1) This is a guitar sound that you don't hear much anymore. It's the front pickup of a 1964 Gibson SG Standard with some of the tone control dialed back, played through a Marshall Plexi. The distortion of the song was a prototype for guitarists for years to come, as is still sought after.
2) The sound of the guitar solo is reported to be what Clapton called his "Women Tone," which was a very early Clyde McCoy model Vox Wah pedal placed in the bass position. I'm not so sure that it's not just the same sound as the rhythm guitar with more of the tone control dialed in. Notice how the rhythm and solo get panned in stereo during the solo section.
3) Clapton gets a bit ahead of the beat that you can hear in the leakage in the B-sections. He also hits a couple of "extra strings" during the final chorus. I never heard either of these before in the track (probably no one else has either), but if were done today you can be sure it would be perfect. Sometimes, all the character is produced right out of records today by going for that perfection, but as we've seen over and over in this blog, perfection simply doesn't matter in a hit. It has to be a solid performance, but not perfect.
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