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A scalable graphic equalizer circuit

2017-08-11 21:35  
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 This article describes a scalable graphic equalizer circuit. Schematics can combine text look better grasp of this principle. This circuit determines the maximum number of increases and decreases, if you want, you can leave it unchanged. ? With the filter circuit shown, allowing a lift and 39 k lower 12 db - it is right in most facilities. ? Value of 10 k will allow up to more than one 5 db. ? Any value between these limits will provide the best for a given environment, which can be scheduled to do? This is a very useful feature, I think it is very unique circuit. All slides pot is connected to the parallel port, "body" at the output must drive all of the filter input, which is also parallel. ? For a 1/3 octave equalizer, which represents an approximately 800 ohm load at U2B. ?  NE5532  be selected as it is one of the few opamps, will drive such a low impedance. ? Do not attempt to use any no rated open such a low impedance, or it will be distorted because the output current limit. ? Another suitable opamp is the OPA2134 (dual), it also has a very high drive capability - no doubt others, but these are the ones I know. Maximum rated input voltage is 1 v (0 business), if you expect, the input will be higher, I recommend an attenuator input. ? The gain can be restored by increasing the value of R8, so if a 3:1 attenuator is used for input (10 db), and then a 30 k (33 k'll be fine) instead of 10 k resistor will bring the overall gain back solidarity. Remember, U2B operations and gain (about 12 db), so the internal overload limit is lower than you might expect. ? The narrow bandwidth of each filter, which can also drive to cut if the input level is too high, it is unlikely to raise voices. Overall, this is a very versatile unit, once the initial shock of the building has been passed, the balance can be used for the most demanding tasks. ? It can also be used in automotive installation, but you must create an artificial earth, the signal voltage limit will be reduced significantly. I suggest that the maximum input voltage remains below 0.5 v RMS - below this will provide a better safety margin will ensure that clipping does not occur regardless of the slider settings.

Figure 4


Figure 1 – Basic Multiple Feedback Bandpass Filter



Octave Band Frequencies
1/2 Octave Band Frequencies
1/3 Octave Band Frequencies
FreqR1R2R3C1,? C2 FreqR1R2R3C1,? C2
3182k2k7160k220nF 50027k82056k47nF
4082k2k7160k180nF 63027k82056k39nF
5082k2k7160k150nF 80027k82056k27nF 2n7
6382k2k7160k120nF 1k08k251018k47nF 4n7
8082k2k7160k100nF 1k48k251018k39nF
10082k2k7160k82nF 2k08k251018k27nF
12582k2k7160k56nF 5n6 2k88k251018k18nF 1n5
16082k2k7160k47nF 4k08k251018k12nF 1n8
20082k2k7160k39nF 5k68k275018k8n2
25082k2k7160k27nF 4n7 8k08k21k218k4n7
31582k2k7160k22nF 2n7 16k8k21k218k2n2
40082k2k7160k18nF 1n5      


Variable Octave Band Frequencies



Figure 2


Figure 2 – Input / Output Stage



Filter Q
BandwidthRequired Q
1/3 octave4
1/2 octave3
1 octave2



Figure 3


Figure 3 – The Filter Bank (Partial Only)


Figure 4

Figure 4 – Frequency Response of a Single Filter

Figure 4 shows the boost and cut of a single filter, centred on 95Hz.? This clearly shows that the Q remains constant – a conventional graphic EQ would have a very broad peak at lower settings, so broad in fact that it would show some noticable effect even at the frequency extremes.? Assuming that the 50% pot setting is flat, these graphs were taken at 25/75%, and 0/100% of the pot travel (cut/boost respectively).The graph is deliberately showing only a decade above and below the centre frequency, so that the response may be seen more clearly.? This was generated using a 39k resistor for R6 in the input circuit – lower values reduce the maximum boost and cut, but leave the Q unchanged.



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