The A4.2 provides the same great functions as the A3.2 with the addition of the Acoustic Soundboard Transducer (AST) and a mix control for blending the pickup and AST.
AST - Acoustic Soundboard Transducer
Pickups
Matched with the B-Band pickup, the A3.2 offers incredibly dynamic, yet soft and well-balanced, acoustic sound. In a live stage set-up, the A3.2 allows the pure acoustics of the guitar to be heard within a band without feedback problems. Onboard controls include volume, bottom and edge.

Simon & Patrick guitars come with optional B-Band A3.2 & A4.2 electronics.

Features:
The AST is an ultra-thin flexible and rugged constant structure all the way to the preamp. Connection to the preamp is an easy "plug in" without soldering.

It has all the advantages of a microphone, without the negatives of feedback and positioning.
Both systems incorporate the B-Band pickup. The construction of the B-Band is unique. It's an incredibly thin (0.4 mm) under saddle transducer that is based on elastic electret film. The B-Band acoustic guitar pickup features absolute acoustic sound, ample gain before feedback, great dynamics and high definition.