Production of tube RC active frequency divider, Active Crossover
Keywords: production of tube RC active frequency divider
Whether it is currently still in the future. The two-channel stereo will still be the main way of family high fidelity and will have been widely used for enthusiasts, which will not die due to the emergence of SACD and DVD-Audio high quality multi-channel systems. This is because the two-channel system is simple, the adjustment and use is convenient, and the system cost is low and the sound quality is quite high. certainly. This does not mean that the sound quality of the two-channel system does not increase the room and necessary. The use of SACD and DVD-Audio is the only way to improve the two-channel sound quality. To further improve the sound quality of SACD and DVD-AUDIO as a two-channel playback, the pre-servic electronic divider is the most economical and practical solution based on existing or original systems. This article introduces the reader to the principle, calculation and production of an excellent tube pre-tube RC divider. The electronic active frequency differs from double line tongue, double-acting driving advantages. Its electroacoustic performance is better than the general LC power division.
The most concise electronic dividend network of the RC crossover network can consist of both components of resistance R and capacitance C. Figure 1 is a schematic diagram of a first-order two-point network and its characteristics.
For a first-order Di-frequency RC network of Figure 1. Whether it is a high pass filter or a low-pass filter, it can be calculated by the following formula. The Fc is the cutoff frequency (Hz) of the Fc is a high pass or low pass filter. The unit of R is KΩ, and the unit C is UF. The decay slope of the first-order crossover network is not large, only 6dB / OCT (times). If the first-order network is connected in series, it can constitute a second order, third order ... divided network. Among them, especially the second-order network is most common. Figure 2 is a second-order two-point network.
Obviously, the attenuation slope of the second-order divided network is superimposed from a first-order network to reach 12 dB / OCT. However, the second-order network is not a simple series of the first-order network, and this network is calculated. You should pay attention to the following two questions: 1. The first-order network is the load of the first-order network. If two exactly the same first-class network is directly connected, mutual interference is generated. In order to avoid this effect, the impedance of the next-order network should be as high as possible. It is generally available for 5 to 10 times the former. Specifically, for high-pass filters (see Figure 2), the rear stage R value should be 5 to 10 times the front stage RH. At the same time, the C value of the post-stage is reduced accordingly, that is, 1/5 to 1/10 of the front stage C value is taken. Similarly, the low-pass filter, the R value of the rear stage takes 5 to 10 times the front stage RL value, and the C value takes 1/5 ~ 1/10 of the front stage C value. Calculate the formula Fc = 159 / RC. 2. Since the second-order network is connected in series. The attenuation slope of the first-order network is -6db / oct, that is, attenuated -3dB at the Fc (Fig. 3A). Thus after the two first-order networks are connected in series, the attenuation amplitude at the Fc will reach -6dB (Fig. 3B), so that the synthetic frequency sound at the divided point Fc occurs. In order to avoid this, it is understood by Figure 3B, the cutoff frequency (-3DB point) Fc of the low pass filter should be appropriately improved, while the cutoff frequency (-3dB point) FH of the high pass filter should be appropriately reduced. If the divide point of the crossover network is taken as an Fc, FL = 1.5Fc, FH = Fc / 1.5 can be obtained. This can generally guarantee that the attenuation amplitude is still from -3dB at the division point Fc, and the integrated frequency is relatively straight without the concession.
Finally, whether it is a frequency division network of FIG. 1 or FIG. 2, it is always subject to the influence of the parallel action of other circuits before, so that the frequency dividing characteristics are shifted. It is usually necessary before the crossover network, then add a first-level buffer amplifier to other circuits. Common buffer amplifiers are cathode followers.
Calculating example The following is the actual example of a second-order Di-frequency network to illustrate the divided point of the second-order di-frequency network to fc = 800Hz, and the R, C value of the division network. When calculating high and low pass filters, their cutoff frequency is not an FC. FH = Fc / 1.5 = 800 / 1.5 = 533 (Hz) is taken to the high-pass filter; FL = 1.5x800 = 1200 (Hz) is taken to the low pass filter. If the capacitor still takes C = 0.01uF, the high-pass filter RH is the low-pass filter R1 is the first first-order network R, C value in the second-order division network (Fig. 5).
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