Metal detection apparatus comprising a balanced coil system with a transmitter coil connected with a first coil terminal and a second coil terminal to a transmitter unit and with a first and a second receiver coil (22A, 22B) connected to an input of a receiver unit, whose output is connected to a signal processing unit, said transmitter unit comprises a controllable frequency generator that provides an input signal with a selectable operating frequency to the input of an amplifier stage, whose output is connected to an adaptation unit, which comprises a coupling transformer with at least one primary coil and at least one secondary coil having a transformer coil terminal and a plurality of transformer tappings (143A, 143B, 143C) and which comprises a plurality of tuning capacitors (144A, 144B, 144C) having first and second capacitor terminals and which comprises first and second switching devices (141A, 142A; 141B, 142B; 141C, 142C), with which the secondary coil of the coupling transformer and at least one of the tuning capacitors (144A, 144B, 144C) is connectable to the transmitter coil, wherein a plurality of individually selectable resonator channels (14A, 14B, 14C) is provided, each resonator channel (14A; 14B; 14C), when selected, comprising the transmitter coil, tapped windings of the secondary coil of the coupling transformer, one of the tuning capacitors (144A, 144B, 144C) connected to one another by the first switching device (141A; 141B; 141C) and by the second switching device (142A; 142B; 142C), which are controllable by a channel selector such that always one of the resonator channels (14A; 14B; 14C) is selectable, characterised in that the first and second switching devices are semiconductor switching devices, and the channel selector comprises for each one of the first semiconductor switching devices (141A; 141B; 141C) and the second semiconductor switching devices (142A; 142B; 142C) at least one isolated driver (145A, 146A), such as a photovoltaic driver, with which control lines are galvanically isolated from control inputs of the first semiconductor switching devices (141A; 141B; 141C) and the second semiconductor switching devices (142A; 142B; 142C). a transmitter coil connected with a first coil terminal and a second coil terminal to a transmitter unit and with a first and a second receiver coil (22A, 22B) connected to an input of a receiver unit, whose output is connected to a signal processing unit, said transmitter unit comprises a controllable frequency generator that provides an input signal with a selectable operating frequency to the input of an amplifier stage, whose output is connected to an adaptation unit, which comprises a coupling transformer with at least one primary coil and at least one secondary coil having a transformer coil terminal and a plurality of transformer tappings (143A, 143B, 143C) and which comprises a plurality of tuning capacitors (144A, 144B, 144C) having first and second capacitor terminals and which comprises first and second switching devices (141A, 142A; 141B, 142B; 141C, 142C), with which the secondary coil of the coupling transformer and at least one of the tuning capacitors (144A, 144B, 144C) is connectable to the transmitter coil, a coupling transformer with at least one primary coil and at least one secondary coil having a transformer coil terminal and a plurality of transformer tappings (143A, 143B, 143C) and which comprises a plurality of tuning capacitors (144A, 144B, 144C) having first and second capacitor terminals and which comprises first and second switching devices (141A, 142A; 141B, 142B; 141C, 142C), with which the secondary coil of the coupling transformer and at least one of the tuning capacitors (144A, 144B, 144C) is connectable to the transmitter coil, wherein a plurality of individually selectable resonator channels (14A, 14B, 14C) is provided, each resonator channel (14A; 14B; 14C), when selected, comprising the transmitter coil, tapped windings of the secondary coil of the coupling transformer, one of the tuning capacitors (144A, 144B, 144C) connected to one another by the first switching device (141A; 141B; 141C) and by the second switching device (142A; 142B; 142C), which are controllable by a channel selector such that always one of the resonator channels (14A; 14B; 14C) is selectable, the first and second switching devices are semiconductor switching devices, and the channel selector comprises for each one of the first semiconductor switching devices (141A; 141B; 141C) and the second semiconductor switching devices (142A; 142B; 142C) at least one isolated driver (145A, 146A), such as a photovoltaic driver, with which control lines are galvanically isolated from control inputs of the first semiconductor switching devices (141A; 141B; 141C) and the second semiconductor switching devices (142A; 142B; 142C).