He sounded like Garcia on an acoustic and he sounded like Garcia when his rig was a Swamp ash natural stock Strat through a Fender Twin. I think his effects back then were a mutron, boss compressor/sustainer....believe it or not, a Wha and a distortion box I can't remember. No Mac, no OBEL and certainly no UGB.
Mattson still sounded like Jerry.
Jerry would sound like Jerry playing a Ukelele. It's in the technique, it's in the fingers and it is also in the brain. You can have Jerry's rig and without the three above ingredients you will not sound like Jer. Just my two cents.
Of course he sounded like Jerry with a stock strat and a Twin. All of the stuff we chase are just variations of that basic setup.
Of course it's in the technique, fingers and brain. That goes without saying.
If Mattson had practiced nothing but Van Halen and played a Les Paul through a Marshall, he'd sound nothing like Jerry.
The Jerry-ness of it ultimately relates to the fact that music is a language, complete with vernacular and regional accents. By hanging out in Grateful Dead land we learn to talk like that. Some of it comes from gear and some comes from simply speaking the language (which in itself has roots in many other lands. My transition to playing the music comes not only from seeing a good amount of shows back in the 70s and 80s but also from independently sharing backgrounds with Phil. I grew up playing classical music, from Bach to Hindemith and Schoenberg (albeit playing oboe and not trumpet, but analogies could be drawn, especially in the world of Bach) and also studied jazz, electronic music, etc. Those are sounds and languages that are ingrained.). The ability of a musician to successfully inhabit the sound and style of a particular music comes from treating it as a cultural experience rather than a technical or athletic experience. At the end of the day, Jerry was a master storyteller. He told the story through notes and tones. The notes are important because they relay the facts, the tone is important because it relays the emotion and context.