Without going really big, I don't know how to do this. So far I use a Roland Mobile AC amplifier. It's just 5 watts, but it sounds beautiful and it's tiny, fits in my backpack, powered by 6AA batteries, with my cords and headset microphone from Audio-Technical, and my acoustic guitar in one hand, I have a very travel friendly busking setup. I actually traveled several cities with it. Just a backpack and guitar, including some change of clothes.
BUT SOMETIMES it is too quiet. I bought a Roland AC-33, also beautiful sound, but on batteries it is only 20W per Roland, and it doesn't sound much louder at all. Certainly not loud enough to justify double the space and that much more weight and 4x the price! Plugged into an AC socket it says to give 30W power. But I usually don't have a place with a socket.
Anyhow, again Roland has a CUBE Street Ex with 50 W power, the only problem (in addition to more weight) is the sound is just not as good for acoustic guitars. It makes no sense because most of the time I see people using it for Acoustic guitars and vocals. Anyhow, that and the price is $500, so now it's 5x the little mobile AC amp, which sounds good and is great for many places.
1) So is there a way to get the extra 10W out of the Roland AC-33 without an AC socket? 2) How much wattage do I really need typically for when I'm on the street and there is traffic noise, buses, and so forth? 3) How much more volume can I get from a 40 or 50W combo amp/PA? Or do I need 100W? (I'm considering a Behringer Europort 40W (8 inch speaker) or 100W (6 inch speaker).)
4) Is there a "thinking outside the box" solution where I can have a really small lightweight amp like Mobile, but louder.
5) I just got a Boss VE-8, which has a pre-amp and effects. Will this increase volume?