Benchmark HPA4 Headphone Amp - Official Thread

This thread is to discuss the Benchmark HPA4 Headphone Amp.

From the manufacturer:

Benchmark Media Systems, Inc. and THX, Ltd. have partnered to introduce the Benchmark HPA4 headphone/line amplifier featuring THX Achromatic Audio Amplifier (AAA™) technology.

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.

Featuring the flagship THX-888 amplifier design, the revolutionary HPA4 headphone amplifier incorporates the same THX AAAtechnology that Benchmark uses in the AHB2 power amplifier. The HPA4 delivers sonic perfection. Hear the music without any contamination from electronic noise or distortion. The HPA4 delivers power, audio fidelity, speed and accuracy over an utterly silent background.

The Ultimate Line Amplifier

The THX-888 amplifier is driven by a Benchmark line amplifier that features relay gain control, relay input selection, and relay muting. The line amplifier incorporates the finest gold-contact relays available. The gain control has 256 steps in 0.5 dB increments. It also features a balance control. Relay closures are precisely timed to deliver silky-smooth volume changes. No other relay gain control offers this level of precision and performance. The HPA4 includes 4 independent 256-step attenuators: two for the L&R headphone outputs, and two for the L&R line outputs. To make this all happen, the HPA4 includes a total of 64 precision relays.


Not to invoke controversy, but a very positive review is up at ASR:

Intro posts for these types of threads need pictures and a summary of the the product, please.

Adding and editing now…in progress…

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I edited the post to put a picture of the HPA4 there; the posted picture was of the LA4.

Thanks – I shouldn’t have tried posting while I was on the phone…

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The measurements look incredible! Still I find solace in the fact that my cheap Atom measures well enough to likely be audibly transparent, so if I don’t need the power or balanced out I’m all set :grin:


I should probably get another copy of this amplifier in to do a direct comparison with the Phonitor X, now that I have the SR1a.

When I first heard it, while I thought it was genuinely excellent, when compared to the direct output of the Chord DAVE (same internal connections feed the RCA and XLR outputs on its rear) it seemed a little on the lean side. I didn’t run into that with the Phonitor X. Which is one reason why I bought the Phonitor X.

That changed with the SR1a … so it may just be that something more resolving was needed to tell other differences apart. So, I’ll go about rounding one up and doing a proper review of the thing, as well as a side-by-side comparison with the Phonitor X (obviously using both in pre-amp configuration as well as headphone-amp mode).

The HPA4 definitely measures better than the SPL unit, though both perform at a level where the differences should be inaudible (see “Failures of Logic”), so that’ll be a particularly interesting back-to-back test for me.

We’ll see when Benchmark have them back in stock.

Other than the “leaness” (and it was slight), and which could just be down to me having an “off day” - as I didn’t do hundreds of hours of listening when I was borrowing it, and the impression (see prior caveat) that SPL’s amp had a more dynamic/impactful delivery with high-impedance cans, the Phonitor X swayed me in other ways.

Most were aesthetic and functional.

I really do not like the screen on the HPA4. It just seems gimicky. Features like making it easy to name the inputs wouldn’t be needed at all if there wasn’t a screen in the first place. Several of the configuration functions are just for the screen/menu system itself. And it’s not very pretty.

None of that has anything to do with the sound, of course, so should be taken as my personal quibbles and aesthetic sensibilities (those matter more to me in audio gear than to most people, I think).

The HPA4 does have other useful abilities. For one, the ability to precisely and repeatedly set the volume level is extremely useful. Absolute lack of channel balanced issues is another (though I’ve not run into any with the Phonitor either). The extra analog inputs are always going to be welcome. I like that is a pure amplifier - especially where the DAC option for the Phonitor X isn’t great. It’s usefully smaller than the Phonitor X. And, like the SPL box, it can take pro-level inputs without clipping it’s input stage.

So, while the above probably reads more negatively than I mean it to (because aesthetics aside, I do think it’s an excellent piece of kit), I would say that the HPA4 is the only other solid-state amplifier I’d consider owning and using at the moment.

Failures of Logic

One thing that is interesting for me, and the only potential point of controversy I see, is that for those that live and die by objective standards for their audio purchases, this thing doesn’t make a lot of sense. Based on the science behind claimed human hearing evaluations, it should not be possible for a person to tell it apart, audibly, from a JDS Labs Atom, at 1/30th the price.

Note: I’m not disputing the objective standards, the measurements, nor the claims about human hearing performance here; merely pointing out iffy logic in going for something like this using those things as arguments to do so when for 99.9% of cases, the Atom should be all that’s needed.


It’s just in case thinking. You’re buying extra margin for error. It’s the same reasoning that leads some of my neighbors in Texas to buy a diesel F350 in case they ever need to tow a bulldozer and then proceed to commute to work in the thing and rarely, if ever, actually tow anything. That doesn’t mean that no one ever actually makes use of those capabilities, but at least sometimes they’re a waste.


Technology always has an initial R&D period (expensive), which is followed by the mass market and commoditization phase. Pre-WW2 cars were often expensive and rare, and early professional watches (e.g., Rolex & Breitling) cost a lot for basic functions. Over time one can get similar functionality for a fraction of the cost, but the luxury market continues. Bugatti and Ferrari and Rolex and Patek-Philippe still do plenty of business.

Benchmark products communicate to visitors (and those on blogs) that one has the ‘best’ and can afford the best. In my case, I posted this because I’m curious about how the Atom and THX are seeming to run the table with amps these days. I myself am likely to shift my hobby budget to something else, as my ears don’t care.


Which is followed by AliExpress.