Do you see that little blue screw?
That’s the SHP-5’s hidden gain control for the microphone.
If you don’t think you’re getting enough volume from your mic, you can loosen the strings and adjust the gain control using a 90 degree screwdriver. Turn counterclockwise to increase the gain. Mic too hot? Try adjusting the gain control clockwise.
Here’s how I get the best tone from the preamp.
If your mic gain, and the guitar’s volume slider are at a good level without feeding back, blend in the piezo little by little using the “blend” slider, until you find a good blend that replicates the sound of the guitar acoustically.