A hearing aid includes a microphone for providing an electrical signal representative of a received acoustic signal, a means for filtering the electrical signal and a means for automatic switching. Upon detecting a presence of a magnetic field, the means for automatic switching enables the means for filtering to modify a frequency response of the hearing aid to boost a low frequency gain and reduce a high frequency gain. Such filtering can be used with or without a telecoil. A hearing aid including a telecoil is configured with a preamplifier, a inductive element, and a switch control integrated onto a single common circuit board.