DCHFG Loaner Program - Benchmark HPA4 Headphone Amp Review

[Chris]

Benchmark HPA4 Headphone Amplifier/Preamp Review

This review is made possible by the DCHFG HiFi Component Loaner Program.



The Sound of Silence.

Benchmark Audio is an engineering focused company with a deep heritage in the recording studio world. With the release of the DAC1, they also grabbed the attention of the Audiophile world and things have never been the same.

The HPA4 is a Headphone Amplifier and Preamp that incorporates the THX-888(AAA) achromatic audio amplifier circuit that was first introduced to the world in the Benchmark AHB2 amplifier. To this day the AHB2 remains the lowest distortion and highest SNR amplifier on the market.

What does all this technology get you from a listening stance is the cleanest and most accurate delivery of sound you are likely to get with any Hi-Fi component. In contrast, this is the direct opposite of the typical sound of tube-based technology that is awash in second harmonic distortion and noise. It is ironic that there is a such a dichotomy between what professional recording and mastering studios are using and what many Audiophiles prefer when listening to tube based components.

The HPA4 is ready to work with just about any modern headphone you care to use and offers 6 watts into 16 ohm and a whopping 11.5 Vrms into 300 Ohm headphones. You will not be running out of power with this device.

Many Benchmark products have a utilitarian interface, but Benchmark has introduced a Touch Screen Control with the HPA4 that might signal a new direction for future Benchmark products. This allows the user to directly access advance features such as balance control, input level offsets, input names, screen dimming, remote control and function locking.

Listening.

I started my listening tests using the HiFiMan HE6se headphones. These headphones are a bit of tough load for many headphone amps. The HPA4 had no trouble driving them and only required a slight increase in gain that was easily available through the touchscreen.

I followed up with my 2022/2023 headphone of the year - the Meize 109 Pro. I used the track "Slink" from the brand-new Artemis album on Blue Note. This track was written by Lyle Mays of the Pat Metheny Group and appeared on his first solo album. It is a very dynamic driving track and the Artemis ensemble makes the most of it. The 109 Pro's sounded excellent being driven by the HPA4 and revealed all the sonic details of this track.

Conclusions.

I did not use the HPA4 in its other intended usage as an ultra quiet line preamp driving an amplifier and speakers. With its ample inputs and outputs, I have no doubt it would perform just as well in that role as it did just driving headphones.

I give the HPA4 my highest recommendation. Using the common Audiophile cliche - this is an end game component. Of course, that is until Benchmark Audio one ups itself with a new improved version which they have a remarkable habit of doing.

[Chris]

Feed-Forward Error Correction

The Benchmark AHB2 power amplifier and HPA4 headphone amplifier both feature feed-forward error correction. This correction system is an important subset of the patented THX-AAA™ (Achromatic Audio Amplifier) technology.

It is one of the systems that keeps these Benchmark amplifiers virtually distortion free when driving heavy loads. It is also the reason that these amplifiers can support 500 kHz bandwidths without risk of instability when driving reactive loads.

This paper explains the differences between feedback and feed-forward systems.

[John Gatski President/Founder]

Chris

  I was the first to review the HPA4 back in 2018; it listed for about $3,000; it is now $3,495.  HPA4 is indeed one of the most transparent HP amp (and line amp) I have ever used. With is resistor-based, high-end, NEC attenuator control and various other direct path design tweaks, it is incredibly quiet (-125 dB+ noise) and dynamic to allow an amazing level of accuracy. With accurate headphones you can hear reverb tails, room delay, instrument overtones that are totally life-like in well recorded music. A couple of HP designers borrowed my HPA4 and reported back that the HPA4 was totally uncolored and delivered ultra-real dynamics — with gain or attenuation. It was reported back by the designers that the HPA4 never added anything under gain and never lost any detail through attenuation with their HPs.

  The HPA4 is optimized for HP listening because it has fewer line I/O options, but if you need just a couple of inputs (2 unbalanced and balanced XLR) it is the same transparency with line sources. When I want to listen to super, revealing audio through accurate, super revealing speakers, I have heard no preamp that beats the transparency of this preamp. No Color, no euphonica; its not warm unless the music is warm. It is not cold unless the music is that way. If there is color in your other components the Benchmark will showcase that as well. Benchmark does make a line stage minus the HP amp (and THX amp stage circuit, which is HP amp only). The LA4A, which is a thousand bucks cheaper, offers only the line I/O with four sets of inputs, balanced and unbalanced. Same chassis same cool touch screen (now with much large numerical display parameters).

   I have found much utility for the Benchmark HPA4 as  a reviewer, including using it as an A/B tester. Because of its ultra-accuracy, its input trims for perfect source matching and fast remote-control input switching, it is a fine A/B tester for HPs or line out to amp/speakers. I have shot out numerous DACs with this HPA4, confident that its neutrality would lead me to hear real differences between DACs, or no differences. That alone is worth the price of entry if you like comparing audio components. Audible effects of analog and digital design in DACs often is subtle for actual discernible difference between products. If they are there and you have the right monitoring HP or speaker tools, you can hear them via the Benchmark HPA4.

  I have owned more than 60 line-stage preamps (tube, ss, digital, hybrids, etc.) since 1986 and was impressed by the sonic delivery by several of them. But few are as  accurate as the Benchmark design, and it is extremly rare that one can outperform it. When the HPA4 (and later the LA4) came out, the reviews were exemplary: ("Benchmark's LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered." — John Atkinson, Stereophile; "The Benchmark HPA4 is one of the most transparent headphone amps I have ever heard — at any price. Just as impressive is the line stage, which delivers volume control that many an esoteric analog or digital preamp could only dream of." — John Gatski, Everything Audio). However, I think a lot of audiophile were not convinced that such a moderately priced preamp could relay such transparency. Well, brother the Benchmark does does, indeed. do all that.

Anyone who wants to try mine with their own cans or line sources, message me back. You can hear for your self.

[SteveF]

Through the DCHFG Loaner Program, I have been auditioning the Benchmark HPA4 Headphone Amplifier for the last few weeks in my two channel audio system.
Here is my Headphone Amp and Source component configuration list used for this review:
Sources:  Tidal and Qobuz High Res Streaming using Bluesound Vault2 streamer, DAC's: Oppo BDP-105 and Topping DX7 Pro+
Headphones:  BeyerDynamic T1 v2
Headphone Amps:  Topping DX7 Pro+ DAC internal Headphone amp, and the Musical Fidelity X-CAN V3
Note that the BeyerDynamic T1 v2 Headphones are nominally 600 Ohms which requires a higher output voltage capable amplifier as opposed to lower impedance headphone loads.
The HPA4 had absolutely no difficulty driving the BeyerDynamic T1 v2 headphones and there were no compromises in performance observed.

My HPA4 Product Impressions:
The overall HPA4 packaging build and color touch screen control are of very high quality, and operation was easy and reliable with a very positive high end feel in every way.
Clearly this is a very High End audio component with no compromises in the overall build quality "feel" with an excellent color touch screen with volume knob operation.  I did not have the remote control to use.
The volume control is a fully balanced audio relay switched precision gain stage variable attenuator.  Operation was quiet and smooth during adjustments.
There are two separate vertical bar graph displays showing the set level of both Headphone and Line Audio outputs at all times.  Nice!
There are both RCA and XLR balanced inputs and outputs, all very high quality.
The HPA4 internal THX-888 amplifier design uses feed-forward error correction technology for an extremely low distortion and flat frequency response. 
This THX-888 amplifier is manufactured by Benchmark under license from THX.  Needless to say the HPA4 amplifier technical specifications are outrageously good in every way!  No compromises!
The HPA4 amplifier is rated to deliver 11.9 Volts RMS into 300 Ohms and 6 Watts into 16 Ohms!  A very significant power output capability for a Headphone amplifier!

So how does the HPA4 sound driving my BeyerDynamic T1 v2 headphones?
Simply stated, unbelievably good and totally clean and dynamic, no coloration at all, super natural and very detailed, best I have ever heard from these headphones 
I had been told that the HPA4 was one of the very best Headphone amps available, and as a lifelong audiophile and professional Electrical Engineer, well I was more than skeptical.
After two weeks of daily listening to all types of music, all in High Resolution from Tidal and Qobuz, and using two different DAC's, I can say without any hesitation that this is the best and most accurate headphone amp I have ever experienced.  Let me explain a little further.

I was able to compare the HPA4 to two other Headphone amps in my collection; the Musical Fidelity X-CAN V3 and the internal Headphone amp in the excellent Topping DX7 Pro+ DAC package.
Headphone Amp Comparison Summary:
The HPA4 was by far the best Headphone amp in every way; more effortless detail, no coloration, smooth and clean, no listener fatigue, super detailed, just perfect!
The second best performance was the solid-state amp in the Topping DX7 Pro+ DAC, and it was very good except the overall transient response was more "soft" and the natural detail seemed restricted with a less open sound stage, and at times harsh sounding in the treble response.  The HPA4 had none of these issues for sure!
The Musical Fidelity X-CAN V3, which is a hybrid two triode and solid-state amplifier design was way less dynamic, had a rolled off treble response, less overall detail and a noticeably narrow sound stage, and a somewhat  unnatural bass response.  The X-CAN V3 two triode tubes are "new" from a trusted source so the X-CAN V3 was just showing the limits of this 20 year old design. 

So what did I really like about the Benchmark HPA4 Headphone amplifier:
-The Sound quality at all volume levels is very natural, effortless, very detailed with a large and natural sound stage, all in a way that seemed just colorless and absolutely true to the recording.
-The HPA4 handled all music genre's equally well; Classical, Male/Female vocals, Acoustic strings, Rock, Jazz, Electronic music, everything with no limitations.  Pretty amazing!
-The sound of the HPA4 is very detailed and revealing, and some might say a little technical in a pure accuracy way.  I like this because there is no perceptible coloration of the recording, for better or worse.
-There is no noise floor or distortion that I could hear, just a super quiet "black" background that reveals detail in recordings I had not noticed before.  What a nice surprise!
-I have the feeling that the HPA4 can drive any headphone on the market with full no compromise performance, however my review is limited to the BeyerDynamic T1 v2 only.
-The HPA4 build quality feels and looks very High End, with a very nice color touch screen and rotary volume knob control.  I did not have the remote control to use.
-Bottom Line is that this is the most accurate and true "no coloration" Headphone amplifier I have ever used.  I love it!

Was there anything with the HPA4 I did not Like:
-In a word, No!
-I will note that some audiophiles do prefer a "softer" and less "technical & highly detailed" sound reproduction, which is a personal preference I respect for sure. 
The HPA4 may not be for you if want the softer presentation and the added "sweetness" of a pure tube based headphone amplifier. 

I did not test the HPA4 in a preamplifier system mode, since my interest was in the Headphone amplifier operation only.
I have no doubt that the HPA4 would make an excellent system preamp with the same exceptional performance noted in my review.
I highly recommend the Benchmark HPA4 with full confidence that you will love this high end audio headphone amp as much as I do!