Susan H - Posted - 11/26/2013:  20:49:53

I just got my Weber SE back from Bruce Weber. He replaced five frets, the nut and tweeked the bridge and the trust rod for me. But, he also installed a K & K pickup. I plugged it directly into my Loud Box mini amp and it sounds wonderful. But, I was wondering if anyone uses a preamp with your mandolin. I will eventually start playing at church where I will be plugged into part of our sound system. I'm not exactly sure what a preamp does either. Can someone explain that to me as well, and do I really need one?  I don't mean to sound so dumb, but I'm used to playing in front of a microphone and someone else controls the volume for me. 

Rob Beck - Posted - 11/27/2013:  03:23:54

I was in a similar situation to you recently, in that I too didn't really understand why pre-amps were needed.  The way I think about it now is like this:  

Peizo pickups (which I am assuming the K&K is) output a pretty "weak" signal.  If you pass this straight into a regular amp or desk (one that is not designed for these weak signals), you then have to turn up the volume in order to hear it, unfortunately you also hear a horrible clanking tone referred to as "peizo quack" as well.  The pre-amp boosts the signal from the pickup to a level that the amp/desk is expecting, and the horrible noise goes away.  You can generally also modify the tone using a pre-amp as well.  Peizo pick-ups are not microphones as such, and will not provide you with the acoustic sound you are probably hoping for, so some tone control is useful.  The do however pretty much eliminate feedback, so definitely have their uses!

Technically, I think the problem is down to impedance matching.  as I recall, peizo pickups have a high output impedance (read as weak output) and many amps expect a low impedence input (they expect a strong signal) The preamp converts the high impedance signal to a low impedance one.

If the amp you are playing into is designed for these weak signals then you have no problem, hopefully the people at your church will know if this is the case!

I hope this helps, although I have to say I am no expert, and have written this in the way that helps me understand what I think is going on.  I am sure that others with more knowledge that me will be along to correct me shortly!

Rob

Ben Venuti - Posted - 11/27/2013:  19:01:25

With an acoustic amplifier you would not need a pre amp. For a non acoustic standard rock and roll amplifier you will need one as you will also need one for most PA systems. K And K has pre amps which would work nicely with their transducers I would think.

swamplunker - Posted - 11/27/2013:  23:10:19

As far as I can see, you've described the problems and solution very well, Robbie.

m - Posted - 11/28/2013:  20:35:20

award-session.com/pdfs/Impedan...ching.pdf