This is a preamplifier for transforming unbalanced to balanced configuration. This balanced output can be connected to a balanced power amplifier, or it can be connected to two identical power amplifiers to form a BTL power amplifier. This is a versatile means of connection since all power amplifier that have enough current capability can thus be connected for BTL and not confine to amplifiers that has non-inverting and inverting input. This is particular attractive for those SE type of class A amplifiers that has low operating voltage but strong current driving capability. The assembly board features 2.0mm board thickness, 75um copper thickness, audio grade MKP coupling capacitors. 2 pieces of Signetics/Philips new old stock NE5532 are used. The opamps can be easily replaced by other dual opamps easily via the IC sockets. We do air shipping worldwide at US$5.50.