US3683128A - Flux-bridging stereophonic pickup - Google Patents

Flux-bridging stereophonic pickup Download PDF

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Publication number
US3683128A
US3683128A US50624A US3683128DA US3683128A US 3683128 A US3683128 A US 3683128A US 50624 A US50624 A US 50624A US 3683128D A US3683128D A US 3683128DA US 3683128 A US3683128 A US 3683128A
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flux
operating
stylus
gaps
operating gaps
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Joseph F Grado
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R11/00—Transducers of moving-armature or moving-core type
    • H04R11/08—Gramophone pick-ups using a stylus; Recorders using a stylus
    • H04R11/12—Gramophone pick-ups using a stylus; Recorders using a stylus signals being recorded or played back by vibration of a stylus in two orthogonal directions simultaneously

Definitions

  • ABSTRACT A phonograph pickup for the reproduction of stereophonic and/0r monaural sound recordings in which signals are induced without substantially disrupting the flux path of the several operating gaps and wherein a flux-bridging member is operatively connected to the moving stylus of the pickup and disposed in proximity to the first and second operating gaps, but out of a direct flux path between such gaps, to effectively shorten the fixed gap length of one of the operating gaps and to correspondingly effectively lengthen the gap length of the otherof the operating gaps and to induce corresponding signals in the pickup related to such stylus motion.
  • the present invention relates generally to phonograph pickups, and, in particular, to an improved phonograph pickup or electromagnetic cartridge for the reproduction of stereophonic and/or monaural sound recordings.
  • Cartridges of conventional structure usually include a cartridge housing on which is mounted a stylus-annature assembly whichincludes a cantilever-supported stylus lever having the requisite compliance such that the stylus thereof may track the usual 45-45 groove of a stereophonic recording disc.
  • An appropriate magnetic structure is provided including first and second pairs of coils, with each coil pair being connected in series. The pairs of coils have signals induced therein which are related to the two modulations derived by the stylus from the stereophonic record groove. Signals or voltages are usually induced in the coils through the provision of a moving iron mass or armature which is disposed within a magnetic gap defined by the permanent magnetic and pole pieces of the magnetic structure.
  • each channel includes two pole pieces carrying respective coils connected in series.
  • a magnetic armature is arranged relative to the faces of the pole pieces to be symmetrically disposed relative thereto and is in a magnetic circuit, the armature either being disposed in an independently completed gap having opposed polarities or itself serving as the opposite pole of the gap relative to the pole pieces.
  • the flux path assumes various directions which introduces the possibility of magnetic distortion (i.e., magnetic hysteresis).
  • the problems of magnetic distortion become more pronounced and more significant at the higher end of the frequency spectrum and may result in substantially total signal distortion.
  • the mechanical motion occurs at a slower rate and the corresponding magnetic distortion is easily accommodated in the magnetic circuit.
  • the flux changes in the magnetic circuit are not easily accommodated and therefore become distorted. This situation becomes even more extreme on a ratio basis as frequencies increase.
  • stereophonic reproduction where the separation signal is as much as 30 decibels below the primary signal, magnetic distortion can lead to a virtually distorted residual signal.
  • an electromagnetic cartridge having a moving stylus and a magnetic structure including pole pieces terminating in opposed faces defining first and second operating gaps, with the respective pairs of opposed faces being of opposite polarity.
  • First and second coils are mounted on said first and second pole pieces and connected in series.
  • a flux-bridging means is operatively connected to the moving stylus and disposed in proximity to said first and second operating gaps, but normally out of a direct flux path between the opposite polarity opposed faces of each of said operating gaps.
  • the flux-bridging means moves in response to stylus motion to effectively shorten the fixed gap length of one of the operating gaps and to correspondingly effectively lengthen the gap length of the other operating gap and to induce corresponding signals related to stylus motion.
  • the fluxbridging means is disposed outside of the profile of the pole pieces defining the two pairs of operating gaps.
  • the stylus will produce corresponding motions of the flux-bridging means which motions from the standpoints of the respective pairs of operating gaps will be independent of each other, that is, the flux-bridging means inherently produces a vector resolution of the stylus motion such that one pair of operating gaps will be related to one stereophonic channel and the other pair of operating gaps will be related to the other stereophonic channel.
  • the flux-bridging means will move toward one of the pole pieces, thereby introducing additional magnetic material along the flux path of the corresponding operating gap, effectively shortening that first gap by increasing the flux density in the first gap and inducing a corresponding voltage in the coil for that first gap and pole piece.
  • the movement of the flux-bridging means effectively lengthens the second gap of the gap pair by decreasing the flux density in the second gap by an amount substantially equal to the increase of flux density in the first gap.
  • the flux-bridging means move substantially perpendicular to all flux paths.
  • the flux-bridging means can operate either in the fringe gap of the gap pair or it can be moved further into the gaps of the gap pair.
  • the distortion increases as the flux-bridging means goes further into the gaps.
  • the amplitude of the resonant peak due to tip mass is controlled completely by the elastomeric damping material and the consistency of such damping material is a large factor in total quality control.
  • this parameter is far less important and the present design enables the tip mass to be removed to 70,000 cycles and response to 20,000 cycles to be essentially flat. If conventional elastomeric damping and conventional cartridge design were used to reduce the resonant peak at 70,000 cycles, non-linearity in the mid-frequency (l-lO kc) would occur. However, by removing the criticality of the elastomeric damping factor, a flat frequency response was achieved to 20,000 cycles.
  • the flux bridger motion operates essentially at right angles to the flux direction, the flux now creates a magnetomotive force in controlling the position of the flux bridger.
  • the result is a magnetic damping action on the flux bridge which is highly controllable and naturally constant in stability.
  • the amount of magnetomotive force applied to the flux bridger which is controllable in the first instance by the current through the coils and/or the permeability of the flux bridger will determine the frequency at which roll-off will begin to occur and the rate of roll-off thereafter.
  • FIG. 1 is a longitudinal elevational view of a typical stereophonic cartridge or pickup embodying features of the present invention, shown removed from the normal cartridge housing that would be associated therewith;
  • FIG. 2 is a front elevational view, taken from the left in FIG. 1;
  • FIG. 3 is a sectional view taken at substantially 45 to the horizontal and along the lines 33 of FIG. 2 and looking in the direction of the arrows, with parts broken away and sectioned and on an enlarged scale;
  • FIg. 4 is a sectional view taken substantially along the line 4-4 of FIG. 1 and looking in the direction of the arrows;
  • FIG. 5 is a diagrammatic and schematic showing of the operating gaps of the pickup intended to aid in an understanding of the function of the flux-bridging member
  • FIG. 6 is a view similar to FIG. 5, but showing the flux-bridging member in a typical pickup position during operation;
  • FIG. 7 is a view similar to FIG. 3, but of a modified stereophonic cartridge or pickup embodying further features of the present invention.
  • FIG. 8 is a sectional view similar to FIG. 3, but of a still further modified stereophonic cartridge or pickup embodying still further features of the present invention.
  • FIG. 9 is a sectional view taken substantially along the line 9-9 of FIG. 8, but turned to an erected position as compared to FIG. 8.
  • an improved electromagnetic cartridge or pickup for stereophonic reproduction generally designated by the reference numeral 10, which may be removably mounted within an appropriate housing which in turn is mounted on the tone arm of a turntable or record player, as is generally understood.
  • Cartridge 10 includes a balanced magnetic structure 12 which includes four pole pieces 14, 16 and 18, 20 terminating in pole piece faces 14a, 16a and 18a, 20a.
  • Pole pieces 14, 16 provide a first diametrically opposed pair having their longitudinal center lines in a substantially common plane at 45 to the horizontal (see 45 section of FIG. 3); and pole pieces 18, 20 provide a second diametrically opposed pair in which the pole pieces have their longitudinal center lines in a substantially common plane at 45 to the horizontal and at right angles to the first pair.
  • a first pair of coils 22, 24 is mounted on the first pair of pole pieces 14, 16 and connected in voltage adding and hum cancelling relation to each other; and a similar second pair of coils 26, 28 is mounted on the second pair of pole pieces 18, 20 and connected in voltage adding and hum cancelling relation to each other.
  • each of the coils 22, 24 and 26, 28 includes a coil bobbin, such as 22a, which is fabricated of a non-ferrous material and a coil proper, such as 22b.
  • Opposed pairs of coils are of substantially identical configuration to avoid introducing any electrical imbalance in the coil arrangements and symmetry.
  • the plural pole pieces 14, 16 and 18, 20 are part of the balance magnetic structure 12 which also includes a rear magnetic plate 30 serving as a pole piece support (see FIGS. 1 and 3), a front magnetic plate 32 disposed in spaced parallel relation to the rear magnetic plate 30 and a permanent magnet 34 interconnected therebetween.
  • the rearward face 32a of the front magnetic plate 32 is in spaced parallel relation to the forward faces 14a, 16a and 18a, 20a of the respective pole pieces which pole piece faces are in coplanar relation and respectively cooperate with face 32a to define four operating gaps symmetrically disposed about the longitudinal center line of the pickup, with the gaps for pole faces 14a, 16a being respectively designated at G and G Similar third and fourth operating gaps are formed by pole piece faces 18a, 20a and the corresponding confronting portions of face 32a. As seen in FIGS.
  • the profiles of the respective pole pieces 14, 16 and 18, 20 and the corresponding confronting portions of front magnetic plate 32 substantially define the radial extent of the respective operating gaps which are somewhat larger than the physical size of the pole piece faces due to fringing of the magnetic fields across the respective gaps, as is generally understood.
  • the support 40 may be fabricated of a single molded plastic piece and includes a base 40a coextensive with the rear magnetic plate 30 through which the pole pieces pass, an axially extending post 40b extending between the pole pieces and an axially extending post extension 40c of smaller diameter than the post and projecting beyond the pole pieces.
  • the leading end of post extension 40c terminates in a conical tip 40d which in turn carries an axially extending flexible pin 42 providing a fulcrum for stylus lever 44.
  • Stylus lever 44 projects through central cutout 32b in the front magnetic plate 32 and at its forward end car- I ries the usual tip or stylus 46, At its rearward end, stylus lever 44 is formed with a substantially conical mounting section 44a into which post extension 40c and pin Operatively connected to the stylus lever 44 is a fluxbridging member 46 which is disposed in proximity to the four operating gaps of the pickup but out of a direct flux path between the opposite polarity faces of each of the operating gaps (see for example, FIGS. 5 and 6 with respect to gaps G G G The flux-bridging member 46 moves in response to stylus motion to effectively shorten the fixed gap effect on the companion operating gap.
  • each gap includes an individual magnetic gap-bridging bar mounted on a common non-magnetic support.
  • each bridging bar for each gap would constitute an individual magnetomotive unit relative to the pickup.
  • the action of such a segmented fluxbridging member will be essentially the same as that of the illustrative embodiment except possibly for better isolation of respective flux paths and correspondingly reduced interaction between channels.
  • the flux-bridging member 46 is in the configuration of a frustum of a cone and includes outer conical surface 46a and inner cylindrical surface 46b and is dimensioned and arranged to be outside of the profile of the four operating gaps. Flux-bridging member is mounted on the conical mounting section 440 of stylus lever 44 at flat 44b which provides an annular mounting surface dimensioned to receive the inner cylindrical surface 46b of the flux-bridging member. This attachment may be accomplished in any convenient fashion, as for example, by the use of an interposed adhesive. As seen best in FIGS. 5 and 6, the larger diameter end 460 of the flux-bridging member 46 is closest to the center of motion or pivot P for the stylus while the smaller diameter end is removed therefrom. Interposed between the flux-bridging member 46 and the small diameter post extension 40c is an elastomeric member 48 which serves to center the stylus-bridger assembly 38 in accordance with the principles which are well understood.
  • the smaller diameter end of the flux-bridging member will move toward one of the pole pieces (i.e., pole piece 14 in FIG. 6) thereby introducing additional magnetic material along the flux path of the corresponding operating gap (i.e., gap G and effectively shortening that gap by increasing the flux density thereof and inducing a corresponding voltage in its coil (i.e., coil 22).
  • the companion operating gap i.e., G and pole piece which is connected in series is effectively lengthened by decreasing the flux density in the gap by an amount substantially equal to the increase of the flux density in gap 6,.
  • the flux-bridging member moves substantially perpendicular to all flux paths.
  • the flux-bridging member further advantageously operates in the fringe of the flux paths of gaps G and G (and gaps G and G for purposes of distortion, since the distortion increases as the flux-bridging member goes further into the gaps. However, it is to be noted that the fluxbridging member may go further into the gaps, if so desired.
  • FIG. 7 there is shown a further embodiment of an electromagnetic cartridge or pickup in accordance with the present invention, generally designated by the reference numeral 110.
  • the cartridge 110 is identical in construction to the embodiment illustrated in FIGS. 1-6, inclusive, it is numbered as part of a 100 series and the description thereof will be directed to the constructional differences between the principal embodiment and this modification.
  • the stylus lever 144 Rather than mount the stylus lever 144 at a pivot which is forwardly of the fluxbridging member 146, in this embodiment, the pole pieces 114, 116 and 118, 120 extend forwardly of the axially extending post 14% of the bridger support 140 and pivot pin 142 is disposed rearwardly of the fluxbridging member 146.
  • post 1401) terminates in a flange 1400 and similarly the cylindrical mounting section 1440 of the stylus lever 144 terminates in a confronting flange 1440.
  • Pivot pin 142 extends axially of post 14% and stylus lever 144 and is appropriately mounted at its opposite ends in parts 140, and 144 with flanges 1400, 1440 being spaced from each other and the intervening space being filled with an elastomer 148.
  • flux-bridging member 146 is a simple cylinder of magnetic material mounted in appropriate relation to the several operating gaps, as previously described. Since the operation of the embodiment shown in FIG. 7 is substantially the same as that previously described, except for the different locations of the pivot and the con- 8 figuration of the flux-bridging member, further description is dispensed with in the interest of brevity.
  • FIGS. 8 and 9 there is shown a still further embodiment of pickup demonstrating further features of the invention, generally designated by the reference numeral 210 and by a series of reference characters as part of a 200 series for convenience in identifying comparable parts.
  • pivot 242 for the stylus lever 244 is arranged rearwardly of the fluxbridging member 246 as illustrated in FIG. 7, but the remainder of the pickup is essentially the same as the disclosed in the principal embodiment, except for the construction of the flux-bridging member 246.
  • the flux-bridging member is a continuous toroid of magnetic material, while in the embodiment illustrated in FIGS. 8 and 9, there is shown a cartridge design wherein the flux-bridging member 246 is segmented and includes individual magnetic means for the respective operating gaps.
  • a substantially cylindrical mounting member 246a which is supported in any appropriate fashion on stylus member 244 and is fabricated of a non-magnetic material, such as an appropriate plastic.
  • the mounting member 246a carrying opposed pairs of flux-bridging bars 246b, 246a and 246d, 246e arranged in opposed relationship to each other and at the requisite 45 orientation, such that separate magnetic members are provided in proximity to the four operating gaps of the pickup but out of the direct flux path between the opposite polarity faces of each of the operating gaps.
  • the flux-bridging member 246 moves in response to stylus motion such that the flux-bridging bars thereof efiectively shorten the fixed gap length of one of the operating gaps of each pair and correspondingly effectively lengthen the fixed gap length of the other of the operating pairs.
  • the segmented flux-bridging member 246 provides an individual magnetomotive unit relative to each gap of the pickup and it is therefore possible to achieve further isolation of the respective flux paths and correspondingly reduce interaction between channels. In those commercial situations where very high orders of isolation is required and the additional cost in manufacturing the segmented flux-bridging member is acceptable, this design attains a more perfect channel isolation.
  • a stereophonic cartridge comprising a support, a magnetic structure on said support including a permanent magnet and means including first, second, third and fourth pole pieces and a front magnetic member defining first and second operating gaps and third and fourth operating gaps, said first and second operating gaps extending symmetrically of a first plane and said third and fourth operating gaps extending symmetrically of a second plane and substantially at right angles to said first plane, a coil mounted on each said pole piece, the coils for said first and second operating gaps being connected in series and the coils for said third and fourth operating gaps being connected in series, a stylus assembly disposed symmetrically of and between said operating gaps and including a stylus lever having its lever axis normally parallel to the length dimension of said operating gaps, means mounting said stylus lever on said support for movement about a center of motion and a flux-bridging member operatively connected to said stylus lever and moving substantially perpendicular to all flux paths such that stylus motion and correspondeing motion of said flux-bridging member will effectively shorten the fixed gap length of oneoperating
  • a stereophonic cartridge comprising a support, a magnetic structure on said support including a permanent magnet and means including first, second, third and fourth pole pieces and a front magnetic member defining first and second operating gaps and third and fourth operating gaps, said first and second operating gaps extending symmetrically of a first plane and said third and fourth operating gaps extending symmetrically of a second plane and substantially at right angles to said first plane, a coil mounted on each said pole piece, the coils for said first and second operating gaps being connected in series and the coils for said third and fourth operating gaps being connected in series, a stylus assembly disposed symmetrically of and between said operating gaps and including a stylus lever having its lever axis normally parallel to the length dimension of said operating gaps, means mounting said stylus lever on said support for movement about a center of motion and a flux-bridging member operatively connected to said stylus lever and dimensioned and positioned to be out of a direct flux path for each of said operating gaps but in the fringe fields thereof such that stylus motion and corresponding motion of said fluxbridging
  • a cartridge according to claim 2 wherein said fluxbridging means is cylindrical and is fabricated of an electromagnetic material.
  • said fluxbridging means includes a support of a non-magnetic material and individual flux-bridging members of electromagnetic material arranged in proximity to each of said operating gaps.
  • a cartridge according to claim 2 including elastomeric damping means interposed between said flux-bridging member and said stylus at a point removed from said center of motion.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electromagnets (AREA)
  • Reciprocating, Oscillating Or Vibrating Motors (AREA)
  • Moving Of Heads (AREA)
  • Signal Processing Not Specific To The Method Of Recording And Reproducing (AREA)
US50624A 1970-06-29 1970-06-29 Flux-bridging stereophonic pickup Expired - Lifetime US3683128A (en)

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US5062470A 1970-06-29 1970-06-29

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US (1) US3683128A (enrdf_load_stackoverflow)
JP (1) JPS5021241B1 (enrdf_load_stackoverflow)
CA (1) CA930674A (enrdf_load_stackoverflow)
CH (1) CH541269A (enrdf_load_stackoverflow)
DE (1) DE2132127C3 (enrdf_load_stackoverflow)
ES (1) ES392652A1 (enrdf_load_stackoverflow)
FR (1) FR2096572B1 (enrdf_load_stackoverflow)
GB (1) GB1318665A (enrdf_load_stackoverflow)
NL (1) NL161647C (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3881073A (en) * 1973-11-12 1975-04-29 Joseph F Grado Replaceable stylus-lever generator module for an electromagnetic cartridge
US4031336A (en) * 1975-02-10 1977-06-21 Grado Joseph F Electromagnetic pickup with magnetic gap displacement generator
US4124782A (en) * 1975-07-29 1978-11-07 Akg Akustische U. Kino-Gerate Gesellschaft M.B.H. Sound pickup having plastic enveloped pole plate to pole rod junction
US4174111A (en) * 1973-11-12 1979-11-13 Grado Joseph F Compressive pivot suspension system for an electromagnetic cartridge

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3060582D1 (en) 1979-05-14 1982-08-12 Akg Akustische Kino Geraete Electromagnetic transducer

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2114471A (en) * 1936-06-20 1938-04-19 Bell Telephone Labor Inc Sound recording and reproducing system
US2444336A (en) * 1946-01-30 1948-06-29 Lionel B Cornwell Electrical sound translating device
US2456338A (en) * 1945-03-26 1948-12-14 Pure Oil Co Catalytic polymerization of olefinic hydrocarbons
US3469040A (en) * 1965-04-15 1969-09-23 Empire Scient Corp Variable reluctance phonograph cartridge

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1541427A (fr) * 1966-10-20 1968-10-04 Matsushita Electric Ind Co Ltd Pick-up magnétique de phonographe stéréophonique
DK124049B (da) * 1969-03-25 1972-09-04 Fonofilm Ind As Magnetisk pick-up.
US3694586A (en) * 1969-11-03 1972-09-26 Joseph F Grado Toroidal armature stereophonic pickup

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2114471A (en) * 1936-06-20 1938-04-19 Bell Telephone Labor Inc Sound recording and reproducing system
US2456338A (en) * 1945-03-26 1948-12-14 Pure Oil Co Catalytic polymerization of olefinic hydrocarbons
US2444336A (en) * 1946-01-30 1948-06-29 Lionel B Cornwell Electrical sound translating device
US3469040A (en) * 1965-04-15 1969-09-23 Empire Scient Corp Variable reluctance phonograph cartridge

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3881073A (en) * 1973-11-12 1975-04-29 Joseph F Grado Replaceable stylus-lever generator module for an electromagnetic cartridge
US4174111A (en) * 1973-11-12 1979-11-13 Grado Joseph F Compressive pivot suspension system for an electromagnetic cartridge
US4031336A (en) * 1975-02-10 1977-06-21 Grado Joseph F Electromagnetic pickup with magnetic gap displacement generator
US4124782A (en) * 1975-07-29 1978-11-07 Akg Akustische U. Kino-Gerate Gesellschaft M.B.H. Sound pickup having plastic enveloped pole plate to pole rod junction

Also Published As

Publication number Publication date
DE2132127B2 (enrdf_load_stackoverflow) 1974-05-16
CA930674A (en) 1973-07-24
FR2096572A1 (enrdf_load_stackoverflow) 1972-02-18
NL161647B (nl) 1979-09-17
ES392652A1 (es) 1973-08-01
FR2096572B1 (enrdf_load_stackoverflow) 1977-01-21
DE2132127C3 (de) 1974-12-12
CH541269A (de) 1973-08-31
GB1318665A (en) 1973-05-31
DE2132127A1 (de) 1972-01-05
NL161647C (nl) 1980-02-15
NL7108816A (enrdf_load_stackoverflow) 1971-12-31
JPS5021241B1 (enrdf_load_stackoverflow) 1975-07-22

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