JPS593603Y2 - Muting circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement in a muting circuit particularly suitable for audio equipment.

As is well known, muting circuits eliminate unnecessary signals such as noise caused by transient phenomena associated with switching, but especially in the case of audio equipment, the above-mentioned noise is eliminated. Since the sound is emitted from the speaker as a so-called buzzing sound, it is necessary to improve the muting effect as much as possible.

FIG. 1 shows a conventional muting circuit of this type applied to a recording/playback switching circuit section of a tape recorder.

In other words, this is an attempt to mute the popping sound that occurs when switching a head circuit (not shown) used for recording and playback from a playback state to a recording state.
A muting signal is generated by a switch SW linked to a recording/playback changeover switch for switching a head circuit (not shown) to drive a muting transistor Q.

Incidentally, in this case, the recording/reproducing changeover switch and the switch SW linked thereto are of a so-called shorting type in which each contact is switched while being in a short-circuited state.

Now, the switch SW is set to play P and record R from the B side.
Assuming that the switch SW is switched to the EC side, since the switch SW is of the shorting type as described above, the 10B voltage on the P and B contact sides will be transmitted to the RFC contact.

Then, at that point, capacitor C passes through resistor r,
It is charged with a time constant of C, and then discharged through a resistor R with time constants of R and C.

If the relationship r<<R is selected here, it is possible to generate muting with charge/discharge characteristics such as rapid charging and then fairly gradual discharging as shown in Figure 2. can.

Then, such a muting signal is transmitted through diode D.
The muting transistor Q, which is supplied to its base via the switch SW, is turned on immediately after switching of the switch SW, and thereafter maintains a constant on state and is cut off.

Then, during this on-state period, the signal line connecting the preamplifier A1 and the main amplifier A2 is short-circuited to ground via the collector-emitter of the transistor Q, thereby muting the popping sound from the speaker SP. This will enable you to perform

However, in the conventional muting circuit as described above, even though the muting signal rises immediately after switching of the switch SW, it actually has a delay time determined by the time constants r and C. Since muting cannot be performed during the delay period, a high-quality muting effect cannot necessarily be expected.

This is a problem that must be solved as soon as possible, especially since modern audio equipment is required to be of high quality in this respect.

Therefore, this idea was made in view of the above points, and is designed to be able to perform muting quickly and reliably with the simplest possible configuration, thereby achieving a high-quality muting effect. The purpose of this invention is to provide a highly improved muting circuit.

That is, when the muting circuit according to this invention is used as main muting, the muting performed by the muting circuit shown in FIG. This is why a speed-up capacitor can be added for this purpose.

In this case, it is not possible to perform main muting that requires a certain period of time simply by speeding up the rise of the main muting signal, so main muting and preliminary muting before that cannot be achieved. It is necessary to combine them organically, and this idea focuses on this point as well.

An embodiment of this invention will be described in detail below with reference to the drawings.

That is, in FIG. 3, IN is an input terminal to which a signal from a head in a tape recorder is supplied, for example, and this input terminal IN is connected to a preamplifier A1 and a coupling capacitor C.
1, C2, tone control circuits T, C, volume VR, and main amplifier A2 are connected to signal line SL leading to speaker SP.

Further, SW is a shorting type switch that is linked to the recording/playback switch (not shown) that switches the head between recording and playback, and its playback side contacts P and B.
is connected to power supply B, and its recording side contact RFC
is commonly connected to one end of each of the capacitor C8 and the resistor r, and the common contact serves as an idle contact.

Further, Q is a transistor whose collector is connected together with a line-out terminal to the midpoint between the capacitors C1 and C2 on the signal line SL, and whose emitter is grounded.

The base of this transistor Q is grounded through a diode D, a resistor R, and a capacitor C of the illustrated polarity in series.

Further, the other end of the resistor r is connected to the connection point between the capacitor C and the resistor R, and the other end of the capacitor co is connected to the connection point between the resistor R and the diode D.

In the above description, the parts from the recording side contact REC of the switch SW to the base of the transistor Q are the muting signal generating section, and together with the muting transistor Q, constitute a muting circuit.

Of these, capacitor C8 is a speed-up capacitor for obtaining preliminary muting, and resistors r, R and capacitor C are charging/discharging resistors and capacitors for obtaining main muting.

It is assumed that these elements are selected to satisfy the relationship r<R, Co<:C.

Next, a description will be given of the muting effect on the signal line SL performed by switching the switch SW from the reproduction side contacts P and B to the recording side contact RFC in the muting circuit configured as described above.

That is, in this case, since the switch SW is of the shorting type and there is a relationship of Co<C, the base of the muting transistor Q is connected to the base of the muting transistor Q through the speed-up capacitor C6 almost at the same time as the switch SW is switched. A preliminary muting signal is provided.

As a result, the transistor Q is turned on instantaneously, and the signal line SL is short-circuited to ground through its collector-emitter path, so that preliminary muting can be applied to prevent popping noise from the speaker SP.

Immediately after such preliminary muting is applied, a main muting signal is generated which has a rapid charge determined by a charging time constant r, C and a discharging time constant R, C, and has a fairly gradual discharge characteristic. be done.

As a result, following the preliminary muting described above, the transistor Q short-circuits the signal line SL to ground for a certain period of time using the main muting signal that continues for a certain period of time.
After that, it is possible to apply main muting that prevents buzzing sounds from occurring from the speaker SP.

FIG. 4 shows the relationship between such a preliminary muting signal and the main muting signal, and the former preliminary muting signal (curve A) is connected to the diode D.
etc. minute resistance r.

r determined by and speed-up capacitor C8
.

, q, which rises with an infinitesimal time constant.

In addition, the main muting signal (opening line) is the second muting signal mentioned above.
Like the one in the figure, it rises with time constants r and C.

In this case, at least the potential at the intersection of the curves A and Q is the threshold potential of the muting transistor Q.
If it is set to be equal to or greater than BE, it is possible to apply continuous muting without interruption between the preliminary muting that occurs almost simultaneously with the switching of the switch and the subsequent main muting.

It goes without saying that this invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of this invention.

For example, the muting transistor Q may be not only a bipolar type but also a field effect type, or may be a switching element other than a transistor.

Furthermore, the muting circuit according to this invention is suitable for audio equipment such as tape recorders, but is not limited to this.The muting circuit is also suitable for use in audio equipment such as tape recorders, but it is not limited to this, and it is possible to substantially disconnect the signal line so that the noise generated due to switching is not extracted from the signal line. It can be widely applied to other electronic equipment in general.

Therefore, as detailed above, according to this invention, in a muting circuit that mutes a signal line by supplying a muting signal generated in a charging circuit through a switch contact to a switching element, By simply inserting a speed-up capacitor between the contact and the switching element, preliminary muting can be applied before the main muting is applied, making the configuration as simple and quick as possible. Therefore, it is possible to provide an extremely good muting circuit that can produce a reliable high-quality muting effect.

[Brief explanation of the drawing]

Figures 1 and 2 are a wiring diagram showing a conventional muting circuit and a curve diagram showing the muting signal characteristics thereof.
3 and 4 are a wiring diagram showing an embodiment of the muting circuit according to the invention and a curve diagram showing the muting signal characteristics thereof. SL...Signal line, SW...Switch, Q...Transistor, r, R...
Resistor, CO, C... Capacitor.

Claims (1)

[Claim for Utility Model Registration] A muting element connected to a signal line, a shorting type switch whose one fixed contact is connected to a power source and which is linked to a mode changeover switch, and this shorting type switch. a first resistor and a first capacitor connected in series between the other fixed contact of the switch and the reference potential point, and a connection point between the first resistor and the first capacitor and the muting element. a second resistor and a diode connected in series between the shorting signal input electrodes, and a second capacitor connected between the connection midpoint of these second resistors and the diode and the other contact of the shorting type switch. and r<<R, where the values of the first and second resistors are r and R, respectively, and the values of the first and second capacitors are C9co, respectively. A muting circuit characterized in that it is set to satisfy the relationship co〈〈C.