Walker telephone amplifier
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Walker telephone amplifier
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Telephone Accessories
Year of fee payment : 4. Effective date : A rocker switch is operated by the handset user to vary the impedance of a FET. The FET impedance varies in proportion to the duration of operation of the switch. The handset receiver "volume" increases or decreases in proportion to the FET impedance. An electret condensor microphone stabilizes the receiver supply voltage and provides improved transmitter linearity and low distortion.
This is a continuation of Ser. The invention relates generally to telephone handsets containing receiver amplifiers for use by the hearing-impaired or for use in environments with high ambient noise levels. Conventional telephone handsets have no means for varying the amplitude of the audio signal received from the telephone subset.
Thus, the volume of the acoustic output of the receiver is not adjustable, and is preset at a level sufficient for persons with normal hearing. This poses an obvious disadvantage for persons having hearing impairments. It is also disadvantageous where the telephone is located in an environment with high ambient noise levels, such as manufacturing facilities. One solution to this problem is to provide a telephone handset with a receiver amplifier and a volume control in the form of a potentiometer.
The potentiometer allows the user to vary the receiver "volume" to suit the user's need. A receiver amplifier of this type is disclosed in U. Other telephone handset amplifiers are also well known. For example, see U. Conventional telephone handsets almost universally employ the variable-resistance granular carbon-type transmitter. This type of transmitter responds poorly to low sound levels and has limited frequency response and appreciable distortion.
A telephone handset amplifier circuit for receiving and amplifying an audio signal from a telephone subset by varying amounts based on the duration of operation of a switch and for converting the amplified audio signal into audible sound. The amount of amplification is determined by a variable impedance element such as a FET.
An RC circuit controls the impedance of the FET based on the state of the switch and the level of a supply voltage generated in the transmitter portion of the circuit. An electret condensor microphone regulates or stabilizes the supply voltage and provides improved linearity and low transmitter distortion.
An object of the invention is to provide a telephone handset amplifier which amplifies the audio signal received from the telephone subset by varying amounts dependent on the duration of operation of a manually operable switch. Another object of the invention is to provide a telephone handset amplifier with a transmitter having improved linearity and distortion.
Other objects and advantages of the invention appear hereinafter. For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. The telephone handset amplifier circuit of the present invention is shown in block diagram form in FIG.
The circuit comprises three basic elements: 1 a transmitter circuit 12, 2 a receiver circuit 14, and 3 a receiver volume control circuit The transmitter, receiver and volume control circuits are disposed on printed circuit boards in a telephone handset. See FIG. A telephone subset 26 is connected by lines to the handset circuits as shown in FIG. The subset 26 comprises a conventional telephone circuit. As is well known, the transmit signal appears at the transmit lines of the subset, and the receive signal is at the receive lines Details of subset 26 are conventional and are not pertinent to the present invention.
Referring to FIG. The transmitter circuit 12 supply voltage is obtained from subset 26 via wires 18 and 20 which are connected to the input of a rectifier bridge comprising diodes CR1-CR4. The diode bridge renders the transmitter circuit 12 insensitive to reversal of voltage polarity on lines 18 and Thus, it makes no difference whether the transmit wires 18 and 20 are connected as shown in FIG. This facilitates connection of wires 18 and 20 to the handset. The microphone is shunted by capacitor C1.
Microphone MIC produces an output voltage which varies in response to an acoustic input. A capacitor C2 coupled to the microphone output serves as a low pass filter. The transistor Q1 may be a 2N transistor. The transistor is biased by resistors R1-R5. The transmitter signal generated at the collector of transistor Q1 is further amplified by transistors Q2 and Q3 which are connected in Darlington configuration.
In operation, in response to an acoustic input, microphone MIC produces an audio signal voltage which is ac coupled to the base of resistor Q1, amplified at the collector of transistor Q1 and applied to Darlington pair Q2 and Q3.
The Darlington pair offers high input impedance to reduce the loading effect on transistor Q1. The current at the collector transistor Q3, then, varies in proportion to the audio signal produced by microphone MIC and is returned to the subset 26 via wires 18 and The supply voltage of the receiver amplifier circuit 14 is obtained from wires 18 and 20 via diode bridge CR5-CR8 in the same manner described previously in connection with the transmitter circuit supply voltage.
The diode bridge CR5-CR8 renders the receiver amplifier circuit insensitive to voltage polarity i. The receiver RX is a conventional permanent magnet diaphragm receiver and is connected in series with the collector of transistor Q4. Thus, the voltage across receiver RX is a function of the Q4 collector current. Capacitor C9 is preferably a tantalum capacitor. Rocker switch S1 is shown in the neutral position in FIG. Referring to the receiver amplifier circuit 14, a transformer T1 receives the audio input generated on lines 22 and 24 by subset Resistors R9 and R14 are connected between the primary of transformer T1 and the receiver RX to "bleed" audio to the receiver RX while touch tones are being transmitted.
The user may therefore hear the touch tones generated when dialing a number. Ordinarily, the voltage transmitted by subset 26 on lines 18 and 20 is dropped automatically during dialing. The supply voltage to transistor Q4, taken off bridge CR5-CR8, drops proportionately so that the transistor Q4 is essentially inoperative.
The resistors R9 and R14 provide enough signal to the receiver RX to make the touch tones audible despite the essentially inoperative condition of transistor Q4.
In operation, an audio signal from subset 26 is transmitted to the primary of T1 via wires 22 and The audio signal is ac coupled at the secondary of transformer T1 to the base of transistor Q4 by capacitor C7. The transformer secondary is shunted by resistor R15 to reduce the load on lines 22 and The FET Q5 is a variable impedance element which is controlled at its gate.
Capacitor C9 is also connected to the center tap of rocker switch S1. Selective operation of the rocker switch by the user enables the capacitor C9 to 1 charge through resistor R10 to the supply voltage generated by bridge CR5CR8 or 2 discharge through resistor R Terminal points C and D remain opened.
This provides a charging path for capacitor C9, and the capacitor charges towards the bridge supply voltage. The charging rate is determined by the capacitor C9 and resistor R10 as long as the rocker switch S1 is in the raised position. As the capacitor C9 charges, the FET gate voltage increases.
As a result, the impedance of the FET decreases, thereby increasing the amplitude of the audio input at the base of transistor Q4. The transistor collector current increases proportionately. As the collector current increases, the acoustic signal produced by receiver RX also increases.
The handset user notices this as an increase in receiver "volume". When the desired receiver "volume" is reached, the handset user releases switch S1 from the "RAISE" position whereby the switch returns to the neutral position shown in FIG. The handset thereafter operates at the desired receiver "volume". Terminal points A and B remain open. As a result, the audio input to transistor Q4 decreases, and the transistor collector current decreases proportionately. The accoustic signal produced by receiver RX therefore decreases.
The handset user notices this as a decrease in receiver "volume". By merely depressing switch S1, the voltage across capacitor C9 is made to automatically and continuously vary between common and the supply voltage generated by bridge CR5-CR8. Thus, the receiver "volume" is automatically and continuously variable at a rate and within a range defined by the RC circuits C9-R10 or C9-R The diode is backbiased when the handset is off the subset cradle.
When the handset is replaced in the telephone subset cradle, however, capacitor C9 rapidly discharges through the diode.
When the handset is placed in the cradle, the input voltage to the bridge, on lines 18 and 20, is automatically removed by the subset As a result, diode CR9 is forward biased by the residual capacitor C9 voltage, and the capacitor rapidly discharges through the diode to reset the FET to the high impedance state.
Accordingly, the receiver "volume" is automatically reset to a minimal level determined by resistor R12 which shunts the source and drain of the FET. The subsequent user of the handset, then, will not be disturbed by the "volume" setting of the prior user. In the preferred embodiment, a voltage greater than approximately one volt at the gate of FET Q5 causes the FET to start to conduct decreasing impedance with an attendant increase in receiver "volume".
Maximal receiver "volume" is achieved with a gate voltage of approximately three volts. The requirement of a FET gate voltage of approximately three volts for maximal receiver "volume" creates a problem if a conventional carbon transmitter is used. This is because the transmitter circuit 12, receiver circuit 14 and volume control circuit 16 obtain supply voltage from the same subset lines 18 and The voltage across a carbon transmitter may vary between two-six volts, depending on how the carbon granules are shaken.
The fluctuation in the load presented by the carbon transmitter will be reflected through bridge CR5-CR8 as a fluctuation in the voltage across lines 18, As a result, the supply voltage at the output of bridge CR1-CR4 shifts, producing a shift in receiver "volume" and degraded operation of the receiver amplifier. In contrast, the electret condensor microphone MIC provides a regulated average voltage of approximately four volts across its terminals so that the load on lines 18, 20 is relatively stable.
As a result, the shift in receiver "volume" is avoided while providing superior linearity and distortion performance. The invention permits rapid, automatic and continuous receiver "volume" control to suit the specific needs of the handset user.
Which Type Of Hearing Aid Will Work For You?
Note: Picture may not represent the actual product. We are continuously working on improving our website and reserve the right to change specifications, availability, and pricing without prior notice. How To Order Log In. Discontinued, Replaced by Model Detail Box. Clarity in-line telephone amplifier. Amplifies incoming calls more than 3 times above normal level with easy fingertip control.
Walker Telephone In-line Amplifier w/ Power Supply - Ash
CapTel i Captioned Phone. Telephones with amplified sound speaker and ringer for those with mild hearing Captioned Phone is a amplified telephone for people with hearing loss that displ Clarity brand phones are designed specifically with the elderly and seniors in m Staying in touch is essential, both for maintaining social ties and for safety reasons. Today, you can choose from a wide variety of phones for seniors, designed to meet both hearing and vision needs. Phone choices include traditional landline phones for seniors, cordless phones for seniors and even cell phones. Phones for seniors with hearing impairment have many sound adjustments to help you better hear your calls. First, look for a phone that enables you to significantly raise the volume on the ringer.
Telephones for Seniors
They are easy to set up and to use and are a very popular solution to help users hear in various difficult hearing situations. If you have been missing calls due to hearing issues or working in a noisy environment like a warehouse or restaurant, you may want to check out some of the latest extra loud ringers and inline voice amplifiers. It has a loud piercing ringer that goes up to dB. It also has a flashing strobe light that is very bright and keeps going while the phone is ringing, so it is hard to miss. The strobe is even easy to see in the daylight.
Robot or human?
A rocker switch is operated by the handset user to vary the impedance of a FET. The FET impedance varies in proportion to the duration of operation of the switch. An electret condensor microphone stabilizes the receiver supply voltage and provides improved transmitter linearity and low distortion. Telephone signal amplifier, comprising: a telephone handset having a receiver cup and transmitter cup separated by a handle portion, an operator accessible switch mounted on the handset handle portion, said switch being operable in [a]at least two states, means disposed within the handset and coupled to said operator accessible switch for amplifying an audio signal generated by a telephone network based on the duration of operation of said switch to either of said states, said means for amplifying said [sudio]audio signal comprising an amplifier and FE Telephone signal amplifier, comprising: a telephone handset having a receiver cup and transmitter cup separated by a handle portion, an operator accessible switch mounted on the handset handle portion, said switch being operable in [a]at least two states, means disposed within the handset and coupled to said operator accessible switch for amplifying an audio signal generated by a telephone network based on the duration of operation of said switch to either of said states, said means for amplifying said [sudio]audio signal comprising an amplifier and FET means ac coupled to the input side of said amplifier for reducing the level of said telephone network audio signal over a range of levels based on the duration of operation of said switch to one of said states, and , a receiver disposed within the receiver cup for transducing the amplified audio signal to sound.
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Note: Picture may not represent the actual product. We are continuously working on improving our website and reserve the right to change specifications, availability, and pricing without prior notice. How To Order Log In. Detail Box Product Brochure pdf. Installs between the existing telephone base and the current handset.
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