BA1701

Audio ICs VSC∗ system processor IC BA1701 The BA1701 is a monolithic audio-compression system controller IC that uses VSC∗. When used in combination with an analog delay circuit and low-pass filter, it can replay recorded audio at 1 to 2.5 times the recording speed, without altering the pitch. FApplications Audio compression systems for tape-based answering machines and learning aids FFeatures 1) Wide operating voltage range (4.5V to 14V). 2) Built-in two-phase sweep oscillator that can directly drive BBD. 3) Built-in motor controller is synchronized with the audio compression ratio. 4) Built-in voltage regulator. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) ∗ VSC is a trademark of The Variable Speech Control Company. This product is manufactured under licence from VSC Ltd. for use in VSC systems. 861 Audio ICs FBlock diagram BA1701 FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 6V, f = 1kHz, and VIN = 1.5VP-P) 862 Audio ICs FMeasurement circuit BA1701 863 Audio ICs FApplication example BA1701 864 Audio ICs FCircuit operation (1) System construction The BA1701 is a monolithic audio-compression system controller IC that uses VSC.When used in combination with an analog delay circuit, low-pass filter, and tape speed controller, it can replay recorded audio at 1 to 2.5 times the recording speed, without altering the pitch (see BA1701 Fig. 3). The BA1701 has a built-in motor driver control circuit that is synchronized with the pitch control that allows the system to be built with just one pitch control potentiometer (see Fig. 4). (2) Principles of audio compression (see Fig. 5) When recorded audio (A) is replayed at high speed, the pitch of the audio increases in proportion to the playback speed (B). By expanding this using an analog delay circuit, a compressed audio signal with the same pitch as the original recorded signal is obtained (C). Partial audio dropout occurs when the audio is expanded, but due to the diffuse nature of speech, the expanded audio does not sound unnatural to the human ear. 865 Audio ICs FApplication board patterns (solder side) BA1701 FApplication board component layout (solder side) 866 Audio ICs FAdjustment procedure (1) With Rate = 2.5X (VR6 = GND), apply DC270mV to pin 12, and adjust VR1 so that the frequency of the waveform on pin 11 is 300kHz. (2) With Rate = 2.5X, apply DC2.462mV to pin 12, and adjust VR2 so that the frequency of the waveform on pin 11 is 12kHz. (3) Repeat adjustments (1) and (2). (4) With Rate = 2.5X, adjust VR3 so that the period of the waveform on pin 12 is 19ms. (5) With Rate = 1X (VR6 = Vref), adjust VR4 so that the frequency at pin 1 is 300Hz. (6) With Rate = 2.5X, adjust VR5 so that the frequency at pin 1 is 750Hz. (7) With Rate = 1X, input VIN = 500mV and fIN = 2.5kHz, and adjust VR7 and VR8 so that the output distortion is minimized. * If you are not using the motor drive control circuit, adjustments (5) and (6) are not necessary. BA1701 FOperation notes (1) Use accurate film capacitors for the VCO time constant capacitor C14 (0.22µF), the RAMP time constant capacitor C17 (1µF), and the BBD clock time constant capacitor (0.0047µF). (2) If the AF output pin (pin 8) has a capacitive load, you must take precautions to ensure that the BA1701 AF amplifier does not oscillate. We recommend that you insert R19 (about 10kΩ) in the signal output line. (3) To prevent oscillation, position the earth point of the BBD clock time constant pin (pin 9) close to the GND pin (pin 13) (see Fig. 6). FElectrical characteristic curves 867 Audio ICs BA1701 868 Audio ICs FExternal dimensions (Units: mm) BA1701 869