Abstract:
A circular audio amplifier positions the weighty components of its power supply at the bottom, and the audio amplifier portions at the top. Modular finned heat sinks about the audio amplifier portions are resiliently mounted to reduce the transmission of vibration therefrom into the audio amplifier portions. Each module of the heat sink includes copper wires spanning its vertical dimension to short out induced current from top to bottom of the relatively poor electrical conduction of the aluminum of which the heat sinks are made. The audio amplifier portions, except for the final amplifiers, are mounted on independently resiliently mounted parallel substrates. The low-signal substrates are mounted the furthest away from the power supply. All cable entries and exits include grooves surrounding them to suppress the entry of electrical interference. Wires between the power supply and the audio amplifier pass through ferrite beads to filter out high-frequency electrical signals.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an acoustic amplifier.  
           [0002]    Conventional acoustic amplifiers generally have a rectangular outer shape with power supply switches and indicators disposed on a front panel and input/output terminals and power supply cables disposed on a rear panel. Heat sinks are formed with a plurality of fins to externally dissipate heat generated by power transistors used for amplification. The heat sinks are disposed inside the amplifier or are disposed on the side panels so that they can be exposed to the outside.  
           [0003]    In amplifiers, one factor in minimizing sound quality degradation is to shorten the signal path between the line-in terminal, which is the input terminal, and the speaker terminal, which is the output terminal. Also, superfluous high-frequency noise and vibration from the power supply must be prevented from influencing other elements by separating the stage for amplifying the audio signal from the power supply stage as much as possible.  
           [0004]    When the amplifier stage and other circuit stages are laid out on a single substrate, there can be crossover between signal lines and power supply lines that negatively affects sound quality. Thus, the amplifier stage must be spatially separated from the other stages.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0005]    It is an object of the invention to provide an amplifier which overcomes the drawbacks of the prior art.  
           [0006]    The amplifier according to the present invention includes: a plurality of substrates disposed roughly parallel to each other in a case; a heat sink formed with a plurality of fins and attached to the case; and an amplifier element attached to the heat sink.  
           [0007]    Briefly stated, the present invention provides a circular audio amplifier which positions the weighty components of its power supply at the bottom, and the audio amplifier portions at the top. Modular finned heat sinks about the audio amplifier portions are resiliently mounted to reduce the transmission of vibration therefrom into the audio amplifier portions. Each module of the heat sink includes copper wires spanning its vertical dimension to short out induced current from top to bottom of the relatively poor electrical conduction of the aluminum of which the heat sinks are made. The audio amplifier portions, except for the final amplifiers, are mounted on independently resiliently mounted parallel substrates. The low-signal substrates are mounted the furthest away from the power supply. All cable entries and exits include grooves surrounding them to suppress the entry of electrical interference. Wires between the power supply and the audio amplifier pass through ferrite beads to filter out high-frequency electrical signals.  
           [0008]    According to an embodiment of the invention, there is provided an acoustic device comprising: a case, a plurality of substrates disposed in the case, and the plurality of substrates being disposed substantially aligned vertically and roughly parallel to each other.  
           [0009]    According to a feature of the invention, there is provided an acoustic device comprising: a housing, a circuit element mounted in the housing, a case on the circuit element, a cover covering a top of the case, an opening disposed on the cover and through which wire passes for connection of the circuit element to other elements in the acoustic device: 8. An acoustic device according to claim  7 , further comprising: an attachment member: the attachment member attaching a bottom of the case to the housing.  
           [0010]    According to a further feature of the invention, there is provided an acoustic device comprising: at least one connecting member disposed at an outer surface of the acoustic device for providing electrical connection with another device: a groove formed to a predetermined depth about a perimeter of the connecting member at the outer surface: a width and depth of the groove being effective for blocking entry of electrical interference into an interior of the acoustic device.  
           [0011]    According to a further feature of the invention, there is provided an acoustic device comprising: a groove formed on the inside of an acoustic device case, at least one wire disposed inside the groove: a cover covering the groove, whereby induction of interference into the at least one wire is prevented.  
           [0012]    According to a still further feature of the invention, there is provided an acoustic device comprising: a hollow pipe disposed inside an acoustic device case: at least one wire disposed in the pipe.  
           [0013]    According to another feature of the invention, there is provided an acoustic device comprising: a heat sink, the heat sink including a base, at least one power amplifier element affixed to the base: a plurality of fins extending roughly radially from the base.  
           [0014]    According to another feature of the invention, there is provided an acoustic device comprising: an electronic part that vibrates when powered is applied thereto, the electronic part being attached to the electronic device via an elastic member to absorb vibration from the electronic part: the elastic member having an elasticity appropriate to a weight of the electronic part.  
           [0015]    According to yet another feature of the invention, there is provided an acoustic device comprising: a power supply, the power supply being substantially circular, a transformer in the power supply, a smoothing capacitor in the power supply, the transformer and the smoothing capacitor are disposed along an outer perimeter of the substantially circular power supply.  
           [0016]    According to a further feature of the invention, there is provided a power supply for an acoustic device comprising: the power supply being substantially circular, positive power supply parts for a positive power supply, negative power supply parts for a negative power supply, a power transformer, the positive power supply parts, the negative power supply parts, and the transformer are disposed symmetrically relative to an imaginary line forming a central axis of the substantially circular power supply.  
           [0017]    The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a perspective drawing of a power amplifier according to an embodiment of the invention.  
         [0019]    [0019]FIG. 2 is a vertical cross-section drawing of a transformer of the power amplifier of FIG. 1.  
         [0020]    [0020]FIG. 3 is a horizontal cross-section drawing of a center sleeve.  
         [0021]    [0021]FIG. 4 is a perspective drawing of a heat sink as seen from the rear.  
         [0022]    [0022]FIG. 5 is an exploded drawing of a heat sink of FIG. 4.  
         [0023]    [0023]FIG. 6 is a perspective drawing with a center sleeve omitted and parts of a power supply and a heat sink cut away.  
         [0024]    [0024]FIG. 7 is a plan drawing of a ferrite bead support plate.  
         [0025]    [0025]FIG. 8 is a cross-section drawing of an AC connector bracket.  
         [0026]    [0026]FIG. 9 is a cross-section drawing of a damper.  
         [0027]    [0027]FIG. 10 is a top-view drawing of a power amplifier.  
         [0028]    [0028]FIG. 11 is a vertical cross-section drawing of a transformer to which reference will be made in describing another attachment method for the transformer.  
         [0029]    [0029]FIG. 12 is a top-view drawing showing the interior of the power supply. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Referring to FIGS. 1 and 10, a monaural audio power amplifier  1  includes a cylindrical power supply  2 . Power supply  2  contains conventional components such as, for example, a power supply switch and power-supply circuit elements such as choke coils, capacitors, and power supply transformers for converting 100-120 V alternating current to 10-90 V direct current. Of the circuit parts in the power amplifier  1 , these parts relating to the power supply are the heaviest. The power supply components of the power amplifier  1  are placed in the lowest possible position to lower the center of gravity. This improves the stability of the power amplifier  1 .  
         [0031]    Referring to FIG. 2, a transformer  51  includes a coil  53  wound a predetermined number of times around a core  52 . The core  52  is sealed in a case  54  by a filler  55 . A cover  57  is attached to the upper part of the case  54 . The cover  57  includes an opening  56  to allow the ends  66  of the coil to extend therethrough. Threaded openings in the case  54  accept screws  58  for attaching the case  54  to a bottom base chassis  50 . Holes in the bottom base chassis  50 , aligned with the threaded openings  54  are unthreaded, and slightly oversized for the screws  58  passing therethrough.  
         [0032]    Disc springs  59 , having a cone-shaped cross-section, are interposed between the bottom base chassis  50  and the heads of the screws  58 . The disc springs  59  provide a relatively light downward holding force on the transformer  51 . This lightly mounts the transformer  51  on the bottom base chassis  50 , which has an adequate strength to support it. The light downward holding force, and the slight oversize of the holes in the bottom base chassis  50 , through which the screws  58  pass, permit vibrations generated when AC power is applied to the transformer  51  to move the transformer  51  slightly on the base chassis  50 . Friction energy between the bottom of the case  54  and the bottom base chassis  50  substantially damps such vibrations to prevent transfer to other parts through the bottom base chassis  50  of the power amplifier  1 .  
         [0033]    The load on the disc springs  59  is set up to be proportional to the weight of the mounted electronic parts. Thus, harder disk springs  59  are selected for heavier parts. This allows vibrations to be converted into friction energy under similar conditions even if the weights of the electronic parts are different.  
         [0034]    Also, since the case  54  filled with filler is attached to the bottom base chassis  50  rather than to the cover  57 , the transformer  51  is attached to the bottom base chassis  50  in a stable manner. Furthermore, since the opening  26  formed on the cover  57  is positioned at the top, there is no need to have the transformer  51  elevated slightly from the bottom chassis  50  to allow wires  66  to be drawn out or to have an opening formed on the bottom chassis  50  to allow wires to be drawn out.  
         [0035]    A center sleeve  3  is positioned above the power supply  2 . The center sleeve is preferably formed from aluminum with a roughly rectangular cross section. Four substrates, to be described later, are disposed in the center sleeve  3 . Four heat sinks  4  is disposed, one on each of the four outer surfaces of the center sleeve  3 . Individual fins  23  of the heat sinks  4  are formed with different lengths to prevent resonance.  
         [0036]    Referring to FIG. 10, the radially outer ends of the plurality of fins  23  of the heat sinks  4  are equidistant about a center O of a top plate  6  of the center sleeve  3  so that the ends of the four heat sinks  4  form a circle. Thus, the heat transferred first to a base  24  of each heat sink  4  is transferred outward on the plurality of fins  23  so that the heat is dissipated. As a result, the heat transfer characteristics do not vary greatly between the centers of the fins  23  and the ends of the fins  23 . This provides efficient thermal dissipation.  
         [0037]    Referring now to FIGS. 4 and 5, two power transistors  38  are mounted on the base  24  of the heat sink  4 . The two power transistors  38  are disposed equidistant from the center of the base and are arranged directly adjacent to each other laterally along the plane of FIG. 4. Thus, the two power transistors  38  are disposed equidistant from the center O of the top plate  6 . As a result, the heat dissipation conditions of the power transistors  38  are roughly identical. This prevents variations in operating characteristics between the two when push-pull operations are being performed.  
         [0038]    In this embodiment, the two power transistors  38  may be operated in a push-pull configuration, four power transistors  38  may be operated in a parallel push-pull configuration, eight power transistors  38  (two each on four heat sinks  4 ) may be operated in a BTL configuration. Thus, the operating characteristics of the power transistors  38  must be made as consistent as possible. The heat dissipation characteristics is made identical by using the same structure for the four heat sinks  4  and by using a layout where the power transistors  38  attached to each heat sink  4  are symmetrical to each other relative to the center line of the heat sink  4 .  
         [0039]    Also, the distances between the power transistors  38  and a power stage substrate  14 , described later, to which the terminals of the power transistors  38  are connected, are kept roughly equal. This prevents discrepancies in operations caused by differences in distance.  
         [0040]    Referring to FIGS. 3, 4 and  5 , openings  33  are formed in the heat sink  4  to allow the heat sink  4  to be attached to the center sleeve  3 . The center sleeve  3  has threaded openings  41  which are aligned with the threaded openings  33 . A coil spring  45  is interposed between a screw  42  and the heat sink  4 . The compressive force of the coil spring  45  urges the heat sink  4  against the center sleeve  3  with a fixed pressure.  
         [0041]    As with the transformer  51  described above, the heat sink  4  is not attached integrally to the center sleeve  3  by the screws  42 . Thus, if the sound pressure from the speaker causes the heat sink  4  to vibrate, the heat sink  4  vibrates relative to the center sleeve  3 . This vibration is absorbed as thermal energy, thus preventing the vibrations from being directly transferred to the sleeve  3 .  
         [0042]    The heat sink  4  is relatively large, with a height of approximately 20 cm and fin lengths of approximately 10 cm. Thus, it acts as a high-frequency antenna which could generate potential differences. If a potential difference is generated, current flows and creates a magnetic field which can influence the circuitry in the power amplifier  1  negatively. To prevent this, three parallel grooves  36  are formed vertically in the rear surface of the heat sink  4 . Mesh wires  37 , formed of copper mesh, with high conductivity are attached in these grooves. The mesh wires  37  are screwed to the upper and lower ends of the heat sink  4 , thus forcibly short-circuiting the upper and lower ends of the heat sink  4  and preventing potential differences from being generated.  
         [0043]    The two power transistors  38  and a thermistor  39 , used to detect temperature, are attached to the back surface of the heat sink  4 . These elements are shielded by a transistor cover plate  48 . The terminals of the power transistors  38  and the temperature-detection thermistor  39  extend through openings  108 ,  110  on the transistor cover plate  48 . These terminals are connected to a substrate, described later, in the center sleeve  3 . An arcuate connecting bar  43  in each heat sink connects the tips of fins  23  together to prevent resonance in the heat sink  4 . Connecting bars  43  are fitted into grooves near the tip of each fin  23 . The connecting bars  43  are affixed using screws  21 .  
         [0044]    Referring again to FIG. 1, pin jack  5 , used as an input terminal, and is disposed on the top plate  6  on the upper surface of the center sleeve  3 . A speaker terminal  7 , used as an output terminal, is disposed on a speaker terminal bracket  8  between the power supply  2  and the heat sink  4 .  
         [0045]    Referring to FIGS. 6 and 9, four shafts  11  are disposed parallel to each other in the center sleeve  3 . Each shaft  11  has four rectangular grooves in its surface. Dampers  12  formed from silicone rubber are fitted into the rectangular grooves in the shafts  11 . A groove at the center of each damper  12  receives the edge of a hole in one of the substrates. The substrates include a pre-amp substrate  13 , a power-stage substrate  14 , a servo stage substrate  15 , and a low-power power supply substrate  16 . These four substrates are supported parallel to each other. It will be noted that there is no rigid connection between the substrates and the shafts. Therefore, the dampers provide resilient support to their respective substrates, thereby reducing the transmission of vibration to the substrates.  
         [0046]    The pre-amp substrate  13  provides preliminary amplification of a signal received from the pin jack  5 . The pre-amp substrate  13  processes the input signal, which is the weakest signal. The pre-amp substrate  13  is positioned at the top, the furthest away from the power supply  2 . This places the pre-amp substrate  13  the furthest away from the transformer  51 , the choke coil  98 , and other vibration and electrical interference generating elements in the power supply  2 .  
         [0047]    After pre-amplification in the pre-amp substrate  13 , the input signal is applied to the power-stage substrate  14 . The heat sink  4  to which the power transistors  38  are attached is attached to the center sleeve  3  by the coil springs  35 , and the leads of the power transistor  38  are connected to the power stage substrate  14  via copper wires (not shown in the figure).  
         [0048]    The amplifier in this embodiment performs class A amplification and controls the bias potential by detecting changes in collector current through temperature changes. The control circuitry used for this is provided in the servo-stage substrate  15  positioned below the power-stage substrate  14 .  
         [0049]    The low-power power supply substrate  16  contains components which rectify and smooth the power supply current received from the power supply  2 . A ferrite beat support plate  17  and dampers  12  support the shafts  11  between the servo-stage substrate  15  and the low-power power supply substrate  16 .  
         [0050]    Referring now to FIG. 7, the ferrite bead support plate  17  is an aluminum plate with a total of six openings  61 . Cylindrical ferrite beads  62 , formed from ferrite, and used for high-frequency noise elimination are fitted in these openings  61  via tube-shaped dampers  63 . All power supply lines from the power supply are passed through central openings  64  of the ferrite beads  62 .  
         [0051]    As is well known, ferrite material is substantially inert at the low frequencies common in power supplies, but tends to block higher frequencies. Thus, high-frequency noise in the feed lines to the substrates  13 - 16  is eliminated by the ferrite beads  62  fixed in the ferrite beads support plate  17  inside the power amplifier  1 . This reduces the transmission of high-frequency interference in the feed lines. In addition, this reduces the effect of unavoidable variations that occur during the assembly of the power amplifier  1 .  
         [0052]    Noise from other stages must be prevented from affecting the output from the power stage substrate  14 . Referring to FIG. 3, wires connecting the power stage substrate  14  and the speaker terminal  7  are disposed in a concave groove  88  formed at a corner of the inner surface of the center sleeve  3 . Then, this concave groove  88  is sealed with an aluminum shield plate  90  to eliminate noise.  
         [0053]    The pre-amp substrate  13  is positioned the furthest from the power supply  2 . As a consequence, the power supply lines supplying power to the pre-amp substrate  13  are easily influenced by the other stages. To reduce noise, the wires supplying power to the pre-amp substrate  13  are passed through the ferrite beads  62  disposed on the ferrite beads support plate  17  and are then fitted into the concave groove  46  formed at the corner opposite from the concave groove  88 . The wires are covered by the aluminum shield plate  90 .  
         [0054]    The wires used to transfer control signals from the servo stage substrate  15  to the pre-amp substrate  13  are fitted into a concave groove  47  adjacent the concave groove  46 . The concave grooves  46 ,  47  are also covered with an aluminum shield plate  92 .  
         [0055]    As described above, the substrates  13 - 16  are separated into individual circuit stages and are arranged parallel to each other in the center sleeve  3 . Thus, sound quality degradation that would occur in a single-substrate design due to cross-over in the power supply lines, the signal lines, and the servo signal lines is avoided.  
         [0056]    Referring to FIG. 12, the transformer  51  is a torroidal transformer used to convert 100-110 V alternating current potential into three different alternating current plus/minus potentials. The transformer  51  is placed on the opposite side of the power supply  2  from an AC connector block  71 . Different AC currents are taken from the transformer  51 , to be rectified by a diode substrate  65 . Diodes  95  on the diode substrate  65  are attached to heat-dissipating heat sinks  94 . The diode substrate  65  is supported via dampers  12  at the center of the power supply  2 .  
         [0057]    The rectified positive power supplies are sent, according to potential, to choke coils  96 ,  98 , and  100  (not shown in the figure since they are below the diode substrate). Similarly, the rectified negative power supplies are sent, according to potential, to choke coils  82 ,  83 , and  84  (not shown in the figure since they are below the diode substrate). Large smoothing capacitors  102 ,  84 , which cannot be mounted on the low-power power supply substrate  16 , are mounted in the power supply  2 .  
         [0058]    An AC line pipe is disposed along an imaginary line extending from the center O of the circular power supply  2  and a center P of the transformer  51 . The choke coils  96 ,  82 , the choke coils  98 ,  83 , and the capacitors  102 ,  84  are laid out symmetrically relative to this imaginary line. Thus, the positive and negative power supplies are placed under the same conditions both electrically and mechanically so that a stable power supply is provided.  
         [0059]    Also, by laying out the transformer  51 , the choke coils  96 ,  82 , the choke coils  98 ,  83 , and the capacitors  102 ,  84  along an outer wall  21  of the circular power supply  2 , a space is provided at the center for the diode substrate  65 .  
         [0060]    Also, by arranging the wires that can be affected by noise in the concave grooves  88 ,  46 ,  47  and sealing the concave grooves  88 ,  46 ,  47  using the shield plates  90 ,  92 , the wires are shielded from noise. Since the wires are fixed in their positions, sound quality variations between individual units caused by variations in wire placement during manufacture is reduced.  
         [0061]    With the widespread use of digital devices such as CD players, high-frequency noise is present around the power amplifier  1 . The existence of such high frequencies may permit the transfer of noise to the surface of the power amplifier  1  by skin effect. High frequency noise transmitted in this way can infiltrate the power amplifier  1  along members such as cables and terminals that pass from the outside of the power amplifier  1  to the inside, thus reducing sound quality.  
         [0062]    Referring now to FIG. 8, to prevent the infiltration of high-frequency noise, a box-shaped AC socket  74  is attached to AC connector block  71 . A power supply plug attached to the end of a power supply cable is connected to the AC socket  74 . A groove  78 , of approximately 1 mm, is formed between the surface of the AC connector block  71  and a lower surface of a top base chassis, and between an upper surface of an opening  73  in an outer wall  72 . High-frequency noise transferred along the surface of the outer wall  72  is prevented by the groove  78  from being transferred to the AC connector block  71 . As a result, high-frequency noise is prevented from infiltrating the power amplifier  1  through the AC socket  74  attached to the AC connector block  71 .  
         [0063]    The AC connector block  71  is attached to a top base chassis  60  in the same manner as the attachment of case  54 , shown in FIG. 2. That is, attachment may using the counterpart of a screw  58  and a disk spring  59  shown in FIG. 2. Thus, if the power supply cable vibrates due to sound pressure from the speaker or the like, the vibrations are transferred to the AC connector block  71  as well. However, the disk spring  59  prevents the vibrations from being transferred into the power amplifier  1 .  
         [0064]    Referring now to FIG. 1, in addition to the power supply cable described above, the cable connections in the power amplifier  1  include the pin jack  5  to which a pin cable is connected and the speaker terminal  7  to which the speaker cable is connected. These can be entry points for high-frequency noise flowing along the outer wall  72  of the power amplifier  1 . Thus, as with the AC connector block  71  above, these connector terminals are attached to blocks formed as members separate from the outer wall  72 . The surfaces of these members are separated by approximately 1 mm from the perimeter of openings formed on the outer wall  72 , thus preventing infiltration of high-frequency noise transferred along the surface of the outer wall  72 . These blocks are attached to the chassis  50  via disk springs so that mechanical vibrations from the pin cable and the speaker cable are prevented from direct transfer into the power amplifier  1 .  
         [0065]    Referring again to FIG. 8, the AC socket  74  is connected to a power supply switch (not shown in the figure) positioned on the opposite side using a wire  77 . The wire  77  is disposed inside an aluminum AC line pipe  76  between the AC connector block  71  and the power supply switch, thus preventing high-frequency noise in the power supply line from radiating into the power supply  2 .  
         [0066]    A cable support  9  (FIG. 10) supports a pin cable (not shown in the figure) connected to the pin jack  5  to hold the pin cable out of into contact with the heat sink  4 .  
         [0067]    In the embodiment described above, the transformer  51  is attached to the bottom base chassis  50  via disk springs  59 . However, the present invention is not restricted to this. Any convenient type of elastic body having a spring constant appropriate for the weight of the electronic parts to be supported may be used. Referring to the embodiment in FIG. 11, for example, conical coil springs  69  are used apply a small downward force on the transformer  51 , as. In this case, the shape of the conical springs  69  permits substantial compression without the coils bumping into each other. Thus, the conical spring  69  may be compressed almost down to its wire diameter without coil-to-coil contact. This permits the use of a conical coil spring  69  which is considerably shorter than would be required if a helical coil spring were used.  
         [0068]    In the present invention as described above, a plurality of circuit substrates are disposed parallel to each other, allowing individual circuit stages to be separated by substrates to provide spatial separation. Substrates processing low-power signals are placed on substrates furthest from the power supply to give minimum influence of magnetic fields and vibration from the power supply on the low-power signals. Extraneous high-frequency electrical noise from the power supply, and mechanical vibration from the power supply and the speaker, are isolated from affecting other elements, thus providing an amplifier with superior sound quality.  
         [0069]    Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.