I've got a Guild GAD-30E that comes stock with a Fishman Matrix Natural pickup. I think that pickup is connected to one of those preamp thingies that sits inside the jack/strap-button at the heel of the guitar. It does not have any onboard controls for volume or tone. Now, I'm not much of an acoustic player (I mostly play my Tele or lap steel with my band), but I'd like to use this Guild for a couple of songs live with my band. We often play small clubs where we have to set the sound ourselves before the gig, no soundman. For that reason I'd like to have something to control the loudness (so I can turn it down when it's not used), and maybe, tone of the guitar - some kind of external preamp, maybe something that can be attached to the guitar strap, or a pedal; preferably on the lower range of the price scale. Any recommendations?