I got a new ukulele and I want to put a pickup in it. I've seen it done with a pre amp and with out one. What are the benefits to putting in a pre amp with the pickup versus just the pickup and an jack? Any information would be helpful thanks
The benefit of having the onboard preamp would be more tone-shaping directly from the instrument, and the preamp can drive a cable without any tone loss that you would normally get from a passive pickup through the same cable run. The drawbacks are increased weight and a more invasive addition. The tradeoff is that if you are ok with just a passive volume control and don't have a very long cable, an onboard preamp starts to just turn into extra weight and complexity that isn't adding much utility.

With a small acoustic instrument like a ukelele I would think that adding a preamp could seriously dampen the vibration of the body. I don't know the first thing about ukeleles but if that's a concern you might want to start without the preamp and see how it works. You can always add one later.
Just an idea for you to consider...

There was a thread in GB&C several years ago that gave me this idea...
A piezo buzzer from something like a smoke detector.
Has 2 wires coming off of it.
If you can secure it inside, underneath the bridge (Or close to that), it makes a very nice pickup.
I did that mod on a cheap nylon string guitar I have and it has loads of output.
I also added tone and volume controls.
I had to use a 1 meg pot for volume because the thing had so much output, the standard 250k - 500k pots wouldn't do shit.

The buzzer I got had 2 isolated piezo elements on it, so I essentially had 2 hots and one ground. I stuck a capacitor and a switch to switch between the 2 hot wires in there to give me the equivalent of a bridge and neck pickup.

As cheap as it was, it sounds surprisingly good.
I brought it into one of the local music stores and the owner was blown away by how good it sounded.

No pre amp needed.

The piezo isn't actually glued in.
I used some kind of foam rubber type insulation that I glued in to hold the piezo element tightly against the wood.

It was kind of PITA to mount everything.
Results :

The thread that inspired me : https://www.ultimate-guitar.com/forum/showthread.php?t=748459&highlight=Piezo

My original post on this including a link to the buzzer I used : https://www.ultimate-guitar.com/forum/showpost.php?p=13449926&postcount=107
Last edited by CodeMonk at Jan 6, 2014,
I already planned on using one of the piezo buzzers in an Strat i am building and have one but i just haven't had time to install it yet. If it works out ill probably do the same to the uke and just run a jack out of it. So it seems like the cons out weigh the pros of a putting a preamp in