Power amplifier circuit this one is a circuit of power amplifiers with a high power output category. This circuit is called the power amplifier matrix with version 1.4 designed by Heru Himawan Tejo Laksono, this power has a character flat voice with low DCO (DC Offset) and low THD (Total Harmonic Distortion), it's very suitable for use in the room or outdoors. Below the circuit schematic of power amplifier driver Matrix 1.4:
Before you make PCB and assemble this power amplifier I will explain a little how to setting DCO and BIAS Power Amplifier on the schematic above that which is marked in blue for DCO (DC Offset) and red for BIAS Voltage.
Before stepping on how to setup DCO and BIAS power amplifier, it would be better if you first met these two terms. Maybe for the audio experts already understand this term, but it never hurts me to discuss again this term. Because these two terms are closely related to our power amplifier and very influential and determine the good quality of the output power amplifier that we produce. Maybe all this time we can only assemble power amplifier can sound, have stopped there. It turns out that there are many variables in the power amplifier that we can set in order to get the best sound quality. Not all power amplifiers have DCO and BIAS settings.
But actually, from all the power amplifier circuit, there must be a DCO and BIAS. So why is there any power that does not have VR DCO and its VR BIAS? Actually, it exists, but already in the patent set or has been fixed with a certain value with the maximum results according to the manufacturer. The goal is to be safe and not in the brain-tweaking again and live just plug the sound directly, of course, this is very profitable for the assemblers, rather than having to struggle first for DCO and BIAS settings.
DCO (DC Offset)
DCO or DC Offset is the DC voltage that comes out on the speaker output power amplifier. The excessively high DC voltage that comes out in the speaker output can be very dangerous and can cause our speaker's spool to burn. Therefore the DC voltage at the speaker output should be avoided. Most large-wattage power amplifiers use dual or symmetrical voltage (positive-ground-negative) and connect the amplifier's output directly to speakers without capacitors. Output amplifier may contain DC voltage although small and not dangerous for a speaker. The DC voltage at the output of this amplifier is called DC offset.
Where potency RV1 10K is used to adjust the DC offset on the output line to the speakers to get DC offset close to 0 volts or must be below 20 mV. How to use multimeter set scale on DC voltmeter in DC range of 2.5 volts range. Then connect the red probe to the speaker output and black probe to ground or CT. Then set VR P1 to get the lowest DC offset (close to zero or below 20mV).
Then about BIAS power amplifier. There are several opinions about this. Some say BIAS is the magnitude of the final tr collector current and some say BIAS is the voltage between the base and the emitter or the base and base of the final transistor pair. And there is also a voltage measurement on both the tr driver base. So there are several kinds of measurements for this BIAS. And there are also some measuring techniques in another way to check this BIAS parameter.
Where RV2 10K is used to set BIAS on the power amplifier. How to use multimeter set of 500mA scale. Then disconnect the VCC + cable and connect the series. For connections are red probes connect to VCC + Elco power supply. And black probe connect to VCC + pcb power amplifier. Turn on the power amplifier and set it until the multimeter points to 50mA. You can check on the VCC voltage path as well.
With the reverse connection ie red probe to VCC- PCB power amplifier and black probe connect to VCC- power supply Elco. To produce a more quality sound output can be set BIAS up to 120mA. But the bigger the Bias current the better the audio quality and the risk is the power amplifier will get hotter. Then you should give the heatsink enough and given fan or fan as an additional cooler, so as not to over heat. In fact you can set Bias current up to 250mA, provided that the resulting offset DC remains close to zero, it will remain safe with the risk of more heat power.
After you understand a little explanation above, just let's make this power amplifier by using PCB Layout design below with size 13cm x 6.5cm:
Power Amplifier is a driver that is not fully maximal amplifier to operate, you must add the final transistor again to be more powerful, for how you can visit this page: Parallel Final Transistor Power Amplifier