This is power amplifier circuit using A1943 and C5200 final transistor, using this transistor to final or booster power amplifier is very very loud and high power amplifier circuit. Complete serie of transistor you may can using 2SA1943 and 2SC5200. This power amplifier have output power about 400Watt RMS at 8Ohm Impedance. See the transistor and circuit diagram of power amplifier A1943 / C5200 below:
- Initally adjust the VR1 & VR3 to 3K8 and 720 ohm resp..
- Install an Amp meter (multimeter set to 500mA) in series between Power board and DX-Amp board , and ensure there is no load on the output (i.e. no speakers connected), turn the power on. The current should be less than 50mA. If current is too high , power off immediately and check for error.
- Adjustment of DC Offset (Center Voltage/Zero Voltage) : Install a DC voltmeter (Multimeter set to DC 2.5V range) across the speaker output (+) and star Ground , adjust the DC Offset trimpot (VR1-100K) until 0V or near 0V (max 20 mV).
- Adjustment of Bias (Quiescent Current) : Adjust the Bias trimpot (VR3 - 1K) until the current (Amp meter in step 2) reach 120mA. You can adjust this bias at your own favour and own risk , and if your heat sink is large enough you can adjust bias over 250mA , but about 120mA gives nice performance.
- Keep power on for 30 minutes, re-check DC offset and Bias for any variation, and refine both if necessary.
- Connect load (speaker) for working certain period of time, refine (3) & (4) if necessary.