Amplifier these receivers can be used in two ways - as dual bridge with a maximum 2x25 watts or as a Quad with a normal load and a "virtual ground". Power in this case is hit. The best known representative of this family - Sony 1253/1853. To work with a subwoofer and you need to use dual-channel configuration.
Fig. 2 (click to enlarge)
The choice of switching circuits, as in the previous case, is made taking into account the sensitivity of the heads. For option And capacitors C1,C2 play a role HPF. And may be waived, if the applied head provide an undistorted reproduction of the lower frequencies. The office of the DC component produced by the internal capacitors in the radio. However, for option B required the presence of two high-pass filter to the stereo and LPF for the total channel. Their goal is to eliminate parallel heads at low frequencies. Since at low frequencies the impedance heads almost equal to their DC resistance, the lack of filters can lead to overload of the amplifier, designed for a load of 4 Ohms. For stereo channels are used, the filters of the first order (C1,C2), for total - second (C3L1R1).
There is another option of a mixed load connection, but within a single amplifier channel. It is convenient to connect the two - or three-way speaker system. The bass head bridged inclusion, and for MF/HF or VHF conventional. The mode switch is set to the position for Quad-channel configuration.
Fig. 3 (click to enlarge)
The dependence supplied to the heads of power from the fader position shown in Fig.3.b. In the process of adjusting the power on the pavement load is reduced a maximum of 6 dB (4 times), because in the end positions of the fader scheme reduces to the usual ("left without signal" shoulder amplifier acts as a "virtual ground"). Note that in the zone of the joint action of the heads, they are connected in parallel, but since at these frequencies is already affecting the growth of the load impedance due to the inductance of the voice coil actually overload the amplifier does not occur.
Author: A. Chechetov; Publication: www.bluesmobile.com/shikhman, www.cxem.net