RAAL-requisite HSA-1a - True Ribbon Headphone & Speaker Amp - Official Thread

The HSA-1a is a newly-released amplifier from RAAL-requisite, intended to drive their excellent SR1a EarField™ Monitor “Headphones” as well as having the capacity to drive speakers and provision for a potential-future circumnaural ribbon-driver headphone release.

The original unit, above, featured support for two sets of SR1a headphones (which makes more sense when you consider the studio-intent for these products), switchable heapdhone/speaker outputs, and both balanced (XLR) and single-ended (RCA) inputs.

An updated unit (the update is available to existing owners), switches one of the SR1a outputs to a conventional headphone output (for your normal dynamic and planar cans), as well as including an adapter to use the remaining SR1a port as a very high-power output for extremely hard to drive cans such as the Susvara (etc):

This is a substantial unit, weighing in at 11.5 lbs, in a 12.5" x 8.5" in an all-metal chassis, with visible heatsinking and RAAL-requisitives distinctive design-language.

Price is $3,900, with an optional hard-case for an additional $350.

  • Load Impedance: 0.3 Ohm – infinity
  • Output Power (one channel driven): 10W /8Ω, 20W/4Ω, 40W/2Ω, 55W/1Ω @ 1khz/sine
  • Ribbon Headphones Drive: 2 x RAAL-requisite SR-1a
  • Freq. Response: 100mv/ in/sin. 15hz – 500kHz
  • Power Bandwidth: 10Hz(-1dB) – 100kHz (-2dB)
  • Distortion: < 0,5% at 1khz
  • Signal to Noise Ratio: Better than 90dB
  • Input Impedance: 40 kOhm
  • Sensitivity: 0,5V /40kOhm
  • Input: IN1- RCA, IN2 – XLR


It’s been talked about, on and off, for a while now.

And it’s why the Jotunheim R has the ability to turn off the step-baffle compensation (it’s not needed for a circumnaural headphone).


Five solid hours of listening with the HSA-1a so far … and loving every minute of it.

This takes everything I find so compelling about the SR1a … and then turns it up to 11.


…and once again the “Torq effect” is taking shape…a few day later, a few $3.9k will be dropped (mine included) in favor of RAAL-requisite. LOL

On a serious note, I do appreciate that you get to try all these amazing gear and most importantly that put the time to share your thoughts/impressions/reviews. Thanks again and I look forward to reading all you have to say about the HSA-1a.




Thank you @Torq for your informative posts.

Will compare it also here in France with our big tubes competitors which for headphones have until now been more appealing than SS amps.

Very little sleep was had here last night; I was deep into “just one more album” territory. The pairing here is excellent. I’d say it has off-the-chart synergy … but it’s a purpose-built amplifier so synergy is not perhaps the best term there … but it does anyway.

So far, this is a super-compelling, in fact downright mesmerizing, setup for those that have the budget and that are interested in, or already own, the SR1a (which I still regard as the best overall headphone listening experience available, period).

Pictures of the unit are a interesting, as it’s a little hard to get a real feel for the size of the unit in some of them. If you’re familiar with Schiit’s Vidar, then the HSA-1a trims about half an inch of each dimension, and comes in at a bit more than half the weight. And if you’re running a Jotunheim R, then this is half an inch narrower, a bit over twice the depth, and not quite twice as tall and 5lbs heavier.

The actual front-plate is almost 9" wide, and the main body of the chassis is almost exactly the same width as the RME ADI-2 DAC/Pro FS. Which actually makes for a fairly attractive and effective combination if you stack the RME on the HSA-1a.

In fact, as a <$10,000 system, that’d be quite a compelling combination. The HSA-1a providing the necessary drive for the SR1a and for efficient passive speakers. The RME acting both as a DAC for the HSA-1a, as well as providing outputs that’ll drive most conventional headphones extremely well, have support for active speakers/monitors etc. And that has on-board EQ and crossfeed to boot (something the SR1a respond particularly well too, even if it isn’t necessary to get actual spatiality out of them).

And a fascinating exchange with Danny at RAAL-requisite this morning has the potential to make this thing even more compelling across the board. But I’ll say no more there until I’ve gotten more time in with the thing.

Anyway, back to listening … which I expect I’ll be engrossed in all day … as this just might be the most engrossing I’ve heard the SR1a to date.


It would be very helpful to know what you think about the AHB2 in comparison with the HSA-1a. Hope you can do it in the future.
Keep enjoying this combo !!

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I’lll put it this way …

I prefer the Jotunheim R over the AHB2 for driving the SR1a.

I prefer the HSA-1a over the Jotunheim R.

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I preferred the SPL s800 over the Jotunheim R. Looking forward to your continuing thoughts about the Raal Requisite HSA-1. I would certainly like to audition one with my SRA-1 earfield monitors.

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The SPL s800 is very good.

It’s definitely different, overall than the Jotunheim R. Though the s800/interface combination ultimately lacked a little separation and detail vs. the Jotunheim R direct when compared blind, the s800 had a bit more tonal weight and overall presence.

Compared to either the AHB2 was a bit lean, dry and sterile.

The HSA-1a, so far, is competing at a higher level than all three. Closer to, maybe exceeding, the Chord, Linn and other more exotic gear (with the interface). And the HSA-1a has the potential to be significantly more flexible than all of them, but I’ll say more about that in the near future.

Personal preferences are what they are, however; so it’s great that there are options.


When the current lockdown situation has ended here, I will see if Danny will send me an HSA-1 to audition with my Roon Nucleus / dCS Bartók Source. From your early observations, it seems to be the optimum pairing with the SR1-a’s. I very much appreciate your opinions and find that I am in accord when auditioning the same units. Many thanks, Ian.


Thanks for your answer .

So … there’s an interesting development with the HSA-1a, for which I’ll update the main post in a little bit, but in advance of that …

  • The HSA-1a has been updated to swap the 2nd headphone output for a conventional balanced headphone output, so that it can be used both to drive the SR1a and also any normal headphone (i.e. not electrostatic) cans as well*.

  • For super-hard to drive headphones, like the HE6(SE) and Susvara, there will also be an adapter cable in the box to allow it to power those properly.

So this turns the HSA-1a into an amplifier that can drive the SR1a, any normal headphone, pathologically hard-drive headphones AND speakers - all from one box!

I will be getting an updated unit in short order (likely this coming week), and that’s definitely a useful and, I think, broadly welcome addition!

Finally, anyone that ordered/received an HSA-1a already will get, or be able to get, the updated unit for no charge (if you need to return a unit for the update, shipping will be covered)!

*It’s not just a socket/wiring swap, there’s more to it than that.


Yup, this is a great move for Raal. :wave: The normal headphone output will probably bypass the circuitry needed to push extremely low impedance of Raal SR1a. Since the affordable Jot R already sounds great with low-impedance planars like Abyss with just socket swap, SR-1a’s normal output will probably sound great driving both low impedance AND high impedance 'phones.


Once an output stage has the ability to drive low-impedance loads, which is really about current and thermal limitations, there’s not really a need to bypass it for higher impedance loads.

You might bias it differently.

You might switch out some number of output devices (one way to increase current capability is to use spread the current load over more output devices, so that each only has to service a fraction of it - which tends to trade capacity for noise).

I suspect it’s more likely scaling (e.g. a different gain or attenuation structure) the output to be more in line with what conventional headphones actually require - both to get the most out of the output as well as to help protect one’s headphones.

We’ll see when it lands …

Either way, I’m excited about the possibilities … especially if it lets me run the same array of cans but with fewer boxes (and even more so if it winds up sounding better with the conventional headphones than my current solid-state amp).


is this even available? the real website doesn’t present it as an option. sounds almost compelling…

The HSA-1a is available to order, yes.

My understanding is that the updated version should start shipping at the end of the week (with due allowances for potential disruptions). That’s when I am expecting my updated unit to ship out (and that’ll be the version I am keeping as my personal purchase).

My assumption is that any orders placed now would be the updated unit, but I would check to be sure ahead of placing an order.

In this case, I think the press-shots and web-site info is trailing the product/engineering (which is a nice change).


thank you, @Torq - looking forward to it