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J, IC5a the the antilog current o keep the balance it sends regain balance. These are the process how to output frequency which is antilog-proportional to the it voltage. The pulse output here is of so nar-width as yet. jt is necessary therefore to 'ide further wave conversion.

IC7 is a multiplexer divided frequency,

IC6 is a frequency dividei to make selection from the

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Sawtooth

IC5a generates sawtooth waveform synchronized to that of the selected frequency. The amplitude of the sawtooth waveform is kept constant by choosing either of R18-R24 by the multiplexer IC7 regardless of any change made at the tone feet. On PROMARS, it has a VCO 9 Board for its 2nd VCO. This Board is in effect just as the same that the VCO section is only taken out from the Module Board stated heroin.

2. VCF and its Peripherals

VCF here is not much different from those on the conventional synthesizer. 1C11 is the high-pass filter. IC12-IC15 are the low-pass filters. IC17 is the circuit for setting Q for the low-pass filters.

IC18 is the electronic potentiometer to control the depth of the cutoff frequency modulation. IC19 (pins 5,6,7) is the cutoff frequency control mixer. Q8 and Q9 are the antilog current generation circuit.

3. Envelope Generatoi

There are two Envelope Generators, one each for VCF and VCA. They are basically the circuits to voltage-control the time or the level of A, D, S, R. Since the signals are now in the pulse form, being voltage-pulse converted on the Module Control Board, the A,D and R controls are to be achieved by controlling the number Level^

of pulses in a given time. Note that, these pulses here are of so narrow width that it may easily be lost of sight from screen on the oscilloscope if the pulse intervals were extended a little long.

IC25 is the flip-flop which inverts itself on arriving at the attack level. IC24 is the gate selecting the pulse for each of A, D, and R by the timing of the flip flop. IC22 is the analog switch which turns on only when there

is a pulse arrival, thus making C20 to charge-discharge, accordingly.

On such charge/discharge, envelopes are developed. The envelopes from C20 are fed through buffer IC21 to obtaine low output impedance.

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