JP6679071B1 - Hum noise removing method and hum noise removing circuit using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hum noise removing method of a vacuum tube type audio amplifier using a direct heating tube, and a hum noise removing circuit using the method. SOLUTION: An alternating current output from a power transformer 220 that supplies power to a direct-heating audio amplifier 40 or a power transformer connected to a commercial power source 10 of the same system as the power transformer 220 is used as a hum noise removal source signal. In the grid of the direct-heat audio amplifier 40, an output obtained by adjusting the phase and / or the amplitude of the AC obtained by doubling the frequency of the hum noise removing source signal by the analog multiplying circuit 32 by the phase adjusting / amplitude adjusting circuit 33 is used as the hum noise removing signal. Hum noise is removed by mixing with the audio signal. [Selection diagram] Figure 1

Description

  The present invention relates to a hum noise removing method for an audio amplifier using a direct heating tube and a hum noise removing circuit using the method, and more particularly, to a power transformer connected to a commercial power supply of the same system as a power supply for supplying an alternating current to a filament of the audio amplifier. The present invention relates to a hum noise removing method and a hum noise removing circuit, characterized in that an AC wave obtained from the above is used as a source wave for canceling hum noise.

 The vacuum tube used in the audio amplifier is a direct heating type in which the heating electrode and the electrode that emits thermoelectrons are the same filament (filament), and the necessary heating is left to the heater insulated from the surroundings to emit thermoelectrons. There are two types of indirectly heated type, in which the electrode (cathode) surrounding the heater is used exclusively. The indirectly heated type is widely used in vacuum tube audio amplifiers because it is easier to handle and can be made smaller than the directly heated type. On the other hand, the direct heating type is still favored by many audiophiles because of the attractive sound quality obtained by alternating-current ignition of the direct heating tube, and its production continues worldwide.

  However, the vacuum tube type audio amplifier using the direct heating tube has a problem that a peculiar hum noise occurs when the filament is AC-ignited and used as a non-feedback or low feedback single amplifier. This is because in the direct heating type, the filament operates as a cathode, and the waveform of the AC power source applied to the filament is mixed in the audio signal. Further, this is because the amount of emitted thermoelectrons (anode current) changes as the filament is heated and cooled periodically.

  In order to solve such a problem, in Patent Document 1 below, an audio input unit, an audio amplification unit, an audio output unit, and an offsetting AC signal generation unit are provided, and the offsetting AC signal is input to the audio amplification unit. In the audio amplifier configured so as to be superimposed and removed with the hum noise generated by the above, the canceling AC signal generation unit is formed separately from the audio amplification unit by using the semiconductor amplification element 34. The AC signal for cancellation has the same or half frequency as the hum noise generated in the full-wave rectifier circuit 20 or the half-wave rectifier circuit, and has the opposite phase, and its amplitude is in the range of 0.1 to 3%. Create a similar waveform distorted by. A technique is disclosed in which a hum noise is reduced by inputting a waveform created by such an offsetting AC signal as an offsetting AC signal to an audio amplification unit.

  However, in the technique disclosed in Patent Document 1, the canceling AC signal is formed as a separate body from the audio amplifying unit using the semiconductor amplifying element 34, so the canceling AC signal does not have the same waveform as the hum noise waveform. , Also, it does not become a similar waveform. This is because commercial power supplies used for vacuum tube audio amplifiers have many harmonic components generated from air conditioners, power inverters of solar systems, etc., and distortion components may exceed 10%. This is because the regular noise component and the AC power supply flicker are superimposed. As a result, it is difficult to effectively remove the hum noise with the canceling AC signal disclosed in Patent Document 1.

  The technique described in Patent Document 2 uses the same direct heating vacuum tube as the audio amplifier to generate a similar AC noise waveform at the same frequency as that generated at the output terminal of the amplifier, and to generate a waveform of either positive or negative phase. A technique for injecting into any electrode of any amplification stage of a target amplifier to cancel AC noise in the final stage is disclosed.

  However, since there are individual differences even in the same direct heating tube as the audio amplifier, the hum noise generated in the audio amplifier and the AC noise waveform are not the same or similar waveforms, and the power source that ignites the direct heating vacuum tube. The different AC noise waveforms will differ. As a result, the AC noise waveform disclosed in Patent Document 2 has a problem that it is difficult to effectively remove the hum noise.

  Patent Document 3 discloses a device for removing hum noise, which sets the phase and amplitude of a removal signal so that the hum noise can be canceled at the output part of an audio amplifier, and synchronizes with the AC power source that causes the hum noise. A first transformer circuit for generating a signal, a frequency doubler circuit for generating a cancel signal source synchronized with a synchronizing signal output from the first transformer circuit, and a harmonic wave from an output of the frequency doubler circuit, Hum noise is output to the first low-pass filter and the first band-pass filter for removing the random noise and the flicker of the AC power source to generate the low-distortion sine wave cancel signal, and the output of the first band-pass filter. A first phase inversion circuit and a first phase shifter that give a necessary amount of phase shift for canceling, and an output of the first phase shifter are used to detect hum noise. A variable gain adder that adjusts and adds the amplitude required for cell addition, and the total harmonic distortion rate of the low distortion sine wave cancellation signal at the output of the variable gain adder is 0.02% to 0. .2% and by generating the low distortion sine wave cancellation signal, only the fundamental wave component or the harmonic component of the hum noise included in the audio signal is removed to cancel the low distortion sine wave. Disclosed is a hum noise canceling device for an audio amplifier, characterized in that the phase and amplitude of a signal can be adjusted independently of each other.

In the technique described in Patent Document 3, the output from the first transformer circuit that generates an AC wave synchronized with an AC power source is used as a hum noise canceling signal source, and a frequency double that of the signal is multiplied by full-wave rectification. It is created by. Then, the distortion component of the generated cancellation signal is removed by the filter circuit in the subsequent stage, and only the sine wave is extracted. Further, the phase shift caused by the filter circuit is adjusted by ± 90 degrees or more by the transfer circuit. However, commercial power supplies used for amplifiers often have harmonic components generated from power inverters such as air conditioners and solar systems, and distortion components may exceed 10%. Therefore, the technique described in Patent Document 3 can deal with the fundamental wave (50, 60 Hz) of the commercial power source, but cannot effectively remove the noise generated by the harmonic component.

  In Non-Patent Document 1 below, the filament hum noise is regarded as an input / output response of a system in which a filament power supply waveform is input, its transfer characteristic is measured for each set, and based on this transfer characteristic, erased from the filament power supply waveform in real time. Techniques for generating a signal and injecting it into the filament of a direct heating vacuum tube to eliminate filament hum are disclosed.

  However, in the technique described in Non-Patent Document 1 below, a cancellation signal of filament hum noise is input to the filament, but a circuit for inputting the cancellation signal to the filament is connected in series to the audio signal current (current from the plate). When connected to, it becomes a current feedback and affects the sound quality. When connected in parallel, the audio signal (excluding the direct current component of the plate current) flows through the circuit for inputting the cancel signal, and the sound quality deteriorates.

  Further, the technique described in Non-Patent Document 1 extracts AC noise from an output transformer, creates a cancellation signal for the AC noise by a hum noise elimination processor, and inputs the cancellation signal to the filament. That is, since the input signal is muted and the hum noise from the commercial power source is extracted before playing the music, the frequency and voltage of the commercial power source cannot cope with fluctuations during the music playback. Further, there is a problem that a filter is required in the subsequent stage, and such a filter causes a phase shift of hum noise, and a circuit capable of wide-range phase adjustment is required to adjust the phase shift.

Utility model registration No. 3193415 Japanese Patent Laid-Open No. 2001-111355 Patent No. 50502231

"In search of the ultimate direct heating tube sound Direct heating vacuum tube AC ignition hum noise elimination technology, Uesugi Laboratory Ltd. May 2018"

  Therefore, an object of the present invention is to generate a characteristic hum noise that is inevitably generated in a vacuum tube audio amplifier using a direct heating tube, regardless of the environment of the commercial power supply used by the vacuum tube audio amplifier and the time fluctuation of the noise generation source. It is to provide a hum noise removing method for a vacuum tube type audio amplifier using a direct heating tube capable of following the above and removing the hum noise, and a hum noise removing circuit using the method.

In order to solve the above problems, the present invention is a hum noise removal method for removing hum noise generated in a vacuum tube audio amplifier using a direct heating tube,
The AC output from the power transformer connected to the commercial power supply of the same system as the power supply to the vacuum tube audio amplifier is a hum noise removal source signal for removing hum noise,
While inverting or keeping the same phase of the hum noise removal source signal, its frequency is doubled by an analog multiplication circuit, and then its phase and / or amplitude is adjusted to generate a hum noise removal signal,
A method for removing hum noise in a vacuum tube audio amplifier using a direct heating tube, wherein the hum noise removal signal is mixed with an audio signal in a grid of the vacuum tube audio amplifier to remove hum noise.

  Commercial power supplies used for vacuum tube audio amplifiers that use direct heating tubes are alternating current with waveform distortion that contains many harmonic components generated from power inverters such as air conditioners and solar systems. Is fluctuating with. In a vacuum tube type audio amplifier using a direct heating tube, since alternating current with such waveform distortion is applied to the filament, hum noise is generated due to the alternating current deforming distortion with time. In the present invention, an alternating current having the same waveform distortion as the alternating current applied to the filament is used as the hum noise removal source signal, and the alternating current after adjusting the phase / amplitude thereof is mixed with the audio signal as the hum noise removal signal. As a result, the hum noise caused by the alternating current of the waveform distortion applied to the filament with time variation can be reliably removed.

It is preferable to adjust the delay phase or the lead phase of the hum noise removal source signal before being input to the analog multiplication circuit. By adjusting the generated phase due to the difference between the internal impedance of the power transformer and the load current of the winding, and then multiplying it by 2 in the analog multiplication circuit, the phase adjustment after the multiplication can be facilitated.

The present invention is a hum noise removing circuit for removing hum noise generated in a vacuum tube type audio amplifier using a direct heating tube,
A power transformer for supplying power to the vacuum tube audio amplifier,
An analog multiplication circuit that doubles the frequency of the hum noise removal source signal by using the AC output from the power transformer or a power transformer connected to a commercial power supply of the same system as the power transformer as a hum noise removal source signal.
A phase / amplitude adjusting circuit for adjusting the phase and / or amplitude of the AC doubled by the analog multiplying circuit;
A hum noise of a vacuum tube type audio amplifier using a direct heating tube, comprising a mixing section for mixing a hum noise removal signal output from the phase / amplitude adjusting circuit with an audio signal in a grid of the vacuum tube type audio amplifier. The removal circuit.

It is preferable to include a phase adjustment circuit that adjusts the delay phase or the lead phase of the hum noise removal source signal before being input to the analog multiplication circuit.

  According to the present invention, the hum noise peculiar to the vacuum tube type audio amplifier using the direct heating tube is inevitably generated, regardless of the environment or time variation of the commercial power supply used for the vacuum tube type audio amplifier. It is possible to provide a hum noise removing method for a vacuum tube type audio amplifier using a direct heating tube capable of following fluctuations and removing the hum noise, and a hum noise removing circuit using the method.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a hum noise removing circuit for removing hum noise of a vacuum tube type audio amplifier using a direct heating tube according to an embodiment of the present invention. The hum noise removal circuit includes a commercial power supply (AC power supply) 10, a hum noise removal source signal generation unit 20, and a hum noise removal AC generation unit 30. The hum noise removal source signal generation unit 20 includes a power supply transformer 220, a filament power supply AC output unit 210 that outputs an alternating current that heats a filament, and a hum noise removal source signal output unit 230 that outputs a hum noise removal source signal that removes hum noise. Equipped with.

  Here, the AC output supplied from the commercial power supply 10 may have a harmonic component generated from an air conditioner, a power inverter of a solar system, or the like, and the distortion component may exceed 10%. The AC output on which the distortion component is superimposed is transformed into a low voltage by the power supply transformer 220, and the same distortion component is also superimposed on the output after the transformation.

  The alternating current from the commercial power source 10 is transformed into a filament power source and a hum noise removal source signal. Here, both may be transformed by the same power transformer or may be transformed by different power transformers. The point is that the commercial power supply 10 is common. When the power supply transformer 220 is common, the AC from the power supply transformer 220 (AC output from the same power supply) is divided into two systems, one of which is a vacuum tube type using a direct heating tube by the filament power supply AC output unit 210. It is supplied to the filament of the audio amplifier 40 to heat the filament. The other alternating current is supplied from the hum noise removal source signal output unit 230 to the hum noise removal signal generation unit 30.

  One of the features of the present invention is that the AC for filament power supply and the hum noise removal source signal use the commercial power supply of the same system. As a result, an AC having a distorted waveform that is synchronized with the AC supplied to the filament and has the same distortion component superimposed thereon can be used as the hum noise removal source signal.

  The alternating current (hum noise removal source signal) output from the hum noise removal source signal output unit 230 is input to the hum noise removal alternating current generation unit 30. The hum noise removal AC generation unit 30 includes a phase adjustment circuit 31, an analog multiplication circuit 32, and a phase adjustment / amplitude adjustment circuit 33, and the audio signal and the hum noise removal signal are mixed in a mixing unit (not shown). .

The phase of the alternating current input to the phase adjusting circuit 31 is slightly different from the alternating current supplied to the grid due to the internal impedance of the power transformer, the difference in the load current flowing through the winding, and the like. The phase adjustment circuit 31 adjusts the phase difference as a whole by ± several degrees.

  The hum noise removal source signal whose phase has been finely adjusted by the phase adjusting circuit 31 is converted by the analog multiplying circuit 32 into a frequency doubled (50 Hz / 60 Hz is 100 Hz / 120 Hz). This is because the fundamental frequency of hum noise is twice the power supply frequency. This is because the filament temperature of the vacuum tube type audio amplifier 40 using the direct heating tube is heated regardless of the direction of the alternating current supplied to the filament, and the temperature change appears twice, and the virtual midpoint in the filament. This is because there is a (physical position at ground potential), the filament is divided into two for convenience centering on the virtual midpoint, and thermoelectrons are emitted from each.

  The hum noise removal source signal doubled by the analog multiplication circuit 320 is adjusted in phase and amplitude by the phase adjustment / amplitude adjustment circuit 330 to generate a hum noise removal signal. The hum noise removal signal is mixed with the audio signal in the grid of the vacuum tube type audio amplifier 40 using the direct heating tube, and removes the hum noise caused by the AC application of the filament.

The present invention uses an analog multiplier circuit to double the frequency of the hum noise removal source signal. In the digital multiplication circuit, the input AC wave must be once converted into a numerical value through the A / D converter and then calculated, and the calculation result must be converted into an analog signal again by the D / A converter and output. Therefore, in the digital multiplication circuit, there is a delay due to the A / D conversion time, an influence on the phase by a low-pass filter that removes a digital component in the D / A conversion, and an influence of noise generated from the digital circuit.

On the other hand, the analog multiplication circuit normally has a sufficient bandwidth within the audible frequency range, and can multiply the hum noise removal source signal and output it instantaneously without delay. Further, since the low pass filter is not required, there is no problem of the digital multiplication circuit as described above. Further, enthusiasts of audio amplifiers using a direct-heating vacuum tube tend not to like digital sound sources or digitally processed audio amplifiers, much like analog records rather than CDs (Compact Discs). In the hum noise removing circuit of the present invention, all circuits are configured by analog to remove the hum noise of the direct heating type vacuum tube.

(Example)
FIG. 2 shows an embodiment of a hum noise removing circuit created according to the present invention. AC power of the same commercial power supply as the commercial power supply supplied to the filament of the vacuum tube type audio amplifier 40 using the direct heating tube is transformed into E1 by the power supply transformer T1. Further, ± 15 V is supplied as the power source of the analog multiplication circuit 320.

In FIG. 2, the voltage E1 of the hum noise removal source signal generator 200 and the voltage E2 applied to the vacuum tube audio amplifier 40 using a direct heating tube are transformed and output by the same power supply transformer T1. Usually, a sine wave of a commercial power source contains many harmonic components generated from an air conditioner, a power inverter of a solar system, etc., and its distortion rate may exceed 10%. A large amount of harmonic components, random noise components, and AC power source flicker are superimposed on the trademark power source. The AC of the commercial power source is a sine wave with distortion, and the distortion changes with time. The alternating current that heats the filament is a distorted sine wave that changes with time, and hum noise is generated by the distorted sine wave.

Here, a slight phase difference occurs between the hum noise removal source signal and the alternating current supplied to the grid due to the difference in the internal impedance of the transformer T1 and the load current of each winding. Further, the hum noise removal source signal has a lead phase by the resistors R1 and R2 and the capacitors C1 and C2. Therefore, the overall phase is adjusted by the capacitor C3, the resistors R3, and VR1. That is, the phase adjustment circuit 310 adjusts the phase of the commercial power source by ± several degrees. The resistors R1 and R2 also have a function of dividing the voltage E1 and dividing the voltage of the hum noise removal AC output unit. It should be noted that the capacitors C1 and C2 can be used as the hum noise removal source signal without using the voltage E1 and by using the AC from the voltage E2 instead of the voltage E1. In such connection, since the bias voltage is generated in the filament, the capacitors C1 and C2 also serve as a coupling capacitor that cuts the direct current.

The analog multiplication circuit 320 has two sets of input ports, and when the hum noise removal source signals of the same phase are input to the input port 1 (IN1) and the input port 2 (IN2), the analog multiplication circuit 32 inverts the phase. The frequency is doubled. When either phase of the hum noise removal source signal input to IN1 and IN2 is inverted and input to each input port, the analog multiplication circuit 320 inverts the phase and doubles the frequency. That is, the switch S1 is a switch that switches the phase of the alternating current output from the analog multiplication circuit 320 to inversion / non-inversion. Note that the phase is inverted / non-inverted because it is necessary to invert / non-invert the phase of the hum noise removal signal depending on the place where the audio signal and the hum noise removal signal are mixed.

The alternating current output from the analog multiplication circuit 320 has a predetermined voltage value by the resistors R6 and R7, and the variable resistor VR2, the capacitor C4, and the variable resistor VR4 perform the phase adjustment and the fine adjustment of the amplitude of the hum noise canceling signal, and mix them. It mixes in the grid of the vacuum tube type audio amplifier 40 using a direct heating tube via the resistance R8 of the container 340. The variable resistor VR3, the condenser C5, the variable resistor VR5, and the resistor R9 are for other stereo channels.

Since the alternating current output from the analog multiplication circuit 320 has a sufficient amplitude (effective value is about 1V to 5V), the amplitude is adjusted by the variable resistor VR2. Since the alternating current from the analog multiplication circuit 320 contains a direct current component, the direct current component is cut off by the capacitor C4 and only the alternating current is passed through the variable resistor VR4. Further, the capacitor C4 plays a role of phase adjustment, and the phase of the capacitor C4 and the variable resistor VR4 is adjusted by 0 to several degrees. This phase adjustment is to adjust the phase delay due to the impedance of the grid circuit of the vacuum tube audio amplifier using the direct heating tube including the resistor R8 of the mixer 340 that mixes the hum noise removal signal and the audio signal. The variable resistors VR1, VR2, VR4 are adjusted so that the hum noise is minimized.

FIG. 3 shows that the voltage E2 supplied to the filament of the vacuum tube type audio amplifier 40 using the direct heating tube is transformed by the power transformer T2, and is transformed into the voltage E1 by the power transformer T1 connected to the commercial power supply of the same system, and the hum noise is generated. It is a figure in the case of comprising a removal signal generation circuit. The voltages E1 and E2 may be obtained by the same power supply transformer as in the embodiment shown in FIG. 2, and the voltages E1 and E2 may be obtained by the transformers T1 and T2 connected to the commercial power supplies of the same system as shown in FIG. You may get it.

FIG. 4A is an AC waveform of the commercial power source displayed on the oscilloscope, and FIG. 4B is a waveform of hum noise generated from the output stage of the vacuum tube type audio amplifier using the direct heating tube. As shown in FIG. 4A, the AC waveform of the commercial power supply is a distorted sine wave, and a large amount of harmonic components, random noise components, AC power supply flicker, and the like are superimposed. As shown in FIG. 4B, the distorted sine wave is doubled and output as hum noise to a vacuum tube audio amplifier using a direct heating tube. The hum noise was measured to be approximately 15.72 millivolts in effective value.

  FIG. 5A is a waveform of a hum noise removal signal generated by the hum noise removal generation circuit 300 created in the above-described embodiment, and FIG. 5B is a waveform of the hum noise removal signal of a vacuum tube audio amplifier using a direct heating tube. This is the output waveform when input to the grid. As shown in FIG. 5B, the hum noise removal signal significantly reduced the hum noise to an effective value of about 0.38 millivolts.

The hum noise removal signal generated by the hum noise removal generation circuit of the present invention is very close to the waveform of the alternating current applied to the filament of the vacuum tube type audio amplifier using the direct heating tube. By mixing the signal path so as to cancel the hum noise, it is possible to cancel the hum noise effectively.

FIG. 3 is a block diagram of a hum noise removing circuit for removing hum noise of the audio amplifier using the direct heating tube according to the embodiment of the present invention. It is a hum noise removal circuit diagram created as one example based on the present invention. It is a circuit diagram in the case of obtaining voltage E2 and voltage E1 by the power transformers T2 and T1 connected to the commercial power supply of the same system. The AC waveform of the commercial power supply by the oscilloscope and the hum noise waveform generated from the output stage of the vacuum tube type audio amplifier using the direct heating tube. The waveform of the hum noise removal signal generated by the hum noise removal generation circuit 300 and the output waveform when the hum noise removal signal is input to the grid of the vacuum tube type audio amplifier using the direct heating tube.

10 Commercial power supply (AC power supply)
20 Hum noise removal source signal generation unit 30 Hum noise removal AC generation unit 31 Phase adjustment circuit 32 Analog multiplication circuit 33 Phase adjustment / amplitude adjustment circuit 40 Vacuum tube audio amplifier 200 using direct heating tube 200 Hum noise removal source signal generation unit 210 For filament power supply AC output unit 220 Power transformer 230 Hum noise removal source signal output unit 300 Hum noise removal signal generation circuit 310 Phase adjustment circuit 320 Analog multiplication circuit 330 Phase adjustment / amplitude adjustment circuit 340 Mixer

Claims (2)

A hum noise removing method for removing hum noise generated in a vacuum tube type audio amplifier using a direct heating tube,
An alternating current output from a power transformer connected to a commercial power supply of the same system as the commercial power supply supplied to the vacuum tube audio amplifier is used as a hum noise removal source signal for removing hum noise,
Adjusting the delay phase or the lead phase of the hum noise removal source signal,
The phase of the adjusted hum noise removal source signal is inverted or the same phase, the frequency is doubled by an analog multiplication circuit, and then the phase and / or amplitude is adjusted to generate a hum noise removal signal,
A method for removing hum noise in a vacuum tube audio amplifier using a direct heating tube, wherein the hum noise removal signal is mixed with an audio signal in a grid of the vacuum tube audio amplifier to remove hum noise. A hum noise removing circuit for removing hum noise generated in a vacuum tube type audio amplifier using a direct heating tube,
A power transformer for supplying power to the vacuum tube audio amplifier,
An alternating current output from the power transformer or a power transformer connected to a commercial power supply of the same system as the power transformer is used as a hum noise removal source signal, and a phase adjustment circuit for adjusting a delay phase or a lead phase of the hum noise removal source signal,
An analog multiplication circuit that doubles the frequency of the hum noise removal source signal output from the phase adjustment circuit;
A phase / amplitude adjusting circuit for adjusting the phase and / or amplitude of the AC doubled by the analog multiplying circuit;
A hum noise of a vacuum tube type audio amplifier using a direct heating tube, comprising a mixing section for mixing a hum noise removal signal output from the phase / amplitude adjusting circuit with an audio signal in a grid of the vacuum tube type audio amplifier. Removal circuit.

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