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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a conventional example,
and FIG. 3 is a circuit diagram of an embodiment of the present invention. 3L, 3R ········ Power
amplifier, MS ······ Monitor speaker, So ··························· JL, JR ······ Jack, SLl, SRi ··· · · Normally closed
switch, S [, 2sSRi · · · · · · · Normally open switch. −
DETAILED DESCRIPTION OF THE INVENTION (1) (Door, ρ) The present invention relates to a
speaker monitor circuit in a stereo portable recorder. Conventionally, some stereo portable
recorders are provided with a speaker monitor circuit as shown in FIG. 1 or FIG. In FIG. 1, from
the preamplifiers IL and IR of the left channel L and the right channel R, it is possible to obtain all
monitor outputs for any of the left and right channels via the changeover switch Sat. Increase:
wide and sent to the built-in monitor speaker 、 In addition, in the one of Fig. 2, a normally
closed switch for external speaker connected to each power amplifier 3Lv 3 R of left channel L
and right channel R From SLI, Jack Jt with SRI, JR, its normally closed switch SL1. The monitor
output is branched via SR1k, and one of the outputs is sent to the built-in monitor speaker 1 via
the changeover switch So. In such a case, when one of the channels is working, the switch soe
seiso tossing in accordance with that, the voice can be picked up by the monitor speaker (2), and
both channels are working as stereo. If there is an external speaker connected to one of the
channels, the other channel can be activated as a monitor speaker MSt by setting the changeover
switch So so that both can be heard as stereo, but on the other hand, the changeover switch They
must be summoned, and in particular they are stereos in Figure 1 but sometimes take 1 in mono
without knowing it. The present invention l seeks to eliminate all such conventional drawbacks.
An embodiment of the present invention shown in 31A will be described below. FIG. 3 shows that
in the above-mentioned FIG. 21A, the front jacks of both channels L and R are always interlocked
with plug insertion. = + So = 'f: each additional switch circuit from the switch contact LS + R8 of h
channel / channel of the switch So to the monitor speaker MS via the normally open switch
5L21SR2 of each other channel It is. (3) With the above configuration, when the external speaker
is not connected at all, the output of the left channel L or the right channel R can be arbitrarily
brought to the monitor speaker unit by operating the changeover switch SO. Also, when the
external speaker is connected by inserting a plug into jack JL or JR of either left or right channel,
normally closed switch SLI or SRI in the connected jack is OFF, and normally open switch SL2 or
SR2 is ON. Thus, the monitor speaker 1 is automatically connected to a non-regular channel to
which the external speaker is connected regardless of the changeover switch SO.
In the history, when an external speaker is plugged in to both jacks, both normally open switches
SLl + SRI are turned off, and the monitor speaker unit is excluded. According to the present
invention, when the external speaker is not used at all, it is possible to listen to monaural sound
by the monitor speaker unit by operating the changeover switch So in the same manner as in the
prior art, and use the external speaker at the jack JL or JR of any one channel. If plug-in
connection is made, the monitor speaker unit is automatically connected to the other channel,
and (4) stereo listening can be performed by the monitor speaker and the external speaker. At
this time, there is no need to operate the changeover switch So at all. There is no need to listen to
monaural without knowing it. Of course, if an external speaker is plug-in connected to the jacks
JLIJR of both channels, the monitor speaker MS is excluded and no trouble occurs. The built-in
monitor speaker can be used advantageously and reliably, which is a useful convenience that is
practically similar.