Benchmark HPA4 pre-amp and HP amp

The Benchmark HPA4 is a high quality pre-amp and headphone amp that - although being digitally controlled - only does analog audio. I admit the HPA4 doesn’t fit the self-imposed profile of my channel since it’s an analog pre-amp but rules are there to be broken and I had good excuses. Some very loyal viewers and supporters of the channel requested a review while another supporter asked me if there could be a sound improvement if he added a pre-amp between his Mytek Brooklyn Bridge and his Arcam power amp. So I decided to make an exception and review the HPA4 while at the same time see if a pre-amp improves the sound. I will not review it as a headphone amp since - as you know - I don’t enjoy headphone listening.

01:01 - Traditionally a pre-amplifier provides source selection, volume control and often tone control. It also can solve interfacing problems by working as a driver, supplying optimal output impedance and sufficient voltage. The pre-amp can be a stand-alone device to be used with a power amp but can also be integrated with a power amp in what most of us would call an amplifier. Let’s see how the HPA4 will be used in practice. As said it is to be connected to a power amp that in turn drives a pair of speakers. You can then connect the analog outputs of for instance a cd-player to the HPA4.

If you connect a streamer it will be 01:43 - connected to your router and over the router to both the internet and to your computer for music files. Again the streamer is connected to the HPA4 using the analog outputs of the streamer. If the streamer has no analog outputs - the well known white and red RCA connectors - you need a digital to analog converter - a DAC - to be inserted between the streamer and the HPA4. By the way, input selection, volume, mute, dim and power can also be operated from the optional infrared remote. The Mytek Brooklyn Bridge is a network bridge and a DAC and can be connected to the HPA4 using the analog outputs of the Brooklyn Bridge.

02:24 - Since both the DAC and the pre-amp have 3-pole XLR connectors, an XLR female to XLR male cable is used. In other cases the well known RCA cable is used. And, of course, if you listen over headphones or in-ears the power amp and speakers are not needed. If the headphones have a cable ending in a 4 pole XLR , you use that output. If it ends in a 6.3 mm jack, the other headphone output is used. When your headphones have a 3.5 mm jack, you need an adaptor plug from 3.5 mm to 6.3 mm.

02:46 - I know it’s a matter of taste but I like the somewhat industrial design of the Benchmark. The front can be either black or silver anodised aluminium, the top, sides and back are always black. It’s 220 mm wide, 237 mm deep and 99 mm tall, including the feet. The sturdy cabinet weighs 3.6 kilos. On the front we find the standby button, the 6.3 mm headphone jack, the 4-pole XLR for balanced headphones and the rotary encoder that does the line output volume, the headphones volume or both. Pressing the know steps through these options. On the full colour touchscreen right the gain to the line output, the gain to the headphones output, the active input, virtual buttons to select inputs, a virtual button for 20 dB attenuation, mute headphones and mute line outputs, set balance, the settings menu and a button to switch off the display. Time to look at the rear.

03:55 - Left we see balanced line input 1and 2 on XLR, then single ended input 3 and 4 on RCA, singe ended line output on RCA, balanced output on XLR, a mono balanced output on XLR to be used for connecting a subwoofer, the IEC mains input and two 12 volt trigger outputs to switch on other equipment like a power amplifier. As can be seen it is rather crowded here. Especially unplugging cables connected to line input 4, balanced output right and balanced output mono when all inputs are populated does need slender fingers. Luckily you don’t need to unplug them frequently. Directly behind the IEC mains input we find a mains filter with in front of it the switch mode power supply in a faraday cage. Remarkable is the hard wiring of the RCA plugs. They are not mounted directly to the circuit board but connected over short wires.

Not a problem 05:00 - but not the easiest product method, especially since the HPA4 is produced in the States. Then we see an audio circuit board. The IC’s have the type number removed. A second identical boards mounted directly below the first one. I presume these boards contain the gold plated relais for input switching and the the 256 step volume controls, two channels for the line output and two channels for the headphones outputs. These are processor controlled, the processor is on the lower board, below the two audio boards. In front of this board we find the THX Achromatic class H Audio Amplifier that is used for the headphones.

Achromatic 05:44 - is a term coming from glass lens technology and means that all colours follow the same path in contrast to a prism that breaks up the spectrum in all colours of the rainbow. In audio it must mean that all frequencies travel through the amp in the same time. Class H is the US variant of class G, that is used by European companies. Both use two or more DC rails that carry different voltages. By switching between them depending on the signal strength provides a more efficient amp that dissipates less energy.

06:22 - The combination of the rotary encoder, the touch screen and the optional remote control makes operating the HPA4 easy and intuitive. Only the input choices might be confusing at first. The four analog inputs are chosen by the left a right arrows on the touchscreen and on the remote. The D1 to D4, analog and USB on the remote are for choosing inputs on a Benchmark DAC. The HPA4 is designed to work with Benchmark DAC’s so if you choose for instance the USB input the infrared remote switches the DAC’s input to USB, not an input on the HPA4.

On the HPA4 you can name each input according to the source connected. For instance DAC for the DAC and TV for the TV. I can imagine that the separate volume settings and indication for line output and headphones is ideal for those that frequently switch from speakers to headphones and back. You could, by the way, couple both but I can’t see why. I couldn’t hear a difference between using the pre-amp of my Audio Note Soro SE and the HPA4. In both cases I used the power amp of the Audio Note. As I have explained before my Soro SE is heavily modified: other tubes, other capacitors, better potentiometers and a separate power amp input that is selected when a 12 volt trigger is fed to the also added trigger input. The HPA4 was fed the balanced output of the Brooklyn Bridge while it send its outputs single ended to the Audio Note - the SE at the end of the model name stands for single ended. The single ended outputs of the of the Brooklyn Bridge were connected to the CD inputs of the Audio Note’s pre-amp. Interlinks by Grimm Audio. Although there were variables like balanced versus single ended cabling, I could not hear a difference sound quality.

There is no direct conclusion to be made here about the absolute sound quality 08:33 - of the HPA4 as pre-amp other than it is at least as good as the Audio Note pre-amp. In the past I have compared my tweaked Audio Note against amplifiers north of 10k only to conclude it performed equal or better with the exception of how deep lows were controlled. And even there the difference was limited. So I think it’s justifiable to rate the HPA4 as extremely good in its price range having refined, silky smooth highs, very natural voices, lots of texture in the lows, a royal but precise stereo image and a blacker than black background. By the way, it is the living proof that a switch mode power supply can be used in high quality equipment when properly designed.

I have not reviewed pre-amps for 09:25 - some time now but I can’t imagine another pre-amp would further improve the sound of my setup 1. But hey, I’ve been wrong before. It is of course a small sidestep and therefore I will not report in detail on how useful a pre-amp is in between a DAC and the power amp. It’s now clear to me that there is no single answer to this question. It appears to depend on the dimensioning of the output circuit of the DAC. With the Mytek Brooklyn Bridge, the Brooklyn first generation and the Yulong DA10 it gave no improvement.

But when using the Chord Mojo, the Allo Boss DAC, 10:07 - Audiophonics RaspDAC LTE I-Sabre ES9038Q2M, the HifiBerry DAC + Pro, the Sonos Connect, the AudioQuest DragonFly Cobalt and the Meridian Explorer² it did make a difference. Let me stress that these DAC’s are fine DAC’s for the money and not of the quality of my setup 1. The Mytek’s and the Youlong have rather powerful line outputs, including balanced outputs. It would be interesting to see what happens with streamers in the € 1000 to € 2000 class that have simpler single ended outputs. Although I have not tested it, the dimensioning of the power amplifier input might be of consequence too.

So, as often 10:51 - with audio, I can’t give a conclusive answer. Although I can’t give that answer, I’m still glad I reviewed the HPA4. Benchmark caught my attention already years ago when I reviewed and I bought their initial DAC 1. As you know I always measure equipment to find if it has technical flaws. The relation between measurements and sound quality is uncertain to say the least. But in this case both measurements and sound quality are of top quality. I know of little amps that measure as clean as the HPA4 and offer equal clean, open, fast, high resolution sound quality. From a friend I heard that that goes for headphone listening too. At around € 3500 including VAT - around $3000 in the States, ex sales tax - it’s not low budget, but worth every cent. That brings us to the end of this video. There will be a new video, as always at Fridays at 5 PM central European time.

If you don’t want to miss that, subscribe to this channel 12:03 - or follow me on the social media so you’ll be informed when new videos are out. If you liked this video, give it a thumbs up. Many thanks to those viewers that support this channel financially, it keeps me independent and thus trustworthy. If that makes you feel like supporting my work too, the links are in the comments below this video on Youtube. I am Hans Beekhuyzen, thank you for watching and see you in the next show or on theHBproject.com. And whatever you do, as always, enjoy the music. .