Ok, first impressions of the SR-007 Mk1 on my CCS-modded SRM-T1S - this post will probably be updated as my assessment of the combo evolves. First of all, the physical impressions:
First of all, the 007 Mk1 feels slightly lighter on the head than the 007A. I haven't weighed both units on a proper scale to be sure yet, but that's the first thing I noticed.
The second thing I noticed is that the 007 Mk1 drivers feel farther away from the ears than the 007A's. This matches spritzer's assessment waay back in 2008 that the 007 Mk1's earpads are more angled than the 007A's, despite the 007 Mk1's earpad springs being wider and less angled than the 007A's.
Most importantly, the earpad seal on the 007 Mk1 is much better than 007A's. As a side effect, though, its Stax farts are loud, more that the 007A's after the blu-tac mod, which makes finding the right fit somewhat annoying. On the other hand, the 007A's earpads are more comfortable and have a more pleasant touch to the skin. This may make 007A a set more suitable for longer listening sessions. I may try later to use the 007A earpads on the 007 Mk1 to see if the increased comfort is worth the ensuing change in sound, this seems doable...
(edit - July 21st 2022) I found that the clamping of the headband arcs on my head was too loose and couldn't maintain the fit. Maybe the elastic band is also loose? Visually it doesn't seem so... As a result, I kept fiddling with the fit and the ensuing Stax farts were driving me nuts! Fortunately, a gentle additional bend on the arcs has improved the fit considerably - now the set seems to stay at the right position, the arcs no longer touch my head and thus I no longer have to deal with deafening Stax farts so often. Still evaluating whether the arc setup has achieved its optimal shape for my head or not, but results so far are encouraging. The set feels more comfortable now, perhaps I won't need to swap earpads with my 007A. Also considering slightly shortening the elastic band so that the set is kept higher on my head, let's see...
As for the sound impressions... wow. I didn't imagine there would be that much difference. I reckon my findings below have mostly been reported ad nauseam by others on this and other forums already, but again, this is mainly for my own record and I find it convenient to have it all in one place, so I apologize in advance:
The soundstage definitely feels wider on the 007 Mk1 than on the 007A. This is particularly noticeable in live tracks such as Blue Öyster Cult's "Veteran of the Psychic Wars" from "Extraterrestrial Live" or opera tracks such as Sir Georg Solti's "Don Giovanni, a cenar teco m'invitasti" from Mozart's "Don Giovanni". This corroborates my impression above about the drivers feeling farther away from the ears on the former.
Instrument separation and fine sound details are more evident on the 007 Mk1, with better resolved low-volume information. Put differently, the 007A sounds darker (more details on that later). For instance, unlike with the 007A, with the 007 Mk1 I can clearly hear the intro's bass line on Metallica's "Master of Puppets" (the DCC 24K Gold remaster, of course - the standard master is obscenely compressed, as most of Metallica's tracks, a trend that got even worse in more recent albums. OK, end of off-topic rant). In the same spirit, I hear a better defined bass line on Rage Against the Machine's "Bullet in the Head" with the 007 Mk1.
Imaging also feels slightly more precise on the 007 Mk1, take e.g. La Venexiana's "Si ch'io vorrei morire" and "Io mi son giovinetta" from Monteverdi's 4th Book of Madrigals, or even Bill Evans's version of his "Waltz for Debby" from the album of the same name.
All of the above probably have to do mostly with the driver position and the far superior earpad seal on the 007 Mk1. One thing that's probably due to something else, though (i.e. tuning?), is the frequency response: even after the blu-tac mod, the 007A retains a slight damping in the upper mids (don't get me wrong, it gets much worse without blu-tac) which still bothers me in some tracks, especially ones with some degree of compression. I've tried to correct this with EQ, but that caused other problems that made the ensuing sound less natural to me, so I gave up that route. This problem is completely absent on the 007 Mk1 - to a fault: (edit - July 22nd 2022) after listening to it for a somewhat longer period, it comes out in fact as a bit shouty in the high mids / lower treble. This alone makes the 007 Mk1 a bit more tiring for longer listening sessions than the more relaxed 007A, even if the latter's characteristic comes at the above price.
Bass still feels slightly stronger on the 007A than on the 007 Mk1, despite the blu-tac mod on the former (which controls the stock 007A's wonky bass response) and the better earpad seal on the latter, but better resolved on the 007 Mk1.
On the other hand, regarding timbral quality the 007 Mk1 and the 007A seem to me so far unsurprisingly quite close to each other, and so does their transient response. You can "taste" the texture and materials of acoustic instruments (particularly guitar, bass and percussion) in a similar way with both units. That's top-notch e-stat speed for you. The 007 Mk1 feels very slightly more resolving, though, but that may be just me - I need more time listening and comparing both. To sum it up so far, it seems that both sets have essentially the same drivers, but with slight differences in tuning. In any case, these are rather minor differences if compared to the former listed above.
Overall, now I get the hype about the 007 Mk1. It's definitely a superior headphone to the 007A in most ways that matter. I'm still evaluating the effect of the 007 Mk1's earpad seal and materials on the long-term comfort; it may be the case that the 007A ends up being more comfortable for long listening sessions - or not. As pointed above, swapping earpads may also settle this issue.
Some claim that the latest (i.e. currently being sold new) 007 Mk2 / 007A is close enough to (maybe even slightly better than?) the 007 Mk1, with many of its earlier versions' problems having been solved, to the point it may make no sense anymore to overpay for a 007 Mk1 (see, on the other hand, how spritzer's opinion on this has evolved compared to the previous two links, to quote one example - wondering here what made him bump the 007 Mk1 above the current 007 Mk2 / 007A in his personal preference between 2018 and 2021 🤔 ), but mine was still a bargain compared to a brand-new 007 Mk2 / 007A, at least here in Brazil (especially considering it came with some Mk1 spare parts and the standard flight case - by the way, this is what the actual carbon fiber case for the very early 007 Mk1's looks like, completely different from mine) and I think I got somewhat lucky with the serial number, so I guess that's a win? 😁
As for the role of the CCS-modded SRM-T1S proper in all this, my impression is that the CCS mod together with the 007 Mk1's efficient earpad seal are usually enough to make the SRM-T1S able to drive these cans in the volumes I typically use (10-11 o'clock, depending on the source), which is good since it'll be quite a while until I can get another, more powerful energizer (if I can get it at all), which may help in a few, more compressed tracks for which I need to raise the volume to noon or higher and hence start hitting the 6CG7's limitations on the SRM-T1S's design. On the other hand (edit - July 22nd 2022), the aforementioned shoutiness of the 007 Mk1 indicates that I may be listening to it at a bit too high a volume, but otherwise I lose resolution and clarity with both 007's. This should be compared to the 9-10 o'clock optimal volume setting of the SRM-T1S with the Lambda SR-L407 and hence signals that the 007's are still underpowered by the SRM-T1S, even after the CCS mod. I may get some minor additional improvements once I change tubes to (say) some Japanese Raytheons (I have a few lying around waiting for their turn), but right now I don't feel compelled enough to do it. I've given up for the time being the idea of rewiring the tube sockets and moving to brand-new JJ ECC99 tubes, based on spritzer's recent advice on the matter.
(as both a side note and a cautionary tale, I noticed an improvement in sound quality and an increase in bass response on the 007A, a few weeks before getting the 007 Mk1, after I changed my glasses - the new frame is much less obtrusive, thus affecting far less the earpad seal. However, I didn't realize the new frame was the "culprit" until the 007 Mk1 arrived, which made me understand more viscerally the importance of a good earpad seal for sound quality in headphones)