I spent my formative guitar years listening to Vai and Satriani, and remember the H3000 being the holy grail of effects units. There are some used units on the market that are at affordable prices now. Was looking at the 4000 model specifically.
I'm wondering if these are typically run in the effects loop...or...just used with a raw power amp?
Do the Eventide units use preamplifier tubes? (12AX7, etc)
Do they generate distortion?
I am wondering if this is something that would make more sense through the loop on a Marhsall, or straight into a Mesa tube power amp.
Any experiences that someone can share?
I'll try. Been years ago (late 80's).
I sounded a lot like Vai back then and did a lot of Whitesnake covers.
I used a Digitech IPS33 for harmony stuff. It did well for all I asked of it. Loads cheaper than a Eventide. The Eventide H3000 does not have a tube as far as I know of and didn't do distortion back then, (the newer ones may) and did not have tubes - it was all digital filter/time based.
I ran my stuff with a separate tube preamp (made by John Kasha) and ran eveything parallel into a stereo mixer then to my amps. It was all midi controlled (including analog switching) but had some stuff pre as well.
Most all your effects will sound better and get better signal to noise ratio in an effects loop.
I replaced my long sold IPS33 recently for $60 at a pawn shop. It does many scales pre-programmed and will follow your notes 3rds, 5ths etc up and down even if you don't play a standard scale.
Hope that helps.
You can see some of my old setup here:
ETA: I have used the H3000 as we had one in our studio and music shop, but I never hooked it up to a guitar, only a synth and only to mess around with it for a few minutes. It was a pricey piece of gear back then. Looks like they may still be making it.