The ornamental design for a portableamplifier, as shown and described.
1. Portable amplifier
1.1: Perspective
1.2: Perspective
1.3: Front
1.4: Back
1.5: Left
1.6: Right
1.7: Top
1.8: Bottom
1.9: Reference
FIG. 1.1is a front, right, top perspective view of a portable amplifier showing a new design; FIG. 1.2is a rear, left, bottom perspective view thereof; FIG. 1.3is a front view thereof; FIG. 1.4is a rear view thereof; FIG. 1.5is a left side view thereof; FIG. 1.6is a right side view thereof; FIG. 1.7is a top view thereof; FIG. 1.8is a bottom view thereof; and FIG. 1.9is a view illustrating an open state of the display unit.