Re: Boss Katana vs Vox Valvetronix
They're both fun for about 3 or 4 days, then you start to realize that NOTHING is as appealing as a good tube amp. I had both, loved them at first, then the sound started grating on my ears. It's a hard-edged distortion that lacks all the appeal of preamp and powertube warmth. They've managed to make them sound warmer, rounder, and emulate the sound of a tube amp, but if you're used to tube amps then you'll be trying to flip it within a week or two. The ONLY passable non-tube amp device that I'd bother keeping would be an AxeFX or Kemper (2nd best). I'm sorry to burst anyone's bubble but they just don't feel or sound right. It's like meeting a chick with makeup in a club, after some drinks, with the lights flickering and the bass thumping in your ears. You take her home and go at it, only to wake up a few hours later and realize she was flawed.
The Katana is great for people who need the flexibility and an amp that can handle any volume situation, but can't afford more. It has a zillion FX, but only a handful are actually useful. A couple are quite good. The fuzz stomps suck as they all sound the same and don't even emulate a fuzz pedal worth a darn. The cleans aren't bad, but the distortion only really sounds decent on the brown sound setting. You have to juice it at maximum gain to get enough sustain to feel fluid under your fingers for legato and shred. If you max out the mids in a live situation, you'll still have a hard time cutting through the mix without sounding harsh.
The Katana head version is the most useful as it also has a little speaker that you can practice with. The Katana combo speaker sounds cheap as you'd expect, so at least you can plug the head into a speaker cab. I will say that having a good speaker is an improvement.
I hate the Valvetronix. All the Vox modeling amps have this really irritating artificial sound. It's warm but inorganic. A first it's OK, but then you realize it doesn't actually sound like any of the amps it's supposed to model. About the only thing you can do that's passable as a non-irritating tone are the clean sounds - if you load them with chorus and reverb. In fact, speaking of chorus, it actually improves the sound of the distortion. Once you figure that out, you want to always have the chorus on when you play distorted.
I have to give them credit for meeting the needs of a wide variety of users who can't otherwise afford good gear, or people who don't care or can't perceive any difference between them and a real tube amp. Otherwise, you know those kinds of guys who like to always show off how many guitars and amps they have, but their stuff is all cheap and never really seems to sound in tune? Those are the kind of people who would love to buy these devices, and are the ones who always want to point out how they only have to spend a fraction of what everyone else spends for good tone even though their intonation is always skewed and they don't seem to have ears with any sensitivity to the presence and treble controls on 10.
The Studio Devil is worth the extra few bucks, though it has nothing on Fractal. Eleven Rack irritates me almost as much as Vox and Katana, so I wouldn't recommend that either. Kemper is second best to Fractal, so I don't get how they're selling for $2700. There's no way I'd spend that much on that box when $2700 can buy me a real good tube amp.
to deal with the huge learning curve & all the bazillions of parameters, settings & sub-settings etc..so yeah, if I had the money for a Kemper, I'd just get a SLO instead 
