plus, of course, playing like srv. i think srv's tone had more to do w/ style than his gear.
my advice on getting the srv tone, is to not take the standard advice. srv can get his tone or approximate his famous tone w/ just about anything. so a good clean amp, ts pedal and a strat is all HE needs. if you don't play like srv or are trying to learn to play to sound more like him, but want a few tone shortcuts, here's what i recommend:
good guitar cable (it might sound like bs, but cables make a difference. i like mogami platinum)
thick picks (again, it might sound like bs, but picks make a huge difference. i rec. extra heavy planet waves black ice picks. nothing is better for a strat in my opinion, esp. if you're looking to warm and thicken up the tone)
i fuller freq. mid boost pedal, not just a ts9. something like way huge pork loin that is set for this particular thing or demeter mid boost.
then a good clear, articulate, and smooth overdrive pedal.
lastly, a fx engineering mirage compressor. not a regular compressor. it's an original design as i understand it. helps smooth out overdrive a bit so you get clean overdrive, less break-up type overdrive. i like a compressor AFTER overdrive, too. i my case, it help clean up the drive a bit. this way you can dial in a bit more overdrive to help feel and response without sounding like you're using more drive.
just my two cents. srv and others can do it w/ much less stuff, but if that tone doesn't come naturally to you or at least not yet, the above can be really helpful and satisfying.
SRV's tone was more HIM than any piece of gear. I mean think about it - you saw him play at least 4-5 different guitars and he always sounded like him. Same with amps - Vibroverb, Super Reverb, Dumble and Marshall - always sounded like Stevie.
The easiest way to get his sound is to play like him, which in his words were "tune low, play hard and floor it"
Thank you for all of the replies. It's good to know it's heavily based on strings and aggressive playing. I really do spend a lot of time working on getting down his licks, learning his songs, etc., but sometimes it's good to know that others have found that those ingredients are all they need to "replicate" that tone.