Great practice amp, but has a bit of a learning curve
Out of all of the popular low-cost, low-power modeling amps (Fender Mustang I, Line 6 Spider IV 15, Peavey Vypyr 15, Roland Cube 20XL, and the Vox VT20+), the Vox was the clear winner for me.
I almost passed it over after a quick test, however. But I am glad that I decided to give it a second chance, fiddling around with the knobs quite a bit.
I found that the presets are mostly junk. Only maybe 20% of the "green" presets (dry / limited effects) are usable. Most of the "yellow" presets (wet / heavy effects) are horrible. The "red" (song) presets are decent, with most sounding pretty close to the songs they attempt to recreate.
Where this amp really shines is in manual mode. But it does take some time to really figure out how to get the best sounds out of it.
The EQ on most of the models has a rather shrill high end, so you need to dial back the treble. In fact, my usual starting point for all 3 EQ knobs is at 10 o'clock, not 12 o'clock as would be typical.
The small 8" speaker puts out a surprising amount of bass, but out of the box it is pretty muddy. Dialing down the bass knob helps a bit, but what really fixed things was to stuff the speaker cabinet with a small pillow (I found this recommendation on the Vox official forums). Don't laugh or discount this! It really helped to tighten up the bass and low midrange.
The 3 separate volume controls (volume, master volume, and power level) can get confusing and take some getting used to. You need to experiment with them to find what works best. Here are my recommendations:
* Keep the power level as high as possible, but no higher than 20 watts. There is a lot of hiss once you get past around 10 o'clock. Raise it until the hiss becomes unbearable, then back it down a bit. But even if you can live with the hiss past the 20-watt setting, I don't recommend going any higher unless you absolutely need the extra volume (which most likely will not be often, this amp is quite loud at 20 watts for in-home use, and it is not intended as a gigging amp). Around 11 o'clock is where I typically have this knob set.
* The master volume regulates how hard the (real, but little) tube in the power section is driven. Raising this does give a nice, warm breakup, but once you go over 2 o'clock, it starts to sound a bit harsh. I usually keep the master volume set somewhere between 10 o'clock and 12 o'clock.
* I then use the volume knob to regulate the overall loudness. Often this is set quite low because I have the master volume and power level set fairly high. Don't go below 9 o'clock, however, because things start to sound bad below this. If you need less volume, then dial back the master volume and/or power level rather than going lower than 9 o'clock on the volume knob.
* The actual volume level for different amp models can vary greatly. This can sometimes get annoying.
So my starting point is as follows:
Gain: 12 o'clock
Volume: 10 o'clock
Treble: 10 o'clock
Middle: 10 o'clock
Bass: 10 o'clock
Master Volume: 11 o'clock
Power Level: 11 o'clock
Pedal Value: Off
Effects Depth: Off
Reverb: Just below 12 o'clock (spring reverb, level around 1/3 of maximum)
From there, it usually only takes slight adjustment of each knob to nail the sound I am looking for.
The "effectiveness" of the 3-band EQ varies greatly between different amp models. For some models, the EQ knobs have little effect, while for others, the tone is vastly changed with relatively small movements of the knobs. And on a few of the amp models, the EQ is "interactive" -- for instance, adjusting the treble can have some effect on the middle and/or bass frequencies. These EQ "quirks" are based on how the amp being modeled actually behaves.
The pedal (stompbox) and rack effects work pretty well, and the reverb is quite nice. There are 3 types of reverb -- room, spring, and hall. I mostly prefer the spring reverb, and sometimes the room reverb. The hall reverb is rarely used.
There is an onboard tuner, but it unfortunately is rather limited. Only standard tuning is supported; you can't even tune drop D with it. The tuner works reasonably well, but an actual chromatic tuner should have been included.
In conclusion, the Vox VT20+ is an excellent modeling amp that is great for in-home use. It can get quite loud, but does start to sound bad when really pushed to its maximum volume, most likely because of the small 8" speaker. You need to spend a good deal of time with this amp to really take advantage of its potential. If you want an amp that you can get good, useable sounds right out of the box with no fiddling, you might want to look elsewhere. Once you learn its quirks and shortcomings, though, your patience will be rewarded, as the Vox Valvetronix system is the most natural-sounding, entry-level modeling amp on the market.