RAAL Requisite CA-1a Ribbon Headphone Review

A few years ago when I was at an event the Schittr, someone grabbed me to check out the RAAL Requisite SR-1a ribbon ear speakers. "Hey Marv, you gotta check these out!" The rest is history. Read about the SBAF Golden Schlong Winner SR-1a here: https://www.superbestaudiofriends.o...udio-sr1a-review-holy-moly-buy-this-now.8041/

TLDR; In a nutshell: https://www.superbestaudiofriends.o...bon-headphone-review.14057/page-2#post-422944

I knew that that RAAL Requisite had been working on a circum-aural version which has come out as the the CA-1a (Yes, I'm a late to the party.) I decided to grab a pair for the SBAF loaner program after a few members mentioned that the CA-1a was worthy, trading off technicalities of the SR-1a for more extended lows and more even frequency response. This is an accurate assessment. The CA-1a comes with two pairs of pads. One set has cutouts to allow more air. The sound of this pad is a cross between the fully encircled pads and the SR-1a. The fully encircled pads actually make the CA-1a tonal response somewhat like an HD650.



The first part of the journey was to find good system synergy. (I don't know what's up with me these days about this system synergy stuff but I seem to be more nitpicky about curating components for the total system approach lately.) The CA-1a while being easier to deal with tonally compared to the SR-1a, still requires careful matching with amp. The transient attack and treble timbre of these ribbons headphones can be a bit "hard" or "spitty" on the wrong set up. We all know that transducer and amp matching with nothing new, e.g. the HD800 can sound dreadful on the wrong system (and even then some people will not like the HD800.) Also, the CA-1a, despite the new TI-1b transformer adapter box (needed because the ribbon is 0.2-ohms, basically a metal foil strip), is still on the inefficient side. We need an amp that has plenty of gain (and power) and that doesn't sound too tightly strung.

I tried quite a few amp pairings with the TI-1b transformer adapter. Here are my notes a la Car and Driver rankings:

1. Sixth Place: Ferrum Orr / Hypsos (with Yggdrasil LiM). I was hoping the Orr's smooth elegant refined presentation and high power would work. However, this amp didn't do anything for me with the CA-1a. From a tonal and timbre perspective, neither worked. This amp was too neutral. It didn't round out the transient attack either. The gain was also lacking. With some tracks, I had the volume maxed out with the Hypsos on high-gain. There wasn't enough dynamic oomph either.
2. Five Place: Saga with Vidar 2 with Yggdrasil MiB). Now we are getting some oomph. I know the Vidar slams like crazy with tight lows. However the highs were too solid-state. And even then, I'm starting to really understand the limitations of ribbons when it comes to monster bass slam. (Still better than e-stats though).
3. Fourth Place: Pietus Maximus. This worked slightly better than the above. The Modius E with with the Cinemag's helped and did better than the Yggdrasil LiM. However, given that Pietus and Ferrum are so similar sounding, it's no surprise this didn't work for me.
   
4. Third Place: Jotunheim 2 (with Yggdrasil LiB). I happened to have this lying around so what the heck. Wow, ain't bad. It's not the end-all-be-all, but it works as a budget solution. FWIW, because of its simplicity (stack a Bifrost 2), I did use this for a while listening to music and even taking a few video calls. The video calls were a revelation of that ribbons can do. I usually take video calls with Grados or Sennheisers. Sometimes with the ESP950. Dang, talking about listening through everything: shitty microphones, compression, how people use their airways, tongue, and lips to make words. That was spooky. I can only imagine what @zerodeefex hears when he takes calls with the SR-1a (with dual mono Tyrs - "certified" to work with the RAAL ribbons). Anyway, I wanted better. Nothing wrong with Jotunheim 2, would totally recommend this, but too mid-fi for me. I'm a high-roller.
5. Second Place: Mjolnir 3 (with Yggdrasil MiB). Hmm, now we are getting somewhere. This is good. Sure, the Mjolnir 3 isn't that dark and only slightly warm. Maybe is has to do with what @roshambo123 said about the Mjolnir 3, that the transients in the highs are rounded. I did have to crank up the Mjolnir 3 quite a bit. Overall very good sounding, lots of plankton, but I couldn't help but feel there could be more slam. This last bit I know is hard for a ribbon. At the end of the day, I couldn't help but play back Paul Simon's Diamonds on the Soles of Her Shoes to remind myself of a listening session I had with the Sennheiser HE1. To be honest, I preferred this set up to the HE 1 (with it's built in DAC). FWIW, my wife who dislikes the HFM nano-planars and all e-stats for having "too much separation" loved this setup.
   
6. First Place: HH Scott 222D Integrated Stereo Amplifier (with LiM). This vintage piece was painstakingly restored by @bobboxbody. Yes!!! This space heater is purrfect. If you think your Mjolnir 3 is a space heater, the 222D is about three times more deadly.

MOD ADD INDEX:

• Frequency Response: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422117
• CSDs: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422120
• FR Comparison with SR-1a: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422136
• FR Comparison with pads provided: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422174
  
• Old studio tricks to tame highs: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422176
• @Tchoupitoulas impressions: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422188
• Distortion surface: https://www.superbestaudiofriends.o...1a-ribbon-headphone-review.14057/#post-422189
• Impedance (with TI-1b transformer adapter box): https://www.superbestaudiofriends.o...bon-headphone-review.14057/page-2#post-422391
• Running with the low-power Piety amp: https://www.superbestaudiofriends.o...low-power-piety-and-power-hungry-ca-1a.14067/
• In a nutshell: https://www.superbestaudiofriends.o...bon-headphone-review.14057/page-2#post-422944

 

A little detour before I take measurements. I'd like to give @bobboxbody a shout out for being such a valuable resource and member of SBAF. @bobboxbody fastidiously restores vintage tube stereo amplifiers such as this: https://www.superbestaudiofriends.org/index.php?threads/hh-scott-lk-48-restoration-mods.13326/

I actually purchased the HH Scott 222D from him a few months ago and just did not have time to unbox it until now where I had a good reason. FWIW, shame on you guys for not buying the amp on the FS section. What @bobboxbody was asking for it was too reasonable - essentially a gift, a labor of love, for 1960s tube amplifiers. This was the time when the secret to good audio transformers was not yet lost. There was no way I was going to let this go outside of SBAF. If I hadn't grabbed it for safekeeping, @zerodeefex was. (And yes, shame on you guys for completely ignoring the Eddie Current Ultralinear, which I think he was asking $1200. I eventually bought it myself and gifted to @ChaChaRealSmooth for being gearmaster).

@bobboxbody not only provided all needed tubes (all vintage except the outputs?), but also labelled where the tubes go in along with biasing the output tubes. appropriate. There are a million tubes that do all sorts of stuff on the amp (I have still yet to figure it out). Finally, he included a full set of tube protectors for the 12AX7s and spade to banana connectors in the back.

Anyway, check out the restoration job. Repainted transformers and shiny parts.


Anyway, hail to vintage meets modern. Hail to two headless panther pieces of gear!

 

RAAL Requisite CA-1a
Frequency Response
Diffuse Field Compensated


RAAL Requisite CA-1a
Frequency Response
Diffuse Field & 1/db Octave Compensated


Response is a big jaggy. We've seen this is underdamped HiFIMan planars. I wonder if the tension is a bit different on the CA-1a compared to the SR-1a, maybe to allow it to extend down to 20Hz. There is a decent dip localized at 3kHz which isn't offensive. I am hearing stuff in the highs that isn't reflected in the FR. Let's take a look at CSDs next.

 

Cumulative spectral decays below. This wasn't expected from the FR: some ringing at 7kHz. Usually we see a big narrow dip in the FR when this occurs. This makes sense and likely a contributor to the subjective hardness or spittyness that I mentioned earlier with some amps. More relaxed or transient rounded amplification works best with CA-1a. The effect is worse in the R channel than left.

Also notable are the "ripples" in the lower-mids to middle-mids. We will see this in some orthos and all e-stats. In the case, they are gone after 1-2kHz. The rest of the floor in the upper mids to high treble is super clean. Overall decay is super duper fast.

I've noted that these ripples, often indicative of underdamped planar types do contribute to a more liquid sound. Yes, the CA-1a is more liquid compared to the SR-1a which is more grainy relatively speaking. It's give-and-take. Tradeoffs. I know some people will prefer the SR-1a. Others will prefer the CA-1a.

RAAL Requisite CA-1a
CSD L


RAAL Requisite CA-1a
CSD R


To be continued. Nap time for me. Curious about distortion and impedance.

 

I believe it was @Hands who said that speedy transients requires thinner lows (same thing as brighter/cooler). I tend to agree with this. Utopia is probably the closest when it comes to good bass with some warmth and speedy transients. Here are SR-1a vs CA-1a frequency responses overlaid:

SR-1a (cyan) vs CA-1a (orange)
Frequency Response

Utopia is better with respect to plankton. However, I'd say that Utopia is relatively easy to get to this level from where I am at and what I've been exposed. It's really just a matter of getting final pieces (tubes, DACs, cables) with DNA Stellaris or my EC 45 Custom. Heck, throw in Starlett, ZDS, DSHA 3F. Maxing out CA-1a is still a little bit of unknown if you are nitpicky like us. I am thinking the x2 Tyr monoblock combo of @zerodeefex would be the way to go for the CA-1a as well. Throw in a DAC with an output stage that can drive an transformer volume control into the Tyrs, and that would be magic. However this set up is ridiculous. More for its size, since Tyr's actually run cool and both suck up less wattage at the output at low output than Aegir (yes, I've measured it).

I should mention that the Mjolnir 3 (and Yggdrasil MiB) is good enough. It's arguably more resolving than the HH Scott 222D, but a bit less slammy, and definitely not quite as lush. Yes, the ribbon sounds lush with the 222D. The Scott is also more mid-centric, this presentation helping to fill in the 3kHz FR dip. However, I can cheat a bit because it's got bass and treble knobs.

Ultimately, I do feel that your assessment of SR-1a being tops overall with technicalities, followed up Utopia, and the CA-1a dropping to positions 4 and 7 may be spot on. The only stat I'd throw up there is the HEV/HE90 Orpheus, the OG Orpheus. The Sennheiser stats have a harder transient attack to STAX and the HE90 is just damn resolving. FWIW, I didn't feel the latest Sennheiser HE-1 was close, and even then the HE-1 had problems in the highs: an obvious spotlit peak at 9kHz "ssss, ssss" (shows up a dip in some measurements) and sort of a mild V shaped tuning. I figured I'd mention this because it seems the Internet is abuzz yet again with the HE-1 as the bestest. For those who have been around in this hobby, it's not. Then again, I'm kind of a theoretical source first person (practically amp first, and only because good vinyl is hard to source), so the transducers are just along for the ride.

Finally, the CA-1a does pass the Bjork Hollow (16-Bit Remix) first minute test. It's not quite as dynamically slammy as the ZMF Atrium, but bass heft and sustain is up there. The expectation is that the bass should be frightening. This is where stats and even the nano-diaphragm to a lesser extent planars fall apart.

 

CA-1a with Open Pads (yellow) vs CA-1a with Closed Pads (orange)
Frequency Response


This is how the open pad looks like.


@penguins: I would be curious how they fit you. I can max out the strap with my big Asian block head, but I think your head is even bigger than mine. I also had some issues with the protruding clip at you see that right. That clip protrudes inward to allow the headband strap to wrap under and through. I had to bend tie headband a bit outward in the middle and then inward a bit at the sides.

I am tending toward the open pads despite less bass below 100Hz. Again, the full closed pads did make it sound HD650ish, reducing technicalities and aspects that make the CA-1a less "ribbon" sounding for better or worse.

Totally get that. I basically hate all ribbons on speakers, except for the bigger RAAL ones. I do wonder if the transformer brick is holding it back. I almost get the sense that the original passive box that came with the SR-1a was better. Would be curious to compare the TI-1b with the open baffle comp barrels and the original passive box with the SR-1a.

 

Here are the Cumulative Spectral Decays for the Open Pads. As expected, they are a bit more ringy, less damped throughout, compared to the fully enclosed pads.

RAAL Requisite CA-1a
CSD L


RAAL Requisite CA-1a
CSD R

 

Finally, you guys know how much I love toilet paper. This is for taming the highs and hard transient edges for greater compatibility with more amps particularly of the solid-statey sounding variety. This can be helpful for the less damped but more lively presentation of the open pads. Or for folks who prefer a darker presentation.

The design of how the pads mount to the cups makes it super easy to do. The pads have tabs at the top and bottom and slide into the cups. A single sheet fits right in between the where clips slide in.



CA-1a with Open Pad with TP over driver
Frequency Response


CA-1a with Open Pads no TP (yellow) vs CA-1a with Open Pad with TP (blue)
Frequency Response

 

RAAL CA-1a Distortion. The following are with the open pads, which have more distortion than the closed pads.

Second Order
Distortion Surface (Distortion is in absolute SPL)


Third Order
Distortion Surface (Distortion is in absolute SPL)


Fourth Order
Distortion Surface (Distortion is in absolute SPL)


Commentary:

• Third order dominant in the lows and upper bass. High distortion at high SPL. The CA-1a doesn't like to be pushed to ear bleeding levels. Third order subsides to reasonable moderate levels below 85db. None of this should be an issue for those who listen a low to moderate SPL.
• High second order distortion at moderately loud to very loud SPL. Even around 85db, a little bit elevated.
• A couple of narrow distortion speaks at specific frequencies, most evident in the second order surface, but existing in the third and fourth as well. Possibly related to the reverberation of the ribbon under tension?
• Quite clean in the mids and highs.

 

There are a couple of FR dips in the upper mids and up. I am assuming the tizzier treble could be an effect of filling these dips in. (We don't know for sure because of the site for Mitch's filters, we only see the measured frequency response and effect of the convolution filter to 5kHz). Getting to perceptive neutral is just as much an art as science. Can't just make the frequency response totally flat. This is coming from someone who has built plenty of speakers and crossover networks. Science gives us a starting point. Final tweaking is always done by ear, a few db here or there to compensate for a transducers distortion and transient characteristics. Finally, I am not convinced the high frequencies are even for any two ribbons.