JPS59167804A - Tape recorder - Google Patents

Abstract

PURPOSE:To attain the clear reproduction by applying an output with the inverse characteristic to a reproduction input to a preamplifier as an automatic level adjusting voltage so as to decrease sound recorded surrounding noise. CONSTITUTION:A sound recorded sound input is AC-amplified by an AC amplifier circuit 30 at the reproduction, rectified at a rectifier circuit 32, converted into a DC voltage having the inverse characteristic to the input and inputted to a differential amplifier 34. Thus, the slope of the input and output characteristics when a switch 36 is turned on and a gain control means is activated is steeper than the characteristic when the switch 36 is turned off and the operation of the gain control means is stopped. As a result, the signal/noise level difference in the reproducing characteristic when the switch 36 is turned on is larger than the signal/noise level difference when the switch 36 is turned off, the separation of the signal and noise is improved and the S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape recorder, and particularly to an automatic recording level N.
The present invention relates to a tape recorder equipped with one circuit.

The block diagram of FIG. 1 shows a schematic internal circuit configuration of a conventional tape recorder such as a micro cassette recorder or a multiple cassette recorder. αO is the microphone, 0
is this microphore (first-stage preamplifier that amplifies the audio input from 10, u4) is the power amplifier connected to this preamplifier α, α: eVi speaker, αe is the recording/playback head, (A) is the bias circuit. (2) is a circuit that supplies a predetermined bias current to the coil wound around the recording head during recording, and (2) is an equalizer that improves frequency characteristics. (C) is an automatic recording level adjustment circuit (hereinafter abbreviated as ALC circuit), which automatically adjusts the level when the audio input signal level is high based on the feedback output of the power amplifier (14) during recording. It has a function of reducing the gain of the preamplifier αa that operates as a recording amplifier.

Note that (E) is a variable resistor for volume adjustment provided in the front stage of the power amplifier I, and R and P are switch terminals that are switched and connected during recording and playback, respectively.

The above-mentioned ALC operation will be explained with reference to FIG.

The figure shows the input/output characteristics of the recording system, and the figure (B) shows the characteristics of the recording amplifier gain with respect to the input level. Point g. When the ALC operation starts at
) starts to decrease as the input level increases. Therefore, as can be understood from Fig. 2 (C), the recording level state of a micro cassette record etc. equipped with this ALC mechanism is Vvoice where there is no voice input VOin.
In the state supported by
In the state indicated by Zvoice where n is present, ALC is activated and the gain of the recording amplifier is lowered. For this reason, with conventional tape recorders, when the signal level is low during recording, the gain of the first-stage recording amplifier is maximized, which causes more ambient noise (including mechanical noise from motors, etc.) than when recording normal audio input.
was recorded at a high level, and as shown in Figure 2 (Sd
There is a problem in that the difference between the noise indicated by the signal and the signal becomes small, resulting in poor clarity during recording and playback.

The present invention has been made in view of the above points, and is a tape recorder equipped with an ALC circuit, which includes a gain control means for generating an output with an inverse characteristic to a playback input, and the output of the gain control means during playback. By operating the preamplifier using ALC as an automatic level-use control voltage and by providing a microphone sensitivity switching circuit between the audio input terminal and the preamplifier, recorded ambient noise is reduced and clear playback is possible. In addition, it is an object of the present invention to provide a tape recorder capable of recording close conversations by lowering the microphone sensitivity when surrounding noise is high.

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 3 is a block diagram showing the internal structure of the first embodiment of the tape recorder according to the present invention. The same reference numerals as in FIG. 1 indicate the same parts, and the explanation thereof will be omitted.

One of the features of the present invention is to provide a gain control means that generates an output with an inverse characteristic to the reproduction input, and to cause the first stage preamplifier Cl2) to perform AI and CvJ by the output of the gain control means during reproduction. This gain control means reproduces an amplifier circuit ω that amplifies the AC input, a rectifier circuit (to) and a differential amplifier circuit to generate a DC control voltage with an inverse characteristic to the input voltage to this AC amplifier circuit (a). It consists of Another feature is that a microphone sensitivity switching circuit @O is provided between the microphone a0 and the preamplifier q3. In addition, g is a feedback resistor for gain adjustment connected to the operational amplifier constituting the AC amplifier circuit (7), and (to)
is an emitter follower, which functions as a buffer for impedance exchange for the input from the playback head αS,
This is provided in order not to adversely affect the AC amplification of the AC amplifier circuit (to).

One embodiment of the present invention is as described above, and the audio input recorded during playback is AC amplified by the AC amplifier circuit (to), rectified by the rectifier port t18@, converted to DC voltage, and then passed through the differential amplifier (to). ) is entered. Now this input voltage is VIN,
Let VALO be the voltage obtained as the output a, = s, R
2: [% and ftLd, vALOα (vCO-VIN) are expressed, and an output with an inverse characteristic to the input voltage is obtained.

Therefore, the input/output characteristics according to this embodiment are as shown in FIG. As can be understood from the figure, when the switch (to) is turned ON as shown by the solid line and the gain control means is operated, the switch (to) is turned OFF as shown by the dotted line.
When the gain control means is cut off at F, the slope becomes steeper. Therefore, as shown in Fig. 7, the playback characteristics are as follows: the signal/noise level difference Sd2 when the switch (7) is turned on is larger than the signal/noise level difference Sd2 when the switch (to) is turned on (JF'F'
The signal/noise level difference Sd□ is larger than that when the signal/noise level is set to 1, and the signal/noise separation is improved and the S/N ratio is improved.

Further, in this embodiment, a sensitivity switching circuit @O is provided between the microphone αQ and the preamplifier υ. To explain this operation, when the ambient noise is at a normal level, recording is performed with the sensitivity selector switch (4) turned OFF.At this time, the output voltage V
If the input voltage is V'IN, the output voltage will be lowered. R+
By selecting a value of '3, the sensitivity can be appropriately reduced. In addition, as shown in Figure 8, the sensitivity changeover switch (@ is configured to operate in conjunction with the aforementioned changeover switch (To)) used in this embodiment;
) shows the switching circuit, (B) is a plan view of the mounted state, and (42a) shows the operating knob. That is, the ON state of the selector switch (to) corresponds to the low sensitivity (LOW) of the sensitivity selector switch (6), and the OFF state of the selector switch (to) corresponds to the high sensitivity (HIGH) of the sensitivity selector switch (@). This improves operability as there is no need to operate each switch independently.Therefore, as shown in Figure 9 (5), when recording at a normal noise level, the built-in microphone is set to high sensitivity. Recording is performed from a position a suitable distance rl away from α0, and when the ambient noise is at a high level, the microphone sensitivity is lowered, for example, by about 10 dB, and the so-called close conversation is performed at a position close to the microphone α0 at a distance rt (rx > r2). By performing the recording, the noise level is kept relatively low and below the LAI, C' operating level.When playing back such recorded audio, the switch (
By turning on (to) and operating the gain control means, it is possible to reduce only the ambient noise and reproduce with a good 8/N ratio.

FIG. 4 shows a block diagram of a second embodiment of the invention, and FIG. 5 shows a detailed view of FIG.

In this embodiment, a capacitor C is connected in parallel to the feedback resistor Rg of the operational amplifier constituting the AC amplifier (7), and a logarithmic amplifier circuit is connected to the rear stage of this AC amplifier (to) to generate an AC current. It is characterized in that the output of the amplifier (to) is logarithmically compressed, and the reverse voltage rectifier circuit is constructed with a PNP transistor (1). In FIG. 5, σQ' is an external microphone, and 00' is an earphone connection jack.

In the second embodiment, as described above, since the AC amplifier (to) is provided with a band-limiting capacitor C, the amount of attenuation in the high and low frequencies is increased, and the frequency characteristics during ALC operation are improved. More clarity and concealment. Also, since the AC amplified output is logarithmically compressed by the logarithmic amplifier θQ and then supplied to the reverse voltage rectifier circuit, the input/output characteristic curve shown in Figure 6 becomes gentler, and the noise removal effect is slightly reduced. The sound is easy to hear. In addition, the reverse voltage rectifier circuit is
Since it is composed of six NP transistors, it is possible to easily obtain an output with an inverse characteristic to the input voltage using discrete components, without using an IC#-composed differential amplifier like in the first embodiment. The substrate occupation rate can be reduced.

As explained above, the tape recorder according to the present invention adjusts the gain of the preamplifier based on the feedback output of the power amplifier when recording by amplifying the audio input via the preamplifier in the first stage and the power amplifier in the latter stage. In a tape recorder equipped with an automatic recording level adjustment circuit,
It has a gain control means for generating an output with an inverse characteristic to the playback input, and is configured to supply the output of the gain control means to the preamplifier as an automatic level adjustment control voltage during playback. A microphone sensitivity switching circuit is installed between the preamplifier, which enables close-talk recording by lowering the microphone sensitivity when ambient noise is high, and also reduces the recorded ambient noise during playback. Clear reproduction may be possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the internal configuration of a conventional cheap recorder. FIG. 4 is a schematic block diagram showing the internal structure of a first embodiment of the tape recorder according to the present invention, and FIG. 4 is a schematic block diagram showing the internal structure of the second embodiment of the tape recorder according to the present invention. 5 shows a detailed diagram of the circuit shown in FIG. 4, FIG. 6 and FIG. 7 show the input/output characteristics and playback characteristics of the tape recorder according to the present invention, and FIG.
The figure shows the interlocking state of the sensitivity selector switch and the output selector switch of the gain control means used in the present invention.
) is a circuit diagram in a connection switching state, FIG. 9(B) is a plan view of a mounted state, and FIG. 8)
(B) shows the case where the noise level is normal, and (B) shows the case where the noise level is high. αO...Microphone 0...Preamp <14
)...Power amplifier (c)...ALC circuit■・
・・AC amplifier circuit (a) ・・rectifier circuit
・Reverse voltage rectifier circuit patent applicant Tokyo Shibaura Electric Co., Ltd. Representative Patent attorney Noriyuki Chika (and 1 other person)

Claims (1)

[Scope of Claims] (1) Automatic recording level adjustment that adjusts the gain of the preamplifier based on the feedback output of the power amplifier when audio input is amplified and recorded via a first-stage preamplifier and a second-stage power amplifier. A tape recorder equipped with a circuit has a gain control means for generating an output with an inverse characteristic to a playback input, and is configured to supply the output of the gain control means to the preamplifier as an automatic level adjustment control voltage during playback. A tape recorder further comprising a microphone sensitivity switching circuit between an audio input terminal and the preamplifier. (2) The gain control means includes an AC amplifier circuit that AC amplifies the reproduction input, a reverse voltage rectifier circuit that generates an output with an inverse characteristic to the input voltage to the AC amplifier circuit, and an output of the reverse voltage rectifier circuit. 2. The tape recorder according to claim 1, further comprising a changeover switch that connects the preamplifier only during playback. (8) The gain control means includes an AC amplifier circuit that AC amplifies the reproduction input, a logarithmic amplifier circuit that logarithmically compresses the output of the AC amplifier circuit, and a gain control circuit that is connected to the output terminal of the logarithmic amplifier circuit and that is connected to the output terminal of the logarithmic amplifier circuit. Claim 1, characterized in that it is comprised of a reverse voltage rectifier circuit that outputs a characteristic opposite to the input voltage, and a changeover switch that connects the output of the reverse voltage rectifier circuit to the preamplifier only during reproduction. Tape recorder. (4) The tape recorder according to claim 2 or 3, wherein the microphone sensitivity switching circuit includes a sensitivity changeover switch that operates in conjunction with the changeover switch. (5) The reverse voltage rectifier circuit comprises a rectifier circuit that rectifies the output of an AC amplifier, and a differential amplifier that generates an output with an inverse characteristic to the input voltage to the AC amplifier. A tape recorder according to items 2 to 4 of the scope. (6) The tape recorder according to any one of claims 2 to 4, wherein the reverse voltage rectifier circuit is configured with a PNP transistor. (7) The tape recorder according to claim 2 or 3, wherein the AC amplifier circuit comprises an operational amplifier including a feedback resistor and a capacitor connected in parallel.