Headphones, system consisting of headphones and HiFi audio tube amplifier

Abstract

Headphones (700), wherein the headphones (700) comprise: a headband (710) with two forks (711), two ear cup housings (720), each attached to one of the forks (711), two electrostatic transducers, each provided in the ear cup housings (720), and at least one cooling unit (730) on the outside of at least one of the ear cup housings (720) for dissipating heat from the electrostatic transducer located therein, wherein the ear cup housings (720) are each rotatably mounted on one of the forks (711) about a pivot axis (B), wherein the headphones (700) comprise a spring unit (750) in the region of the pivot axis (B) for returning the ear cup housings (720) to a central position, wherein the spring unit (750) comprises a spring wire (752) the ends of which are each attached to a fastening unit (751) on the ear cup housing (720) are attached and is guided through an opening (753a) in a fork axle (753).

Description

[0001] The present invention relates to a HiFi audio tube amplifier.

[0002] Audio amplifiers with tubes are nowadays only used in guitar amplifiers or hi-fi amplifiers. The tubes serve to amplify the audio signals, which are present as electrical signals.

[0003] It is an object of the present invention to provide a HiFi tube amplifier which enables improved amplification of an audio signal.

[0004] This task is solved by a HiFi audio tube amplifier according to claim 1.

[0005] Thus, a hi-fi audio tube amplifier is provided with multiple tubes for amplifying audio signals and multiple housing units, each enclosing one of the tubes. The housing units are cylindrical and each surrounds a single tube. This ensures that the tubes are particularly dustproof.

[0006] The casing unit can have a cylindrical shell made of quartz glass or glass. Optionally, one end of the casing unit is attached to or inside a housing. This can be done, for example, by a screw or bayonet fitting. A seal can optionally be provided at this end of the casing unit.

[0007] According to the invention, the casing unit seals the tube dust-tight. This allows for decoupling of the tubes from ambient noise. In particular, the casing unit keeps airborne noise generated by ambient sounds away from the tubes. This addresses the tubes' susceptibility to microphonics. Microphonic susceptibility means that mechanical vibrations of the tube have an undesirable effect on the tube's electrical output signal.

[0008] According to the invention, a tube amplifier is provided with a plurality of enclosure units, which have a cylindrical shell made of glass or quartz, a lid (e.g. made of metal) at one end and an open end which can be attached in or to a housing of an amplifier, so that the enclosure unit completely surrounds the tube and decouples it from external noise.

[0009] Optionally, the lid can be made of metal to dissipate the heat from the tube. This occurs through convection. Alternatively, the lid can be made of brass.

[0010] The HiFi audio tube amplifier according to the invention provides high-quality quartz tubes which surround the (vacuum) tubes and thus eliminate any sound influence that is transmitted via the air.

[0011] The tube amplifier according to the invention has 99.9% silver-plated copper cables, which ensure optimal conductivity in order to transmit the signal, for example, to headphones.

[0012] The headphones, which can optionally be connected to the tube amplifier, feature an amplifier stage within the headphones to provide ultra-high impulse fidelity and 200% greater efficiency compared to other headphones currently available for sound reproduction.

[0013] Further embodiments of the invention are the subject of the dependent claims.

[0014] The advantages and embodiments of the invention are explained in more detail below with reference to the drawing.

[0015] Fig. 1 to Fig. Figure 3 shows a view of a HiFi audio tube amplifier according to a first embodiment.

[0016] Fig. 4 and Fig. Figures 5 each show a perspective view of a HiFi audio tube amplifier according to a second embodiment,

[0017] Fig. Figure 6 shows another view of the HiFi audio tube amplifier according to the first embodiment,

[0018] Fig. 7 and Fig. Figures 8 each show a perspective view of a HiFi audio tube amplifier according to a second embodiment,

[0019] Fig. Figure 9 shows a schematic representation of a HiFi audio tube amplifier according to the invention,

[0020] Fig. Figure 10 shows a schematic representation of a HiFi audio tube amplifier according to the invention,

[0021] Fig. Figure 11 shows an exploded view of a tube and a casing unit according to the invention,

[0022] Fig. 12A to Fig. Figures 12F each show different views of a headphone according to the invention,

[0023] Fig. Figure 13A shows a schematic representation of the receiver of Fig. 12A to Fig. 12F,

[0024] Fig. Figure 13B shows a detailed view of the suspension of the fork on the headband, and

[0025] Fig. Figure 13C shows a schematic representation of part of the auricle.

[0026] Fig. Figure 1 shows a schematic front view of a hi-fi audio tube amplifier according to a first embodiment.

[0027] Fig. Figure 2 shows a top view of the HiFi audio tube amplifier according to the first embodiment.

[0028] Fig. Figure 3 shows a rear view of the HiFi audio tube amplifier according to the first embodiment.

[0029] The HiFi audio tube amplifier according to the first embodiment has a housing 500 with multiple controls 610 – 640 , a tube housing section 300as well as a storage box 400 for a headphone. The casing 500 has a base 530 for the tube housing section 300 as well as a second base 540 for the storage box 400 on.

[0030] The tube housing section 300 exhibits a plurality of envelope units 200 for holding (vacuum) tubes 100 on. These casing units 200 and the (vacuum) tubes 100 are retractable into the tube receiving unit 300 planned.

[0031] There is a flap on the back of the HiFi audio tube amplifier. 510 designed to have a magnet 511 can be kept behind the flap. 510 Technical markings can be hidden. There are also several connections on the back. 520 planned.

[0032] The storage box 400a case 420 as well as a lid 410 on.

[0033] Fig. Figure 4 shows a perspective view of the HiFi audio tube amplifier according to the first embodiment.

[0034] Fig. Figure 5 shows a perspective view of the HiFi audio tube amplifier from Fig. 4, where the envelope units 200 with the tubes contained therein 100 are extended. The shell units 200 with the tubes contained therein 100 are used for cooling from the housing section 300 booted up.

[0035] Fig. Figure 6 shows a perspective view of the HiFi audio tube amplifier according to the first embodiment. Fig. 6 is in particular an operating position of the HiFi audio tube amplifier. 1000 shown. For example, by operating the control unit 610 can the tube amplifier 1000be switched on. When the tube amplifier is switched on, the controls move. 610 – 640 out. Furthermore, the cladding elements extend 200 with the tubes contained therein 100 from the housing section 300 out. Furthermore, the lid 420 opened the storage box.

[0036] Inside the storage box is an inlay. 430 for holding a headphone 700 intended. For example, when the amplifier is switched on by the control element. 610 The inlay is moved from a rest position to an operating position. During this process, the inlay can 430 Especially when tilted upwards, this is particularly advantageous because it makes it easier to remove headphones from the storage box in the operating position when they are in the inlay. 400 can be removed. In the storage box. 400 It can also include a connection socket unit 440with a connection socket 441 The connection socket is provided. 441 It serves to hold the plug of a headphone, which is inserted into the inlay. 430 can be placed.

[0037] According to the invention, the bushing unit 440 Do not proceed during operation or when switching on.

[0038] Fig. Figure 7 shows a schematic representation of the HiFi audio tube amplifier according to the first embodiment. Fig. 7 is the lid 410 opened up and the inlay 430 has been moved into the operating position. In the inlay 430 is a headphone 700 with a headband 710 and two earlobes 720 placed. By raising the inlay 430 The headphones located therein are moved into the operating position. 700 Move upwards so that part of the headphones protrudes over the edge of the storage box. 400protrudes. This makes it easier to remove the headphones from the storage box. 400 can be taken.

[0039] Fig. Figure 8 shows a perspective view of a HiFi audio tube amplifier according to the first embodiment. Fig. 8 is the lid 410 not shown and the inlay 430 is in the resting position. A headphone is located in the inlay. 700 It will then be completely contained within the storage box.

[0040] The HiFi audio tube amplifier according to the first embodiment thus has a storage box integrated into the housing. 400 for a headphone 700 up. In the storage box 400 is an inlay 430 for holding a headphone 700 provided. The inlay 430 It can move between a rest position and an operating position. In the rest position of the inlay 430 is a listener700 completely in the storage box 400 recorded. In the operating position, the inlay 430 raised or tilted upwards, so that a receiver 700 It can be removed more easily because the earpiece is in the operating position of the inlay. 430 protrudes above the top edge of the storage box.

[0041] The headphones have a cable that plugs into the jack. 441 is plugged in. Since the socket 441 inside the storage box 400 As intended, the handset and cable can remain completely inside the storage box, thus remaining protected. The cable can transmit both the audio signal and a power supply.

[0042] The lid 410The storage box can have a tinted glass lid with UV protection, so that the receiver is safe but protected against aging, for example from sunlight, in the storage box. 400 can be stored.

[0043] When the HiFi audio tube amplifier is switched on according to the first embodiment, operating elements 610 – 640 driven out, the shell elements 210 the tubes are made from the housing element 300 driven out and the lid 410 the storage box 400 It is folded up. At the same time, the inlay 430 move into the operating position.

[0044] According to the invention, the cladding elements 200 the (vacuum) tubes 100 The covers extend when the device is switched on to ensure better cooling performance, and retract back into the housing element when the device is switched off. 300retracted, which serves to better protect the casing elements.

[0045] According to one aspect of the present invention, the elements located in the cladding elements 200 located (vacuum) tubes 100 when the device is switched on (by pressing the control element) 610 ) and are already heated when the casing elements are raised. The tubes are also heated when the controls are extended, when the tubes are extended, and when the lid is opened and the inlay is extended. 430 heated up. If the inlay 430 Once the unit has been moved into the operating position, the (vacuum) tubes are heated up accordingly and the tube amplifier is fully operational.

[0046] The tube amplifier according to the invention is activated by pressing the control element. 610 switched on. After switching on the tube amplifier, the controls are optionally activated first. 610 – 640 from the case500 pulled out. Then the shell elements are 200 with the tubes contained within it from the housing element 300 extended. When the envelope elements 200 Once the (vacuum) tubes are extended, then the lid 410 opened and the inlay 430 It is moved from the rest position to the operating position, allowing easy removal of headphones located in the inlay. During the power-on process, the (vacuum) tubes heat up and, after the inlay is moved, are ready for use. 430 Once moved into the operating position, it is fully heated up.

[0047] The case 500 can be made from a natural stone such as a block of marble.

[0048] The tube amplifier according to the invention has 8 tubes.

[0049] According to the invention, the housing 500Spring-mounted to reduce the microphonic sensitivity of the (vacuum) tubes. This allows for vibration decoupling.

[0050] According to one aspect of the present invention, the control element can 610 It may be designed as a volume knob. When this control is pressed... 610 The amplifier is switched on. Alternatively, this can be done via a remote control. First, the four control elements are activated. 610 – 640 Extended. This can take, for example, 6 seconds. Extending the tubes takes approximately 7 seconds, meaning the tubes are fully extended approximately 13 seconds after the control is activated. 610 Extended. Opening the lid takes approximately 12 seconds, meaning the lid is fully open approximately 25 seconds after the control is activated. 610 Extended. The inlay lifts simultaneously with the opening of the lid. The other controls can then be accessed. 620 – 640The tubes are automatically rotated into a desired position. This may take, for example, 4 seconds. The entire switch-on process may therefore take approximately 29 seconds, meaning the device is ready for operation 29 seconds after being switched on. However, precise adherence to these time intervals is not required; a deviation of + / - 50% is permissible for each interval. According to the invention, the entire switch-on time of, for example, 29 seconds is used to heat up the tubes so that they are in an operating state after the switch-on process.

[0051] According to one aspect of the present invention, the control element 610 as a volume and power button and the controls 620 – 640 It is designed as an input select button, a cross-feed button, and an output button. This makes the control element... 620It features an input select knob and can, for example, have 5 positions: "Balanced analog input", "Unbalanced analog input", "USB input (digital)", "Coaxial input (digital)" and "Optical input (digital)". The control element 630 (The second knob) has three positions: "off," "low," and "high." "Cross Feed" means that the two signals (e.g., stereo L and R) are each mixed into the signal for the other ear at a reduced volume. This creates the listening experience of listening to a stereo signal through loudspeakers.

[0052] The control element 640This then represents the control element for the "Output" and can have 3 positions: "Headphones (standard operation)", "Mute (suppress output)" and "Line (Only the amplifier is used and its signal is output via a jack located on the back of the housing. This can be fed to a speaker system, for example. The headphones are then not used.)".

[0053] To turn off the amplifier, the user can press the control element while it is running. 610 Press the volume knob or the remote control. All components (controls, tubes, inlay, and cover) will then return to their resting positions. The controls can be reset to a default setting, so they are always in the same position when the unit is switched off. The amplifier may have a memory function. This saves the last selected operating state for the four controls. 610 – 640The settings are saved, and after switching the device on again, all 4 controls are returned to the last selected position.

[0054] According to one aspect of the present invention, the operating elements 620 – 640The smaller rotary knobs each have detents for the described functions. When these knobs are operated directly, the detents should be tactilely perceptible. Therefore, a mechanism with a spring is provided that presses a spherical surface into designated recesses at the detents. If, instead, a different position is selected via the remote control, the control element can be moved to a new operating position without an audible click. In addition to a motor for rotating the respective control element, the spring is therefore equipped with an electrical return mechanism. This pulls the spherical surface out of the recess, then the motor rotates the control element to a new position, and then the return mechanism is deactivated, so that the spring then presses the spherical surface into the recess corresponding to the new position.

[0055] Fig. Figure 9 shows a schematic representation of a HiFi audio tube amplifier according to the invention. The tube amplifier has a housing. 500 , a floor area 550 with feet 551 , with at least two springs 560 on, which the case 500 wear. Thus, the case 500 Spring-mounted. The springs support the heavy casing. 500 (e.g., primarily made of marble). A bump against a table or surface then results in a brief deflection of the springs. However, the housing will hardly change its position under its large mass, so vibrations of the surface result in a much smaller deflection of the housing. The housing features a tubular housing section. 300 with a plurality of tubes (these tubes are prone to microphonics). By using the springs 560This provides additional vibration protection, which can ensure a reduction in interference with the output signal.

[0056] Fig. Figure 10 shows a schematic representation of a HiFi audio tube amplifier. 10 according to the invention. The HiFi tube amplifier 10 a case 300 with a plurality of (vacuum) tubes 100 to amplify the audio signal. To each vacuum tube 100 is a unit of envelope 200 provided for. The shell unit 200 has a cylindrical shell 240 made of glass or quartz, a lid 210 e.g. made of metal and with a fastening unit at its open end 220 for attaching the shell unit 200 on a case 300 of the amplifier. The mounting unit 220 It can be a screw cap or a bayonet fitting. A seal is optional. 230in the area of ​​the fastening unit 220 be provided for.

[0057] This means the vacuum tube 100 completely on three sides of the shell unit 200 surrounded. If the enclosing unit 200 using the fastening unit 220 If it is attached inside or to the housing, then the tube 100 Dustproof within the enclosure unit 200 sealed.

[0058] Fig. Figure 11 shows an exploded view of a tube and a casing unit according to the invention. The tube 100 has a tube base 110 on and is mounted on a circuit board inside the housing 300 attached to the audio amplifier. Above the tube 100 becomes a shell unit 200 placed. The shell unit 200 has a cylindrical shell 240 made of quartz or glass and a lid 110 for example, made of metal. Furthermore, the casing unit has 200a fastening unit 220 on, which is in a bayonet unit 310 can be attached to the housing.

[0059] The invention relates to an audio amplifier, in particular a headphone amplifier, with a plurality of tubes as part of the amplifier circuit. By means of the housing unit 200 The tubes can be shielded from ambient noise to reduce interference from microphonics.

[0060] Optionally, the lid can be 210 on the coat 240 to be glued together.

[0061] The lid 210 It serves as a cooling unit to dissipate heat generated by the operation of the tube within the casing unit. 200 arises, to derive.

[0062] The casing unit significantly reduces the mechanical vibrations of the tube caused by ambient noise.

[0063] Fig. 12A to Fig. Figures 12F each show different views of a headphone according to the invention. The headphone 700 For example, it can be used together with the HiFi audio tube amplifier after one of the Fig. 1 to Fig. 11 can be used. In particular, the headphones can be used. 700 in the inlay 430 be placed. The headphones 700 features a headband 710 with two forks 711 at its ends, which are used to hold the ear cups 720 It serves a purpose. A cooling unit is integrated into the ear cup housings. 730 for example in the form of cooling fins 731 intended. The material from which the ear cup housings are made. 720 The material used is aluminum. Preferably, the ear cup housing, including the cooling fins, is made from a single piece of aluminum.

[0064] For example, in Fig. At 12C, the cooling unit extends 730 with the cooling fins 731essentially on one side of the ear 720 .

[0065] As in Fig. 12E shows the ear cup housing 720 on one side 721 narrower than on the opposite side 722 , on which the cooling unit 730 with the cooling fins 731 is provided for. Thus, it is also possible for something to be located inside the ear cup housing. 720 The transducer can be positioned at an angle. This is advantageous, for example, because the angled transducer is then parallel to the auricle.

[0066] The earpiece housing can contain an electrostatic push-pull converter with an integrated amplifier. The cooling unit 730 Its purpose is to dissipate the waste heat generated at the receiver to the outside.

[0067] The electrostatic push-pull transducer can comprise a diaphragm electrically charged by an applied polarization voltage, two counter electrodes subjected to highly amplified signal voltages, between which the diaphragm is mounted to vibrate. The counter electrodes are subjected to highly amplified signal voltages. Furthermore, a high-voltage amplifier, powered by a mains supply, can be provided for the highly amplified signal voltages acting at the two counter electrodes. The high-voltage amplifier can be integrated into the headphones. The counter electrodes can be made of ceramic to reduce resonances or natural vibrations, thus minimizing distortion.

[0068] The sound transducer according to the invention can, for example, correspond to a sound transducer described in DE 43 29 991 64.

[0069] The cooling unit 730The power to be dissipated per earpiece is less than 1 watt, for example 0.4 watts. The heat sinks provided for this purpose 731 Although they are oversized for such a low power output, this prevents the earlobe or cooling unit from heating up to such an extent that the heating is not noticeable.

[0070] According to the invention, the sound transducers are located in the ear cup housing. 720 They are arranged in such a way that they are approximately parallel to the ear of a listener when the headphones are placed on the listener's ears. This results in a wider area behind the ears. 722 than in front of the ears 721 (when the user is wearing the headphones). The cooling unit 730 particularly in the broader area 722 planned.

[0071] Fig. Figure 13A shows a schematic representation of the receiver of Fig. 12A to Fig. 12F. The auricle 720It can rotate around axes A and B. Around axis A, the auricle, together with the fork, can move 711 They can be swivelled. The ear cup is located at the ends of the fork. 711 Rotatably mounted around axis B.

[0072] Fig. Figure 13B shows a detailed view of a suspension. 740 the fork 711 on the headband 710 For this, a spring is used. 741 designed, the ends of which are inserted into holes in a plastic part 743 are placed. The spring wire 741 will be between four domes 742 clamped. If a torque acts between the ends of the headband and the forks, the spring will be clamped. 741When the spring is tensioned, the headphones are placed on the head and adapt to the head shape. However, if no external torque acts between the headband and the ear cup, the spring relaxes and pulls the ear cup back to a neutral position. According to the invention, it is thus provided that the ear cups 720 The earcups are in a neutral position when not in use. Furthermore, rattling noises from the earcups at the rotational limits are prevented. The rotational or pivoting movement of the earcup around axes A and B is limited to + / - 10° to + / - 20°. The return of the earcup to the neutral position is controlled by a spring. 741 realized.

[0073] Fig. Figure 13C shows a schematic representation of part of the auricle. 720 and the fork 711 , wherein the auricle is pivotable about axis B. In Fig.Figure 13C shows an enlarged section, in particular the spring unit. 750 The spring unit is shown. 750 features a spring wire 752 , a fork axle 753 and two mounting options 751 in the shell. in the fork axle 753 is a hole 753a provided through which the spring wire 752 can be guided so that the ends of the spring wire 752 in the fastening units 751 can be attached to the ear. The spring wire 752 is specifically designed as a straight spring rod that passes through the fork axle 753 is pushed. When the shell rotates from its central position, the spring 752 However, if no external force acts on the shell, the spring remains tense. 752 the auricle 720 back to a middle position. QUOTES INCLUDED IN THE DESCRIPTION

[0074] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0075] DE 432999164

[0068]

Claims

[1] HiFi audio tube amplifier ( 1000 ), with a case ( 500 ), a tube housing section ( 300 ) and one attached to the casing ( 500 ) integrated storage box ( 400 ) for a headphone ( 700 ), where the tube casing section ( 300 ) a plurality of tubes ( 100 ) exhibits. [2] HiFi audio tube amplifiers ( 1000 ) according to claim 1, wherein the storage box ( 400 ) a lid ( 410 ) and a retractable inlay ( 430 ) to hold the headphones ( 700 ) exhibits. [3] HiFi audio tube amplifiers ( 1000 ) according to claim 2, furthermore with at least one control element ( 610 until 640 ) to turn the amplifier on and off ( 1000 ), when the amplifier is switched on ( 1000 ) the at least one control element ( 610 – 640 ) from the housing (500 ) exits, which contains at least one tube ( 100 ) from the tube housing section, the lid ( 410 ) is opened and the inlay ( 430 ) is being restarted. [4] HiFi audio tube amplifiers ( 1000 ) according to claim 3, wherein the at least one control element ( 610 – 640 ) from the housing ( 500 ) exits, then at least one tube ( 100 ) emerges from the tube housing section, and inlay ( 430 ) raised when the lid ( 410 ) is opened. [5] HiFi audio tube amplifiers ( 1000 ) according to one of claims 2 or 3, wherein the lid ( 410 ) is transparent and has US protection. [6] HiFi audio tube amplifiers ( 1000 ) according to one of claims 2 to 4, wherein the storage box ( 400 ) inside it a connection socket unit ( 440 ) to accommodate a headphone plug (700 ) has, wherein the connector unit ( 440 ) is not movable. [7] HiFi audio tube amplifiers, in particular HiFi headphone tube amplifiers, in particular according to one of claims 1 to 6, comprising a plurality of tubes ( 100 ) for amplifying audio signals, and a plurality of envelope units ( 200 ), which the tubes ( 100 ) surrounded on three sides. [8] HiFi tube amplifier according to claim 7, wherein the envelope units ( 200 ) a cylindrical shell ( 240 ) made of glass or quartz, a lid ( 210 ), especially made of metal, and a fastening unit ( 220 ) for attaching the casing unit ( 200 ) in or on a housing ( 300 ) of the HiFi tube amplifier ( 10 exhibit. [9] HiFi tube amplifier according to claim 7 or 8, further comprising a sealing ring ( 230) in the area of ​​the fastening unit ( 220 ) the envelope unit ( 200 ). [10] Enclosure unit for a HiFi audio tube amplifier, in particular according to one of claims 7 to 9, comprising a cylindrical shell ( 240 ) made of quartz, a lid ( 210 ) made of metal and a fastening unit ( 220 ) for attaching the casing unit ( 100 ) in or on a housing ( 300 ) a HiFi tube amplifier ( 10 ). [11] Headphones for a HiFi audio tube amplifier according to one of claims 1 to 10, with a headband ( 710 ) with two forks ( 711 ), two ear cup housings ( 720 ), each attached to one of the forks ( 711 ) are attached, two electrostatic transducers, each located in the ear cup housings ( 720 ) are planned, and at least one cooling unit ( 730) on the outside of at least one of the ear cup housings ( 720 ) for dissipating waste heat from the electrostatic converter. [12] Headphones for a HiFi audio tube amplifier according to one of claims 1 to 10, with a headband ( 710 ) with two forks ( 711 ), two ear cup housings ( 720 ), each attached to one of the forks ( 711 ) are attached, where the forks ( 711 ) around a first axis of rotation (A) at the ends of the headband ( 710 ) are rotatably mounted, and a first spring unit ( 740 ) to guide the auricular housings back ( 720 ) into a middle position, where the first spring unit ( 740 ) a spring wire ( 741 ), the ends of which are attached to retaining elements ( 743 ) on the fork ( 710 ) are held, and four domes ( 742 ) exhibits, each of which is a part of the spring wire ( 741 ) to clamp. [13] Headphones for a HiFi audio tube amplifier according to one of claims 1 to 10, with a headband ( 710 ) with two forks ( 711 ), two ear cup housings ( 720 ), each attached to one of the forks ( 711 ) are attached and are rotatably mounted about a second axis of rotation (B), and a second spring unit ( 750 ) in the area of ​​the second axis of rotation (B) for returning the auricular housings ( 720 ) into a middle position, where the second spring unit ( 750 ) a spring wire ( 752 ) has its ends each attached to a fastening unit ( 751 ) on the ear cup housing ( 720 ) are attached and through an opening ( 753a ) in a fork axle unit ( 753 ) is led.

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