GB934999A - An audiometer circuit, more particularly for an electronic transistorized metronome - Google Patents

Abstract

934,999. Metronomes. M. E. BERNSTEIN. Feb. 22, 1962, No. 7012/62. Class 139. [Also in Groups XV and XL (c)] In a speech training device the level of the speaker's voice is indicated on a meter 100 (Fig. 1), and to enable the speaker to maintain a desired rhythm, a loud-speaker 24 and/or a lamp 40 produce audible and/or visible (flashes) signals (metronome signals), the repetition frequency of which may be raised by respective controls 28, 46. Additionally, a clockwork timer 102 of the elapsed-time bell-signalling type including visual indication of remaining time is provided. For the indication of speech level the output of microphone 60 is supplied via a transformer 64 (Fig. 4) and level control potentiometer 66 to a two-stage transformer coupled amplifier including transistors 78, 86 and thence via transformer 90 to an integrating transistor stage 96, the collector current of which is indicated on the meter 100 which preferably comprises a D.C. mincroammeter. For producing the audible metronome signals a transformer coupled transistor blocking oscillator the R.C. constant of which may be varied by the control 28 and having a loud-speaker connected to the transformer is employed (Fig. 2, not shown), and for the production of the visible flashing signals a neon lamp circuit the R.C. constant of which may be varied by control 46 is employed (Fig. 3, not shown). A circuit producing both the audible and the visible signals (metronome signals) is shown in Fig. 5, and comprises a blocking-oscillator circuit including a transistor 110, transformer 112, capacitor 114 and adjustable resistor 115. A second transistor 122 is connected in series with the battery 118 and transistor 110 and is so biased by resistor 124 that the level of current flow from a battery 126 is insufficient to light a series-connected incandescent lamp 128 except on the occurrence of a blocking oscillator pulse. Ganged switches SW1, SW2 allow the production of the audible signals only or the visible signals only or the production of both signals simultaneously. When one signal only is selected, changes in the discharge circuit of capacitor 114 are prevented by switching in an equivalent resistance to replace the element not in use. When visible signals only are produced the loud-speaker is replaced by a resistor 132 and when audible signals only are produced the lamp 128 is replaced by an equivalent reistor (not shown).