| 摘要 |
PURPOSE:To quicken a rise time by greatly shifting the center frequency of the electronic variable tone filter to the low pass side by connecting a capacitor. CONSTITUTION:When a tone signal is led into the electronic variable tone filter 1, one of Rr-Rx is selected in order by the code selector 8, it is connected in parallel to the resistor R13, and a tone signal of its preamble and code is made to pass through. A tone signal which has passed through the filter 1 is sent to the level detection circuit 2 and the zero-crossing detection circuit 3. The circuit 3 leads in a part of the tone signal from the circuit 2, too, as a comparison signal, and sends out a zero-crossing signal. This sinal is sent to the gate circuit 5, and the circuit 5 generates an output at the time of zero-crossing after the tone signal has been counted by 4 waves by the counting circuit 4. A part of its output is sent to the timer 6 as a reset signal, and the timer 6 sends a reset signal to the circuit 4 after a prescribed time has elapsed, and cuts off a gate signal from the circuit 4. As a result, the switching circuit Se is turned on, and the capacitor Ce is connected in parallel to the OP amplifier Q3. |
