I realize this is a bit of a zombie thread, but I'm gonna chime in anyway since I'm a huge R.E.M. fan and I've been trying to piece together a comprehensive history of Mike Mills' gear over the past few years.
Mike has played a lot of different basses in his time, despite the fact that he's known best for either playing his Jetglo Rickenbacker 4001 or his Blonde Fender Precision.
In the really early days of R.E.M., Mike Mills played a Höfner 500/1 with the "toaster" style pickups After that, he got the aforementioned Ampeg Dan Armstrong bass, which I'm almost 100% sure is what was used on the 1981 "Radio Free Europe" Hib-Tone single. Then he briefly switched to a Fender Musicmaster Bass for some shows. Then, of course, he got the Rickenbacker 4001 (which, in modern interviews, is labeled as a 1971, but I've seen old rig rundowns that label it as a 1973), which was used on the Chronic Town EP, Murmur, and Reckoning. It's worth noting, though, that he did play a mid-70's era Fender Jazz Bass at least once around this time (as seen in their 1983 appearance on British TV show "The Tube"), but that bass may have been a rental.
When the horseshoe pickup went bad on the 4001, he switched to a Guild Pilot, which was used on the Fables of the Reconstruction album. At some point while touring Europe in 1985, he also used a Rickenbacker 2030 Hamburg Bass (I've only ever seen him use it in this video where he's miming to the studio backing track of Driver 8: ), but like the Jazz Bass, it was probably also rented, seeing as Peter was using a Ric 325 and Bill was on a Pearl drumkit (he played Rogers drums exclusively at the time).
Now, here's one spot where things get a little muddled: I've read articles stating that he also had a Ric 4003 around this time that had a Bartolini P-J set installed in it (I'm assuming to match the tone and output of his Guild). However, I asked Mike directly in 2016 what that Ric was, and he told me that it was his original 4001, but gutted out and given the Bartolini P-J treatment. It's could be that Mike is mis-remembering, because while it's certainly possible to replace the pickups, fill the old pickup holes, and refinish the bass, it doesn't seem likely that his tech at the time would've totally cannibalized it like that... especially given the fact that it was then restored later. But either way, THAT bass can be seen in their Rockpalast 1985 performance, after Mike accidentally breaks his input jack on the Guild Pilot.
1986 is the era of the all-black Ibanez Roadstar II RB650. He used it on Lifes Rich Pageant and the supporting tour.
I'm pretty sure that by 1987, he got the black Fender Precision that is seen on Tourfilm. If so, he played it on Document, Green, and Out of Time, as well as those albums' respective supporting tours/promo spots (pretty much all of their tour dates for Out of Time were acoustic, but there were a few promotional TV spots they did where they played full electric, and Mike uses the black Precision on those).
It wasn't until 1992 that Mike would get his famous Blonde Precision Bass. There's a bit of contention as to the exact year of the bass. For a very long time, it was believed to be a 1969. In more recent interviews, it got called a 1970. To add even further to the confusion, Craig Brody, owner of The Guitar Broker vintage guitar shop in Ft. Lauderdale (who sold the bass to Mike), has called it a 1967 in interviews. But either way, it became his main bass for the remainder of R.E.M.'s run, and he played it on every album from Automatic for the People right up to their last album Collapse Into Now.
That said, he did play a few other basses either live or in the studio during that stretch of time.
For the Out of Time-era acoustic shows (including their first MTV Unplugged show in 1991), he played a Guild acoustic bass guitar (not sure of the exact model, but it was most likely a B30E).
For the Automatic album, he played an upright bass on "New Orleans Instrumental No. 1" (and 2, a B-side), which might be the same upright you see on their 1998 Sesame Street appearance (Furry Happy Monsters, anyone?). And on the track "Monty Got a Raw Deal," he's actually playing a Guild Ashbory Bass.
For the Up album, Mike told a story about finding some big no-name solidbody bass ("just this huge wooden thing with no name on it") that he used on the track "At My Most Beautiful."
For their 1998 set at the Bridge School Benefit concert, he used an Ibanez AEB50LG.
For their second MTV Unplugged show in 2001, he used a Taylor AB-2.
Lastly, he does own at least one fretless bass, because you can hear it on the song 1991 song "Fretless" (it wasn't on an R.E.M. album, but rather the soundtrack to the movie "Until the End of the World"), and you can also see him playing a fretless Jazz Bass (with a P-J pickup config) in the Perfect Square concert film on the song "Animal" (which was likely also used to record the studio version for their hits/B-sides compilation In Time: The Best of R.E.M. 1988-2003).
At some point around the late 2000s, he had his 4001 fully restored (though it's not clear if he used it on any R.E.M. songs from that time), and he has been using that a lot post-R.E.M. (including when I saw him with The Baseball Project almost 4 years ago now). He's also used a Godin Shifter Classic 4 on certain occasions.
As far as amps are concerned, in his REALLY early pre-R.E.M. days, he used a rig that was basically identical to what Berry Oakley of the Allman Brothers was using: Dual Showman Reverb amps and a matching 2x12 cab & 4x10 cab. In the very early R.E.M. days, he tended to stick with 2x15 cabs, and it seems as though his choice of cab varied a lot in the 80s (or maybe he was content playing through backline gear?). He's seen in pics & videos using Peavey, Fender, and GK. He either used Fender Dual Showman heads or Peavey PA heads to power them.
Studio sounds were a different story. For Murmur, at least, he just ran through the Ampeg B-15 that was at Reflection Studios.
By 1985, his live rig rundown evidently went like this: "The bass goes into a QSC power amp and Lost parametric pre-amp, then to an electronic crossover cabinet with two twelve-inch JBLs and one fifteen-inch Gauss speaker. Mills has a dbx 160 limiter/compressor."
I'm not exactly sure how long he used that setup, but by at least 1989 (possibly earlier), he had switched to Mesa/Boogie cabinets, as well as the Bass 400 head, and he used that rig for the Green, Monster, and Up tours. For the Monster tour, as mentioned before, he had a Big Muff fuzz for certain songs ("Circus Envy," "You," "Departure," "Binky the Doormat"). I'm not 100% on where he used the phaser or delay pedals though.
By 2003, when it was time to promo & tour on their new best-of album, he was pretty much an Ampeg guy through-and-through. Vintage SVT head, 8x10 cab. And from what I've seen, that's been his go-to rig ever since for most shows. Not only that, but he had once again been using B-15s in the studio since at least 1998.
Let's see, what else? Strings, perhaps? He was a Dean Markley guy for a very long time. His gauge of choice has become lighter over the years. In the '80s, it was .050-.105, then in the '90s he moved down to .045-.105. Now, from what I've read, he's switched to D'Addario and plays .045-.100.
I think that just about covers it all. Let me know if I missed something or if any of my info is bad, but I'm pretty sure that this is about as accurate as it gets for Mr. Mills.
