Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03G—CONTROL OF AMPLIFICATION
  • H03G7/00—Volume compression or expansion in amplifiers
  • H03G7/002—Volume compression or expansion in amplifiers in untuned or low-frequency amplifiers, e.g. audio amplifiers
  • H03G7/005—Volume compression or expansion in amplifiers in untuned or low-frequency amplifiers, e.g. audio amplifiers using discontinuously variable devices, e.g. switch-operated
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03G—CONTROL OF AMPLIFICATION
  • H03G3/00—Gain control in amplifiers or frequency changers
  • H03G3/20—Automatic control
  • H03G3/30—Automatic control in amplifiers having semiconductor devices
  • H03G3/3005—Automatic control in amplifiers having semiconductor devices in amplifiers suitable for low-frequencies, e.g. audio amplifiers
  • H03G3/301—Automatic control in amplifiers having semiconductor devices in amplifiers suitable for low-frequencies, e.g. audio amplifiers the gain being continuously variable
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03G—CONTROL OF AMPLIFICATION
  • H03G7/00—Volume compression or expansion in amplifiers
  • H03G7/002—Volume compression or expansion in amplifiers in untuned or low-frequency amplifiers, e.g. audio amplifiers
  • H03G7/004—Volume compression or expansion in amplifiers in untuned or low-frequency amplifiers, e.g. audio amplifiers using continuously variable impedance devices

Definitions

• the present invention relates to a circuit arrangement for limiting the dynamics according to the preamble of claim 1.
• a circuit arrangement for regulating or limiting the dynamics usually serves to change the amplification of an amplifier stage as a function of the signal level of the signal to be amplified. This means that signals with a low level can be amplified sufficiently. On the other hand, it is avoided that signals with a high level lead to an excessively strong output signal.
• the signal to be amplified is an acoustic signal
• damage to the system connected to the amplifier such as loudspeakers, headphones, etc., can be avoided by limiting the dynamics.
• a circuit arrangement for automatic control or limitation of the dynamics is known for example from DE-OS 30 27 715.
• the circuit arrangement presented there causes the amplification of the system used to be reduced as quickly as possible in the event of a sudden increase in amplitude.
• the dynamics of an amplifier connected to the circuit arrangement according to the invention be limited only after a predetermined time after the level of an input signal has been exceeded.
• a timing element is provided to which, on the one hand, a signal is supplied which represents a measure of the difference between a predetermined level and the actual level of an input signal.
• the timing element causes the dynamics to be limited only after a predetermined period of time.
• the predetermined level is selected as a function of an electroacoustic transducer connected to the amplifier device in such a way that above a corresponding sound pressure level, long-term exposure to a listener is likely to cause health damage, this is avoided by the circuit device according to the invention.
• Fig. 1 the block diagram of a first preferred embodiment
• Fig. 2 the circuit diagram of the embodiment shown in Fig. 1;
• Fig. 3 the block diagram of a second preferred
• Fig. 4 the circuit diagram of the embodiment shown in Fig. 3;
• FIG. 1 the block diagram of a first embodiment is shown.
• An audio playback device 10 contains a power amplifier 11, to which signals from stages, not shown, are fed via its input.
• the output signal of the power amplifier 11 is supplied on the one hand to a loudspeaker 12, or generally an electroacoustic transducer, and on the other hand to the input of a smoothing element 13.
• the output signal of this smoothing element 13 reaches a threshold value stage 14 and the control input of an actuating stage 15.
• the threshold voltage stage 14 is supplied with the reference voltage Ur as the threshold value and the output of the stage 14 is on Timer 16 connected, the output signal leading to the control input of a switching means 17. If the switch contact is closed, the first signal connection 15a of the control stage 15 is connected to ground.
• the second signal connection 15b leads to the center tap of a volume control 18 and to the volume control input 19 of the audio playback device 10.
• FIG. 1 The function of the exemplary embodiment according to FIG. 1 is explained with the aid of FIG. 2, in which a preferred version of this exemplary embodiment is shown on the basis of a circuit diagram.
• the signal amplified by the power amplifier 11 is rectified, sieved and smoothed by the smoothing element 13.
• a semiconductor diode 13a is provided, at the anode of which the amplified signal arrives.
• the signal rectified in this way is smoothed by a charging capacitor 13b and a filter element which consists of a filter resistor 13c and a filter capacitor 13d.
• First connections of the capacitors 13b, 13d are connected by the resistor 13c and second connections of these capacitors lead to ground.
• the signal thus smoothed is fed to the input of the threshold stage 14, more precisely to the first connection of a first input resistor 14a.
• a second input resistor 14b at the first terminal of which the negative reference voltage Ur is present in this version, is connected with its second terminal to the second terminal of the first input resistor 14a.
• This common connection is connected to the non-inverting input of an operational amplifier 14c, the inverting input of which is connected to ground.
• the output of this operational amplifier 14c is on the one hand through a feedback resistor 14d connected to the non-inverting input and the other to the input of the timing element 16.
• the smoothed signal present at the first input resistor 14a exceeds a threshold value predetermined by the value of the reference voltage Ur, the positive operating voltage, which is supplied to the operational amplifier at a supply input (not shown), is present at the output of the threshold value stage 14.
• the timing element 16 following the threshold value stage 14 consists of a timing capacitor 16a, which is connected to ground, and the second terminal of which is connected to the output of the timing element 14 via a timing resistor 16b.
• the choice of the values of the components 16a and 16b determines a time constant or a time period after which the switching means 17, here consisting of a switching potentiometer 17a, a switching resistor 17b and a switching transistor 17c, is switched through.
• the actuating stage 15 in this exemplary embodiment consists of an npn actuating transistor 15c, at the base of which an adjusting trimmer 15d is provided, which leads to the output of the smoothing element 13.
• the collector of the control transistor 15c is connected to the volume control input 19 of the device 10 via a variable resistor 15e.
• control transistor 15c acts between its emitter and its collector like a variable resistor which is connected in parallel with the volume control 18. With strong control, this resistance becomes small, which leads to the voltage on the volume ke control input 19 is reduced without actuating the volume control 18. At high levels of the output signal of the output stage 11, this leads to a reduction in its amplification and thus to a limitation of the dynamics.
• Diode 13a AA 143 (npn-Ge; low threshold voltage),
• Capacitor 13b 0.22 uF (electrolytic capacitor),
• Capacitor 13d 100 uF (electrolytic capacitor),
• Resistor 14b 11 kOhm
• Transistor 15c AC 187K (npn-Ge; low threshold voltage),
• Capacitor 16a 330 uF (electrolytic capacitor),
• Resistor 16b 3.3 kOhm
• Resistor 17b 10 kOhm
• Transistor 17c BC 548 (npn silicon),
• Converter 12 headphones with impedance of 30.6 ohms
• the threshold value stage 14 outputs a signal with a first value (here the positive supply voltage) when the level of the input signal rises when the smoothed signal at the non-inverting input of the operational amplifier 14c exceeds the first threshold.
• the value of the signal delivered to the timing element 16 remains until the smoothed signal at the non-invertie ring input of the operational amplifier 14c falls below a second threshold. Then a signal with a second value (here negative supply voltage) is output to the timing element 16.
• the first value of the above-mentioned signal causes the time capacitor 16a to be charged and to switch on the switching transistor 17c when a predetermined voltage is exceeded.
• the second value of the above-mentioned signal causes the time capacitor 16a to be discharged, so that the switching transistor 17c is blocked when the voltage falls below the predetermined value.
• threshold level 14 should respond in such a way that a longer, about 3 seconds long exceeding a sound pressure level of 83 dB leads to a limitation of the dynamics.
• the negative operating voltage is present at its output. This causes the time to discharge and the dynamic limit to be reduced.
• FIG. 3 The block diagram of a second exemplary embodiment is shown in FIG. 3.
• the main difference compared to the first embodiment is that a difference value from the smoothed input signal and the reference voltage is used as the control variable for dynamic limitation.
• an amplifier stage hereinafter referred to as an intermediate amplifier 20, is provided, which is connected between a preamplifier 21 and the power amplifier 11.
• the dynamics of this additional amplifier stage are limited.
• the output signal of the preamplifier 21 is supplied to the smoothing element 13, which supplies a rectified and smoothed signal to the threshold value stage 14 and to a first signal connection of a signal switch 27.
• the threshold value stage 14 is supplied with the reference voltage Ur as the threshold value, which also reaches the first signal connection of a reference switch 28.
• the control inputs of the switches 27, 28 are connected to outputs of the timer 16.
• the second signal connections of the switches 27 and 28 lead to the non-inverting and the inverting input of a differential amplifier 29.
• the differential amplifier 29 compares the rectified and smoothed signal voltage with the reference voltage Ur.
• An output signal the value of which depends on the difference in the voltages, is output by the differential amplifier 29 to a control input of the intermediate amplifier 20, the gain factor of which is reduced by the value of the output signal as the difference increases.
• the differential amplifier 29 has a circuit known per se which contains an operational amplifier.
• the repeater 20 includes an operational amplifier 20a and a feedback resistor 20b.
• An input resistor is formed from the resistor 20c and a field effect transistor 20d, the gate of which forms the control input of the intermediate amplifier and is connected to the output of the differential amplifier 29.
• the reference voltage Ur is obtained by a voltage drop at the center tap of a reference voltage resistor 30 which is connected between the positive supply voltage + Ub and ground.
• the positive reference voltage thus obtained is fed to the inverting input of the operational amplifier 14c.
• the field effect transistor 20d changes its value and the gain of the intermediate amplifier 20, at the input of which the output signal of the preamplifier 21 is present, is controlled. Since the output signal of the repeater 20 is supplied to the final amplifier 11 as an input signal, the dynamics of the entire system, which includes the device 10, is limited.
• Versions of the second exemplary embodiment can have at least one of the following variants: a field effect transistor can be used as the intermediate amplifier 20, which is connected with source and drain connections between the positive supply voltage + Ub and ground. Via its gate connection, it can be controlled by a superimposed signal from the input signal and the differential signal in such a way that an output signal can be tapped off at its drain connection and can be fed to the output amplifier 11; Furthermore, the difference signal can serve as a control signal in order to operate a field effect transistor as a variable resistor. The modulated input signal obtained in this way can be fed either to the power amplifier 11 or to an intermediate amplifier 20 with a predetermined gain factor.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Amplifiers (AREA)

Priority Applications (1)

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Publications (1)

Family

ID=6869037

Family Applications (1)

Country Status (4)

Citations (2)

• 1991
  • 1991-07-06 DE DE9108349U patent/DE9108349U1/de not_active Expired - Lifetime
• 1992
  • 1992-01-24 CA CA 2112909 patent/CA2112909A1/en not_active Abandoned
  • 1992-01-24 JP JP4503027A patent/JPH06508724A/ja active Pending
  • 1992-01-24 WO PCT/EP1992/000153 patent/WO1993001655A1/de active Application Filing

Patent Citations (2)

Non-Patent Citations (1)

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