GB2038139A - Stereophonic pick-up - Google Patents

Abstract

In order to eliminate cross-talk in a pick-up of the electro-dynamic or magneto-dynamic type an auxiliary coil in one channel is directly coupled with a main coil of the other channel, so that the signal flowing through the main coil of said one channel generates, by means of the auxiliary coil, a signal in the other channel that is in reverse phase with respect to the cross-talk signal in said other channel caused by the useful signal in the main coil of said one channel. <IMAGE>

Description

SPECIFICATION Pick-up for a stereophonic record player The present invention relates to a pick-up for a record player of the dynamic type for the scanning of stereophonic sound tracks, said pick-up including for each sound channel a separate magnetic circuit with coil, there being provided an auxiliary coil cooperating with said (main) coils of both magnetic circuits. A pick-up of that type is known from German Auslegeschrift 1.102.429.

When scanning a stereophonic sound track in a grammophone record with a needle, which splits the record motion, being composed according to the 45"-45" modulation method, into two mutually perpendicular vibrations, each occurring under 45 , and each being transferred on to separated stereophonic channels, i.e. to individual magnetic transducing circuits of the electro-dynamic or magnetodynamic type and amplifyers, it cannot be avoided completely that the signal destined for said one channel is influenced by the signal destined for the other channel.If said one signal is formed by modulations of the track causing the needle to deflect in a 45 direction, and said other signal by modulations of the track in a 45 direction perpendicular to said former direction, it will be clear that the resolution of the composite signal imparted to the pick-up by the track, into a horizontal and into a vertical motion does not give a pure separation between a signal of one type and a signal of the other type. Said one signal has always a small percentage of said other signal. Therefore it will be obvious that the movement of one track (for example that of the left hand channel) causes also a small (undesired) interference movement in the cantilever according to the motion of the right-hand channel.This phenomenon is called "cross-talk" and the invention has for its object to eliminate or at least to diminish said "cross-talk".

Diminishing of the cross-talk is likewise the object of the pick-up known from German Auslegeschrift 1.102.429 already mentioned.

In the known pick-up the auxilliary coil of each channel is constituted by a winding or coil, which coils together form one continuous winding being completely isolated from the main coils and being coupled therewith only inductively. Each auxiliary coil is further connected in series to a capacitor. It cannot be ascertained with certainty how the auxiliary coils are wound around the two individual magnetic cores. However, it appears that on assumption of a certain winding sense for one auxilliary coil, this one is in the same sense or in phase with that for the other auxilliary coil.

For the main coils a winding sense may be supposed both in the same sense and in the opposite sense to that there might be an embodiment in which the correlated signals derived from a useful signal and transferred through the auxilliary element into the other channel, compensates the cross-talk signal that likewise is generated therein. The auxilliary winding is also frequency-selective due to the presence of capacitors.

The differences between the known and the present systems are principally of constructive nature, like the fact that in the present pick-up the main coil of one channel is mechanically coupled with the auxilliary coil of the other channel, so that there is a direct influencing of the correlation signal and the cross-talk signal and the signals being derived therefrom inductively. Moreover, in the present system all coils are wound in the same sense.

In the known construction the correlation signal that has to compensate the cross-talk signal is formed indirectly by the fact that the auxiliary coil is coupled with the main coil not directly but indirectly, and by the fact that no cross-coupling is effected between the main coil in one channel and the auxilliary coil in the other channel.

Due to this implementation of the cross-talk compensation system in the known device a considerable time-delay occurs in the magnetisation which is both frequency dependent and besides has to take place twice so that there is not question any more of a direct signalcorrection.

The first magnetisation occurs namely in the original channel (say for example the right hand channel). This is because the position change of the magnet results in an increase of flux which, in turn, leads to some increase of magnetisation after some time. This magnetisation increase produces, in turn, the coil voltage, which originates both at the output coil (the main coil) and the small auxilliary coil. This auxilliary coil voltage, in turn, yields, through the coupled coil in the other channel, an auxilliary flux, and the latter, in turn, produces a magnetisation in the main coil of the left hand channel. The question remains whether, apart from the fact that the signal transfer is acting with some time delay, such signal is still representative for the original signal after so many conversions.

As regards the addition of capacitors it is to be noted that application of two capacitors causes losses, whereas moreover at resonance there occur phase jumps so that if there ever be question of an opposite winding sense, the entire effect gets lost due to these phase jumps. Viz. a reversed phase can degenerate all at a sudden into complete phase-correctness, so that the effect to be fought against just becomes greater instead of smaller and that is precisely what should be avoided.

Further there is no mention at all in the German "Auslegeschrift" of the phase-situation as a whole which especially at high frequencies is largely subject to jumps. And where reversed phase and in-phase can alternate without more ado, the cross-talk characteristic obtains clearly a phase sensitive character. Therefore an adequate cross-talk elimination must be deemed excluded.

The invention seeks to provide a better and at the same time a more elegant solution of the cross-talk problem, in that each main coil is directly coupled with the auxilliary coil cooperating therewith. An additional advantage is: by the addition of passive elements, like coil or capacitor, the pick-up can be optimalised externally.

The coupling of the main coil to the auxilliary coil can be established in various manners. In one embodiment the auxilliary coil of one channel is coupled in reverse phase with the main coil of the other channel. This measure is based on the idea that if a current travels through the main coil of the left hand channel, there is generated through the intermediary of the auxilliary coils of the left hand and right hand channels eventually in the main coil of the other (right hand) channel a voltage, being in the reversed phase therewith but also in the reversed phase with any cross talk signal possibly generated in the main coil of the right hand channel, so that in this manner said cross-talk signal is eliminated.

In a preferred embodiment the auxilliary coil of one channel and the main coil of the other channel are connected in series.

In a particular embodiment each auxilliary coil is connected in parallel to a capacitor, said coil and said capacitor constituting together a circuit whose quality is adjustable once or continuously.

By the quality Q of the tuned circuit the band width is also defined, this being determined by the quality of the components used.

Among other components there is the ohmic resitance of the coil: the higher this resistance, the lower is the Q. Also the in parallel connected resistor defines the Q-factor. The lower this R-value, the lower is the Q-factor and the greater is the band width. The crosstalk is stronger at higher frequencies. By increasing the voltage output of the auxilliary circuit the cross-talk at higher frequencies can be damped more effectively.

Another possibility is that the auxilliary coil of one channel and the main coil of the other channel are connected in parallel. In that event the circuit must be optimalised externally by means of resistors, for in that case the most favourable point for damping in which cross-talk is eliminated, can be found.

The parallel connection, however, is less suitable than the series connection.

A third possibility is thus that the two auxilliary coils are replaced by one single auxilliary coil being common to both chan nels. This is based upon the conception that if the two main coils are positioned under an angle of 45 with respect to the vertical, an auxilliary coil being arranged vertically or horizontally, is wound under 45 with respect to the wall of the track and also with respect to the motion of the track wall. This means that whichever track wall moves, a voltage is always generated in said small coil. If the right hand channel carries a signal and the left hand channel does not, the left hand channel does carry an interference signal of the right hand channel (consequent on cross-talk). This is in the reversed phase with the small auxilliary coil so that this interference signal is destroyed.

The solution according to the invention is usable in a magnetic circuit both of the electro-dynamic type in which the magnet remains still and the coil moves, and of the magnetodynamic type in which the magnet moves and the coil remains still.

In the present invention the active element is constituted by the auxilliary coil. The more the system gets "out of order" the stronger the signal in the auxilliary signal becomes and the stronger the cross-talk damping is. This damping is to a substantially degree independent of the scanning angle.

By optimalising a better adaption to the play-back conditions is obtained. At each deviation of the position of the cantilever (other than 20 , for this is now the standard), the signal voltage in the auxilliary coil is greater and thus the damping or obstruction is also greater.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which Figure 1 shows the coil arrangement of the magnetic system of a pick-up cartridge according to the invention, in which the main coils and the auxilliary coils are connected in series; Figure 2 shows a similar arrangement, in which the main coils and the auxilliary coils are connected in parallel; and Figure 3 shows an arrangement, in which the main coils are connected to a common auxilliary coil.

In the Figures shown L, and L" represent the main coils and I, I, and 1" represent auxilliary coils. With C a capacitor and with R a resistor is indicated.

It follows from the embodiments as disclosed in the Figures that due to the cross wise connection as applied the main coil L, or L,l of one channel I or ll is directly coupled with the auxilliary coil 1" or 1, of the other channel II or I. This is in direct contrast with the known coil arrangement where a certain voltage is converted first into a magnetic flux, this flux into a voltage (in the first auxilliary' winding), after which next this voltage is converted into a magnetic flux, which-in turn-generates a voltage in the main coil.

This is altogether a very cumbersome way of conversion which results in rather great timedelays.

Claims (9)

1. A pick-up for a record player of the dynamic type for the scanning of stereophonic sound tracks, said pick-up including for each sound channel a separate magnetic circuit with coil, there being provided an auxilliary coil cooperating with said (main) coils of both magnetic circuits, characterized in that each main coil is directly coupled with the auxilliary coil cooperating therewith.

2. A pick-up according to claim 1, characterized in that the auxilliary coil of one channel is coupled in reverse phase with the main coil of the other channel.

3. A pick-up according to claim 2, characterized in that the auxilliary coil of one channel and the main coil of the other channel are connected in series.

4. A pick-up according to claim 3, characterized in that each auxilliary coil is connected in parallel to a capacitor, said coil and said capacitor constituting together a circuit whose quality is adjustable once or continuously.

5. A pick-up according to claim 2, characterized in that the auxilliary coil of one channel and the main coil of the other channel are connected in parallel.

6. A pick-up according to any of the preceding claims, characterized in that the two auxilliary coils are replaced by one single auxilliary coil being common to both channels.

7. A pick-up for a record player, substantially as described herein with reference to Fig. 1 of the accompanying drawings.

8. A pick-up for a record player, substantially as described herein with reference to Fig. 2 of the accompanying drawings.

9. A pick-up for a record player, substantially as described herein with reference to Fig. 3 of the accompanying drawings.

1 0. The features as herein described, or their equivalents, in any novel selection.