A stable transcutaneous transmission of power and signal via two coupled coils with minimized dependence on the relative spacing of external and implanted coil is possible by employing "critical coupling" between implanted and external circuits. Optimizing coil geometries and preventing the RF output amplifier from saturating is necessary to approximately maintain critical coupling despite placement tolerances within a reasonable range. Based on these considerations a transcutaneous signal transmission system for an auditory prosthesis has been designed. This transmission system can also be used for several other stimulation purposes needing accurate control of stimulation parameters.