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OverviewThe circuit was designed to create a 3-way active loudspeaker with the use of a tweeter, a mid range, and a woofer. Terminology- TL072 – a low noise JFET input operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at the JFET input stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumption
- 4093 – a quad 2-input NAND with Schmitt trigger inputs integrated circuit, generally characterized by small fluctuation in voltage supply, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption
- 7812 – 3-terminal 1A positive voltage regulator with short circuit protection, thermal overload protection, output transistor safe operating area protection, output current up to 1A, and output voltages from 5V to 24V
- STK4044XI – an AF power amplifier used for split power supply with features such as distortion reduction via pure complementary circuit, cascade circuit, and current mirror circuit, compact packaging for slimmer designs, facilitates thermal design of slim stereo sets due to simpler heat sink design, supports addition of electronic circuits for thermal shutdown and load-short protection circuit, and series designed from 50 up to 150W with pin compatibility
Circuit ExplanationA loudspeaker can be considered as active as it contains it own amplifier with minimal distortion due to the absence of inductors. It has very small value capacitors, a built-in active crossover filter and its drivers are connected directly to the power amplifiers. For the full loudspeaker system, the adjustment of frequency response and the optimization is made possible by the use of active method without expensive external equalizers. The crossover circuit used in this design implies the Butterworth type where a flat frequency response is passed with a cutoff frequency of 200 Hz and 3.5 KHz. The values can still be changed as required. The crossover circuit is not seen in the PCB but can be added with its connector through 8-pin J2A plug. Alternatively, a flat cable can be used for transferring voltages and signals. The main PCB is supplied by 15V source. The resistors in parallel may be omitted if not needed as well the trimmers used to adjust the mid and high speaker level.
The delay system and DC protection is performed by a relay where RL2 detects the continuous voltage. The high and mid frequencies are connected to the contacts of RL1 with RL2 contacts connected in parallel. The output of IC7 is connected to the low frequency speaker. The speakers are being driven by the power amplifier circuit with the use of SANYO-manufactured STK4044XI with 100W output power for each speaker. This power rating is widely used by most high level commercial speakers with very good sound quality. The model XI has been chosen for its more modern and better internal design. After the design, a suitable wooden box is used to enclose the speakers where an aluminum sheet is placed at the rear to hold the transformer, bridge rectifier, S1, main power plugs, fuse, RCA plug, and LED D27. ApplicationThe 3-way speaker includes a mid range speaker that is smaller than the woofer and takes the operation from the middle of the frequency spectrum. This allows one speaker to be used for producing saxophones, trumpet, and human voice. The circuit provides frequency balance and excellent sound imaging in complex acoustic surroundings.
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