The Benchmark AHB2 is a power amp meant to power speakers. There seems to be an interest in it for hard to power headphone enthusiasts on the forum even though Benchmark makes the HPA4 which is a headphone amp. That said, folks trying to drive the Hifiman HE-6 and Susvara gravitates towards this piece of gear. If you have frequented the Susvara thread on Headfi, you’ll see the growing pains of finding a good/sufficiently powerful amp spanning over 200 pages last time I checked. Finally, I pulled the trigger on the AHB2 and couldn’t be happier.
This review and walkthrough/guide will focus on the AHB as a tool to drive headphones. For 2-channel systems, maybe Google other reviews. Also, as disclaimer, none of these have been provided to me. I bought everything pictured.
The Tech: I will keep the boring part short and simple because you will find all the numbers and parameters on their website; hence no point parroting them here.
It uses the THX tech, so it has two-way feedback resulting in ultra clean output. As Golden Sound put it, it is the objectively best measuring power amp and it shows. The THD+N numbers are off the charts (technically reverse of that as in they are so low that they won’t show up in a plot; think obscene numbers of zeros before a digit shows up). For completion, it operates in full class A – if that matters to you.
Inputs/outputs: It is a simple balanced power amp – nothing too fancy except for one thing which I’ll mention in about three sentences. As inputs, it takes balanced XLR and RCA inputs that are pretty standard. For output, they have the standard Banana and spade binding posts. Now for the cool part, namely, the SpeakON connectors. I didn’t know about these before buying the AHB2. Instead of binding posts, the SpeakOn are more robust XLR-like jacks that can accept two 2-poles outputs or a single 4-poles. The latter is a Godsend if you are want an elegant cable run. Details on that later in the writeup when I tackle how to connect your headphones. Apart from this, you can use a bridge mode to use two AHB2s in a monoblock configuration should you be so inclined but for headphones, that would be overkill if you ask me. Well, using a power amp for headphones is overkill to begin with. Yet, here we are, trying to power the Susvara with all our might.
How do you connect headphones to the AHB2 (which is a speaker amp): This is likely the most asked question and one I struggled when I was starting out. Before starting to talk about it step by step, we need to get the fact out of the way that the AHB2 does not have a volume control – it will just push with all its might. Which is basically recipe for disaster i.e., blowing up your headphones. But fear not! That will not happen. Even if you are careless, it still won’t happen – as much as naysayers will warn you. So, this necessitates the need for a preamp to control the volume. The process is as follows and it’s not just how I do it but this is the standard regardless of what gear you have.
- First, let’s start with the DAC. Let’s assume you have a DAC with no volume control. This is where the music starts (after the source/streamer/computer). I have a Holo Spring 3 and let’s consider it as a standalone DAC with no volume control. If you have a DAC/Amp combo, ignore the next point.
- Then in the chain, the DAC gets connected to a preamp. Preamps come in many flavors. If you just want a volume control to attenuate the AHB2’s signal then you want a passive one. Goldpoint makes one of the best ones out there for this. However, I use a Burson Soloist 3xp or Schiit Mjolnir 2 that are both headphone amps with preamp functionality. To keep it simple, let’s consider preamps just as volume controls so that the AHB doesn’t push at all its glory, hence the preamp is a volume control in this discussion. If this sounds too alien to you, Golden Sound’s Holo Serene review video has a very good explanation on what this is. But for simplicity, to reiterate, let’s take preamp to be a volume control in this case.
(The video is relevant because it discusses why you need a preamp)
https://www.youtube.com/watch?v=lD2Fj1tTu8Y&t=997s
- Now that your DAC is connected to a preamp, the preamp needs to be connected to the AHB2. If you have balanced gear, use XLR interconnects, or you can use RCA cables. If you want to go from single ended to XLR, Benchmark has their own ones and you have to use those (they are inexpensive). Okay, so you are all connected in your chain at this point. To recap, this is what the chain looks like: DAC->preamp->AHB2 (->headphones) [the last part in parenthesis is the last piece of the puzzle, and puzzle it is!].
- Speaker amp to headphones: This is probably why you are reading this. The AHB2 has banana binding posts and alternatively SpeakON connectors as outputs, so let’s pick one of the two options. I’ll explain both as I have gone through both choices and found the latter to be more elegant.
Banana approach: Okay, what you need is a Bananas to 4-pin XLR female cable to plug in your headphone. They can be had from Moon Audio, LQI cables and probably other places too. You can see a picture below. Now it’s making sense I hope. What you do is plug in the Banana plugs in the AHB2’s binding posts and connect your headphones to the XLR female plug. And you’re done! Or are you? Make sure to always put your preamp volume down before you start playing because at full power the headphones will be so loud, you might lose your hearing. But people fret too much on this, just don’t. Even at normal listening volumes on the pre while urning on, hard to drive headphones act just fine powering up.
(Picture source: LQI cables)
SpeakON approach: This is a novel and more elegant option offered by Benchmark. Think of SspeakON as the modern Banana alternative. They are more robust and not unwieldy like bananas. This accomplishes what the Banana part does but in a nicer way. For this you want a SpeakON to female XLR cable. Unfortunately, these are made to order unlike Bananas but I highly recommend this route. You have two options for this too. You can use two 2-pole SpeakON connectors (they call this NL2) or a single 4-pole (called NL4) connector to 4-pin XLR female connector. The amazing skedra (vikingweavecables@gmail.com) from Viking Weave made me a very nice single run adapter to go from 4 pole SpeakON connector of the AHB2 to 4 pin female XLR. He is based in UK and he is the greatest cable maker I have met in the hobby. Slightly pricey but no one makes cables better – so I feel it is justified. Now just plug in the SpeakON end behind AHB2, plug in your headphones, turn up your preamp, and wallah!
(The 4-pole SpeakON to 4-pin female XLR cable skedra made for me)
But wait, people say I need a resistor box/attenuator so that I don’t blow up my headphone: Naah! As long as you are driving hard to drive, low sensitivity headphones like the Susvara or HE-6, you really do not need a resistor box. If this is the first time you are hearing about this and it makes you worried, this is exactly what is already being achieved up there in point 3. So, you’re good. As long as you will not be using IEMs on a speaker amp, you’ll be fine. If you do, you have more serious things to worry about like re-evaluating life choices.
Sound: Alright, now that we are all set up, let’s play some tunes. This needs some context as well. Before getting the AHB2, I had the Burson Soloist 3xp, which is a great amp in its own right. It played the Susvara really well. It was loud and musical and I was happy … until I was not. I won’t lie, with the hundreds of pages of the Susvara thread reading up on Bakoon 13r (and not being able to afford it), Pass Labs amps – only to name a few, I wanted the cleanest chain and AHB2 trumps all that. If you do not agree, it’s okay. If I want to color my sound, I will do that in the preamp level and inject the “color” onto the AHB2 because it is clean as a whistle and outputs the cleanest most transparent sound. Well, there, that’s the sound signature in one word – `transparent’. If you are in this tier yet want to be practical like me (I’m a student with limited money), the best bet is to color your sound at the preamp level. There are two advantages to this. First, you get the cleanest, most transparent power, and the flexibility to use preamps like tubes when you want not-so-objective a sound. I strongly suggest you watch Golden Sound’s WA22 review where he talks about this aspect of the AHB2.
(The video is relevant because it discusses how your preamp can color the sound to your liking)
https://www.youtube.com/watch?v=Gsu5nguXS14&t=6s
Why the AHB2 when you can buy $10,000 amps: Okay, I feel I should say a bit more about the sound besides just calling it clean and transparent. Assuming you have a Susvara or He-6, until you have run it through the AHB2, you are premuably very happy already but the dynamic swings you will uncover with this power amp is something you probably have not experienced until you actually hear it. For the naysayers who will be like, “Ohh but I already use something like a PrimaLuna and 10 grand+ power amps” – I say that’s fair but the AHB2, owing to its cleanliness makes it the most versatile player for it to become a chameleon. You can tube it, you can make it pure solid state, go all objectively sound or go nuts with distortion given what you put before it in the chain. That is exactly why you buy an amp as clean as this! Furthermore, the AHB2 is a sheer king when it comes to pinpoint imaging and staging. The air between instruments is provided like a champ - beating out amps that cost twice or three times more.
Parting thoughts: To conclude, if you want to drive the Susvara or HE-6, I cannot recommend anything better. To add, I run the HD800s along with my trusty HE-560 v1 on it as well, and they sound glorious. Also, as a parting note, if you judge THX as the tech that dictates the sound signature of the 789 – think again. The AHB2 is not at all sterile as that amp. Also, Benchmark is an excellent company. They have a 30-days no-gimmick return policy, if I hadn’t liked it, I’d have returned it; but boy do I love it.
. About the resistor box, initially I thought I’d need it but then two things happened - Hifiman stopped selling it and the helpful folks on Golden Sound’s server assured it wouldn’t be a problem with a good preamp. Hence, went with a chain like this. Cheers!