There was never meant to be a Sandwell District album. Certainly the idea had never crossed Karl O'Connor's mind – and wasn't he in charge, kind of? He had impulsively minted Sandwell in 2002 as a German-distributed offshoot of his Downwards label, but he had no grand plans in terms of what to do with it. Over the course of that decade he guided its metamorphosis into something else entirely: not just a label proper, but an artists' collective, a laboratory for the post-minimal techno experiments of four battle-hardened producer allies: David Sumner (Function), Juan Mendez (Silent Servant) and Female (Peter Sutton) and Regis (O'Connor himself). By 2009, and by word of mouth alone, Sandwell District had come to be revered by the global techno underground; each of its sporadic, imperious 12" releases feverishly anticipated and slavered over. Why would they want to do something as old-fashioned as make an album?

But then, in 2009, people started telling O'Connor how excited they were about the LP. Sorry, what? He was directed to a magazine interview with David Sumner in which he alluded, unambiguously, to a forthcoming "Sandwell District album". He called Sumner, more perplexed than pissed-off. "What are you talking about, Dave? There is no album." "Well, man," Sumner replied. "Now we have to make it."

A year later, I was in David Sumner's apartment in Prenzlauer Berg during a visit to Berlin. I ended up being the first person outside of Sandwell personnel to hear that album – entitled Feed Forward, it was released in December 2010, in an obnoxiously limited edition of 500, vinyl-only copies. Addled and antsy, I wasn't really in the mood for a serious listening session, but I did my best to focus. The moment I heard the mournful air-raid-siren and staccato phaser-stun of 'Immolare', it was obvious that this album wasn't going for the jugular. It felt psychological, inward-looking, wilfully isolationist. But as the booming kickdrum made clear, it was also very much techno. Feed Forward's mechanism is one of gnawing anxiety meets pure propulsion.

In the corner of the room was Sumner's modest studio set-up, scene of much toil in the preceding year or so. Feed Forward was a group effort, with Mendez and Sutton contributing remotely from their respective bases in LA and Birmingham; but it was steered by O'Connor and Sumner, who both lived in Berlin and could work obsessively together on tracks over dissolving days and nights. "We lost the plot," O'Connor told me that night in 2010, yet to come down from the experience. "Dave would make me drive across town just so he could play me a tone he'd come up with on the synth. A fucking tone!"

The three-part 'Immolare' reaches its conclusion: a wrecked Mercedes, gleaming and groaning, spitting blood and glass. 'Grey Cut Out' rides the kind of coiled, concussive breakbeat pattern that Regis and Female pioneered with their Downwards co-conspirator Surgeon in the early 2000s, but we're a world away from British Murder Boys: the swooning strings draped across 'Grey Cut Out' are closer in spirit to Detroit techno at its most vulnerable ("O'Connor: "Dave wanted everything to sound like Carl Craig").

"What do you think?" Sumner asked me, point-blank, as only a native New Yorker could. O'Connor was pacing the room, joking, dissembling, but still curious. On the table was an empty bottle of prescription Adderall, the fuel that drove Feed Forward to its completion. What did he want, a review? He'll have to wait 13 years for that. I tried to lighten the mood: "Yeah, I like it. It's good… for techno."

We listened to the end of the album and they ejected the CDR, invited me to hold onto it. I somehow mislaid it before I'd even got back to London. A week later they got in touch to tell me that they'd lost the files, and the only copy of the album-as-intended is that CDR. So what was eventually released as Feed Forward is substantially different, but it doesn't matter: the mood is consistent, and anyway, no Sandwell track was every truly finished. They were subject to endless reshaping, in the studio and on the road, seeking a perfection by its nature always just beyond reach. The Feed Forward 2LP was followed by a CD edition with a substantially different tracklist; then came a further digital release of alternate versions, officially titled Sandwell District; various 'Test Session' 12"s offered further remixes and edits of album tracks. This was a project more about process than product.

Skip forward a few years to 2013. Sandwell District were about as big as an underground techno act can be: coming on after Bryan Ferry to close out the main stage at Barcelona's Sonar festival, contributing the sixty-ninth instalment of Fabric's banner mix CD series, commanding eye-watering DJ fees, generally basking in glory. Feed Forward was hailed by many as an instant classic, its hallowed status not exactly hindered by its scarcity. But at that point, the perma-touring Sumner and O'Connor resembled nothing so much as a jaded rock & roll band: all black sunglasses, black leather, black denim, black moods. On-stage, they delivered the goods; back-stage it was drink, drugs, clashing egos, temper tantrums, burn-out. There were fistfights in business lounges. An arrest by the Dutch military after they invited the entire club back to their hotel room for an afterparty. A lifetime ban from Air Berlin for smoking on-board. Throughout all this they remained professionally capable. But like any operation propped up by pills and powder, it was only a matter of time before the whole thing crashed to the ground.

For Sumner the beginning of the end came when O'Connor agreed to a Sandwell cover shoot for Groove magazine, then decided not to show up, just to make a point. For O'Connor, the last straw was when Sumner decided not to show up for a gig at Fabric in 2013, possibly also just to make a point. By this time O'Connor had grown tired of Berlin, and was in the process of relocating to New York (point definitively made). They wouldn't see each other again for ten years.

Feed Forward was the making of Sandwell District, then, but also the catalyst of its undoing. Now, in 2023, UK label Point Of Departure, apparently encouraged by a less than obvious superfan, the late Mark Lanegan, has reissued the original album as a 3LP vinyl boxset, including a previously unreleased track and a 16-page booklet of Juan Mendez's iconic artwork. It's not quite the Sandwell District box set I'd hoped for – this would include the best of the Sandwell label's crucial pre-Feed Forward 12" releases, a run which began with Female's mighty 'Serverlan' (SD3, 2005), and really hit its stride with Silent Servant's 'The Silent Morning' (SD05, 2006) and Function's 'Anticipation' (SD10, 2008): skulking and street-tough, austere and suspenseful, drawing deep on the Chain Reaction dub-techno sound, Jeff Mills at his sparsest and bleepiest, and the monkish, monotone cold cuts of Sleeparchive and Mika Vainio.

By 2009 the Sandwell sound had become harder, faster and more expansive: more big room. It's a shift attributable in part to Berghain, which in the late 2000s became the global focal point of techno – and a regular gig for Silent Servant, Regis and Function. Its hulking architecture and the aerobic endurance test of its Saturday-into-Monday Klubnacht called for a style of techno both monstrous and subtle, and Sandwell District's productions naturally mutated to fit the bill – see Feed Forward's brutally locomotive, concrete-pulverising 'Hunting Lodge'. Along with the early Ostgut offerings of Dettmann & Klock (in 2009 Dettmann appears on SD13, while Function and Regis remix Klock's 'Subzero' to thrilling, scudding effect) Sandwell's music at this time gives a slightly flattering idea of the Berghain sound, one it's difficult to maintain once you've entered the building and heard Len Faki basically play the same tune for eight hours.

There was no fear, though, of Sandwell District's music becoming generic warehouse fodder. Its near-gothic concentration of atmosphere made sure of that. Juan Mendez's dark, heady, but always playful cut-and-paste artwork played a massive role in how the music was perceived: deftly collaging countercultural influences from Process Church, Psychic TV, Kenneth Anger, rockabilly, bikesploitation movies, Cabaret Voltaire… This has been perhaps the most enduring, and least credited, legacy of Sandwell District. In 2010, the marriage of cutting-edge techno to this kind of psych-o-delic imagery was out on a limb, almost scandalous. Mendez's kinetic collages essentially reclaimed for dance music an aesthetic of rebellion that had fallen away; all those exploding heads and shark-headed greasers and death-race chevrons repositioning techno as a music of alienation, disaffection, dissent.

Karl O'Connor moved to Berlin in 1999 to consummate a teenage fantasy of artistic exile in Charlottenburg. Professionally, the lure was techno; spiritually it was Isherwood, Bowie, Neubauten and the rest. Sumner followed a few years later, craving (and finding) the physical and psychological space to dedicate himself to music – a space no longer existing in Manhattan. Feed Forward is an explicit celebration of Berlin's waking dreamlife, and for O'Connor, a farewell to the same. It is, unquestionably, one of the great Berlin Albums. The touchstone, of course, is Bowie's Low, with its mood of existential enquiry and stopped time, its sonic language blurring modernity and a kind of antique modernism. A walk among the ruins of the self.

I'm not suggesting they're equals, of course, but they are intimately related: both are products of, and tributes to, Berlin's potential for rebirth: a city of disappearances whose empty, reverberant streets not only permit but encourage you to remake, reset, or restore your identity – perhaps by letting go of it altogether. And so the most astonishing music on Feed Forward are the two coda-like pieces that were annexed to a bonus 7" accompanying the original 2LP, but are reinstated as part of the album proper in the 2023 boxset: haunted, beatless, crackle-wreathed abstract pieces, bridging dewy ambient techno and suppurating industrial music. They rise, they fall, and ultimately consume themselves – burning up in a fire of their own making. They're Feed Forward's equivalent of Low's second side, dazed and elegiac, nostalgic for something which departed long before they – never mind we – arrived.