JPH026483Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention amplifies the microphone signal from the built-in microphone during recording, and then directs it to the magnetic head, and when playing the tape, the tape playback signal from the magnetic head is The present invention relates to a howling prevention circuit for a tape recorder which amplifies the signal and then outputs the signal to a speaker. (B) Prior Art Conventionally, such a tape recorder has a circuit configuration as shown in FIG. 1 to prevent the microphone signal from the built-in microphone from being led out to the speaker and causing howling when recording with the built-in microphone. That is, 1 to 4 are the first to fourth recording/playback switching switches;
Reference numeral 5 denotes a built-in microphone to which operating voltage +B is applied via the movable contact 1a of the first recording/playback switch 1 and the recording contact R during recording with the built-in microphone, and its microphone signal output is connected to the fixed contact 6a of the external microphone jack 6. The movable contact piece 6b → input to the front stage side of the preamplifier 7 through the recording contact R of the second recording/playback switch 2 and the movable contact piece 2a, and after being amplified by the preamplifier 7, the input signal is input from the rear stage side. 4 Movable contact 4a of recording/playback switch 4 and recording contact R → Recording path 8 → Recording contact R of third recording/playback switch 3
and is led out to the recording/reproducing magnetic head 9 side through the movable contact piece 3a. Reference numeral 10 denotes a playback path which amplifies the signal output from the downstream side of the preamplifier 7 in the main amplifier 11 and then leads it to the speaker 12 side.Therefore, during tape playback, the tape playback signal from the recording/reproducing magnetic head 9 is Movable contact piece 3a of third recording/playback switch 3
and playback contact P -> playback contact P of the second recording/playback switch 2 and movable contact 2a -> preamplifier 7 -> playback path 10 to lead out to the speaker 12 side.
13 is a muting system that prevents the microphone signal from the built-in microphone 5 from being amplified by the preamplifier 7 and then being led out to the speaker 12 side through the playback path 10 (i.e., to prevent howling) during recording with the built-in microphone. In the circuit, the muting transistor 14 has its collector-emitter path connected to the signal line 15 of the playback path 10 and the ground side, and its base connected to the recording contact R side of the first recording/playback switch 1. There is. Therefore, when recording with the built-in microphone, the mutating transistor 14 becomes conductive and the signal line 15 is grounded, so that the microphone signal from the built-in microphone 5 is transmitted to the playback path 10.
There is no risk that howling will occur due to being led out to the speaker 12 side. The reference numeral 16 is connected to the preamplifier 7 through the fourth recording/playback switch 4 for negative feedback, and when recording with the built-in microphone, the movable contact 4a of the record/playback switch 4 changes from the playback contact P side to the recording contact R side. This is an equalizer circuit whose circuit constants are switched from playback to recording by switching to . However, such conventional circuits require a separate muting circuit to prevent howling between the built-in microphone and the speaker during recording with the built-in microphone, resulting in an increase in the number of circuit components. (c) Purpose of the invention The present invention was developed in view of the above, and is a method for preventing howling in a tape recorder when recording with a built-in microphone without using a separate muting circuit as in the past. It is intended to provide a prevention circuit, and specifically, it aims to reduce the number of circuit components and simplify the circuit by effectively utilizing the equalizer circuit provided in the preamplifier. (d) Structure of the invention In other words, the invention consists of an amplifier into which the microphone signal from the built-in microphone is input during recording and a tape playback signal from the magnetic head during tape playback, and an amplifier into which the tape playback signal from the magnetic head is input into the rear stage of the amplifier. A movable contact piece is connected to a recording/playback switch that switches the movable contact piece from the playback contact side to the recording contact side when recording with the built-in microphone, and the recording/playback switch is connected to the playback contact side of the recording/playback switch and is connected to the amplifier when playing back a tape. a playback line that directs the tape playback signal amplified by the microphone to the speaker side; and a recording circuit that is connected to the recording contact side of the recording/playback switch and leads the microphone signal amplified by the amplifier during microphone recording to the magnetic head side. A negative feedback connection is made to the circuit and the amplifier via the recording/playback switching switch, and when recording with the built-in microphone, the movable contact of the recording/playback switching switch is switched from the playback contact side to the recording contact side, thereby changing the circuit constant. It consists of an equalizer circuit that can be switched from playback to recording, and when recording with the built-in microphone, the microphone signal flowing from the recording contact side of the recording/playback switch to the playback path is attenuated by passing through the equalizer circuit. , which is configured to prevent howling. (E) Embodiment An embodiment of the present invention will be described below with reference to FIG. Incidentally, parts that are the same as those in the prior art will be given the same drawing numbers and their explanations will be omitted. That is, according to the present invention, the muting circuit in the circuit of FIG. 1 is deleted, and the preamplifier 7
The latter stage side is connected to the movable contact piece 4a side of the fourth recording/playback changeover switch 4, and the playback path 10 is connected to the playback contact P side of the fourth recording/playback changeover switch 4, respectively. Therefore, during tape playback, the tape playback signal amplified by the preamplifier 7 is applied to the playback contact P side of the fourth recording/playback switch 4 via the movable contact piece 4a, and the playback contact P side From regeneration route 1
0 to the speaker 12. Also,
When recording with the built-in microphone, the microphone signal from the built-in microphone 5 amplified by the preamplifier 7 is used as the fourth microphone signal.
The voltage is applied to the recording contact R side of the recording/playback switch 4 via the movable contact piece 4a, and the recording contact R
from the side to the recording/reproducing magnetic head 9 side through the recording path 8 , and is also connected to the equalizer circuit 1 in circuit terms.
However, since the microphone signal is sufficiently attenuated when passing through the equalizer circuit 16 , there is a risk that such a microphone signal may be led to the speaker 12 side and cause howling. There is no (f) Effects of the invention As described above, according to the circuit of the invention, when recording with the built-in microphone in which the microphone signal from the built-in microphone, which has been amplified by the amplifier, is led out to the recording system, the reproduction system of the microphone signal is The circuit is configured so that the derivation of the signal is performed via the equalizer circuit (that is, it is sufficiently attenuated within the equalizer circuit), so when recording with the built-in microphone, the microphone signal is sent to the speaker side through the playback path. There is no risk of howling being caused by the noise, and since the existing equalizer circuit is used instead of adding a separate circuit to prevent howling, the circuit configuration can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1 to 4...first to fourth recording/playback switch, 5...built-in microphone, 7...preamplifier, 8 ...recording system, 10 ...playback system.

Claims (1)

[Scope of utility model registration request] When recording with the built-in microphone, the microphone signal from the built-in microphone is input, and during tape playback, the tape playback signal from the magnetic head is input into the front stage of an amplifier, and a movable contact piece is connected to the rear stage of the amplifier. The movable contact piece is connected to a recording/playback switch that is switched from the playback contact side to the recording contact side, and to the playback contact side of the recording/playback switch to send the tape playback signal amplified by an amplifier during tape playback to the speaker side. A regeneration path to be derived,
a recording line connected to the recording contact side of the recording/playback selector switch and guiding the microphone signal amplified by the amplifier during microphone recording to the magnetic head side; and a negative feedback connection to the amplifier via the record/playback selector switch. The built-in microphone consists of an equalizer circuit whose circuit constants are switched from playback to recording when the movable contact of the recording/playback switch is switched from the playback contact side to the recording contact side when recording. Howling in a tape recorder characterized in that during microphone recording, the microphone signal flowing out from the recording contact side of the recording/playback switch to the playback path side is attenuated by passing through an equalizer circuit to prevent howling. prevention circuit.