphone amplifier is specified at 6W into 16 ohms, maximum output current of 1.5 amps, and a maximum output voltage of 11.5V RMS.

Listening with the HPA4 and Susvara—I used the HPA4's balanced outputs for all my Susvara listening—and playing the full hour of Horowitz in Moscow (16/44.1 FLAC, Deutsche Grammophone/Qobuz) was the first full-length unmitigated musical pleasure I achieved with the HPA4. Shortened reverb tails were not a distraction. On this recording, with the HPA4, the notes from the master's piano were displayed with a weighty force and overtly pacey momentum that showed me more hammers and less pedal. The Benchmark-Susvara pairing moved the performances right along, emphasizing the authority of Horowitz's execution.


Astor Piazzolla's Tango: Zero Hour (16/44.1 FLAC Nonesuch/Qobuz) is an album I consult frequently during component comparisons. It features only five instruments (bandoneon, bass, guitar, violin, and piano) with some added crowd sounds; there is something about its mix that makes it a difficult recording for less-than-the-best audio gear to sort out and present clearly. After my HPA4-Horowitz experience, I had a feeling the Benchmark's absolute clarity coupled to the Susvara's legendary resolving powers would finally show me what the album's producers heard.

Footnote 1: The HPA4 is in fact identical to the LA4 preamplifier, which KR reviewed in our January 2020 issue, except for the addition of the headphone amplifier and outputs.
Benchmark Media Systems, Inc.
203 East Hampton Pl., Ste. 2
Syracuse, NY 13206
(315) 437-6300

Charles E Flynn's picture

I was unimpressed with the industrial design of Benchmark’s products when I saw small photos of them online. I dismissed their efforts as the “American garage aesthetic”, and hardly ever read anything about them. I was astonished when I saw the closeup of their AHB2 amplifier at The more I look at the photo, the more the design grows on me. The heat sinks on the sides of the AHB2 remind me of the Quad 909.

tonykaz's picture

and got kicked off Headfi for troubleshooting Schiit's Asgard, a new little headphone Amp c.2011 ( that I owned one of ).

Mr.NwAvGuy loved comparing to Benchmark, which he seemed to consider the Gold Standard Company and Product. Now, today, our wonderful Mr.HR seems to agree with the pro-audio world on Benchmark's deserving designs.

I would too except for Schiit's fair pricing policy, Made in USA by loyal employee philosophy, exemplary if not outstanding engineering & performance and loooooooonnnnnnggg tail accessible warranty. ( what's not to like ? ). Schiit destroy the concept of making gear in "China"! ( my GM Lady CEO loved quoting Schiit to China promoters )

Benchmark seems to remain the Gold Standard that I don't need to keep handy unless I need to describe a Tube as it compares to a 100% verified Standard.

I hope Mr.HR keeps this tool handy for reviewing work, he will be one of the few to maintain such an accurate reference. ( I know of only a small few others that maintain such systems, myself included )

Tony in Venice Florida where it's a bit to cold to swim

ps. Benchmark is a Quality Product, "Made in USA" by loyal employees, for a fair price !!! It's probably the highest quality product being reviewed, this month, in Stereophile . ( maybe even this year )

Kal Rubinson's picture

I hope Mr.HR keeps this tool handy for reviewing work, he will be one of the few to maintain such an accurate reference.

I, too, hope so and suggest that anyone serious about audio cannot ignore but, at least, try out the Benchmark amps and preamps.

Ortofan's picture

... accurate reference probably do so because they prefer "pleasant" sound quality to "accurate" sound quality.
This situation is little changed from what it was 30 years ago.

tonykaz's picture

Me too, I prefer and go out of my way to find beautiful "Sounding" Gear which typically seems to have pre-amp tubes doing the Singing.

My audiophile customer base at Esoteric Audio would purchase based on audition but sometimes based on : "Reviewers" preference i.e. an HP blessing. ( some folks don't/can't trust their own ears )

I don't own a Benchmark PreAmp but would like to so that I could have a reliable Standard to help me describe differences and explain shortcomings. ( A problem well stated is a problem half-solved ! ). I could become a Tube grader and reliable Seller. Tube grading is a Black Art.

Tony in Venice Florida

Glotz's picture

I wanted to see what HR might find if coupled with some of his power amp references, preferably with his Rogue or something similar.

Will a comparable tube amp lengthen ambient cues or reverb trails to a more musical outcome? Being in the market for a sub $5k power amp, it might be interesting to see if this line amp rises to the occasion.

My next audition will be with a circa-2004 Audio Research VT-100 Mk3.

rschryer's picture

I owned an ARC VT-100 Mk3 and found it uninvolving. I sold it.

YMMV of course.

Glotz's picture

I will audition it at home, but that is insightful, critical information.

Thank you Robert!

rschryer's picture

Good luck with your search.

Ortofan's picture

It's priced under $5K, is compatible with about a dozen different output tube types and has remote-controlled switching between triode and ultra-linear operating modes.

Glotz's picture

I have read only good things from PrimaLuna! Well worth an audition.

With the Magneplanar 1.7i's, power will be an issue.. the 400... hmmm.

Intrigued with tube/solid state hybrids, but still need to be won over on Class D. Class G/H? Sure! Uggh... I got listening to do!

tonykaz's picture

... clearly illustrates the importance and significance of Stereophile and Mr.Atkinson's contributions with accurate measurements.

We Audiophiles seek out gear that sounds better to our ears and sensabilities unlike Pro-Audio people like Bob Katz who need and demand Accuracy.

It's interesting to realize that Audiophile Gear Manufacturers seem to own and use Reference Accuracy gear in developing the products we buy and love the sound of.

Some Audio sound quality designers are Virtuoso in the designs they produce, I suspect that Stereophile writers know fully well who they are and are delighted to share a "find" when it happens.

Thank you,

Tony in Venice Florida

Ortofan's picture

... used in the evaluation of this product has input level controls, could HR not have connected the output of his DAC directly to the power amp and then compared the resultant sound quality to that with either the Benchmark or the Rogue preamp in circuit in order to determine conclusively which preamp more accurately reproduced the reverberant information in various recordings?

Given that reverberant information is a relatively low level signal with decaying amplitude, shouldn't the preamp (Benchmark) with a S/N ratio about 30dB greater than another (Rogue) be better at reproducing such reverberant information?

barrows's picture

That is for sure the question. I agree, that considering the ability to follow reverb tails deep as they approach the noise floor requires superb resolution of low level detail, one would expect the Benchmark to be superb at such.
What is the answer? Perhaps the tube based amp is actually adding information that is really not there via some kind of memory effect? In loudspeaker systems, I sometimes wonder if tubes' microphonics are "enhancing" perceived ambience effects by the addition of microphonic artifacts, but I do not see how this might happen in headphone listening. It is curious...

Glotz's picture

From what I hear and see, louder 2nd order harmonics create longer sustain or longer reverb trails/cues in tube gear. They enhance notes to sound more like live music (in a similar but very different way modern Magneplanars do operating as dipoles by adding or creating something that is there in the chain but not to the extent of what is purely accurate, ie: at the proper relative loudness levels in time and FR).

I've owned solid-sounding tubed Counterpoint gear in the past, and despite being a really happy owner of the HPA-4 for almost a year, there is sustain, if not a liquidity between notes that tubes are famous for and I do miss.

The question I hope to have HR answer is can tube magic be added later in the chain at the power amp side? It'd be fun to see what he thinks, and others.

This is counter to what traditionally has been suggested with my current solid state amp.. a newly-modified Belles 150a Hot Rod in conjunction with a great tube preamp, like Audible Illusions (or Rogue or whatnot).

RS gave me some direction in that area and I am grateful for that, and it is a great opportunity to challenge myself in the on-going battle with my biases between accuracy and musicality.

I've never given up on tubes, I just feel there way too expensive for normal people to afford. Lol..

I kid, but not really.. $10k seems like the magic satisfaction point for both amp and preamp or even an tubed integrated. Lotta cash for anyone less the retired or super-successful. (The Cary Audio 120 watter looks like another candidate...)

helomech's picture

I think you nailed it in your first paragraph.

It is quite obvious in my comparisons of a very low-distortion chain (Topping D90 into passive Schiit Freya+ into AHB2) and tube gear. Merely switching between the tube and passive outputs of the Freya make this apparent. Tubes add harmonics that can be pleasant, however, they should not be mistaken for truth/accuracy...especially by veteran reviewers.

Unfortunately, the other components Mr. Reichert employed in this review were somewhat of a bottleneck, albeit good pieces in their own right.

Having gone from tubes to an entire chain of near similar performance to the LA4/HPA4, I now find it a little difficult to enjoy tube gear — what I used to perceive as ambience and decay is too often now heard as what it is — distortion. An analog source can mostly offset that though, probably due to a phenomenon of complimentary distortion and higher noise floor.

Glotz's picture

...that really cannot be reduced to tubes are inaccurate vs. solid state are more accurate based on existing measurements. The test you are using with the Freya is not endemic of expensive tube performance. I do agree what you hear is what you hear, but with inexpensive tube equipment it is easier to hear deviations from accurate vs. expensive tube equipment.

Moreover, the cabling between the Topping and Freya to the AHB2 will also have a huge effect on the opinion of the Freya in-line, as well as its attendant impedances (and other factors) to and from each component.

For example, Audio Research tubed gear is leagues more accurate while bringing additional 2nd order harmonics into play without being an even slightly-obvious deviation from accuracy. It can and does sound far more accurate than most solid state gear while pulling off magical things in the midrange FR spectrum, extension in the treble with refinement, and space retrieval that only 'expensive' tubes can provide.

If inserted the Freya in between an AR preamp and amp, we would hear the Freya sour the sound and measurements for that combo as well. (Not disparaging Topping or Schiit- I own the Modius and it is a great DAC for the money.)

It sounds like bs, but again better parts quality makes audible the 'unmeasureables' that one won't hear in cheaper equipment.

Think like 'microscopes that magnify different things'. Magnifying 2nd order harmonics may give the impression of poorer performance but it adds liquidity of the time presentation that is more like real music in a live space, and therefore to the ear, more 'truthful', but technically not more 'accurate'.

Outside of strict FR deviation, the argument is as arbitrary as saying 'what do you want to magnify in the spectrum of all areas of audio performance?'.

Again, it really comes down to MF's "You pay, you get".

The T&A Headphone and amp and the Audio Research REF 6E reviews show insight here, as they 'improve' upon the HPA-4 without necessarily having better measurements. They add things but retain accuracy and deviate positively from 'strictly accurate' in the high treble and other areas of performance. Parts quality is the culprit.

helomech's picture

I’ve owned more expensive tube gear and have heard cost-no-object tube-based systems. The Freya is quite competitive despite its price and measurements back that up. And no, Audio Research gear does not perform better in bench tests.

In most cases, I’d agree that you get what you pay for, especially when it comes to speakers and analog. When it comes to amps, preamps, CD players and DACs, I no longer find that to really be the case, not within the last few years anyway. Some of the Chi-Fi tube amps are embarrassingly good, same for DACs.

And yes, when it comes to linearity, distortion and dynamic range, Benchmark’s products are indeed more faithful to the original signal, more so than any tube-based product. That’s indisputable. Why it is that so many fans of tube gear can’t simply admit they prefer colored, inaccurate sound is beyond me. There’s nothing wrong with preferring a particular flavor of sound, but to deny the science as so many do these days is a bit silly. Unfortunately, that’s the way this country is trending. I figure it won’t be long before we’re holding witchcraft trials in town squares.

Glotz's picture

I do own the HPA-4. I do love tubed gear. In the room, they can be paired to provide a number of musical combinations.

Both can produce accurate, uncolored sound. One costs more to get there, and that does matter. In the case of AR, one is just splitting hairs about measurements and not really talking about sound at all when noise gets 90-100db down in level. An extra 30 db less noise in the the HPA-4 is a lot theoretically, but it may be missing other critical areas of the musical spectrum by not adding artifacts that do sound better.

Is it necessary that the REF 6SE be lower in distortion to sound better? No, I say.

I think when tube fans get down to listening at very low levels, they believe that splitting hairs on noise, accuracy and truth is better fought with closer-toleranced and more expensive parts to bring about changes in other parts of the spectrum of sound (which do have an somewhat smaller impact on distortion figures, yet do improve).

I think HR explains it well below on S/N ratios and how tubes find details that solid state can miss, depending on quality and implementation level.

JHL's picture comes to linearity, distortion and dynamic range, Benchmark’s products are indeed more faithful to the original signal, more so than any tube-based product. That’s indisputable. Why it is that so many fans of tube gear can’t simply admit they prefer colored, inaccurate sound is beyond me."

That's simply untrue - it's an assumption followed by an assertion. An associate recently moved out of a Benchmark system into two others; one a very advanced triode amplifier and the other a Naim Nait. Both trounced the former - which he had been quite taken by, owing to its excellent spec and sound - in no uncertain terms.

It was a costly move. There were no regrets. The *latter* made less colored, more accurate sound.

How do we know this? By *ear*. Why, technically? Nobody knows.

We can't make assumptions, follow them with conclusions not based in fact (or technical knowledge) and make sweeping generalizations that reach all the way back into the other listener's head. That's not credible.

We can have opinions but they stop where they stop. The admission that must be made is that one.

helomech's picture

on the measurements. Fact: other amps are more distorted with higher noise floor. Preferring more expensive gear doesn’t make it more honest, just as perceiving the Earth as flat doesn’t make it so. Ironic and fitting that you use Naim as an example.

JHL's picture

Obviously the statement that X sounds like X and Y sounds like Y *because of Z measurement*, when 1) measurements are obviously inherently limited and 2) human perception is the reason to do audio, is an assumption.

You're conflating limited data and all sound when you may not conflate them if you are to be, as I suspect you endeavor to appear, objective. (You'd also performed some intentionalism above, which is antithetical to objectivity as well as being bad personal form).

Herb Reichert's picture

One of the chief reasons I prefer pure low-feedback analogue is that it allows me to listen into the noise floor of a recording—where much of this micro-level ambient and reverb-tail information resides.

That being said, I can’t remember auditioning a properly functioning line-level amplifier that was too noisy or distorted. Can you?

Unfortunately, I’ve heard more than a few line stages that obtrusively color the sound of every source connected to them. Haven’t you?

So then somebody . . . please explain the connection between signal-to-noise ratio and an audio amplifier’s linearity or its ability to recover and accurately reproduce small-signal music information? To my knowledge, quiet and accurate are two totally separate performance characteristics.

More to the point: how much reverb-tail information exists below 100mV? Probably most of it.

How much low-signal (10mV or less) music information got lost or phase-canceled trying to achieve the Benchmark’s extra 30dB noise reduction? I don’t know, but I do wonder.

So then . . .

Why not put a single quiet piano note into the RP-7’s and HPA4’s inputs; then compare its decay on their outputs via an oscilloscope, or better yet, a real time analyzer?

Wouldn’t that settle this dispute?

Glotz's picture

I would love to read your thoughts on that, Herb.

PS- You are super New York cool man. Kudos.

Ortofan's picture

... you be able to detect "micro-level ambient and reverb-tail information", then why choose a preamp whose residual noise level forces you to listen into the noise floor to discern that information?
Instead, why would you not want not use the preamp that JA1 described as "the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered?"

Regarding the speculation as to "how much low-signal (10mV or less) music information got lost or phase-canceled trying to achieve the Benchmark’s extra 30dB noise reduction", you should put that question to John Siau at Benchmark and let us know what is his answer.

As far as using a "single quiet piano note" as a test signal, alternatively you could simply use a low-amplitude and relatively low-frequency square wave as a test signal and observe which preamp more accurately passes the sequence of (odd) harmonics that comprise the square wave. Also, check for the presence of any even harmonics at the preamp output, of which there should be none.

JHL's picture

... you be able to detect "micro-level ambient and reverb-tail information"; then using Herb's remark, would you not choose a preamp whose residual noise level "forces" you to listen into the noise floor to discern that information?

(Really, really great record playback doesn't remove noise. It demodulates it into a space where it's irrelevant. It also doesn't succeed because of lightspeed dynamic range and separation; rather it removes veils to the absolute perceptible floor of information. Can we measure this as the benchmark of sound? Who cares. It works as *sound*.)

Objectivist premises are not infrequently faulty: Validate the hypothetical that you would, to achieve the goal Herb has highlighted, question the ear by instead employing a device "described as 'the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion'" device if the ear may not prefer it.

And, as far as using a "single quiet piano note" as a test signal, why not just hook the thing up and use it as intended?

The premises are not infrequently faulty. There doesn't have to be fealty to the bench or to a shortened list of presumed phenomenon. Just use the gear.

We need a Save Stereophile campaign.

JHL's picture

One of those rings-like-a-bell remarks that prove so rare in such threads. Kudos.

I think your remark resonates like it does, Herb, because it differs so markedly from the usual conclusions established on unproved premises.

For example: I observe A in the class of B components, which surely comes from C phenomenon. Therefore C must surely flow from all A.

Well, no. it's been widely hypothesized that in the case of consistently excellent-sounding amplification, transient recovery - ergo "pure low-feedback analogue" - is a consistent design goal, one not generally revealed in the specs or the observed data.

The simple fact we see, for example, H2, H3, et al does not mean they are all that exists to differentiate sound. And in fact, recently an associate vigorously and without hesitation sold off his [Highly Approved] modern amplifier of the type under test in favor of a much more authentic sound from a [Far More Traditional] amplifier marque. He did this by ear and in no uncertain terms; without the slightest hesitation.

And the difference did not, to any *observable phenomenon*, arise from harmonic distortion, sufficiently low or otherwise.

I propose we reconsider our tendency to forget what we know because we've been biased to by the data. SN is only SN.

helomech's picture

Benchmark’s feed-forward error correction does not operate in the same manner as a traditional feedback design. Not that proper use of feedback was ever the true culprit of poor sound anyway:

When you perceive greater inner-detail from tube gear, you’re really just hearing a non-linear response. Don’t get me wrong, this can certainly be fun and enjoyable, but it’s not accuracy.

JHL's picture a misnomer. There either is no such thing or there are versions of it, each then semantically inaccurate.

If I take a triode circuit, develop it well, apply no feedback, and achieve a THD of, say, 0.025%, where in the output is found the audible non-linear response? More importantly, what does it sound like?

(A similar question applies to "proper" versus other kinds of feedback. Where is the dividing line and what does each sound like?)

PS: Be aware that sophisticated audio work tends to have forgotten about as much as some (too many?) publications have yet gleaned, and that the latter tend not to be true authorities on developed, complicated subjects. Let's start with defining exactly where distortion lies and what it sounds like before making sweeping generalizations.

hemingway's picture

Barrows, your suggestion that tubes 'enhance' ambience effects seems consistent with one of HR's own articles ( quoting Nelson Pass, which states:

"So why is the phase important? Well, it's a subtle thing. I don't suppose everyone can hear it, and fewer particularly care, but from listening tests we learn that there is a tendency to interpret negative phase 2nd [harmonic] as giving a deeper soundstage and improved localization [of images] than otherwise. Positive phase seems to put the instruments and vocals closer and a little more in-your-face with enhanced detail."

When I read this benchmark review, it could be that Pass's description of negative 2nd order distortion is the difference Herb observed between the straight ahead benchmark and the tubes, with the tubes adding a negative second order distortion, and the benchmark, not distorting (see the measurements)...

Given the measurements of the benchmark products, I just really have a hard time with this statement in the article:

"Which of these two reproductions [tube versus benchmark] best reflects the original analog tape? I concluded: The truth probably lies somewhere between these two exaggerations."

I cant wrap my head around how or why the benchmark product, based on its measurements, does not simply reproduce what is on the recording and nothing more or less.

You can't fault somebody preferring one or the other. But to say that one is potentially more "true" than the other, cannot be the case.

barrows's picture

"Why not put a single quiet piano note into the RP-7’s and HPA4’s inputs; then compare its decay on their outputs via an oscilloscope, or better yet, a real time analyzer?

Wouldn’t that settle this dispute?"

While this might be an interesting exercise, it would not settle any disputes with me, as one has no way to know if some of that reverb information "recovered" is actually really in the recording, or an artifact of the playback system. What I would like to determine is to be able to distinguish between "accuracy" and artifacts which may be euphonic in nature to some listeners.

Herb Reichert's picture

input signal IS the recording

the output of either amp will easily show whether information has been added or subtracted from the recording

epping4est's picture

Curious. Five days ago, exactly at this point in the comments, I registered a new account and left a comment of my own [relating to the fact that the Benchmark HPA4's 4-pin XLR headphone output is not balanced]. In fact, 4 days ago, I got a reply from John Atkinson.

Today, however, I discovered that my account [and my comments] had been obliterated, necessitating that I create a new account. I say "obliterated" because I was even able to create a new account using my original username -- i.e. I did not get a "username already exists" error.

What's up, Stereophile?

John Atkinson's picture
epping4est wrote:
Curious. Five days ago, exactly at this point in the comments, I registered a new account and left a comment of my own [relating to the fact that the Benchmark HPA4's 4-pin XLR headphone output is not balanced]. In fact, 4 days ago, I got a reply from John Atkinson.

Today, however, I discovered that my account [and my comments] had been obliterated, necessitating that I create a new account. . . What's up, Stereophile?

First thing I do every morning is delete all the new accounts that had been created overnight by would-be spammers but had not yet been used. (These accounts are created by real people but are then handed over to spambots.) It is possible that I deleted your account in error. If so, my apologies.

John Atkinson
Technical Editor, Stereophile