GB1373215A - Electrical attachment devices - Google Patents

Abstract

1373215 Microphone circuits; loud-speaker circuits; radio receiving apparatus OLYMPUS OPTICAL CO 19 Nov 1971 [20 Nov 1970 28 Dec 1970 29 Dec 1970] 53728/71 Headings H4J and H3Q An electrical attachment device which may include an amplifier and loud-speaker, a matching F.E.T. and condenser microphone, or an F.M. tuner, is for use in conjunction with a tape recorder and draws its power supply from a socket on the tape recorder designed for remote control of the tape recorder. In a first embodiment (Fig. 3) the tape recorder includes a power source 1, a motor 3, an amplifier 2, an on-off switch 4, an earphone socket 13, a remote control socket 13 and a microphone socket 6. An output amplifier 21 which feeds a loud-speaker has two input plugs 23, 24. Plug 23 has its centre terminal connected to its shield through a switch 25 which, when closed (and assuming switch 4 is closed) is connected to the positive terminal of power source 1. Plug 24 has its centre terminal connected to the output of amplifier 2 through socket 13 for transfer of audio-frequency signals while its shield provides, through socket 13, a connection from amplifier 21 to earth. Switch 25 acts as a remote control for the tape recorder and may, if desired, be omitted (Fig. 2, not shown). An electrical attachment device (Fig. 5) includes a condenser microphone 32 and an impedance matching F.E.T. 33. Into the remote control socket 5 of the tape recorder is inserted a plug 34, the centre terminal and shield of which are normally shorted together by a switch 42 which acts as a remote control for the tape recorder. Power supply for the F.E.T. 30 is provided by the positive terminal of the power source 1 through plug 34 and socket 5, an earth connection being provided through plug 35 and socket 6. Audio frequency output from the F.E.T. is through the centre terminal of plug 35. Preferably an R.C. network prevents oscillation of the condenser microphone circuit. The microphone 32 and F.E.T. 33 are in one case 31 and the switch 42 and R.C. network are in a second case 41 located along the cable between microphone 32 and plugs 34, 35, Fig. 6. In a modified circuit (Fig. 7) the case 41, together with the switch 42, is on a spur leading from the plugs 34, 35 (Fig. 8, not shown). An F.M. tuner (Fig. 9) may alternatively form the electrical attachment device and draw its power supply through the remote control socket 5 of the tape recorder, the earth connection being provided through the tape recorder microphone socket 6. The tuner output is applied to the tape recorder amplifier 2 through the centre terminal of plug 58. An F.M. transmitter 52 may receive intelligence from a microphone 51 physically spaced from the tape recorder.