I have a couple small amps that you could do that on. One is an Acoustic 30 By Electar, a gibson family product. The other is a Fender Acoustasonic 30. I practice with a looper on both amps. Their vocal abilities a very adequate, but not a real lot of control with minimum effects on them.

My friend has a Fishman Loudbox, I think its about 120 watts rms. Its small and light and very powerful.