The THR10ii and THR30ii mostly do the same thing. The THR10ii is “20 W” and the THR30ii is “30 W”.
However, the output wattage is almost meaningless out of context. The only thing it tells you, in this case, is that the THR30ii will go louder than the THR10ii.
It won’t really tell you much about the difference in volume between the THR30ii and another amp (the Spark, for instance).
In my experience, the THR10ii gets very nearly as loud as the Spark (which claims to be “40W”) and it does so with less compromise to the output. I find the Spark starts to sound a bit distorted and muffled at higher volumes.
Both get pretty loud and there have been few instances where I have needed to turn them up above around 6-7. If you think you need something louder, then you should probably look at something like the Katana 50.
The other differences between the two THRs is that the THR30 has extra physical controls on it which give you more control without using the app, and the THR30 can be connected to an external amp via stereo line outputs. The THR30 possibly has better speakers, but I don’t know. the speakers in the Spark are OK.
By the way, I personally find the physical controls on the THR10ii a little better than on the Spark. The main issue I have on the Spark is the amp-type selector is a knob which physically points at the amp type selected. If you change that using the app (or by selecting one of the presets) it still points at what you set it to originally.
So, for instance, you could set it to “acoustic” on the top panel, and then change it to “lead” or “bass” by selecting a patch, and it will still be pointing at “acoustic”. Because of this I find myself hardly using the physical controls and only using it with the app.
On the THRs, the knob doesn’t have a physical arrow. Instead there are LEDs indicating the current setting. When you change the setting, the correct LED lights regardless of how you make the change, so the physical control on the amp always shows what you have. When I use the THR, I typically use the physical controls rather than the app most of the time.
The other difference between the THR and the Spark is the Spark specifically tries to emulate well known real-world amps, where the THR really doesn’t make any specific claims. There’s a lot of speculation about what the different settings are closest to, but this is purely speculation based on what people think it sounds like.
If modelling specific amp types is important to you, the Spark may be a better fit. If you just want a selection of great sounding amp tones and don’t care what the manufacturer claims they sound like, then the THR delivers.
Cheers,
Keith