JPS632197B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides an MM (moving magnet) type cartridge and an MC (moving coil) used for playing records.
The present invention relates to an improvement of a cartridge amplification circuit suitable for common use with type cartridges, and particularly to provide a cartridge amplification circuit that can achieve sufficient effects with a small number of elements. The output impedance of the MM type cartridge is relatively high, on the order of several kilohms (depending on the frequency), and the output signal level is also relatively high, on the order of several millivolts. On the other hand, the output impedance of the MC type cartridge is relatively low, on the order of several tens of ohms, and the output signal level is also relatively low, on the order of several hundred microvolts. Therefore, conventionally, an amplifier circuit for amplifying the output signal of the MM type cartridge and the output signal of the MC type cartridge has a configuration as shown in FIG. In Figure 1, 1 is the first input terminal to which the output signal of the MC type cartridge is applied, and 2 is the MM type cartridge.
A second input terminal to which the output signal of the type cartridge is applied; 3 is an MC head amplifier circuit for amplifying the signal applied to the first input terminal 1; 4 is an equalizer amplifier circuit; 5 is the MC head amplifier circuit. 3 is a changeover switch for selectively applying the signal applied to the second input terminal 2 to the equalizer amplifier circuit 4, and 6 is an output terminal.
Therefore, the equalizer amplification circuit 4 is configured to sufficiently amplify the output signal of the MM type cartridge.
It has a predetermined input impedance (for example, 50 KΩ as the impedance seen from the first input terminal 6 including the voltage dividing resistors 8 and 9) and a predetermined gain. Therefore, as mentioned above, the signal from the MC cartridge, which has a low output impedance and a small level, cannot be directly amplified by the equalizer amplifier circuit 4. The head amplifying circuit 3 having the following characteristics was provided to convert impedance and increase the signal level. However, the addition of the MC head amplifier circuit 3 has the drawbacks of complicating the circuit and increasing costs.Also, since input switching is performed by the changeover switch 5, it is necessary to route the input line. This is undesirable because it causes disadvantages such as induction of noise, and therefore, a new amplifier circuit for cartridges has been desired. The present invention has been made in view of the above points, and will be described below based on embodiments with reference to the drawings. Fig. 2 shows an embodiment of the present invention, and 6 is MM.
7 is a second input terminal to which an output signal of the MC type cartridge is applied; 8 and 9 are terminals 8 and 9 which separate the input signal applied to the first input terminal 6; voltage dividing resistor 10 is a predetermined input impedance (e.g.
50KΩ) and a bare gain G, to which the output signal of the MM type cartridge divided by the voltage dividing resistors 8 and 9 is applied to the positive input terminal; 11 is the output terminal of the amplifier section 10; A filter 12 is inserted between the second input terminal 7 and the negative input terminal of the amplification section 10 to give a frequency characteristic to the output signal obtained by the amplification section 10 and feed it back to the negative input terminal of the amplification section 10. The first
A resistor 13 is connected to the first switch 14 together with the first switch 14.
A second resistor 15 is connected in parallel with the resistor 12, and a first contact 16 connected to the first input terminal 6, a second contact 17 connected to ground, and a second resistor 15 connected to the second input terminal 7. This is a second switch consisting of three contacts 18 and a movable piece 19. Currently, an MM type cartridge is used for playing records, and when using the cartridge amplification circuit shown in Fig. 2 for amplification, the first switch 14 is opened as shown, and the second switch is opened. As shown in the figure, the second contact 17 and the third contact 18 of the 15 movable pieces 19 are brought into contact with each other. Then,
The second input terminal 7 is in a grounded state, and the amount of negative feedback of the amplifying section 10 is
The value is determined by Therefore, the frequency characteristics and gain of the amplification section 10 also become predetermined values, and the output signal of the MM type cartridge applied to the first input terminal 6 is amplified normally. Next, we will explain the case of using an MC type cartridge for playing records. When using an MC type cartridge, the first switch 14 is closed, and the movable piece 19 of the second switch 15 is moved to the first position.
The contact 16 and the second contact 17 move to a position where they are in contact with each other. Then, the first input terminal 6 is grounded and the MC
The output signal of the mold cartridge is applied to a second input terminal 7, and the signal applied to the second input terminal 7 is
The signal is applied to the negative input terminal of the amplifying section 10 through the parallel connection of the first resistor 12 and the second resistor 13. When the first switch 14 is closed, the second resistor 13 is connected in parallel with the first resistor 12, and the value of the second resistor 13 is set to be less than the value of the first resistor 12. If this is done, the input impedance seen from the second input terminal 7 to the negative input terminal of the amplifying section 10 will be reduced. For example, if the value of the first resistor 12 is 1KΩ and the value of the second resistor 13 is 100Ω, the input impedance will be approximately 100Ω, which is an impedance suitable for an MC type cartridge having a low output impedance. At the same time, the first switch 1
4 is closed, the amount of negative feedback of the amplifying section 10 becomes a value determined by the filter 11 and the first and second resistors 12 and 13. This is smaller than the value determined by the filter 11 and the first resistor 12, and as a result, the gain of the amplification section 10 increases. Therefore, the output signal of the MC type cartridge is appropriately amplified by the low input impedance, high gain amplifier circuit, and a normal output signal can be obtained at the output terminal 20. As described above, the cartridge amplifier circuit according to the present invention only has a single amplifier section, and the cartridge amplifier circuit according to the present invention can
This device can appropriately amplify the output signal of the type cartridge and the output signal of the MC type cartridge, and is particularly advantageous in that it can achieve the above effects by using only two changeover switches, simplifying the circuit and reducing costs. It is something that

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional cartridge amplifier circuit, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Explanation of main figure numbers: 10...Amplification part, 12...First resistor, 13...Second resistor, 14...First switch, 15 ...Second switch.

Claims (1)

[Claims] 1 an amplifier section having positive and negative input terminals and an output terminal;
first and second input terminals; a transmission line that supplies the signal applied to the first input terminal to the positive input terminal; a first resistor that supplies the signal applied to the second input terminal to the negative input terminal; , a series circuit comprising a second resistor connected in parallel to the first resistor and a first switch;
It consists of a second switch that selectively grounds the first input terminal or the second input terminal, and an equalizer element inserted between the output terminal and the negative input terminal of the amplification section, and the second switch When the first input terminal is grounded, the first switch is closed and the second
When the switch grounds the second input terminal, the first
1. An amplifier circuit for a cartridge, characterized in that the first and second switches are switched so that the switch is opened.