Abstract: A bias current compensator to supply the input bias current of a transistor. The bias current compensator may be used, for example, with the controlled amplifiers used in an automatic gain control system. The bias current compensator prevents bias current changes, caused by a varying control signal, from appearing in the output of the controlled amplifier. The bias current compensator includes a current source, first, second, and third transistors, and a feedback amplifier.

Abstract: A hearing aid that is compact and efficient and that provides a high degree of control over its frequency response and also over its output level versus input level characteristic. The frequency response control includes an adjustable four pole high pass filter and an adjustable four pole low pass filter, to define the pass band, and an adjustable slope filter, to define the slope within the pass band. The control over the output level versus input level characteristic includes an input AGC system with well defined, independent control of compression threshold and compression ratio, an adjustable peak clipper, and a selectable output AGC system that tracks the peak clipper setting.

Abstract: A differential voltage threshold detector that may be used in a hearing aid circuit. The configuration includes an inherent differential/full wave operation, without the need for additional circuitry. The detector includes a differential transconductance stage, first and second "top" current mirrors (which respond to the transconductance stage), first and second "bottom" current mirrors (which respond to the top current mirrors) and a detector (which responds to the current levels in the mirrors). The detector effectively issues an output signal when the voltage applied to the threshold detector varies by more than a predetermined amount.

Abstract: A voltage regulator for producing first and second reference voltages. The regulator includes first and second transistors, of a first polarity, having coupled emitters, and third and fourth transistors, of a second polarity, having coupled emitters. A first amplifier is driven by the collectors of the second and third transistors, and provides a signal to the bases of the third and fourth transistors. A fifth transistor, of the first polarity, has its collector interconnected to the base of the second transistor, and the emitter of which is interconnected to the emitter of the first and second transistors. A second amplifier is driven by the collectors of the first and fourth transistors, and provides a signal to the bases of the first and fifth transistors. The wiper arm of a variable resistance whose end terminals are connected between the base and collector of the fifth transistor provides an adjustable reference voltage output over the range of the first and second reference voltages.

Abstract: A current source provides an output current that is substantially exponentially related to a difference between input voltages. The output current is also substantially linearly related to an input current. The current source includes first, second and third transistors interconnected to one another. The basic current source may be used as a "building block" to produce more complex control functions.

Abstract: An ear wax barrier for a hearing aid to prevent ear wax from contacting and damaging the internal components of a hearing aid or hearing aid receiver. The barrier includes a housing defining a central axis of passage, as well as a plurality of projections and a variable acoustic attenuator. The projections extend inwardly from the interior surface of the housing, each projection partially occluding the cross-sectional area of the housing. The projection provides a tortuous path for ear wax migrating into the hearing aid. The variable acoustic attenuator and the projections provide a constricted passageway for damping of the acoustic response of the hearing aid.

Abstract: An apparatus for storing and dispensing small batteries. The apparatus eases the process of inserting such batteries into small electrical devices. The apparatus includes a plurality of handles, a base member removably attached to each of the handles, and a cover to envelop the plurality of handles and the cover. A small battery is removably attached to the end of each handle, allowing the use of the handle for assisting with the insertion of the battery into a small battery well. The plurality of the handles are stored in a "matchbook" type package, allowing the removal of one handle and continued storage of the remainder.

Abstract: An improved compansion system that more effectively increases the dynamic range of other circuit elements. The system includes both a compression circuit to limit the input signal amplitude for a circuit element, such as a filter, and an expansion circuit to receive and modify the output of the circuit element. The expansion circuit restores a substantially linear input-output amplitude relationship and may prevent substantial overloading in the circuit element, thereby increasing the dynamic range of the circuit element.

Abstract: A hearing aid that is compact and efficient and that provides a high degree of control over its frequency response and also over its output level versus input level characteristic. The frequency response control includes an adjustable four pole high pass filter and an adjustable four pole low pass filter, to define the pass band, and an adjustable slope filter, to define the slope within the pass band. The control over the output level versus input level characteristic includes an input AGC system with well defined, independent control of compression threshold and compression ratio, an adjustable peak clipper, and a selectable output AGC system that tracks the peak clipper setting.

Abstract: A system for suspending a receiver in a hearing aid and acoustically linking the receiver with the region external to the hearing aid. A shaped mandrel is placed inside the shell of the hearing aid and a liquid material is poured into the shell. The liquid material polymerizes to form an elastomer that is around the mandrel and in contact with the shell. The mandrel is then removed from the shell, leaving a receiver cavity and sound channel. A receiver is inserted into the receiver cavity. The receiver cavity holds the receiver, and the sound channel grippingly engages an acoustic output port on the receiver. The sound channel extends between the receiver and shell, acoustically linking the receiver with the external region.

Abstract: An electrical film resistor. The film resistor includes a substrate, resistive film, and first and second terminals. The first terminal includes a first electrode. The second terminal includes second and third electrodes. The second electrode is close to the first electrode, and the third electrode is spaced apart from the first electrode. Moreover, the second and third electrodes are electrically interconnected. A kerf may be cut in the resistive material to increase the resistance between the two terminals and eventually substantially electrically isolate the second electrode from the first terminal. Thereafter, kerfs may be cut in the resistive material between first and third electrodes to further increase the resistance between the two terminals.

Abstract: An improved process for making a vent for an "in the ear" hearing aid. A cavity is formed which corresponds to the structure of the ear canal and outer ear of the hearing aid user. A molding liquid, such as acrylic, is poured into the cavity. The liquid is allowed to partially cure and form a thin-walled shell inside the cavity. An elongated mandrel is then placed along the inside of the thin-walled shell, and additional liquid molding material is poured into the thin-walled shell around the elongated mandrel. The wall of the shell accordingly becomes thicker, enveloping the mandrel. The mandrel may then be removed, leaving the vent in the wall of the shell.

Abstract: An electrical film resistor. The film resistor includes a substrate, resistive film, and first and second terminals. The first terminal includes a first electrode. The second terminal includes second and third electrodes. The second electrode is close to the first electrode, and the third electrode is spaced apart from the first electrode. Moreover, the second and third electrodes are electrically interconnected. A kerf may be cut in the resistive material to increase the resistance between the two terminals and eventually substantially electrically isolate the second electrode from the first terminal. Thereafter, kerfs may be cut in the resistive material between first and third electrodes to further increase the resistance between the two terminals.

Abstract: An electronic power control circuit for a hearing aid amplifier. The circuit includes a feedback stage, output stage, and output transducer. The feedback and output stages cooperatively define a current regulator that controls the current of the output stage. A variable resistor is provided for adjusting the maximum signal level that can be applied to the output transducer in the hearing aid. Such adjustment prohibits the output transducer from producing an undesirably loud acoustic output. Adjustment of the variable resistor also simultaneously varies both the quiescent current of the output stage and the hearing aid gain.

Abstract: An improved nubbin and acoustic damper for the elimination or production of resonance in the sound transmission tubing of a hearing aid. The nubbin and nubbin sound conduit include a right angle corner. The damper comprises a plug having three body portions: a plug portion that is insertable into the conduit, a longer diameter block attached to the plug portion and forming a shoulder therewith that limits movement of the damper into the nubbin, and a plate attached to the block and being of greater diameter than the block. The damper has parallel grooves for sound transmission in its outer surface, with the grooves longitudinally and continuously through the plug portion, block and plate.

Abstract: An eyeglass hearing aid including a channel having a serpentine shape for providing a compact acoustical path for extending the path of sound transmission. A sweat guard is positioned around a volume control aperture formed on the upper surface of the eyeglass aid. Alignment structure serves to fix a curved printed circuit board in position relative to the flat lower surface of the paddle portion of the eyeglass aid. These particular structures are incorporated in an eyeglass hearing aid in order to utilize a printed circuit board of a behind-the-ear hearing aid and to provide the same frequency response as a behind-the-ear aid.

Abstract: A hearing aid circuitry comprising a high pass filter and a low pass filter, for filtering the sound wave signals to permit adjustment of the gain of the high end of the frequency spectrum relative to its low end. The low pass filter is formed of a differential amplifier which performs a subtraction of the sound wave signal and the output signal of the high pass filter. The outputs of both filters are individually added together in proportional quantities by a single control. The use of the differential amplifier, or alternatively, a simple R-C filter of 6 dB fall off, minimizes frequency effects in the output signal in the frequency range where the high pass filter and low pass filter overlap.

Abstract: An improved battery door structure is provided which has advantageous use in compact electronic apparatus, as for example a hearing aid, electronic watch, miniature calculator and other types of small battery operated devices. The structure includes a body member including a power source, such as a small battery. The structure is provided with a battery receptacle which has a hinged door, which may be opened and closed at will from the outside of the body member. In one preferred embodiment, the body member may be readily removable and replaceable from the remainder of the structure. The body member as a unit is provided with plastic members forming plastic hinge means for the battery door. The battery door includes hinge pivot pin means wherein the door and hinge pivot means preferably are molded as one piece.

Abstract: A feedback transistor, whose base and emitter are connected respectively to the base and emitter of a common emitter output transistor, conducts a collector current which is directly proportional to the output current. The collector current of the feedback transistor is fed back to the input of an amplifier which drives the output transistor. The resulting negative feedback controls overall gain, reduces distortion, and controls the quiescent current of the output transistor. Application of this linear current feedback technique to both class A and class B amplifiers is disclosed.

Abstract: A combined package and carrier for a hearing aid battery adapted to securely hold and uniquely position the battery within the holder and the hearing aid and yet provide as small as possible a package. A carrier of molded plastic and functioning as a handle to insert and withdraw the battery from the hearing aid.