This audio
amplifier designed uses two LM3886 per channel, in parallel circuit, based on the PA100 parallel amplifier detailed in National Semiconductor's application note AN1192. This amplifier can deliver about 50W into a 8 ohm speaker and 100W into a 4 ohm speaker. This is a stereo amplifier and therefore 4 LM3886s are used.
The PCB is designed in a way that the power ground is separated from the signal ground, as you can see from the below layout. The signal ground is located in the middle and surrounded by the power ground. There is a thin trace near C5 connecting them. The PCB layout is done by using PADS Power PCB 5.0. I think it is a powerful layout software.
The LM3886 circuit is in a non inverted configuration, so the input impedance is determined by the input resistor R1, i.e. 47k. The 680 ohm and 470pF resistor capacitor filter network is used to filter out the high frequency noise at the RCA input. The 220pF C4 and C8 capacitors are used to shot out the high frequency noise at the LM3886 input pins.
I used high quality audio grade capacitors at several locations: 1uF Auricap at the input for DC blocking, 100uF Blackgate for C2 and C6, and 1000uF Blackgate at the supply
filter.
The PCB is designed in a way that the
power ground is separated from the signal ground, as you can see from the below layout. The signal ground is located in the middle and surrounded by the power ground. There is a thin trace near C5 connecting them. The PCB layout is done by using PADS Power PCB 5.0. I think it is a powerful layout software.