RAAL-requisite - Official Thread

RAAL-requisite represents the coming together of two well known names in the high-end audio firmament. The Serbian “RAAL” group, probably best known for their ribbon tweeters and speakers, and “Requisite Audio Engineering”, out of California, producers of a gamut of highly regarded studio components.

As a joint venture, they’re are know for their SR1a EarField™ Monitor ribbon-driver headphones, and the HSA-1b Switch-Drive headphone/speaker amplifier.

New, pending, releases mean its long overdue to give the brand as a whole its own thread, even while the existing products have their own, respective, dedicated threads.

So this is the spot to discuss RAAL-requisite as a brand, and for commentary and speculation on what they may bring to the market in the near, and not-so-near future.


There has been some high-level discussion from RAAL-requisite, across different interviews and so on, about what they have in the pipeline.

The two most immediate projects of interest for SR1a/RAAL-requisite fans are the long-rumored circumaural (over-ear) ribbon-drive headphones and the much more recently mentioned tube-based amplifier. RAAL-requisite has a goal of showing both of these new products at the upcoming CanJam in September - though aren’t quite ready to commit to that yet.

Things of note so far …

Circumaural “SR1a”:

I don’t know what this will actually be called … maybe “SR1a C” or “SR1c” … or something entirely different.

Current commentary has it targeting a $2,900 (or lower) price-point. It will use a shorter ribbon than the SR1a, though no word on whether it is wider and/or has greater/lesser surface area. Native bass reproduction should be flat to 30 Hz. And the cups will be setup such that they are angled relative to the ear by 15 degrees, which should help preserve some of the SR1a’s much-vaunted ability to image and stage in a speaker-like fashion.

Tube Amplifier

I’ve heard this referred to as the “VM1a”, tubes mentioned were 6LZ for signal and EL34 for power. A single-ended, push-pull design (single-ended means it should retain more tuber-goodness than a balanced design would do), with a currently projected price of $6,500.

I am likely in for one of each … especially if the VM1a ups the available power for conventional headphone and speaker drive (assuming it retains both those capabilities from the HSA-1b … which I’ve not heard anything about).


The YouTube clip mentions it’ll be a 3" ribbon vs. 4" in the SR1a (25:39).


I vote for CR1a! I hope Florida is treating you well…


Excellent news! Both the circumaural phones (for more ribbon goodness) and a direct drive tube amp, which I didn’t think would come about from any source to power the SR1a. As much as I like The HSA-1b over my Jot R
I am really becoming addicted to the sound of the SR1a with my PrimaLuna EVO 400 with EL 34’s in Ultralinear mode and 70 watts/channel into the interface. Spooky good sound.

When I read that, it reminded me of those little button batteries.

1 Like

Just thought of something, I hope they stick with the same headphone connector type, I’ve already got some aftermarket cables set up with those 3.5mm’s.

Don’t use aftermarket cables with the raals. They are so low impedence that cable inpedence will measurably change FR. You need cables specificaly designed for them unfortunately

The specifics of impedance and pin assignments have been taken into account by this manufacturer in this case and I have communicated directly with the owner who makes their TOTL cables himself. The proof as always will be in the listening.

(and I have tried one pair from a different outfit where i don’t think these factors were taken into consideration and I think the female connector is wired out of phase, live and learn). LOL!


They should.

Since the overall impedance of the cable assembly is so low, the 3.5mm TRRS connector gives more connection surface area than mini-XLR or even more common 3.5mm TRS connections - which helps keep the impedance as low as possible.

The headphone is actually wired to use all four connection points to take full advantage of that.


Speaking of SR1a cables …

I’ve talked about the ones I’ve built in the SR1a thread. They’re lower impedance than the official ones, which results in a slight, but apparent, reduction in treble energy when used with the ribbon-interface box.

To listen at my desk (which is deliberately further from my headphone rig now than a normal cable will reach) I’ve taken to using my 0.05 ohm SR1a cable, which is as big as can be practically used without becoming an ergonomic pain, in conjunction with a separate extension cable.

This extension cable is something I run to a clip on the side of my desk (or you could run it to your feet), as it is too thick and heavy to actually run to the headphones themselves … not to mention the conductor bundles for each channel/phase are individually too large for the the cable entry on 3.5mm TRRS jacks. But it only adds 0.03 ohms total to the cable impedance, so I can then plug my custom SR1a cable into that.

Net result is an overall <= 0.08 ohm cable (extension plus headphone cable), up to 21 feet long.

When listening without the extension cable, i.e. when I’m sitting near my rig just to listen, I use the 0.1 ohm direct cable I built originally.


Yoy mention on the adapter box specificaly. Is this less of an issue on the hsa-1b?


Less of an issue on both the HSA-1b and the Jotunheim R.

1 Like

Based on a picture posted here, it looks like there may be some additional developments on the RAAL-requisite front …

I have no inside information, just extrapolating/guessing from what I can see/read in that picture.

Three new amplifiers?


Tube-based conventional (planar and dynamic) headphone amplifier (no ribbon drive), possibly OTL.


Solid-state conventional (planar and dynamic) headphone amplifier (no ribbon drive). Looks like it has selectable output attenuation; maybe to support both easy to drive cans (needing lower-noise, hence attenuating rather than selectable “gain”) and hard to drive to drive stuff.


Previously mentioned direct-drive tube-based ribbon headphone amplifier. Still looks like 6LZ signal tubes and EL34 for power. Selectable compensation for either CA (circumaural) and open-baffle (can’t read the label, could be “OB” or “EF” or something else), on the smaller red dial.

Clearly something else there, too, on the left site, but that’s obscured by the headphones.

And then on the far left, next to the PDT-1a, it looks like what I assume is the circumaural ribbon-headphone prototype.



Retains mostly the look of the SR1a but with what looks like a thicker metal headband. I wonder if RAAL-Requisite will release an updated interface box, one without or a switch to disable, the baffle compensation.

“BoyNamedSue” over at Head-Fi posted this:

Rumored to be priced at $1900.


It looks like probably a direct HEDDphone competitor… it must be interesting to compare.
Les bulky, less heavy, less cheap plastics … it can be at least far more resistant through time than my HEDDphone is.

For the interface box specifically (as opposed to the direct-drive amplifier options) it might turn out that no switching is actually necessary. Which doesn’t mean they won’t do it; if it is needed I can’t imagine that they won’t … but I’m not sure it’s required.

I’m speculating on what they might do here, but this is possible because:

The interface box applies its compensation passively:

This means that the overall resistance of the headphone (and its cable) plays a part in how the compensation network behaves. Alex, the designer, posted early in the life of the SR1a about how very small changes in cable impedance skew the frequency response coming from the interface.

The lower the net impedance of the cable/headphone the less treble output there is.

The shorter ribbon in the circumaural version (3" vs. 4" in the SR1a) means lower resistance by 0.025 Ω, so instead of a 0.2 ohm impedance from the ribbon you’ll be at 0.175 Ω. That’s enough to lower the upper treble (and above) output measurably and audibly.

Note: This effect is much smaller (or even non-existent) with the direct-drive amplifiers as their compensation is applied using active circuitry. Thus they still require a switch to turn it on or off (as seen on the new VM-1a tube amplifier*).

Circumaural Tuning:

The circumaural design will change the effective response of the headphones. It should provide low-end re-inforcement (I’d heard, indirectly, that bass extension increases directly by another 3 Hz, and the roll-off is slower) and some attenuation of higher frequencies.

That would shift the free-space/open-baffle response of the driver.

Thus the combination of these factors may be enough to offset a need for a different compensation in the passive interface, with it’s primary purpose being there to load-match (provide increased impedance) to the driving amplifier.


Some more thoughts/guesses on what the pictures appear to show of the new RAAL amplifiers …


On the VM-1a (“big tube amp”), some additional pictures from CanJam posted here, are interesting.

For one, you can clearly see that the tubes are 6x EL34 and 1x 6SL7.

For another, there is a a switch for something nestled between the tubes. At a guess, and it is a wild-ass guess, it might be to switch the EL34s between Pentode drive and Triode operation.


This has an external switch on the rear to change the input attenuation on the XLR connections. On the HSA-1b this had to be done by opening the unit and flipping some DIP switches.

It also appears to have switches for lifting ground connections. I can clearly read an XLR GND switch, not sure what the other says.

Interesting stuff.

More interesting for me is the VM-1a, however. A direct-drive tube amplifier is quite appealing to me, as I have no tubes anywhere in the SR1a chain I use at the moment (I drive them either of the HSA-1b or via the interface and a Chord Ultima 5).

However, it is interesting to note that the front panel only shows connections for RIBBON headphones, where the HSA-1b can drive ribbons or conventional headphones …

Which makes me wonder if it will still be possible to (safely and usefully) drive conventional headphones from the ribbon outputs using an adapter.

I don’t really want to have to have a VM-1a and an HSA-1b. And since the HSA-1b is the only solid-state headphone amplifier I have (excepting for electrostatics), that might mean having either giving up solid-state drive for headphones entirely or having to choose another dedicated solid-state headphone amplifier for more demanding stuff (like the LCD-5 and so on).

Interesting times …


Aleksandar from RAAL-requisite’s response with a bit more info on their latest offerings:

In particular, of interest to me, the SR2a:

They are definitely ugly! That headspring in reality is not what it was on the computer screen, but there was no time to change anything before the show…But, we’ll change all that. I’m not promising some great beauty, though! :) I’ll do my best to make piece between functionality, reliability and good looks (in that order)…

The earpads were makeshift as the initial variations of suede leather/memory foam, perforated, non-perforated, foam combinations, etc. ALL had too much bass (!) and too much midrange suck-up, so more leakage was needed, therefore the naked foam type quick-fix before the show, as any type of foam wrapped in any type of leather just had too much “loudness” effect.

So, we’ll work more on earpads as they are the dominant factor in tonal balance of open-backs.
The goal is to bring up the bass but not overdo it. For now, the ticket seems to be naked foam pads to let the sound get out freely from the earpad chamber, so the bass-pump isn’t too effective.