Benchmark HPA4 – Headphone Amplifier – Review

Benchmark HPA4 – Headphone Amplifier – Review

Without hesitation, I give my second “Outstanding” product award to the incredibly precise and transparent Benchmark HPA4

Here’s my review of the wonderful Benchmark HPA4.  Without understating the Benchmark HPA4, it is just an analogue headphone amplifier, just a really good one with a pretty special line stage pre-amplifier as well.

Following my trip to Hifonix a couple of months ago I was incredibly impressed with the understated block of electronics that is the Benchmark HPA4.  I was listening with a pair of Focal Utopias, beautiful for their space, lightness and accurate bass delivery.  It was clear at the time in Hifonix that the Benchmark HPA4 was doing very little but delivering a perfect input source, which happened to be a Benchmark DAC3.


The Benchmark HPA4 is a pure analogue headphone amplifier and line stage pre-amplifier.  It features THX Achromatic Audio Amplifier (AAA™) technology.  Benchmark  describes THX AAA™ as follows:

THX AAA™ reduces harmonic, intermodulation, and crossover distortion by 20 to 40 dB to guarantee a realistic and fatigue-free listening experience. It accomplishes this using a patented feed-forward topology to null conventional distortion and noise mechanisms, resulting in the world’s most linear amplifier. THX AAA allows the amplifier to reach its maximum output power and sound pressure level (SPL) without producing the distortion that normally accompanies increased output levels in traditional amplifiers.

So,  it is so good because it adds nothing to the source other than amplification.  The gain control is controlled with total accuracy using 256 steps in 0.5 dB steps.

Benchmark HPA4The HPA4 has 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.  There is a 1/4″ TRS and a 4-pin XLR output to headphones as well at the front.

There is no remote, as standard, in the UK, it is not included with any of the range. Rather Benchmark reduces the price a little. The reason for this is that it works both the DAC3 and HPA4/LA4. To avoid customers pay more for an extra remote they won’t need, Benchmark leaves it as an option @ £105inc VAT.

The Benchmark HPA4 has a very functional touch screen LED display that allows you to adjust the gain on both headphones output and line output.  You can also adjust balance, input names, input offsets and control the screen brightness.


Benchmark HPA4The Benchmark HPA4 is solidly put together, it is a small heavy metal block about the size of a couple of Wisden annuals (if you know what that is, well done)!  It is 8.5 inches square from above and about 4 inches high (incl. feet). The HPA4 is a solid 3.6 kilos.

The inputs at the back are lovingly presented with plenty of detail but also plenty of room.

At the front, the 1/4″ TRS and a 4-pin XLR output to headphones are presented under the LED screen.  There is an unnamed power button at the front too, I like this understated facia.  The volume knob clicks along with sublime accuracy at the front.


From the Benchmark HPA4 site and SCV.

THD: -125 dB (0.00006%)
SNR: 131 dB, unweighted, 20-20 kHz
SNR: 135 dB, A-weighted
Frequency Response:- 0.006 dB at 10 Hz: -0.014 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)

256-Step Fully-Balanced Relay Gain Control, 0.5 dB Steps
Precision Timed Relay Closures
Precision Metal Film Resistors
Gold-Contact Relays
Balanced and Unbalanced I/O
6 Watts into 16 Ohm Headphones
11.5 Vrms into 300 Ohm Headphones
Short-Circuit Protection
DC Protection
Over-Voltage and Over-Current Protection
Thermal Protection
Touch Screen Control
Benchmark HPA4IR 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’m reviewing with the Auralic Vega G1 streaming DAC, balanced output to XLR input 1 (that I have managed to rename Vega G1 very easily), and using the Meze Empyrean a pair of balanced cable Oppo PM-2s.  I’ve also had a listen with the Meze 99 Neos and some Focal Spirit headphones for the fun of it.

I have not reviewed the Line Out functionality but it would go to a Benchmark AHB2 Power Amplifier as a perfect partner (I’m hoping to do this in the coming months so watch this space).

Performance with Meze Empyrean headphones

The Empyreans … allow you to wander between instruments absentmindedly

This really is a treat, a Top Line Streaming DAC and a glorious pair of soft to the ear headphones.  My first duty (!) is to listen to ‘Amnesiac’ for 43 minutes, blimey it is good.  With the background noise fading out in ‘Pyramid Song’ and the off-tempo piano pushing you along, music and HiFi don’t come better than this.  The Empyreans are still light, spacious and allow you to wander between instruments absentmindedly.  What about the Benchmark HPA4 I hear you call, well what about it?  I can’t actually hear it so what can I say?  The HPA4 is just amplifying the signal without any fuss to the headphones.

I’ve played about with the input name, screen brightness and turned all of the unused inputs off to minimise any possible interference.  All I can say is the gain control from the knob at the front is as accurate as of that on the Moon 600i v2, my volume knob of choice thus far!

… listen to Calexico/Iron and Wine’s “Father Mountain” you can just hear each instrument when you choose…

Finally, at low volume, the HPA4 comes into its own with a careful presentation to the drivers with no hint of loss of fidelity.  If you have a listen to Calexico/Iron and Wine’s “Father Mountain” you can just hear each instrument when you choose and the harmonies are almost broken down into individual voices, remarkable, really.

with Oppo PM-2 planar magnetic headphones

The PM-2s, being planar magnetic come across a bit more lively to the Empyreans but again the precision of the vocal or resolution of instruments is still as good.  They are capable of this level of precision.  With the transparency of the HPA4 you really feel like you are listening to familiar tracks for the first time.  Like James Bay’s ‘Let it Go’, with the snare brushing in at 1′ 23″ and the controlled bass line in the background.

other Headphones

I’ve had a play with a pair of Focal Spirit headphones, pretty nice standard retail headphones as well as the remarkable Mexe 99 Neos.  Again, both of these are elevated by this precision block into something more than they are.


Without hesitation, I give my second “Outstanding” product award to the incredibly precise and transparent Benchmark HPA4; it does not add anything to the music you are listening to, or take anything away, it just gives you the music, perfectly.  And, I’ve not even looked at the Line Stage section of this HPA4 but I have no doubt that too will be exceptional.

If I was to run away and disappear into a hole, I really do believe a leather bag with a Vega G1, this Benchmark HPA4 and a pair of headphones with a bunch of XLR cables could probably sort me out for the rest of my life (assuming I had some WiFi!).



Gain control


Totally understated look


The power on/off button

Touch screen LED


For nothing

Thanks again to SCV Distribution for a look at the HPA4 which is available here.

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