JPS6327763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape recorder circuit using a novel recording circuit.

Recently, tape recorders have become increasingly smaller. Along with this, there is a tendency to reduce the number of batteries used as a power source, and the operating voltage of recording circuits is becoming lower. As a result, the dynamic range of recording circuits has become narrower. Therefore, in order to ensure sufficient high frequency compensation and recording level, the impedance of the magnetic head must be made low. However, if the impedance of the magnetic head is lowered, the reproduction sensitivity of the magnetic head will decrease and the SN
The ratio deteriorates, making it extremely difficult to play back high-fidelity stereo signals.

Therefore, the present invention provides a recording circuit with two-channel amplifiers whose phases are inverted to each other, and applies the outputs of the amplifiers to both ends of the magnetic head, thereby increasing the dynamic range of the recording signal even if the operating voltage of the amplifier is low. To provide a tape recorder which can record a sufficiently large amount of data.

The present invention will be explained below with reference to the drawings. 1 is a microphone; 2 is a magnetic head for recording or reproducing signals on a tape 3; 4 is a recording circuit for amplifying the electric signal obtained from the microphone 1; it has a pair of output terminals 5a, 5b; terminal 5b
is connected to one end of the magnetic head 2 via a constant power supply circuit 6 and a bias oscillation circuit 7, and the other output terminal 5a of the recording circuit 4 is directly connected to the other end of the magnetic head 2. Reference numeral 8 denotes a reproducing circuit for amplifying the electric signal reproduced by the magnetic head 2, and its output is applied to a power amplifying circuit 9. As shown in FIG. 2, the recording circuit 4 includes a preamplifier 10 connected to the microphone 1, a phase inverter 11 that inverts the phase of the output of the preamplifier 10, and a buffer amplifier 12 that amplifies the output of the phase inverter 11. It consists of a buffer amplifier 13 that directly amplifies the output of the preamplifier 10, and buffer amplifiers 12 and 1.
Recording signals having a phase shift of 180 degrees and having the same magnitude are taken out from the output terminals 5a and 5b of No.3.

Next, the operation of the present invention will be explained. To perform recording now, the recording replay switches 14 and 15 are switched to a state different from that shown. When sound is applied to the microphone 1 in this state, the sound is converted into an electrical signal by the microphone 2, and the converted electrical signal is applied to the recording circuit 4 which is activated.

Therefore, the electrical signal is first amplified by a preamplifier 10, a part of which is directly applied to a buffer amplifier 13, and the remaining part is inverted in phase by a phase inverter 11 and then amplified by a buffer amplifier 12. Therefore, the output terminals 5a and 5b have the same magnitude and phase.
You can obtain positive and negative recording signals that differ by 180 degrees. The positive recording signal at the output terminal 5b is applied to one end of the magnetic head 2 together with the bias signal from the bias oscillation circuit 7, and the negative recording signal at the output terminal 5a is applied to the other end of the magnetic head 2. The signal is recorded on tape 3. Since positive and negative recording signals are applied to both ends of the magnetic head in this way, the dynamic range is increased, the impedance of the magnetic head 2 can be set high, and stereo high-fidelity reproduction is possible during reproduction. By the way, when the above-mentioned recording signal path is expressed as an equivalent circuit, it becomes as shown in FIG. As can be seen, the output terminal 5a,
The internal impedance of recording circuit 4 seen from 5b is
When Zin is assumed, a closed circuit is created in which the internal impedance Zin→constant current circuit 6→bias oscillation circuit 7→magnetic head 2→internal impedance Zin. Here, the internal impedance Zin is the impedance Z ₁ of the constant current circuit 6 and the impedance of the magnetic head 2.
It needs to be sufficiently small compared to Z ₂ . If the internal impedance Zin is large, it will not be possible to supply the necessary bias voltage to the magnetic head 2, and the bias voltage applied to the output terminals 5a and 5b will increase, and the superimposed voltage of the recording signal will decrease by that amount, causing the dynamometer to There were disadvantages such as a decrease in the range of water.

The above means that the constant current circuit 6 on the output terminal 5b side
This can be compensated for by adjusting the size of the resistor or bypass capacitor, but since the output terminal 5a side is directly connected to the reproducing circuit 8, the above measures cannot be taken.

Therefore, the buffer amplifier 12 is formed by a differential amplifier 16 as shown in FIG. 3, and the input impedance Z _2o of the differential amplifier 16 is
The open loop gain A of the differential amplifier 16 is set to a sufficiently high value compared to the output impedance Zs of 0.
is set to a sufficiently high frequency fo of the bias signal, and the negative feedback circuit including the feedback resistors 17 and 18 is configured such that Aβ becomes sufficiently large when the feedback rate is β and the open gain is A.

As a result, the recording signal is amplified by the differential amplifier 16 as before and supplied to the magnetic head 2 from the output terminal 5a, but the equivalent input impedance of the differential amplifier 16 as seen from the bias oscillation circuit 7 becomes a very low value.

Analyzing this, i=(Z ₁ /1+Z ₂ /1+Z ₃ /1)(Eo−Eo')...(1
) However, i...Current Eo to the differential amplifier 16...Output terminal 5a of the differential amplifier 16 when it is not operating
Voltage Eo'... Voltage at output terminal 5a when differential amplifier 16 is in operation Z ₁ ... Impedance Z 2 of magnetic head ₂ ... Impedance Z ₃ collectively referring to other loads such as the amplifier circuit in the subsequent stage... Voltage of resistor 17 of feedback circuit 19 Impedance Zf
The impedance is the sum of the impedance Zs of resistor 18.

On the other hand, the input impedance Zin of the differential amplifier 16
is sufficiently large compared to the impedance Zs of the resistor 18, so the negative feedback current i ₃ ′ is i ₃ ′=Eo′/Zf+Zs…(2) and the negative feedback rate β is β=Zs/Zf+Zs…(3) Input impedance of differential amplifier 16
Since the internal impedance of the preamplifier 10 is sufficiently small compared to Zin, the positive input terminal 20 of the differential amplifier 16 can be considered to be grounded. Therefore, the voltage Ezs induced in the resistor 18 is Ezs=i ₃ ′Zs=βEo′ (4) Since this is applied to the negative input terminal 21 of the differential amplifier 16 and amplified by the open gain A, Eo−Eo′ /A=βEo…(5) ∴Eo−E′=AβEo…(6) Eo′/Eo=1/1+Aβ≒1/Aβ…(7) For example, if Eo=6V Aβ=300, Eo′=6× 1/300=20mV Impedance _Z1 of magnetic head 2 is 9Kppm,
Also, if the internal impedance Zn seen from the output side of the differential amplifier 16 is Zn/Zn+Z ₁ ×Eo=Eo′ Zn×6=0.02×(Zn+9000) Zn≪Z ₁ =9000 6Zn≒0.02×9000 Zn≒90/3= 30 (Ω) In this way, the internal impedance Zn of the differential amplifier 16 becomes very small, 30Ω, and can be made almost unaffected by the bias signal.

As mentioned above, the tape recorder circuit of the present invention extracts recording signals that are equal in magnitude but differ in phase by 180 degrees from the recording circuit and applies these recording signals to the magnetic head, so that the dynamometer of the recording signal applied to the magnetic head is You can get a large amount of honey cleanse. Therefore, the impedance of the magnetic head can be increased, and the reproduction characteristics can be improved.

Furthermore, since the internal impedance seen from the output terminal of the recording circuit, which is a problem when extracting a recording signal having the same magnitude and a different phase from the recording circuit, can be reduced, it is possible to prevent the bias signal from adversely affecting the recording signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a tape recorder according to the present invention, FIGS. 2 and 3 are block diagrams of a recording circuit and a differential amplifier used in the tape recorder circuit of the present invention, and FIG. 4 is a recording signal path according to the present invention. FIG. 1...Microphone, 2...Magnetic head, 4...
...Recording circuit, 7...Bias oscillation circuit, 10...
Preamplifier, 11... Phase inverter, 12, 13...
...Batsuhua amp.

Claims (1)

[Claims] 1. A recording circuit having a microphone, first and second buffer amplifiers that are connected to the microphone and generate recording signals that are equal in magnitude and have a phase difference of 180 degrees, and one end of which is connected to the second buffer amplifier via a bias signal source. and a magnetic head whose other end is connected to a first buffer amplifier without going through a bias signal source, the buffer amplifier being constituted by a differential amplifier circuit, and the input impedance of the differential amplifier circuit being compared to the output impedance. The tape recorder circuit is characterized in that the open gain of the differential amplifier circuit is set to be sufficiently high with respect to the frequency of the bias signal, and the negative feedback rate is set to be sufficiently large.