26
If you don't find the resistances for low frequencies, since they are very big, you could
change the capacitors C2 and C3 to 33 nF, and divide the resistor value of the table by
10. This could only be made between frequencies in the range of 25 Hz and 2 KHz, since
the RF and RF' resistors could never be less than 2 K
Ω
.
As in the gain calculation, it is always advisable that use 1% resistors, since if use 5%
resistors, the frequency has more variation with regard to the table.
BANDWIDTH CALCULATION (Q):
The Q is the filter bandwidth. So that the Q is the filter center frequency divided by the
difference of the higher and lower frequency, which the amplitude response is three dB
down from the filter center frequency: Q= (Fc/ (Fs-Fi)).
The next picture show a filter with different Q at the same frequency and gain. How
you could see a high value of Q indicates a small bandwidth and a low value of Q a big
bandwidth.
F = 1 KHz.
Q=0,5
Q=1,0
Q=2,5
Q=5
There are two resistors in the equalizer card called RQ and RQ,' that configure the
bandwidth (Q) of the equalization point. These two resistors should be equal RQ = RQ.'
The next table shows the resistor that you should use for bandwidths (Q) from 0.1 to
10. The maximum value allowed for the RQ and RQ' resistors are of 150 K
Ω
. If you want
an intermediate bandwidth, you are able to calculate an intermediate value:
Q
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
5% RESISTORS
1 K
2 K
3 K
3,9 K
5,1 K
6,2 K
6,8 K
8,2 K
9,1 K
10 K
1% RESISTORS
1 K
2 K
3,01 K
4,02 K
4,99 K
6,04 K
6,98 K
8,06 K
9,09 K
10 K
Q
1,1
1,2
1,3
1,4
1,5
1,6
1,7
1,8
1,9
2
5% RESISTORS
11 K
12 K
13 K
--
15 K
16 K
--
18 K
--
20 K
1% RESISTORS
11,0 K
12,1 K
13,0 K
14,0 K
15,0 K
16,2 K
16,9 K
18,2 K
19,1 K
20,0 K
Q
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8
2,9
3
5% RESISTORS
--
22 K
--
24 K
--
--
27 K
--
--
30 K
1% RESISTORS
21,0 K
22,1 K
23,2 K
24,3 K
24,9 K
26,1 K
26,7 K
28,0 K
28,7 K
30,1 K
