I got this relatively cheap electric violin by Cecilio (model CEVN-1NA) and wanted to see what was under the hood. Performance-wise, using a Sony MD 7505 headset, the sound was quite noisy and rather muddled. Tone adjustment just maded the sound even more so and appeared to crackle when turned to the max. Perhaps I may have gotten a defective unit, but the volume was rather minute. I tried several headphones including the stock ones without improvement. Putting the volume adjustment knob to max still yielded under acceptable levels.
Looking at the PCB, there are two main ICs in the built-in amp – one for tone, one for volume.
Here’s a rough schematic of how all the components are connected.