A totally implantable cochlear implant system forming a single implantable unit (40). The unit (40) has an implantable power source (43) that provides the power requirements of the implantable unit (40). The unit (40) also has an on-board microphone (42) that detects external sounds, such as speech, and outputs acoustic signals representative of the detected sounds. The unit further includes speech processor circuitry (44) that directly receives the acoustic signals from the microphone (42) and converts the signals into stimulation signals representative of the detected sounds. An electrode array (20) suitable for insertion of the cochlea (12) of an implantee receives the stimulation signals and transmits electrical stimulations to the implantee'auditory nerve (9).