I built one of these preamps
http://www.diyguitarmods.com/guitar-preamp.php (http://www.diyguitarmods.com/guitar-preamp.php)
and it works lovely for picking up the piezo im using in a spring verb project.
I was wondering if there was a way to boost the output a little by swapping any components.
Any thoughts?
Cheerz!
Try varying the 2.2k resistor in the FET source leg. You could also try bypassing it with various values of capacitor, which will allow you to alter the frequency response a bit.