Kenwood TS-950S Service Manual

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TS-950S/SDCIRCUIT DESCRIPTION+ Analog unit1) High-pass filter 1C1, IC2 (MC74HC4052F)The high-pass filter used for modulation processingis not a digital filter, but an analog filter because of theprocessing ability of the DSP. This high-pass filterallows to operator to program up to 4 different cut-offfrequencies in order to select the desired tone.MIC input high-pass filterThis active high-pass filter is configured as a fourthdegree Butterworth filter and is controlled in four stepsby C1 and !C2. 1c4 caomicsoning174!c42C4372)$1HPF1| HPF2.Y xiCut-offfrequency(-3dB)o4e]i|1|¥3|x3]75Hz4.5.91|0|ya|x2186Hz2.6|o|!4max1300Hz370a|Yo|xo400HzIcsGAIN: O4BHPFHPF2Fig. 44 MIC input high-pass filter2) Limiting amplifierIC6 (NJM4560M), 1C7/1 (NJM4558M)When a signal with too much amplitude is applied tothe A/D converter it is possible to experience largelevels of distortion. To prevent this, the amplitude ofthe incoming signal is clipped by up to 3.2 Vp-p by alimiting amplifier to ensure that the level applied to theAID converter (IC12 pin 1) does not exceed 6 Vp-p fullscale.When the output amplitude is between the speci-R34 33Kfied limits (as illustrated in the accompanying diagram)the limiting amplifier operates as a 20-dB amplifier.When the amplitude exceeds these limits, D2/1turns on. When the amplitude exceeds Vc-, D2/2turns on to clip the amplitude so that the output ampli-tude is between Vc+ and Vc-.The shapes of the signal peaks become irregularbecause of the delay of the operational amplifier (IC6)and diode (D2), but this poses no problem.57