Hi. I play violin and experimented with amplifying it a lot.
For piezo pickup i used http://tagboardeffects.blogspot.com/2014/04/acoustic-piezo-preamp.html
It's loud enough if you plug it to the amp with preamp.
The barry 3000a preamp is much quieter but has tone controls (I don't think you want them if you plug it to an amp with eq).
Anyways, my favourite violin tone so far is that when I use an electret microphone. Beats the piezo but is prone to feedback. I use it at present, without preamp onboard - just the V+ to hot wire. The microphone is attached (glued) with elastic arm to violin chin (I use cheep microphone+arm from disassembled headset). Then, there is also glued jack socket under the chin (between the body and chin). If you're interested I'll attach photoes of it.
The electret microphone will work well only with the hollow body instrument though. If you're building solid body electric violin, piezo is the only solution . THE BARRY 3000A should be good choice.