CONSTRUCTION
N. SHARMA
Audio CrossOver EM TESTED EM TESTED
TED EM TES MUDIT AGARWAL
Audio crossover split the incoming audio signal into termed a subwoofer when limited to only low separate bands that do not interact and when frequencies below all other drivers) The output added together output the signal unchanged in signals is feed to six separate amplifier to drive the both frequency and phase response. Speaker woofer, tweeter and middle range loudspeaker. classified as an "N-way" speaker. N is a positive Circuit diagram is shown in figure. 3. Left channel whole number greater than 1, and it indicates the and right channel is shown each of the left and right number of filter sections. A 2-way crossover consists section uses 12 Op - Amp (TL084) each. The TL084 of a low-pass and a high-pass filter. A 3-way JFET-input operational amplifier family is designed crossover is constructed as a combination of low- to offer a wider selection Each of these JFET-input pass, band-pass and high-pass filters. The BPF operational amplifiers incorporates well-matched, section is in turn a combination of HPF and LPF high-voltage JFET and bipolar transistors in a sections. Block Diagram is shown in figure 1. monolithic integrated circuit. The devices feature 4-way crossovers are not very common in speaker high slew rates, low input bias and offset currents, design, primarily due to the complexity involved, and low offset-voltage temperature coefficient. Op- which is not generally justified by better acoustic Amp IC1(a), IC1(d), IC2(c), IC3(b), IC4(a),IC4(d), performance. A number of manufacturers have IC5(c), IC6(b) as as input and output buffer and developed 5-way crossover. This usually indicates other Op-Amps IC1(b), IC1(c), IC2(a), IC2(b), the addition of an extra bass driver (commonly IC2(d), IC3(a), IC3(c), IC3(d), IC4(b), IC4(c),
IC5(a), IC5(b), IC5(d), IC6(a), IC6(c), IC6(d) act as
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a 80dB/decade active filter. A filter is an electrical Preamlifier LowPass Current Stage Stage Amlifier Stage Woofer network that alters the amplitude and/or phase
HighPass Current characteristics of a signal with respect to frequency. Stage Amlifier Stage Tweeter Ideally, a filter will not add new frequencies to the
HighPass Current input signal, nor will it change the component Stage Amlifier Stage Tweeter frequencies of that signal, but it will change the
Preamlifier LowPass Current relative amplitudes of the various frequency Stage Stage Amlifier Stage Woofer
components and/or their phase relationships.
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reject signals in other frequency ranges. Such a filter Fig. 1 : Block Diagram of Audio CrossOver has a gain which is dependent on signal frequency. As an example, consider a situation where a useful e
d signal at frequency f1 has been contaminated with u t i t e an unwanted signal at f2. If the contaminated signal p d Filter u m t i t A is passed through a circuit (Figure 2) that has very
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m A = V low gain at f2 compared to f1, the undesired signal A Input {0.1@f2 Output can be removed, and the useful signal will remain. Note that in the case of this simple example, we are f1 f2 f1 f2 Frequency Frequency not concerned with the gain of the filter at any Input Spectrum Output Spectrum frequency other than f1 and f2. As long as f2 is Fig. 2 : Filter Block Diagram CONSTRUCTION
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Fig. 3 : Circuit Diagram of Audio CrossOver CONSTRUCTION
Fig. 4 : PCB Layout of Audio CrossOver (80% of Actual Size)
R2 Leftt Leftt R1 R21 C17 Woofer Midrange C11 R9 R20 R19 Leftt C18 Input C22 C2 C1 R9 Left C19 C13 Tweeter C10 C3 R8 R22 C14 IC3 IC2 Ic1 R23 R10 R24 R18 PR1 C20 R14 R17 R12 C4 R13 R11 C8 R4 R21 C21 C16 C12 C5 C6 R5 Pr2 Pr3 C15 R16 C7 C9 R6 R3
Right R25 1 R45 Right Woofer Midrange C33 R33 R26 IC7 R44 R43 Right C39 C35 C24 C23 Input C44 Right D1 C45 C46 R31 C47 C40 R42 C32 Tweeter C36 C25 R32 D2 R46 IC6 R34 R47 C41 IC5 IC4 C48 C49 R48 R37 PR4 D4 C42 R38 R35 R36 C26 D3 R41 C29 R27 R29 IC8 1 R45 C43 C34 C27 C28 C50 PR5 R40 PR6 C38 C30 C31 R30 R28 C37
Fig. 5 : Component Layout of Audio CrossOver (80% of Actual Size) sufficiently attenuated relative to f1, the domain. Thus, curves of gain vs frequency and performance of this filter will be satisfactory. In phase vs frequency are commonly used to illustrate general, however, a filter's gain may be specified at filter characteristics, and the most widely-used several different frequencies, or over a band of mathematical tools are based in the frequency frequencies. Since filters are defined by their domain. A low pass filter is one that allow the lower frequency-domain effects on signals, it makes frequency to pass and block the higher frequency. sense that the most useful analytical and graphical So a circuit that drives a woofer called Low pass descriptions of filters also fall into the frequency filter since it delivers frequencies below 200HZ. A CONSTRUCTION
COMPONENT LIST a circuit that drives a tweeter called High pass filter. SEMICONDUCTOR DEVICES When we cascade a low pass filter and a high pass IC1(A-D),IC2(A-D) TL084 filter, their combination will pass a band of IC3(A-D),IC4(A-D) TL084 IC5(A-D),IC6(A-D) TL084 frequencies hence it is called band pass filter. IC7 7812 Here for each low and high pass filter we are using IC8 7912 two 40 dB/decade filter cascade to make a total D1-D4 1N4007 roll off 80 dB/ decade. In the figure you will find out CAPACITORS two capacitor each of equal value is used since it is C1,C23 1 uF difficult to obtained capacitor values exactly double C2,C24 220pF C3,4,5,6,7,8,9,10,11,12, of other. The input to left channel is fed via RC filter 25,26,27,28,29,30,31,32 2.2nF to roll off frequency above 100 Khz and applied to 33,34, IC1 (a) which is used as unity gain amplifier. It drive C13,14,15,16,17,18,19,20, 21,22,35,36,37,38,39,40,41, two high pass filter stage IC1 (b), IC1 (c) and two 41,42,43,44 47nF low pass filter IC2 (a), IC2 (b). The output of second C45, C48 1000uF/25V high pass filter IC1 (c) is connected to non-inverting C46, C47, C49, C50 0.1uF RESISTORS amplifier IC1 (d) of gain 2 via preset PR1. The R1,R25 47K output of low pass filter IC 2 (b) feeds high pass filter R2,4,6,7,8,9,10,11,12,13,16, based on IC2 (d), IC3 (a) the output of high pass 18,17,19,20,21,22,23,24,26, 27,30,31,32,33,34,35,36,37 filter is feed to another non-inverting amplified IC2 40,41,42,43,44,45,46,47,48 10K (c) of gain 2 via preset PR2. The output of low pass R3,5,14,15,28,29,38,39 20K filter IC2 (b) also drives other low pass filter IC3 (c) PR1,2,3,4,5,6 100K (Preset) MISCELLANEOUS and IC3 (d) which further connected non-inverting Transformer 12V amplifier IC3 (b) of gain 2. PCB Layout is shown in figure 4 and component layout in figure 5. High pass filter is one that allow the higher frequency to pass and block the lower frequency. So