Benchmark HPA-4 – Headphone Amplifier/Pre – Review

It’s been a while since I managed to get some time to write on HeadMania, as it gets harder and harder to find time between work and family these days. It’s also been a while since I have been this excited about an audio product.

As I have mentioned before, HeadMania is part of my audiophile hobby. I don’t get money out of it and it actually costs me to keep it alive. So, my reviews contain my honest impressions as I don’t have any interest other than sharing my experience. Sometimes it might feel like I am overreacting. That’s just me being very excited and passionate about the sound offered by some product. This is about passion after all. This is why it’s important to hear the components for yourselves if possible before buying them. 

I do have a good queue of products that deserve a review here, especially in the headphone department: Audeze LCD-2C, Quad Era-1, Brainwavz Alara. Hopefully I will get some time for them as well. However, in the meanwhile I am using them to test this wonderful wonderful headphone amplifier.

I am actually trying to get my hands on a benchmark product to test and review since 2 years ago, the benchmark ahb2 speaker power amplifier. I have been trying to convince a few dealers here in Romania that Benchmark should be on their list of products to bring to the local market. Most of them were stubborn or didn’t show any interest, because they were concentrating on their line of products.

However, in the meanwhile someone seems to have convince a big local dealer, AVStore and I am happy we finally have these products in Romania. This unit is actually a loaner from my friend Sandu from SoundNews, one of the best audio reviewers I know, but also a good friend of mine. He is one of the reason I got into this hobby and into writing. You should also check out his review on this product. We are definitely on the same page with our impressions. 

Looks & Build Quality

benchmark hpa4 review

Coming from bigger amps in the past, like Audio GD Master 9 for example…. monster in terms of size and weight, seeing the HPA4 is actually very very refreshing. It has a very small footprint and it’s really lightweight. The case is made of well finished aluminium that also works as heat dissipation.

It also has a good quality touchscreen for settings. I like the touchscreen and the implementation. It’s fast and easy to get used to. However, it might be a little overkill for people who are used to simple button settings. It’s possible that using the extra remote would help with this, simplifying the day to day use and bypassing the touchscreen. If you have read some of my reviews before, you might already know that I don’t have a lot of patience for unboxing or giving a lot of details on how the unit works or how it looks like. I am more excited about describing the sound. For getting more details about how it looks and unboxing check out Sandu’s video review.

Rückseite HPA4

Specs and Technology


I think that this is the best headphone amplifier in terms of specs. I hard to find anything like it or possibly even close to it. Benchmark is one of the first audio companies, if not actually the first that started to use the THX AAA technology.


As you see in the picture above, the THD offered by THX is amazingly small.
Of course, the implementation around it is very important and Benchmark seems to have done a wonderful job with that.


THD < -125 dB (0.00006%)
SNR > 131 dB, unweighted, 20-20 kHz
SNR > 135 dB, A-weighted
Frequency Response – 0.003 dB at 10 Hz, -0.001 dB at 20 kHz
– 3 dB Bandwidth exceeds 0.1 Hz to 500 kHz
Output Impedance, near 0 Ohms
Output Noise < 2.45 uV at Unity Gain, 20-20 kHz
Maximum Output Power, 6 Watts into 16 Ohms
Maximum Output Current, 1.5 A
Maximum Output Voltage, 11.5 Vrms into 300 Ohms
Crosstalk < -133 dB @ 1 kHz, -115 dB @ 10 kHz (XLR4)


THD < -125 dB (0.00006%)
SNR > 135 dB, unweighted, 20-20 kHz
SNR > 137 dB, A-weighted
Frequency Response – 0.003 dB at 10 Hz, -0.001 dB at 20 kHz
– 3 dB Bandwidth exceeds 0.1 Hz to 500 kHz
Output Impedance 60 Ohms
Output Noise < 1.9 uV at Unity Gain, 20-20 kHz
Maximum Input and Output Voltage, 20 Vrms (+28 dBu)
Crosstalk < -133 dB @ 1 kHz, -116 dB @ 10 kHz


8.65″ W x 3.88″ H x 8.33″ D – Including Feet
8.65″ W x 3.47″ H x 8.33″ D – Excluding Feet
8.0 lbs., 12 lbs. shipping


18W Typical Input Power
35W Maximum Input power
0.33 W Standby Power (when off)
Internal Universal Power Supply

Benchmark HPA4 Headphone Test

The HPA4 is the first and possibly the only THX-888 Dual Mono implementation from the market today. Some other interesting features:

  • 256-Step Fully-Balanced Relay Gain Control, 0.5 dB Steps
  • Precision Timed Relay Closures
  • Precision Metal Film Resistors
  • Balanced and Unbalanced I/O
  • 6 Watts into 16 Ohm Headphones
  • 11.5 Vrms into 300 Ohm Headphones
  • 0.01 Hz to 500 kHz BandWith
  • SNR > 135 dB
  • THD < 125 dB (0.00006%) under full load
  • Short-Circuit Protection
  • DC Protection
  • Over-Voltage Protection
  • Over-Current Protection
  • Thermal Protection
  • Touch Screen Control
  • IR Remote Control (optional)
  • 2 Balanced Stereo Line Inputs
  • 2 Unbalanced Stereo Line Inputs
  • 1 Balanced Stereo Line Output
  • 1 Unbalanced Stereo Line Output
  • 1 Balanced Mono Sum Output
  • 2 Bidirectional 12V Trigger Ports

I know that there are a lot of audiophiles that say that specs don’t matter. In my perspective it does. How much? It depends on your system and your ears. In my experience if the specs are done correctly without cheating to extract good numbers, specs matter. And progress is needed in any domain. If nobody cared about improving the specs and the numbers behind, we would only have different products on the market that just sounded different, not better. 

But enough about the numbers and specs. Let’s see how this baby sounds. 

Listening Impressions and Tests


The tests were performed with   MSB Analog DAC with quad usb + custom lps, Soekris 1541 R2R DAC,  Audeze LCD-2C, Quad Era-1, Brainwavz Alara, Sennheiser HD650 Kiss Mod, Massdrop THX-AAA headphone amp. 

By the way, probably you know that at one point I was a big fan of Audio GD Master 9 headphone amplifier. It was a good amplifier for that time, but in time I realized that I actually liked that amp very much with HD800 because it gave some soul, bass weight to HD800 and reduced some fatigue from the treble. With planar headphones it wasn’t as great (kind of slow and not very clear leading edges, not very powerful attack, slower decay). Let’s just say that LCD-2C sound better on HPA4 than LCD-4 on Master 9 and leave it at that….. And LCD-4 was not at fault.

In the meanwhile I bought the MassDrop THX-AAA amplifier that is based on the cheaper THX-789 chip. It was undeniably better than the audio gd and I will briefly compare HPA-4 to it later in the review.

What I can say for now is that it bought life to my headphones. It kind of reminds me of my thoughts on why people love music : Music is organized vibration and vibration is life. 

It’s the first time when I have heard the headphones mentioned above to their full potential. In the first minute my jaw dropped…. At one point I was blaming my MSB Analog Dac for slightly less impact / attack / dynamics that I really want. The poor DAC does a great job at that, but it was actually limited by the amplification. 


The HU – Yuve Yuve Yu

I discovered this song recently and I just love it. Everything in this song was amazing on HPA4. It offers a very organic and impactful drum/heavy guitar experience but in a very accurate, fast, detailed and neutral way. The voice is also guttural, very well textured and present. The voice is so guttural/throaty  and so organic that you can feel the guy near you.

Rodrigo Y Gabriela – Echoes

Man….it cannot get better than this… when the song starts you get some really crisp and very very well detailed guitar plucks. You can feel the chords in your body, even if the song starts with more delicate plucks… But at one point (1:20) the plucks explode and the artists also hit the guitar’s body for drum like effect. This comes out of nowhere after some delicate plucks. The sound just explodes….the dynamic range is off the freaking scale with this amplifier. The level of impact, the detail, the crisp clear leading edges….I literally got goosebumps and maybe also a tear or two :))

2Cellos – Vivaldi Storm

I could use a lot from the description from the previous song, however the difference is that instead of guitar plucks you have cello strings that concentrate more on the vibration/texture than on the pluck itself. If your system is not pulsating with mesmerizing energy on this song and with the cello strings and body, you can certainly improve something in your system. With HPA4, Analog Dac and the headphones especially Quad, and Alara, but also 2c to a smaller degree, you start to vibrate with the cello, you become the cello itself :))

Tina Guo – The Rains of Castamere

Yes, this is also a cello song, but I felt the need to add it here. All the description from above is also relevant here. I added this song  because I got goosebumps over 5 times while listening to it. Due to the level of detail, texture and life given to the song by hpa4, the emotion transmitted by this song is huge. What is actually funny here is that in audio when you talk about emotion it usually means that one of the components is more “natural” or warmer. In this case, the HPA4 doesn’t add anything to the song, it’s neutral. It just leaves the rest of the system to sing to it’s full potential.

I am not going to go through more songs, as I can go like that forever with this amp. I am going to try to summarize my experience below. 




This is the fastest and the most controlled bass I have ever heard. It goes deep, it’s organic when it needs to be, but it doesn’t linger at all. It’s controlled by an iron fist. The punch is really really fun and strong. The speed, impact and control is mesmerizing. When I listened to infected mushroom I was paralyzed for a few minutes, being hypnotized by the accuracy, speed, impact and energy. 


The midrange is really pure and lively. The instruments and voices have vibrating, lively and pure textures. The sounds pulsates with life and purity. 


The treble is really extended, very detailed and sparkly. It doesn’t have any touch of brightness, but it does brighten up the place in a good way if you know what I mean. If you hear people saying that HPA4 is bright, it’s not actually the amplifier’s fault and the problem is either the DAC or the rest of the system. 


The level of detail is amazing on HPA4. I seem to discover other sounds in some songs that I did not notice before. However there are two types of detailed audio components out there. The bad type is when the details are extracted in an unnatural way and thrown into your face. With HPA4 it comes in a natural and effortless manner. 


The voices are incredibly pure and textured. Depending on the artist and the song, the voice can sound incredibly pure, stammeringly clean and extended, but also guttural/throaty in other cases.

Tonality – Coloration? Emotion?

When you talk about natural sound, about emotion in this domain it usually means that the audio component adds some coloration that give a more natural tonality, more weight to the sound, more present voices, less harshness, etc. In this case the emotion comes from the purity of the sound from the fact that HPA4 completely removes itself from the system. It’s kind of funny to pay the price to add a component that removes itself from the system right? :)) But it does make sense and it does an incredible job at that. HPA4 doesn’t add or takes anything away from the music. 


There are actually two things to mention here. The level of purity you can find in the music with HPA-4 is amazing. You just get the music, dead black background and very clean sound in general. There is another level of transparency that is important to mention here. Probably a lot of you have heard in audio that simplicity usually helps the sound, as in the more components you add to the system, the more you take away from the purity and transparency. With HPA4 you actually remove one component from the system, the pre-headphone amp. What do I mean by this? With HPA4 you just listen to the rest of your system. It’s amazing. I think it’s the first time I have actually heard my DAC. When I switched to Matrix Element X, the difference was day and night between the two dacs. 

Transients – Energy – Dynamics

This is another area where the HPA4 excels! The transients are fast and explosive. The attack is really strong and the decay is fast but detailed in the same time. You don’t lose any micro details from either. Also the leading edges from each note is crispy clear. It’s amazing how clear the leading edges are actually and the accuracy of this amplifier. This also translates into incredible dynamics and energy that transpire in the songs. You vibrate and become part of the music with this amplifier. 

Imaging – Separation – Soundstage

The imaging / separation of instruments is really really good, mostly because of the clarity of the leading edges, leaving a lot of space between notes/instruments. The soundstage is good, natural and nicely layered. Can’t say that this amp excels in this area. I can’t say that I feel anything missing here, but I can’t say that the soundstage is great either. 

Brief comparison to Massdrop THX-AAA 789

The 789 is actually an amazing small amplifier. It’s hard to beat it, especially at that price. It sounds amazingly clean, transparent, detailed, fast and sparkly. What I felt it was missing is some emotion, meaning that it may sound a little clinical and even if the dynamics are generally good, it sometimes misses some vibration/energy/life. 

HPA4 doesn’t sound clinical, but it’s still neutral, more neutral than 789 for that matter, because it adds/takes less from the music, leaving every instrument and voice to offer its best. HPA4 has clearer leading edges, better impact and attack, better bass control, depth & punch and more energy. Instruments and voices pulsate with life and energy on HPA4, while on 789 they sound less engaging. 



From my perspective this is the best headphone amplifier I have ever heard. It’s no competition really. It’s not cheap, I can give you that. Is it worth it? That is up to each and every one of you, but if you really want the best amplifier out there, an end game amplifier…this is it.  As I said above it’s funny to pay the money to add a component to the system that actually removes itself from the system, right?

It is funny, but it makes sense. If you have a great DAC and recently DACs have evolved quite nicely, it would be a pity to restrict its performance with a lesser amplifier. In my case, I think it’s the first time I have heard my Analog Dac to its full potential. 

Let’s say you have a state of the art DAC with awesome measurements, specs and also great sound quality. If your amp is not in the same ballpark, you will lose some of the sound in it. This is not the case with HPA4 and I actually think that there is no DAC out there yet to outperform the HPA4 in terms of specs/measurements. 

OK, you don’t believe in measurements or you don’t care? Fine, but this amp depending on the rest of your system can sound amazing. However, being very transparent, it won’t hide any problems or flaws you have in the rest of the audio chain. If the music will be bright you would most probably have to look at your DAC or headphones / speakers to fix the issue, or stick with another amplifier that hides the problem. 

I have heard people complaining about the price. I don’t want to comment on that, just that I want to add that this is actually a pre-amplifier as well and it is as impressive as the headphone am section.


  • Incredible Bass performance – staggering impact, speed, control
  • Very pure, lively and detailed midrange
  • Well extended and detailed treble
  • Incredible dynamics and energy
  • Amazingly clear and crisp leading edges, exploding attack and fast but detailed decays
  • Very good imaging and instrument separation
  • Emotional through sound purity
  • Neutral sound
  • Incredibly transparent and clean sound
  • Very good build quality and nice design
  • Very good pre-amplification section


  • Some may consider this pricey
  • The soundstage is good, natural and nicely layered but not impressive. Can’t say that this amp excels in this area. I can’t say that I feel anything missing here, but I can’t say it’s impressive either