Typically, for high quality sound speakers are used to several dynamic head and passive filters that divide a signal into frequency components. But such passive filters have a significant effect on the signal by increasing the input resistance of the column and introducing additional distortion.
Significantly improve the quality of a reproduced signal separation method allows the frequencies in the preliminary stages of amplification. Then on each speaker speaker is fed a "clean" signal to the desired frequency range.
scheme shown here is designed for such frequency division. At the output we get the signal separately for the woofer and mid-high frequency.
Accordingly, for each frequency channel will require a separate power amplifier, but the power of each of these amplifiers can be much smaller than in the case of the single-sideband embodiment.
For example, the power amplifier for the low frequency channel may be on the order of 50-100 watts, and for the medium-high frequency power will be sufficient about 25-30 watts.
At the output of each channel can deliver a variable resistor (volume control), which will in operation quickly change the gain of each channel.
So it will be easy to adjust to any used dynamic head and adjust the overall frequency response (frequency response) of your choice.
Furthermore, in this case it will be possible to get rid of the need for tone control, adjusting the frequency response of these resistors (varying gain levels LF and MF / RF channels).
under this scheme here provide filter slope at the edges of the recession frequency range of about 18 dB per octave. Frequency bands section depends on the nominal values of capacitors C1, C2 and C3 and the resistors R3, R4, R5.
The frequency partition can be shifted by changing the nominal values of these elements. It can be calculated using the formula: F = 0,4 / C1R3. Furthermore, during operation, the frequency can be varied within certain limits by means of the variable resistor R5.
Operational amplifiers can be used any imported (they have a standard pinout), single or double. For example TL072, BA4558, LM2904 and similar.
Better quality select variants with a high rate of increase of the input voltage and low noise. Then, this scheme will not make any further changes to enhance the quality of the entire audio path.
Driving is not difficult to assemble, has a good "repeatability" and does not require any settings. When serviceable parts and there are no errors in the installation begins immediately. To supply circuits need low power bipolar power supply (stabilized) with an output voltage of +/- 12... 18 volts.
The circuit has unity gain and does not introduce any changes to the existing gain path, then there it can be incorporated into the finished, your existing amplifier between stage preamplifier and amplifier power. But, of course, you will need to add one more final power amplifier of the second amplification band.