Features NE5532P Chip: Other op amp chip such as OPA2604AP OP275G TL072, etc. can also be replaced, very simple and practical. Board Structure: 3 channel output, treble, bass, midrange, which ensures good sound quality and more audio enjoyment. Crossover Point: 500HZ, 5kHZ, that is, 20HZ‑500HZ is bass output, 500HZ‑5KHZ is midrange output, 5KHZ‑20KHZ is treble output. Filter Type: Subtractive divider, also comes with ‑24dB/Oct attenuation slope, so the preamp module has high efficiency. Easy to Install: Designed to have a light weight and a compact size as well, the installation is very convenient. Specification: Item Type: Preamp Module Model: NE5532 Material: PCBA Attenuation Slope: -24dB/Oct Product Size: Approx. 98 x 84 x 20mm / 3.86 x 3.31 x 0.79in Power: DC positive and negative, dual 9-15V.  Package List: 1 x Preamp Module Note: The 10k resistor in the picture above cannot be changed.The R calculated by the calculation software is too large, such as C=1nF, f=5kHz, according to the formula f=0.707/(2X314Rc) the data is very accurate, R=22k. So the following number.According to (Increase C by 10 times, R remains unchanged, f becomes 1/10 of the original) For reference only:When C=1nF, f=5kHz, R=225k (the accurate data should be 22k)C=1nF, f=4.7kHz f, R=24K.C=1nF, f=4.4kHz #f, R=256k.C=1nF, f=4.1kHz f, R=183kC=1nF, f=3.8kHz Hf, R=19.7k.When C=1.5nF, f=3.5kH, R=214kC=1.5nFWhen f=35kHz, R=21.4kWhen C=15nF, f=32kHz, R=235k (I used C=15nF, R=22k, use the formula f=3333Hz, use soft piece f=3410Hz)C=2.2nF, f=3kHz Hf, R=17kC=2.2nF, f=2.8kHz Hf, R=183kC=2.2nF, f=2.5kHz f, R=20.5k.C=2.2nF, f=2.2KHz Hf, R=233kC=2.7nF, f=2.2kHz Bf, R=19k.C=2.7nF, f=2KHz Hf, R=20.8k.C=3.3nF, f=1.8kHz Hf, R=19k.C=3.3nF, f=1.5kHz f, R=22.7kWhen C=47nF=1.3kH, R=184kC=4.7At 1kHz, R=24kC=6.8nF, f=1kHz f, R=16.6k.When C=68nF, f=900Hz, R=18.4kC=6.8nF, f=800Hz f, R=20.7kC=6.8nF, f=700kHz Hf, R=23.6K.When C=10nF, f=700Hz, R=16.1kC=10nF, f=600Hz Hf, R=18.8k.When C=10nF, f=500Hz, R=225k (the accurate data should be 22k)The good effect is related to the relative accuracy of the resistance and capacitance data, especially the resistance needs to be relatively consistent in size. Choose the largest and smallest capacitance in the parallel connection place, so that the error will be smaller. Package List 1 x Preamp Module