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

DACs and Digital
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Today is my third day with the HSA-1a (latest revision) and SR1a:

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A few random observations thus far

I am very happy with synergies between amplifier and headphone, and the sound of the combo. This headphone system is truly unique and competent across many genres, definitely a keeper. Initially the sound appeared bright, I am getting accustomed to it (equipment and/or brain burn-in) and may leave it as is (no eq or tube buffer - tbd).

Overall the purpose of the HSA-1a is to make the SR-1a shine. This objective was accomplished 100%.
Buy the HSA-1a for that, and take the other features as freebies, then you likely won’t be disappointed. I would not buy the HSA-1a with the expectation of not being tempted to use other amps for different headphones; that would change in the sub $1000 range (probably HSA-1a could compete there), but given the system price of $7k it seems unlikely that potential buyers would be shopping at that level?

HSA-1 with non-ribbon headphones

  • The sound is competent, detailed, sufficient slam, quiet, with accurate stage
  • At the same time very dry, 10/10 - not my cup of cake, I want to enjoy music, not get a completely sterile reproduction
  • With the Sr1a the music is much more coherent, and not as “thin” sounding; the HSA-1a doesn’t exhibit the same virtue with the dynamic and planar phones I tried
  • The amp succeeds quite well in reproducing “medium grain” details
  • but misses out on sculpting out very fine nuances (like e.g. AK SP2000 on TIA Fourte Noir) and/or the macro flow of the music (Cayin N8-ish, or my ML 585 driving headphones, or even my good old Liquid Fire)

Some headphone pairings I tried (and then lost interest, I might continue with Stellia, Utopia, Audezes, … but right now the SR1a experience is so much better that I have just no motivation to try)

  • Sony MDR-Z1R: Not recommended, sounds hollow and brings out the worst out of the Z1R
  • Sennheiser HD800: Listen to this if you want to exit the headphone hobby …
  • Hifiman HE6 (original 2010 vintage): Best out of the three, needs the full power “Ribbon out” (the left plug), then the amp has a good amount of power to drive (on the low power headphone out I found myself having to turn volume all the way up for moderate levels)

HE6 is the only one I would deem enjoyable from the HSA-1a.
With phones like HD800 or Z1R (see below) would take amps like Focal Arche, Hugo 2 (even though that one is not very emotional either), Cayin N8 ss or tube, … any day of the week.

DAC synergies

As sources I mainly used my Metrum Adagio, also experimented with AK 2000 and Cayin N8 ss and tube, as well as Hugo 2 to get an impression of DAC flavors/pairings and synergies. Adagio is so far most satisfying.

  • For complex classical music there was additional detail and sparkle when upsampling with HQPlayer (384k or 768K depending on DAC).
  • DSD on the SP2000 and Cayin (from HQPlayer upsampling to DSD128 or DSD256) was an interesting and sometimes enjoyable option that projected a more cohesive flow of the music compared to PCM.
  • Longer term listening and other genres work better for me in NOS mode.

Construction

No money was wasted with the HSA-1a on pretentious gold coating or lacquer, this suits me just fine.

Less impressive are some engineering choices to not provide complete insulation e.g. between RCA and XLR inputs. With some short RCA silver cables without insulation connected (used for tests with DAP sources), on the XLR selection there was a significant amount of audible RF noise with no music playing.

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Did you try switching the HSA-1a between the “Ribbon EarField™ Monitors” and “Ribbon Circum-Aural Headphones”?

If so, which headphones did you try in each mode?

I ask in case it is not obvious that you need it in the “up” position for the SR1a, and ideally in the “down” position for everything else.

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I was wondering the same thing. I’m curious to see the headphones used in each mode.

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Yes, I switched them all to Circum-Aural (thanks to the earlier post on this forum, indeed easy to miss).

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Huh, it seems surprising that HSA-1a would be satisfying with SR1a but be “very dry” and “completely sterile” with other 'phones. Something seems amiss if the 4-pin XLR female “low power” jack is indeed so much lower in power and requires volume knob to be turned much higher. Now I have to wonder how the female jack is wired internally, i.e. adding a bunch of resistors in signal path?

Have you tried any 'phones, especially HE-6, from the speaker terminals? How about trying any actual speakers?

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Not necessarily.

Remember, if it is setup properly to drive the SR1a there’s a significant frequency compensation curve being applied there. The result is warmer/richer with more low-end heft than the Jotunheim R (with its curve enabled).

Turn that off, as you would to drive normal headphones (and as was done above), and it
is entirely possible that the “natural” response of the amplifier is dry or sterile.

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I tried the HE6 from the full power (left) headphone out with the adapter cable supplied by Raal in the box; power was sufficient (unlike the right headphone socket)

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My baseline to define an amplifier as “dry and sterile” is the Drop THX 789 that I used to own before the arrival of the Phonitor X.

I’m currently listening to the Utopia (good pick to highlight dry and sterile sounding sources/amps imo) using the HSA-1a’s regular headphone output (baffle compensation off), and I don’t consider this sterile and dry at all. I’m hearing a warm sound, with excellent bottom end grunt and control, realistic midrange with some “weight and body” to the vocals, well extended treble with no harshness of any kind, and zero listening fatigue.

Using the M-Scaler / Hugo TT2 as a source to both the HSA-1a and Phonitor X, the main differences are aligned with my initial impressions, the Phonitor X is more neutral but with more grunt and control and an expanded stage, more air around the notes and slightly more refined (better resolution and does a better job highlighting nuances within the recording) than the HSA-1a. After all, we all hear differently but I doubt that people would find the HSA-1a dry and sterile unless my baseline is completely skewed off. Perhaps Amp/headphone synergy might not be great with the headphones listed by @chianti.

The HSA-1a “flaws” that I could point out were only relative to the Phonitor X, and I would have a hard time identifying them if I didn’t have the PX on hand for sure but I wouldn’t consider it similar to the THX 789.

I’m not that experienced in evaluating gear and not being a native English speaker makes it even harder for me to properly describe and convey what I’m hearing, so take my impressions for what it’s worth.

Tracks used for this quick evaluation
A Tribe Called Quest - Solid Wall of Sound
Noordpool Orchestra - Weird Fishes
Childish Gambino - Redbone
Patricia Barber - Use me
Dead Can Dance - The Snake and the Moon
Carach Angren - Lingering in an Imprint Haunting
Prince - Tamborine

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I’m not saying the HSA-1a does sound dry or sterile when using the conventional headphone output. I’ve not heard a unit that has that modification. Just espousing the potential, and reason, that it could be the case.

If I’m lucky, I may have the latest unit this coming week. Too late to review in a timely fashion, but perhaps soon enough to be able to decide to buy and keep it prior to my departure. So I may be able to make some observations of my own in the near future.

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Yes sir, you made that clear in your post - you put it as a possibility, not a fact!

Fingers crossed for your unit’s arrival…if possible, ask Danny to use overnight shipping option to reduce the waiting time and the possibility of a mistake made by the shipping carrier - they tend to get it right on most of my overnight shipments.

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Quickie: by “dry and sterile”, do you mean no sound coloration of any sort? After amplification, of course.

Thanks!

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Nope, that would be neutral in my books. By “dry and sterile”, again using the 789 as a reference, I mean that it’s boring, it sucks the “life and emotion” out of the music, and sometimes it sounds thin and metallic, with some “hotness” at the top end of the frequency response and fatiguing over some period of time albeit non existent coloration of any kind.

I was extremely impressed when I first heard the 789 but that died down after a week or so of ownership and I found myself not reaching for it as often which led me to acquire the Phonitor X after Torq’s excellent review.

Unfortunately this can’t be backed by measurements of any sort, just by how one hear and perceive the sound presentation, so once again take it with a grain of salt.

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@MrCypruz, Appreciate your insights!
I tried your list, unfortunately I am not sufficiently familiar with any of the tracks to tell you if they “sound right” …

Let me reiterate that I am still enthusiastic, very satisfied, and super happy with the Sr1a on HSA-1a. No regrets.

However … :frowning:

Some tracks that I don’t appreciate on HSA-1a via “regular” headphones, trying to pick some widely familiar material

  • Madonna - Like a Virgin: On bad amp/phone synergies her voice sounds like Mickey Mouse on helium, with a lisp (… Madonna detractors would claim she always sounds like that :wink: ); also listen for the drum licks e.g. between 0:40-1’ - do they sound natural?
  • Michael Jackson - Dirty Diana: Chorus and crescendo after 1’ with bass line at 1:15 and following
  • Paul Simon - You can call me Al: Listen for the drums and background singers ("I can call you daddy at 3’)

To avoid sample bias, I continued the audition letting Roon play in “radio” mode (e.g. listening to Elton John - All the Girls Love Alice right now).

I tried the Focal Utopia, encouraged by your positive observations. To some degree on HSA-1a vs. other amps they are dark and dumb sounding, like a speaker in the corner of a basement full of cobwebs. Decidedly Mid-fi:
To me the tonality sounds similar to an impedance mismatch (e.g. when running the headphones off the taps of a speaker amp through -15db attenuators). I am not saying that this is the root cause, I am hearing a similar shift in frequency (subjectively, I have no way to measure).
I would characterize my irritation as comparable to the difference between moving the frequency adjustment on the back between open to circumaural, only that “the truth” would be a bigger shift in the “circumaural” direction?
I haven’t tried yet to counteract with equalizer since the amp by default for me is too far off an ideal target.

Just for fun I also plugged the Utopia in the left headphone jack (with the low efficiency headphone) adapter cable that comes in the box. Overall I liked this initially better (volume between 10-15). It adds some headroom for macro “punch” - e.g. Bruce Springsteen - Glory Days, sounding less tame compared to the alternative “high-efficiency” (right) headphone connector. Tonality still not as expected, e.g. Bruce Springsteen - Backstreets (on Born To Run).

Switching back to the right connector - ouch, this is super flat and not engaging (still Utopia) - the Boss deserves better.

Notable with Utopia in the left slot is a hum with no music playing. This is, together with the observed RCA signal bleed into XLR inputs, a lesser score on pure technicalities (amp construction).

Net/net I would not likely listen to Utopia on HSA-1a as there are better alternatives (for me).

Since nobody will buy the HSA-1a without the SR1a, I can see no reason not just use the SR1a (which will be far superior to any other headphone I have, when driven by this amp)?

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Thanks. I’ll keep that in mind.

Not that I’m questioning you, it’s just I’m in the part of the journey you probably were (many) years ago. :wink:

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From your description, with non-Raal 'phones, what you are objecting to is HSA-1a sounding too warm and not as open/airy/sparkly on top, more along the lines of lacking “breath of life” or liveliness. This would be understandable since that kind of tuning is needed to bring SR1a towards neutral…

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A good benchmark that I would like to propose is to simply compare SR1a on the HSA-1a to the other headphones.

  1. If other headphones sound “significantly different” from the SR1a (tonality, dynamics, whatever is relevant to our enjoyment …), we might hypothesize that the HSA-1a is mostly optimized for the SR1a.

  2. To investigate the hypothesis, we can listen to the non-RAAL headphones on different amp(s), specifically zooming in on the observed areas of difference.

  3. if on a different amp the headphone sounds “more like the SR1a” (if we make that our gold standard reference) vs. HSA-1a, that would support our hypothesis?

This is mostly where I am coming from … Utopia on a TOTL amp is not night and day inferior to the SR1a, where on the HSA-1a the performance and enjoyment delta is far greater (Utopia almost sounding like an under-amped Sennheiser HD 650).

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@chianti. I also appreciate your insight and a detailed response sharing your impressions with music that you’re familiar with.

I tried the songs you listed and they are very “thin” sounding overall and give a sense of being “poorly recorded” but that might be just the nature of how they were recorded.

After going through your list looking for your observations on each song and A/B’ing with the PX on the same passages you referred, the weaknesses you pointed out become more apparent when coming from the PX to the HSA-1a - there’s a sense of “hotness”, maybe a “brighter” presentation and a very slight shift in tonality but I still wouldn’t call it dry and sterile, at least to my ears.

The switch from the Ribbon tap to the regular headphone tap might make the latter be perceived as flat because of the output power and current differences between the two taps and the “volume” which is louder on the ribbon tap…and yes regular headphone tap sounds indeed “less” dynamic and “boring” when compared to the ribbon tap.

I think that the Utopia (or anything as efficient) will reveal the hum and noise floor on most amplifiers delivering similar levels of power/current specially at sub $4k price point. You would have to go to excellently designed and implemented amps to not hear anything (noise) with the Utopia from taps outputting that kind of current, and those will most likely cost you twice as much if not more. For reference, you can’t hear anything from the SR1a and the Susvara using the adapter, due to do their low efficiency nature.

All in all, I won’t use the HSA-1a as a single box solution because I have my trusty PX and Hugo TT2 and I like both better for circum-aural cans. The HSA-1a was meant for the SR1a and does its job with excellence. The normal headphone tap shall be seen as a welcome “last minute” add-on to it and will most likely be improved on the final production units that will be available in the coming months.

I completely agree with you here, my primary use for the HSA-1a is going to be to drive the SR1a and occasionally, mostly due to laziness, I might just plug circum-aural headphones to it but it won’t be my preferred option for normal cans…and this is just because I have better options in my possession, not because I find the HSA-1a dry and sterile.

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Thanks so much for your observations I was wondering if the HSA-1a could serve both the SR1a and my Utopias.

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My HSA-1a has been updated and is on its way back to me. Assuming no shipping snafus, I should have it back in my hands on Thursday. That might just be in time to spend some time with the conventional headphone output so I can complete my review of the unit before I vanish.

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After two days filled with lots of listening time using the Utopia with HMS/DAVE headphone output and Phonitor X (PX) using HMS/DAVE as a source, I decided to re-assess the HSA-1a normal headphone output .

Plugged the Utopia in to listen to Once I wished a Tree Upside Down by Trilok Gurtu (Great Indian percussionist), in the first 35 seconds of this track there’s a series of shakers being played, one of them is played in an “elliptical” fashion going rounds around the head and the other is going sideways on a straight line from left to right and vice-versa, the HSA-1a struggles to delineate each instrument with the precision and clarity of both DAVE and PX (D&PX). Then the percussion starts with the sounds coming from both sides and there’s one slightly off-centered to the left further back that is easily pin-pointed by D&PX and not so much by the HSA-1a because the sounds just gets flattened out, the percussion notes carry some nuanced bass to it that can be easily heard on the D&PX but not in the same refined way on the HSA-1a. The overall dynamics also take a hit on the HSA-1a when compared to D&PX.

Put on Danse Macabre by Vladimir Horowitz from Piano SoundScapes Vol.12 album, and both D&PX striked with delicacy and extension on the high piano notes, you can hear the notes “fade away” and accurate reproduction of weight and sub-bass on the low-end notes that are not as discernible on the HSA-1a, the high notes are not as refined and extended and low-end ones are loose and a bit “uncontrolled”.

Moved on to Brazilian traditions and queued Djavan’s Meu Bem Querer from his well recorded Djavan “Ao Vivo” album, both D&PX are more coherent and faithfully reproduce the entire frequency spectrum and cues about the venue and people singing along with Djavan. With this recording, it’s apparent to me that there might be indeed a shift in the frequency response going on with the HSa-1a on circumaural mode, something just doesn’t sound right and the dynamics are also incompetent when compared to the Earfield mode and D&PX.

When compared to both D&PX, the HSA-1a (normal headphone output in circumaural mode) sounds less dynamic, not as coherent and refined, has a smaller and shallower stage (It loses depth and a bit of width) and there might be something going on with the frequency response that become more apparent when A/B testing some recordings and hard to tell with others. Once again as stated in my previous posts, I wound’t call it dry and sterile, it is not as refined and as dynamic when compared to the solid state headphone amps I currently have (Dave, Hugo TT2 and Phonitor X).

The Earfield mode was probably the one that the tuning of the HSA-1a was based on because the SR1a has been a huge success and a priority for RAAL-requisite, which in turn didn’t allow for extensive testing and tuning of the circumaural mode, specially with normal headphones (non-ribbon) since it’s not their priority (maybe??) - I’m just speculating here.

When I first put my hands on the HSA-1a, I felt like the build quality was solid but it was a somewhat “unfinished” product or a “finished prototype” to be improved upon after some early adopters feedback. I contacted Danny and reported the most evident flaws and a few other kinks that needed to be fixed and refined that I’m not going to list here because those issues might very well be particular for the unit I got, some of them couldn’t be replicated on other units that they had with them and other findings were fixed in those units.

The HSA-1a is shipped from Serbia, and all 14 units were shipped and tested there for driving 2x SR1a and speakers, then they were modded in the US to replace one of the ribbon headphone output by a regular one. Some units that were already shipped to customers and reviewers without the mod had to be sent back to RAAL-requisite to be modified, parts for the mod and sufficient man-power became an issue due to the global pandemic so I would expect that the production units coming out around July will be properly tested and optimized for both types of headphones.

If the Phonitor X leaves the collection as part of my consolidation efforts, it won’t be because of the HSA-1a but because of The Hugo TT2 and the Dave - one of them will become my main solid state option to listen to efficient cans and the HSA-1a ribbon headphone output with the custom adapter as a decent solution for hard to drive cans.

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