doctorbadwolf
Heretic of The Seventh Circle
This is a prime example of a concept that begs for multiclassing.As per the legend of Robert Johnson: A musician seeking unearthly musical skill, glory and all that comes with it, sells their soul at the crossroads to an infernal being.
How do you make that character for D&D? Bard? Warlock? Something else?
Hexblade or Archefey Tomelock/Glamour Bard. Possibly Changeling, or Half-Elf, maybe Hexblood, but in story they're a human or halfling.
Hexblade because it allows you to also be able to fight in an unnatural, "how are you strong enough to swing that hammer!?" kind of way that gives a strong hint that they aren't normal, and their instrument can be the item they have a "pact" with. I do think there should be an instrument pact boon (and a spellcasting focus item boon), but let's stick to RAW. It also has a darker vibe that fits crossroads deals, you can turn people's ghosts against their friends when you kill them, and Hexblade works fine for an EB spammer, too, if you want to dance around the fight hurting people while playing your fiddle, or whatever.
Archfey goes a little more into the charm and such that you'd expect from such a character, and suggests a specific patron. IMO Fiend ironically doesn't offer much, here.
Glamour Bard is obvious. They didn't just give you musical gifts you never had, they made your voice and music powerful. I'd probably go more Bard than Warlock, but IMO neither class relies all that much on having a certain level of spell at a given level, and low level control spells don't really ever become weak spells to have. I don't think you'll miss anything by multiclassing.