From a schematic standpoint, the amplification section consists of:
Amplifier
Modern amplifiers are built with the very latest technologies reconciling miniaturization with reliability, and are mainly comprised of microprocessors internally integrated with “amplification stages”.
When passing through each amplification stage, the electrical signal is increased until reaching the final stage, after which it is sent to the receiver.
Controls
The function of the tone controls is to attenuate or emphasize portions of the frequencies transduced by the hearing-aid.
The volume controls, also called potentiometers, are devices that modify the voltage in the amplification circuit, varying the resistance; in this way the level of amplification varies according to the modification produced by the potentiometer.
These external controls can and must be adjusted directly by the wearer according to surrounding conditions.
Power Supply
For a hearing-aid to work it must be fed, i.e. provided with electrical power; in this case provided by the battery.
The elements characterizing the battery are:
- shape, expressed in numerical values;
- voltage, expressed in volts (v);
- capacity, expressed in milliamperes/h. (mA/h)
Depending on the size of the hearing-aid, the sizes are:
- 675, for behind-the-ear and glasses hearing-aids;
- 13, for behind-the-ear, glasses and in-the-ear intraconch hearing-aids;
- 312, for in-the-canal hearing-aids;
- 230 or 10A, for very small in-the-canal hearing-aids.
- AAA, for pocket appliances, also called “with case”.
In order to guarantee constant gain, ordinary hearing-aids require a voltage of 1.3 - 1.5 v , with consumption of current expressed in milliamperes, which varies considerably according to the type of hearing-aid used and its conditions of use (time of use, volume, control adjustments, signal applied, etc.).
Therefore, calculating the life of a battery simply by dividing capacity by consumption (mAh/mA = h) gives a false value, well outside the real potential of the battery during real use.
