[. . . ] The A 1 is a hearing amplifier for people who wish to improve their hearing only in case of need. [. . . ] the automatic gain control is set in the factory to provide optimum comfort. Adjusting the frequency response Using the adhesive strips provided, the small holes in the receivers transducers can be closed. The frequency response changes depending on how many holes are covered in this way (see illustration on last page). If all holes are left open all sounds are balanced, to a considerable extent. Power supply The A1 has an economical and environmentally-friendly power supply in the form of the BA 90 storage-battery module. Longer operation is possible when a second battery module (accessories) is used. [. . . ] Technical data Frequency range Transducer principle Microphone Acoustic amplification Characteristic sound pressure level Operating time Weight Scope of delivery (except for supplementary package No. [. . . ]