Long before this year's sold-out Ryman Auditorium stand and high-profile Bob Dylan tour dates, bassist Jimbo Hart's first show with Jason Isbell took place at a Chattanooga fried chicken joint in 2006.

"There was this old gold velour wallpaper and it was kind of shady," Hart says, recalling the now-shuttered Lamar's Restaurant. "It might have been house of ill-repute at one point." The Lamar's setlist included songs later released on 2007's "Sirens of the Ditch," Isbell's debut solo LP after parting ways with underground southern rockers Drive-By Truckers. A cover of Thin Lizzy's "Jailbreak" also was part of that night's show, which singer/guitarist Isbell, Hart and drummer Mike Dillon played as a three-piece. "I think our drummer had to throw somebody out of the room whenever the settlement was going or something," Hart says with a laugh. "It was pretty wild. It was like that for a long time too. That's where you've kind of got to start, you know?"

Eleven years later, Hart is still riding shotgun musically with Isbell as part of the singer's longtime backing band, the 400 Unit. However instead of the Ford Econoline vans they drove across the country for years, the musicians now ride from concert to concert in two Prevost tour buses, the industry standard. The 400 Unit also features drummer Chad Gamble, keyboardist Derry deBorja and guitarist Sadler Vaden. Violinist/backing vocalist Amanda Shires, who is married to Isbell, also records with the band and tours with them when her solo artist schedule permits.

2013's acoustic-heavy "Southeastern" and 2015's "Something More Than Free" were credited solely to "Jason Isbell." However, Isbell's latest album "The Nashville Sound," which features more of a "band" sound, is credited to "Jason Isbell and the 400 Unit." It's the first time the group's name has been on the cover since 2011 LP "Here We Rest," which produced songs like "Alabama Pines" and "Codeine," still essential parts of Isbell's live repertoire.

Isbell, a Greenhill native, informed the band of his decision towards the end of "The Nashville Sound" recording sessions at RCA Studios.

Jason Isbell and the 400 Unit drummer Chad Gamble. (File photo)

"I was thrilled," says Gamble, who's been drumming for Isbell for about nine years now. "I didn't necessarily expect it on this record, but I felt (the band name) was going to come back at some time. He asked if it was alright with everyone else, and of course nobody objected to that, not that any of us minded playing on what was deemed his solo stuff. Everybody's happy being who they are in the band. But it was a morale boost for sure - not that morale was low - but seeing the trajectory of how this is going right now, 'Yeah, get the band name back there again. That's awesome.' It's a generous thing for him to do too. He could have just as easily kept it like it was for the past two records."

deBorja, who's been playing keys with Isbell for about 10 years, was also excited but says, "it wasn't like this, 'Oh finally' kind of moment or anything like that, because even through the Isbell solo records we were the band. We've always been there. And it's not like he ever left us to do those things by himself."

It's difficult to imagine Isbell's current three-album hot streak - and its critical accolades, two Grammys, the top 10 debuts, getting props from legends like Bruce Springsteen - without the 400 Unit's sonic support. The musicians have a keen sense of what to play on Isbell's lyrically rich songs, a smart mix of folk, rock and country. And what not to play. Dave Cobb, the Nashville producer behind the board for the last three Isbell LPs has played a significant role too. But just as Cobb has become Nashville's hottest producer for handmade music, the 400 Unit clearly deserves recognition as an elite ensemble, a la Tom Petty's Heartbreakers, Springsteen's E Street Band and Neil Young's Crazy Horse.

Hart first met Isbell at a high school marching band competition - Isbell played trumpet for Florence's Rogers High and Hart played bass and tuba for Sheffield High. He'd already heard of Isbell and his guitar skills. "You cross paths when you're kids in a small town," Hart says. "There was a Mexican joint [the now-closed La Fonda Mexicana] we could always go to underage and hang out and eat nachos and watch the bands. They would get us to sit in and play stuff."

Jason Isbell and the 400 Unit bassist Jimbo Hart (File photo)

Hart began playing bass the age of 11, learning songs like Pink Floyd's "Money" early on, as well as material by Pearl Jam and Metallica. Now 38, he finds it surreal to have struck up a friendship with former Metallica bassist Jason Newstead: "Every time I hear from [Newstead] my inner 12-year-old just wants to jump up and down on the couch and smash something, you know?" Dr. Dre's hip-hop classic "The Chronic" also played a formative role in Hart's approach to bass. Later as an adult, Hart lived in Austin, Texas and played with touring blues-funk artist Papa Mali. After returning to the Shoals and before joining up with Isbell, the bassist worked with Gary Nichols, now a Grammy winning artist with bluegrass outfit The SteelDrivers.

Many Isbell songs, from "Nashville Sound" rogue ballad "Tupelo" to nostalgic Truckers gem "Outfit," are chord based, leaving ample wiggle room for the 400 Unit to do their thing, whereas on riff-based songs guitars, bass and keys often need to be playing the same thing to sound right. Still, finding the right music to support Isbell tunes presents challenges, Hart says. "Do you need to be out of the way of this lyric here? Or this vocal? Do I need to be tight with the kick drum so it produces this vacuumless note? Or do I need to play a little behind it so it creates a bluesy vibe?"

"Something More Than Free" track "Children of Children" is one of the band's most transportive moments, both onstage and in the studio. Underneath Isbell's evocative lyrics about young parents, Hart's plays hippie-rock bass grooves that feel descended from Led Zeppelin's "Ramble On." Gamble does a dusky shuffle with just the right amount of jazz in there. deBorja's Mellotron strings provide swooping counterpoint to the comet-trail guitar. "The dynamic builds from nothing and then goes way beyond where you'd even think it would go," says Hart, whose 15-bass collection includes an early-70s Fender Precision used heavily on recent Isbell records.

deBorja finds it interesting how instead of getting bogged down in aspirations and personal complications, each successive Isbell record becomes easier to make. "I don't feel that we've ever forced anything onto a track or a song or onto an album," deBorja says. "The parts that we put on a record, they come very naturally. As a band I don't think we've ever had an identity crisis or felt that we had to change things up. We've always stayed true to Jason's vision." When they're working on a new album, The 400 Unit musicians hear a new Isbell song for the first time the day they're going to record it, when he does a run through in the studio for them.

In recent years Isbell has made more than a few TV appearances to promote his music. New York's Ed Sullivan Theater - lately for "The Late Show with Stephen Colbert" and previously "Late Show with David Letterman" - has become Hart's favorite TV gig. "Every time we go there it's awesome," the bassist says. "That's where The Beatles did it, that's where everybody did it. Makes you be on your toes a little bit."

In 2015 Hart's name was accidentally left off the "Something More Than Free" liner notes, prompting the addition of "FEATURING JIMBO HART ON BASS" hype stickers to the packaging. Hart says when Isbell was telling the 400 Unit about his plans to put their band name on "The Nashville Sound," the singer also said to him, "And we're definitely going to put you in the liner notes," which was good for a laugh.

Gamble's first few years with Isbell included the occasional gig at venues so small he'd have to pare his kit down to just snare, kick and high-hat. But, Gamble says, "I was always impressed no matter how small the room was about 80 perfect of the time it was packed. I was impressed he already had that sort of following." Scrunching onto a tiny bandbox is no longer an issue for the 400 Unit. This year they headlined the Baltimore area's 19,000-capacity Merriweather Post Pavilion. In 2016, the band played Colorado's picturesque Red Rocks Amphitheatre, a venue Gamble calls "overwhelming": "When you're on that stage, those seats seem to go up at a 90-degree angle. It looks like a massive wall of people in front of you." Isbell and the 400 Unit return to Red Rocks this September.

The first drum kit Gamble ever had was a Muppets set with Dr. Teeth and The Electric Mayhem depicted on the kick drum, at age 4. Now age 43, Gamble recently received his first custom kit from Gretsch, the same company who makes drums for The Rolling Stone's Charlie Watts. Gamble's Gretsch kit is a blue sparkle beauty. He joined Isbell the 400 Unit after they'd released their 2009 self-titled album, which featured drums from Matt Pence. Before Isbell, Gamble paid his share of dues, including countless blues gigs with touring Shreveport, La. act The Bluebirds and Tuscaloosa bar band Salty Papa. He also toured and recorded in the vintage funk and soul inspired Gamble Brothers Band, with his brother/keyboardist Al Gamble, "that suffered through the same crap as any other little band." The brothers' fortunes have improved considerably. Just as things have taken off for Isbell, Al Gamble found success with successful Birmingham combo St. Paul & The Broken Bones. The brothers never speak of their simultaneous upturns though, "for fear it might go away," jokes Chad, who resides in his hometown of Tuscumbia. Isbell, deBorja and Vaden live in Nashville.

Drawing from the likes of Levon Helm, Art Blakey and The Allman Brothers Band, Gamble has the taste to lay-out on quieter Isbell songs like "If We Were Vampires," and the wallop to make the snare spits on rockers like "Cumberland Gap." Gamble calls his drum style "pretty subdued." However, those are some pretty rad tom-tom rolls at the end of "Hope the High Road."

Jason Isbell and the 400 Unit keyboardist Derry deBorja. (File photo)

The dynamic changes each night in Isbell's set when deBorja pulls out his Hohner Anacleto accordion for wry acoustic number "Codeine." The fans dance more. Isbell smiles more between his vocal lines. Something about deBorja playing that accordion, not exactly the most rock 'n' roll of instruments, on that song raises the entire room an inch or two. "It's probably just the interaction we have as a band, it changes," deBorja says of "Codeine." "Everyone is out and about the stage at that point. I think that's probably a big draw of it."

Growing up in the Baltimore/Washington area, deBorja started playing piano at age six in the '80s, a time when rock and pop were intermingling in a major way. "It was a nice melding of keyboards and guitars and how they worked together," deBorja, now 44, recalls. That all coalesced when he first heard Tom Petty and the Heartbreakers and how well that group's keyboardist, Benmont Tench, played off guitars. Tench has remained a touchstone throughout deBorja's career: the early years with atmospheric Washington band Canyon, a stint with alt-country icons Son Volt, and in those timely organ swells on Isbell's "Hope The High Road."

deBorja's story with Isbell goes back to when Son Volt was touring with Drive-By Truckers - the two musicians met for the first time outside that tour's opening night venue, in between making mobile phone calls. Isbell first mentioned the prospect of deBorja joining Isbell's solo band at a festival where they watched The Who perform. "He kind of knew he was going to be leaving the Truckers at that point," deBorja says.

On "The Nashville Sound" deBorja's Wurlitzer and Rhodes filigree can be heard on "White Man's World," "Tupelo" and "Last of My Kind." There's some backwards piano on intimate strummer "Chaos and Clothes." While the 400 Unit (named after a Florence mental treatment facility) has undeniable chemistry as a whole, according to Hart, deBorja's keyboards are "the thing that really makes it work. It makes everything have a nice bounce and tension." Away from music, deBorja has a continued interest in photography, which he studied in college. In addition to pianists like Thelonious Monk, deBorja draws keyboard inspiration from Angelo Badalamenti's "Twin Peaks" instrumentals and hopes to one day do some soundtrack work too.

On the current Isbell tour, harder rocking "The Nashville Sound" songs like "Cumberland Gap," "Hope the High Road" and "Anxiety" are going over particularly well, the 400 Unit musicians say. The group also digs into some Trucker era classics, like snarling contraband anthem "Never Gonna Change." deBorja loves how newer fans have embraced "Alabama Pines" live, adding, "I love how that song has grown." For those who discovered Isbell through his last three LPs, Hart recommends checking out older tracks like "Seven Mile Island" and "The Blue," while Gamble points to "No Choice in The Matter."

When Isbell and the 400 Unit are on the road and have an afternoon or night off, they and their 10-person crew might get together for a matinee movie, disc golf game or "steak night" dinner. There's also the occasional visit to a karaoke bar, where Vaden has been known to bring down the house singing Bob Seger hits. But as the musicians reach closer to age 40, they also have increasing family obligations, so there's a balance to be found there.

For years, whenever Isbell and the 400 Unit would play shows in Charleston, S.C., Vaden's hard-rock trio Leslie (named after the rotating speaker frequently paired with Hammond organs), would open for them. "They would just mop the floor with us every single time," Hart says. Later on, Vaden joined southern alt-rockers Drivin' N' Cryin' as lead guitarist and Isbell caught a performance by that band in the Muscle Shoals area. About four years ago, Isbell manager Traci Thomas called Vaden about joining the 400 Unit. "Jason had just made 'Southeastern' and was about to put it out and realized he was playing lot more acoustic so he needed another guitar player," Vaden says. His first gig with Isbell was a 2013 performance at Huntsville's Crossroads Music Hall, the final show ever at that venue. "There was no rehearsing or anything," Vaden says. "They told me to just show up at the gig."

According to Hart, Vaden has pushed Isbell, an accomplished soloist, to bring his A-game each night. And vice versa. "I like playing with Jason," Vaden says, "because he does things I don't do or wouldn't think of and I feel like I do things maybe he wouldn't think of. And I think that's always good in creating something a little bit fresh and new. We're not reinventing the wheel or anything. But I feel like we are putting a fresh spin on that kind of rock 'n' roll guitar duo. And it seems to be coming to light more on this record and this tour as well."

Back when he was 13, Vaden got the chance to meet Springsteen guitarist Little Steven Van Zandt after winning an essay contest at school. The young Vaden asked Van Zandt what advice he had, and he replied, "Always play for the song." And that's exactly what Vaden does with Isbell. Even though he has the Jimmy Page-like chops to frequently melt faces, with Isbell and the 400 Unit, he's more in the role of longtime Tom Petty guitarist Mike Campbell. A cool fill here. Some tasty accents there. Onstage, Vaden plays a lot of the signature themes Isbell recorded, like the brilliant slide from "24 Frames," while in the studio Vaden's work is more foundational. The 12-string on "Cumberland Gap." The charged strum on "Hope the High Road." Of these newer propulsive songs, Vaden says, "I'm just a rock 'n' roller, so I like the fact Jason wrote some songs that rock a little more, but they're still really good songs. To write a really good rock 'n' roll song and have it mean something is really hard."

Vaden's rocker spirit is on full display when he breaks out some Pete Townshend-style windmills onstage with Isbell. Vaden tours with six guitars, including his beloved Gibson SG, and uses all of them every night during the show. He was first inspired to play the guitar at age 10 after his parents took him to see Farm Aid at Columbia, S.C.'s Williams-Brice Stadium in 1996. "During Neil Young & Crazy Horse's set we stood up on our seats so I could see," Vaden recalls. "They opened with 'Hey Hey My My' and my whole chest was rattling. I thought I was going to fly off the chair." His parents also gifted Sadler Vaden with a name likely to have predisposed him to become either a rock-god or "Star Wars" villain. "I've gotten called 'Darth' my whole life," Vaden says, referring to a certain Vader.

Before shows, Isbell and the 400 Unit briefly congregate on the side of the stage to make sure everyone's ready and their in-ear monitors are functioning. Lately, Isbell's young daughter Mercy will join these moments, strumming on the guitars or bass a little. "Having her around has been such a blessing," Hart says. "She's so smart and she's kind of running things already."

Away from the gig, Gamble and Isbell routinely text each other back and forth an assortment of "dad jokes," the drummer says. "I'm a little shocked and amazed to how well he took to fatherhood, just knowing him like I knew him," Gamble says, calling in for this phone interview on the way to pick up his own daughter from a friend's house. "But he's so great with Mercy. It's a beautiful thing, man."

Since Isbell's career took a sharp turn upwards following "Southeastern," most press coverage about him have focused on: one, how good his lyrics are; and two, how bad his drinking used to be. As years passed and sobriety remained, the alcoholism storyline is beginning to fade into the background some. The focus rightly on the musical work. The 400 Unit isn't just Isbell's band they're his friends too, so they couldn't be happier for how their singer's life is going: the career zoom; the accomplished, cool and beautiful wife; their adorable daughter.

"He's always been immensely talented," Hart says. "When he decided to get sober he got his focus back, and his intelligence lined up with his focus instead of just kind of being out-there. It's good to watch him grow up a bit and it's helped everybody else do the same thing. So it's been great for everybody." After Isbell quit drinking, the rest of the band scaled back their intake as well. A welcome relief for Hart. "When you're standing onstage and a guy hands you a bottle of whiskey you don't just say, 'No man I'm cool' and pass it back. You hit it. I did it more out of necessity for a while and when he stopped I was like, 'Thank God I can stop frying my brains with whiskey.'"

After gigs some 400 Unit musicians might go out for a drink, others do not. But band imbibing before and during the gig has pretty much halted. "We're not on autopilot, and I feel like for a while there in those early days that could get to be the case," Gamble says. "Just to get through the gig." The drummer says in recent years Isbell, who tended to be shy around new faces in the past, has opened-up more. deBorja thinks the biggest thing that's changed about Isbell, is "the way he's grown in terms of how he handles responsibility, for himself, for his band, for his family and to his audience. And in songwriting too. I think he's much more comfortable with it being more personal, rather than someone else's story. More and more, he's there in it."

The lives of the 400 Unit have changed too. After slogging it out on the road for so long, there's a new stability with playing bigger and higher-profile venues. DeBorja savors "the convenience of being able to do what I love to do without having so many hurdles in the way, just the ease, being able to tour and not feeling like we're killing ourselves anymore." Financially, they don't have to live gig-to-gig now either. "When I am home (off the road) I still like to play with people," Gamble says. "But now if I want to, I can stay home this weekend. It was my mentality for so long if I was home, trying to scrape up a gig. Now I don't have to hustle quite as much. That itself is a luxury and not something I take for granted." For years, Hart owned automobiles "in various degrees of health." But recently he was able to purchase a used Acura that's "solid and reliable and fast when I want it to be." Alas, he can't fit a standup bass in his new ride, "so I kind of shot myself in the foot there."

Vaden likes knowing he can pay his water bill and afford some groceries. But the 400 Unit's climb with Isbell has also made the longhaired guitarist want to work even harder, "because there's more people who want to see it. Now isn't the time to let off the gas pedal, you know?"

Jason Isbell and the 400 Unit (with Amanda Shires) will play a sold-out show 8 p.m. Aug. 25 at Huntsville's Von Braun Center, address 700 Monroe St. Upcoming shows in Florence (Aug. 26) and Anniston (Dec. 16) are also sold-out. The band plays Mobile's Saenger Theatre, address 6 S. Joachim St., 8 p.m. Sept. 27 and tickets are currently available via ticketmaster.com. More tour dates and info at jasonisbell.com.