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  • Manufacturer or author: Intersil Corporation
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current is modified by the bias current. FIGURE 1. EQUIVALENT DIAGRAM OF THE OTA

3 NON-INVERTING

FIGURE 2. CURRENT MIRRORS W, X, Y AND Z USED IN FIGURE 3. THE OUTPUT CURRENT TRANSFER

Transistors from CA3046 array. AGC System with extended input range. FIGURE 6. A CIRCUIT SHOWING HOW THE SIGNAL FIGURE 7. TOTAL SYSTEM GAIN vs AMPLIFIER BIAS FIGURE 8. CA3080 TRANSFER CHARACTERISTIC FOR THE FIGURE 9. CA3080 TRANSFER CHARACTERISTIC FOR THE

0.01 GAIN

transistor will never become forward biased. FIGURE 19. A CA3080 PREAMPLIFIER

Note that the expressions for high frequency gain are identical for both bass circuits, while the expressions for low frequency gain are identical for the treble circuits. Figure B2 shows cut and boost bass and treble controls that have the characteristics of the circuits of Figure B1. The value R EFF in the treble controls of Figure B1 is derived from the parallel combination of R1 and R2 of Figure B2 when the control is rotated to its maximum counterclockwise position. When the control is rotated to its maximum clockwise position, the value is equal to R To compute the circuit constants, it is necessary to decide in advance the amounts of boost and cut desired. The gain expressions of Figure B1 indicate that the slope of the amplitude versus frequency curve in each case will be 6dB per octave (20dB per decade). If the ratios of boosted and cut gain are set at 10, i.e. then the following relationships result: Bass Circuit: ALOW Boost() 10A MID= A LOW Cut() A MID Treble Circuit: AHIGH Boost() 10A MID= A HIGH Cut() A MID Bass Circuit: R1 10R 2= R 3 99R 2= Treble Circuit: C1 10C 4= C 2 10C 4 FIGURE B1 (A). BASS BOOST FIGURE B1 (B). BASS CUT FIGURE B1 (C). TREBLE BOOST FIGURE B1 (D). TREBLE CUT FIGURE B1. FOUR OPERATIONAL AMPLIFIER CIRCUIT CONFIGURATIONS AND THE GAIN EXPRESSIONS FOR EACH R 2 R 1R 3 C 1 ES EO A R 1 R 2 R 3++ R 2  1S C R 2R 3 R 1R 3+() A LOW FREQUENCY R 1 R 2 R 3++ R 2 +-R 2 R 1 C 2 ES EO R 3 A R 1 R 2 R 3++ 1S C R 2R 3 R 1R 3+() 1S C 2 R 2R 3 + A LOW FREQUENCY R 1 R 2 R 3++ R EFF C 1 ES EO C 4 C 3 A C 1 C 4+ C 4  1S R EFF C 1C 4 C 3C 4 C 1C 3++() A LOW FREQUENCY C 1 C 4+ C 4 R EFF ES EO C 4 C 2 C 1 A C 1 C 4+ C 4  1S R EFF C 1C 4 C 2C 4 C 1C 2++() A LOW FREQUENCY C 1 C 4+ C 4 Application Note 6077

The unaffected portion of the gain (AHIGH for the bass control and ALOW for the treble control) is 11 in each case. To make the controls work symmetrically, the low and high frequency break points must be equal for both boost and cut. Thus: since R3 ≅R 2 + R3,C 2 = 10C1 and since To make the controls work in the circuit of Figure 14, breaks were set at 1000Hz: for the base control and for the treble control Response and Control Rotation In a practical design, it is desirable to make “flat” response correspond to the 50% rotation position of the control, and to have an aural sensation of smooth variation of response on either side of the mechanical center. It is easy to show that the “flat” position of the bass control occurs when the wiper arm is advanced to 91% of its total resistance. The amplitude response of the treble control is, however, never completely “flat”; a computer was used to generate response curves as controls were varied. Figure B3 is a plot of the response with bass and treble tone controls combined at various settings of both controls. The values shown are the practical ones used in the actual design. Figure B4 shows the information of Figure B3 replotted as a function of electrical rotation. The ideal taper for each control would be the complement of the 100Hz plot for the bass control and the 10kHz response for the treble control. The mechanical center should occur at the crossover point in each case. Bass Control: C 1R 3 R 1 R 2+() C 2R 2R 3 and C 1R 3 C 2R 3 R 1 R 2+() Treble Control: R1 C 1C 4 C 3C 4 C 1C 3++() R 1R 2 R 2C 3 R 1R 2  C 1C 4 C 2C 4 C 1C 2++() C 1 100C 2 C 2,≅ C 3 and C1 10C 4 R 1, 9R 2== = 0.1C1R 3 R 1C 3 R 2 CW R 3 CCW R 1 C 2 C 1 FIGURE B2 (A). BASS CONTROL C 1 CW R 1 CCW C 4 C 2 C 3 R 2 FIGURE B2 (B). TREBLE CONTROL FIGURE B2. CUT AND BOOST BASS AND TREBLE CONTROLS THAT HAVE THE CHARACTERISTICS OF THE CIRCUITS IN FIGURE B1 10 100 1000 10K 100K FREQUENCY (Hz) EO /ES (dB) 68Ω 15K 0.01 µF 0.0011.8K 0.12µF 0.001µF 820Ω EOES 0.02 0.2 100K 10K µF µFQ = 1.0 Q = 0.99 Q = 0 Q = 0.98 Q = 0.96 Q =0.914 Q = 0.85 P = 1.0 P = 0.99 P = 0 P = 0.98 P = 0.96 P = 0.92 P = 0.8 P = 0.5 P = 0.3 P = 0.1 P = 0.05 P Q µF FIGURE B3. A PLOT OF THE RESPONSE OF THE CIRCUIT OF FIGURE 14 WITH BASS AND TREBLE TONE CONTROLS COMBINED AT VARIOUS SETTINGS OF BOTH CONTROLS Q = 0.75 Q = 0.5 Q = 0.2 Application Note 6077

All Intersil semiconductor products are manufactured, assembled and tested underISO9000 quality systems certification. Intersil semiconductor products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time with- out notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see web sitehttp://www.intersil.com References For Intersil documents available on the internet, see web site http://www.intersil.com/ Intersil AnswerFAX (321) 724-7800. [1]AN6668 Application Note,“Applications of the CA3080 and CA3080A High Performance Operational Transconductance Amplifiers,” H. A. Wittlinger, Intersil Corporation. [2]“A New Wide-Band Amplifier Technique,”B. Gilbert, IEEE Journal of Solid State Circuits, Vol. SC-3, No. 4, December, 1968. [3]“Trackability,” James A. Kogar, Audio, December, 1966. ELECTRICAL ROTATION OF BASS CONTROL GAIN (dB) 1000Hz 100Hz 31.6Hz FIGURE B4 (A). 1kHz ELECTRICAL ROTATION OF TREBLE CONTROL GAIN (dB) 31.6kHz 10kHz FIGURE B4 (B). FIGURE B4. THE INFORMATION OF FIGURE B3 PLOTTED AS A FUNCTION OF ELECTRICAL ROTATION Application Note 6077