April 2021

RAAL Requisite HSA-1b Headphone / Speaker Amplifier Review
The pinnacle of personal audio.
Review By Gary Peter Pialis

  When RAAL Requisite released their true ribbon earfield monitors last year, it literally took the world of personal audio by storm! These headphones very quickly captured many raving reviews for their incredible speed, transparency, and incredible sound staging capabilities. Our own Frank Iacone reviewed them here and noted "The RAAL-requisite SR1a Earfieled Headphone Monitor is a crowning achievement of what is possible in headphone design. The beautiful sound coming from the ribbon monitor was sensational. The exceptional imaging made all performers come alive and made the equipment get out of the way." Being a huge fan of near field speakers, but having a young family, I longed for the sound staging that speakers could bring to so many of my favourite recordings.

Headphones are by their design, limited in this regard and while some stellar headphones can really impress with imaging, I've always felt wanting more. When I purchased my SR1a headphones, I was absolutely floored with their incredibly high level of transparency and clarity, but I was truly overjoyed with their ability to cast both a wide and deep soundscape! When played through the Schiit Audio Jotenheim R, these headphones are among the very best I've heard through my many years in this hobby. So when RAAL Requisite introduced the new dedicated HSA-1b amplifier, my interest was piqued, to say the least!

Dealing with the folks at RAAL Requisite was a pure joy. You'll never find a nicer and more passionate group of people who truly believe in what they do! Out of the box, the HSA-1b is a beast of an amplifier; it is heavy and extremely well built with truly outstanding casework and appearance! The design aesthetics really set this unit apart from the competition and it really shines in your setup! The red 24-step volume attenuator just pops and works brilliantly when trying to dial in your ideal volume setting. To call this amplifier the "jack-of-all-trades" is an understatement. Not only can it power the world-class SR1a earfield ribbon monitors, it could drive literally all of the other headphones I have on hand!

From the very efficient 35 Ohm Focal Stellia to the very power-hungry orthodynamic HiFiMAN Susvara or Abyss Phi TC headphones (and everything in between)! Throw in a speaker amplifier section and the only thing missing is the kitchen sink! With both balanced and unbalanced inputs, the HSA-1b offers you the flexibility to hook it up to your source; though I did find the balanced inputs a tad more dynamic and punchy with a "blacker" background when played with my Chord DAVE DAC, both inputs were truly outstanding. The full list of specifications for this amplifier are:

Load Impedance: 0.3 Ohms – Infinity

Output Power: 10W / 8 Ohm 20W / 4 Ohm 40W / 2 Ohm 55W / 1 Ohm @ 1kHz/sine (one channel driving)

Ribbon & Headphone Drive:  RAAL-Requisite SR1a, Dynamic Driver & Planar Magnetic Driver

Speaker Drive:  8, 4, and 2 Ohm Loads

Frequency Response:  100mW in/sin. 15Hz – 500kHz

Power Bandwidth: 100kHz (-3dB @ 1kHz)

Signal To Noise Ratio: Better than 90dB

Input Impedance: 40 kOhm

Distortion: Less than 0.5% @ 1kHz

Sensitivity:  0.5V / 40 kOhm

Inputs:  Two RCA (unbalanced) and two XLR (balanced)

Maximum Power Consumption: 150W, without signal: 25W

Dimensions: 3.54" x 8.58" x 12.60" (HxWxD)

Weight:11.7 pounds

Prices: Amplifier is $4500, seven foot upgrade cable is $1050
            10 foot upgrade cable is $1500

Optional Accessories: Waterproof Flight Case with handle and Casters $350

Also included with this amplifier was a seven-foot new upgrade headphone cable designed and manufactured by RAAL Requisite. This new cable is available in 7 foot (SR728) and 10 foot (SR1028) lengths and contains high silver conductors. Using an annealing process and conductor geometry, the cable designers were able to achieve the tonal balance that they desired. Overall I found this cable incredibly detailed and transparent, but still smooth and musical at the same time. The dielectric used was Kapton. Finally, there is a whopping 196 feet of silver in each cable and after many iterations, tweaks and prototypes my ears can confirm that they hit the bullseye with this cable and in the end, I found it the perfect finishing touch to the SR1a + HSA-1b combination!

I couldn't wait to try my SR1a headphones by RAAL Requisite on this amplifier and boy was I in for a memorable experience! As I write this a few weeks after this experience, I still find myself smiling from ear to ear. "Jazz at the Pawnshop" in DSD is a particular favourite recording of mine that I keep to test sound staging and the ability of a headphone and subsequent setup to truly immerse me in a real-life location and put me there at the centre of things. Well, I can easily say that this was truly the most immersive and true-to-life experience I've ever had with personal audio! Simply put, I was literally transported in both time and space to that pawnshop in Sweden in the mid-1970s! Previously I've thought, boy this recording just doesn't get any better, but boy was I wrong after experiencing this album with the SR1a + HSA-1b combination (and I've heard it on some truly stellar setups through the years).

As mentioned previously, this setup is not only expansive from left to right, but the front to back imaging is simply off the charts! Each musician is clearly portrayed on stage and the instrumental separation was truly on-par with the venerable Stax SR-009 electrostatic headphones. So having that level of clarity, speed and transparency with the sound-staging reminiscent of near-field speakers really had me thinking that I was both having my cake and eating it too!

While the SR1a earfield monitors sounded truly glorious out of the Schiit Audio Jotenheim –R (Jot –R) amplifier ($799), the level of clarity and transparency was on a whole new level with the HSA-1b. With slightly less overall warmth, the HSA-1b was able to come even closer to what I consider to be "dead-neutral" and still sound very musical at the same time. The value proposition for the Jot –R is off the charts and I could very happily live with it as my amplifier to my SR1a headphones, but after hearing them with the new HSA-1b, the differences were very impressive indeed! The tonality was as perfect to neutral as I've come across with incredibly textured and impactful bass that both satisfies with regards to impact and energy, but is never obtrusive with the mid-section. Vocals are both upfront and clear with a level of realism that is very rarely achieved in audio reproduction. Finally, the treble was as "life-like" as I've heard, both extended and transparent, cymbals were incredibly detailed without a hint of harshness or stridency. This amplifier and the SR1a offered me a lot of "ands" this is great "and" that is too! Truly one of the very best setups that I've ever heard... period!

I then wanted to put the HSA-1b through the gauntlet and try this amplifier with the most difficult-to-drive headphones that I have on hand. The HifimanSusvara are among the top headphones on the planet, they sound incredibly detailed, quick and transparent and maintain their musicality throughout the experience. However, all this goodness does come at a price...power! With a 60 Ohm impedance and a lower 83 dB/mW, many folks have resorted to either very powerful headphone amplifiers (4W minimum-ish) or speaker amplifiers to drive these power-hungry headphones. In order to get the maximum power from the HSA-1b, RAAL Requisite includes an adapter that allows the user to plug in their headphones into the SR1a output and access the speaker amplifier from the front of the unit without having to resort to using the speaker taps on the back and thus making the whole setup a lot easier. "Transformer" by Lou Reed was released the year I was born and I've been a big fan of this album since I was a teen. With so many rock classics, this album is my favourite released by Lou and I decided to stream it off Amazon.HD for this session.

Right off the bat, I could tell the HSA-1b was more than up to the task of driving the Susvara and with plenty of "head-room" to spare! I never felt I had to go above the 11 o'clock setting on the volume dial and I was treated with an incredibly dynamic and punchy presentation! So I can emphatically state that the HSA-1b can very much be an "end-game" solution to driving even the most power-hungry planar magnetic headphones that you may have on hand. Starting off with Lou's vocals on "Perfect Day", I found the HSA-1b offered a brilliantly live and upfront mid-range that featured the unique stylings of Lou's voice just brilliantly. Life-like and liquid all at the same time would be the best way I could describe this experience. Conversely, the bass on "Walk on the Wild Side" was deep, taught and impactful. Simply put, this was among the very best I've ever heard the Susvara sound through any setup (speaker or headphone amplifier).

Treble was measured, extended and clear without any sense of fatigue. The dynamic nature of this amplifier really kicked the Susvara into electrostatic territory for me with a sense of quickness and transparency that I've only experienced with the RAAL Requisite SR1a or Stax SR-009 headphones. The ability to use this SR1a amplifier on other headphone technologies like planar magnetic or standard dynamic headphones is a huge bonus. Throw in the fact that this amplifier will not only drive them, but it will do so at a level that will compete with the very best around; if not surpass pretty much anything you can think of.

Finally, I decided to go back to the SR1a and this time I wanted to incorporate the new 6N Silver Cable that RAAL Requisite will be releasing to the market. This upgraded cable is 7 feet long and is manufactured using high quality silver conductors instead of copper for the standard cable. For this session, I decided to use "Fanfare to the Common Man" by The Minnesota Orchestra featuring Eiji Oue. This is a stellar recording of this classic work by Aaron Copland. As the timpani beats started up I could immediately tell that this setup was on a whole new plane of reality when compared to so many other flagship setups that I've heard through the years. The sense of depth and detail was off the charts and the speaker-like presentation have me goosebumps. The only downside was that recording anomalies that other headphones seemed to only hint at were all laid bare with this ruthless setup.

The SR1a drivers when powered with the HSA-1b amplifier and the upgraded silver cable easily picked up these recording anomalies. I suppose that is the one downside of having such an incredibly transparent setup is that you will have to pick your music with some care as it will let you hear even the smallest details in your recording with ease... both good and bad. That said, I absolutely loved this experience overall. The bass offered by these ribbon drivers was again deep and impactful with gobs and gobs of transparency and clarity. And throughout the audible frequency range, this setup offered one of the most balanced and musical presentations I've ever experienced. Throw in what I consider the best sound staging capabilities of any personal audio setup I've ever experienced, you have truly one of the finest experiences I've ever had in audio.

What else can I say about this stellar combination of the SR1a true ribbon earfield monitors and the HSA-1b that I haven't already said? It is simply right there with the very best personal audio can get...period! Incredibly transparent, clean and open sounding, this setup really will have you smiling every time you listen to your favourite songs. If that wasn't enough the ability to have a truly endgame amplifier for even your most power-hungry orthodynamic headphones like the Abyss Phi TC, HiFiMAN Susvara or Audeze LCD-4, the value proposition of this amplifier really shines through. And if that wasn't enough, hook up any pair of efficient desktop speakers to the taps on the back of this amplifier and you really have the Swiss Army knife of amplifiers. The HSA-1b has punch, dynamics and a level of transparency that is truly outstanding and will have you staying up late at night just to listen to one more track. If you already own the SR1a headphones and are looking for an end game amplifier, look no further than the HSA-1b amplifier! Especially if you're like me and have a collection of other great headphones that you're looking to drive, this amplifier will scratch every upgrade itch you may have in the future! Highly recommended!

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Specifications
Type: Stereo headphone and loudspeaker amplifier
Load Impedance 0.3 Ohms – Infinity
Output Power: 10W @ 8 Ohm, 20W @ 4 Ohm,
                     40W @ 2 Ohm, 55W @ 1 Ohm (one channel driven @ 1kHz/sine)
Ribbon & Headphone Drive: RAAL-Requisite SR1a, Dynamic Driver & Planar Magnetic Loudspeaker Load: 8, 4, and 2 Ohm
Frequency Response: 15Hz to 500kHz (100mW in/sin.)
Power Bandwidth: 100kHz (-3dB @ 1kHz)
Signal To Noise Ratio: Better than 90dB
Input Impedance: 40 kOhm
Distortion: Less than 0.5% @ 1kHz
Sensitivity: 0.5V / 40 kOhm
Inputs: Two RCA (unbalanced) two XLR (balanced)
Maximum Power Consumption: 150W, without signal: 25W
Dimensions: 3.54" x 8.58" x 12.6" (HxWxD)
Weight: 11.7 pounds
Prices: Amplifier: $4500
         7 Foot Upgrade Cable: $1050
         10 Foot Upgrade Cable: $1500
Optional Accessories Waterproof Flight Case with handle and Casters $350

Manufacturer
RAAL Requisite
2175 Goodyear Avenue
Suite 110
Ventura, CA 93003

Voice: (818) 437-0779
E-mail: danny@raalrequisite.com 
Website: RaalRequisite.com