JPS6236340Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a phono input circuit for inputting the output of a pickup cartridge to an amplifier.

As is well known, the amplifier's phono input circuit corrects the frequency of the output signal of a moving coil (MC) type cartridge or moving magnet (MM) type cartridge based on the RIAA playback curve, and adjusts the output signal to the same signal level as the output of a tuner, tape deck, etc. It is intended to amplify the

In this way, the phono input circuit uses relatively low level signals (0.1 to 0.3 mV for MC type, 1 to 5 mV for MM type).
Because it deals with , it is particularly susceptible to the influence of external high-frequency signals. That is, the high frequency signal is detected by an equalizer amplifier and becomes a signal in an audible frequency band, which causes noise.

It is particularly easy to be induced by input terminal pins exposed outside the device case, and has a large effect on MC type phono input circuits that handle lower level signals.

To prevent this, a phono input circuit shown in FIG. 1 has been considered.

In the figure, 1 is the input terminal pin, 2 is the coil 2a
and a high-cut filter consisting of capacitor 2b, 3 is an equalizer amplifier, and 4 is an NFB circuit for imparting RIAA reproduction characteristics.

That is, this input circuit attempts to block high frequency signals using the high cut filter 2, and the desired effect can be obtained.

However, according to such an input circuit, an induced current is generated in the coil 2a due to leakage magnetic flux from a power transformer for equipment, etc., and this is superimposed on the input signal and amplified, causing an increase in noise.

Therefore, in such an input circuit, it is necessary to shield the coil 2a of the high-cut filter 2, the power transformer, etc., which causes an increase in product cost as the number of parts increases.

This invention is based on a phono input circuit having such a high-cut filter, in which the coils constituting the high-cut filter are formed of two or more even numbered coils with different winding directions, and the direction of the generated electricity in the even numbered coils is This is a phono input circuit designed to mutually cancel different induced currents, and the embodiment shown in FIG. 2 will be described in detail below.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same structural members, and the explanation thereof will be omitted.

Reference numeral 21 denotes a high-cut filter, which is connected between the phono input terminal pin 1 and the equalizer amplifier 3.

The high-cut filter 21 consists of a capacitor 2b and coils 21a, 21a connected in parallel, and the coils 21a, 21a are connected so that the winding directions are opposite to each other.

That is, the winding start ends and winding ends of coils having the same winding direction are connected together, or the winding start ends and winding ends of coils having different winding directions are connected together.

The coils 21a, 21a are placed as close as possible so that they are placed within the same magnetic flux.

According to such a configuration, the induced currents I generated in the coils 21a and 21a due to the leakage magnetic field are generated in opposite directions since the winding directions are opposite.

Therefore, the induced currents are mutually canceled and no induced current is input to the equalizer amplifier 3.

FIG. 3 shows the output noise characteristics of the input circuit of the present invention shown in FIG. 2 and the conventional input circuit shown in FIG. 1, with reference numeral 31 showing the characteristics of the invention and 32 showing the characteristics of the conventional example.

Furthermore, the inductance of coil 2a is 22mH.
The coils 21a and 21a each had an input end short of 44 mH, and the output end voltage of the amplifier was measured when the volume of the amplifier provided with each phono input circuit was at its maximum.

As is clear from the figure, the phono input circuit of this invention can suppress the output noise to -35 dB or less, compared to the conventional phono input circuit.
It can be improved by about 17dB.

FIG. 4 shows another embodiment in which only a high-cut filter is included.

In this embodiment, two coils 21a, 21a having different winding directions are connected in series, and the effect is the same as that of the embodiment shown in FIG. The inductance of the coil 21a is preferably twice the inductance desired for the filter in the parallel connection shown in FIG. 2, and 1/2 the value in the series connection shown in FIG.

As explained above, this invention is based on a phono input circuit in which a phono input terminal is connected to an equalizer amplifier via a high-cut filter. By constructing an even number of coils connected in parallel or in series, the induced current flowing through each coil can be mutually canceled by reversing the flow direction, thereby suppressing output noise due to the induced current. Even with an extremely simple configuration, a sufficient output noise suppression effect can be obtained, making it an extremely useful device in practice.

In the case of an MC type input circuit, a head amplifier may be connected between the high-cut filter and the equalizer amplifier.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram of a conventional phono input circuit, Figure 2 is a wiring diagram of a conventional phono input circuit.
The figure shows the wiring diagram of the phono input circuit of this invention example.
FIG. 3 is a noise output characteristic diagram of each amplifier equipped with a phono input circuit according to the prior art and the embodiment of this invention, and FIG. 4 is a circuit diagram of another embodiment of the high-cut filter used in this invention. 1 is the input terminal, 21 is the high cut filter,
3 is an equalizer amplifier, and 4 is an NFB circuit.

Claims (1)

[Scope of utility model registration request] In a phono input circuit in which a phono input terminal is connected to an equalizer amplifier via a high-cut filter, the high-cut filter is connected to at least a capacitor such that the winding direction is opposite to the capacitor, and the high-cut filter is connected to the capacitor in an induced magnetic field having approximately the same strength. 1. A phono input circuit comprising an even number of arranged coils, characterized in that induced currents generated in each coil have approximately the same magnitude and opposite directions.