Considering Queen’s live performances deliberately favoured the visual/theatrical aspect just as much as the strictly musical one, it’s understandable that they weren’t trying to recreate the studio versions of their material, leading to noticeable differences in the instruments used and the way they were amplified:

  • Heirlooms, relics from childhood and one-of-a-kind instruments used for recordings were replaced by more standard versions. That was the case with the ukelele-banjo (which Brian’s father had taken to the war with him), the Hallfredh acoustic guitar and Roger’s Esquire guitar. The exception is, of course, the homemade BHM original (aka 'the Red Special').
  • Certain acoustic instruments, in particular, could sound quite well in a studio setting (soundproofed walls, specific mics and soundboard equipment) but wouldn’t necessarily be as reliable on stage. That might have been the case with the acoustic guitar on '39: Brian recorded it on a six-string, which might have been the Martin D-35 he used in 1976 for that song’s live renditions; from 1977 onwards, he switched to a twelve-string Ovation Pacemaker 1615. That might have been the case with some synthesisers as well (e.g. the Fairlight CMI-II, used very often in the studio but not when touring).
  • Multi-tracking allowed members to multiply their roles in the studio. Teo Torriatte, for instance, featured Brian playing acoustic piano, electric piano, electric harmonium, and several layers of guitar; when doing that song live, he’d stick to piano (1979 to 1981), go from piano to guitar (1982), go from not playing anything to playing electric guitar near the end (his solo tours), or play acoustic guitar (QPR and QAL eras). There are no documented versions with harmonium or electric piano.
  • Similarly, the fact they could try as many takes as they could and even use some studio trickery to punch and edit meant they could try out some instruments they weren’t necessarily skilful at and which they wouldn’t try out when playing live: double-bass, harp, koto… Financially speaking, it’d make little to no sense to take a harpsichord on the road just in case they performed Master-Stroke (and think about how tricky it would’ve been to mic it just for a two-minute song), or to have an electric piano just for Best Friend, so instead they’d simply have Mercury play them both on the same acoustic grand piano he was using for the rest of the concert. The exception was the gong, which they took on the road and had the road crew set up only to be hit once or twice per night.
  • If a guitar string was broken during a studio recording, there was time to stop, install another one, retune the instrument and try again in a few minutes; on stage, they had to have a spare ready to go and then at least that song would be finished with it, giving the crew time to sort out the problem with the main one.

Generally, amplifiers and mics would feed the Public Address System (aka PA or Tannoy), which would then direct the sound to loudspeakers strategically placed for the entire audience to hear properly and to a fold back so the performers would hear what they were doing either via monitors or canalphones. Technology marches on, of course, so what Queen had relied on back in 1970 was completely different to what they used in 2020 just before the pandemic hit.