After finished the layout, I send it to a PCB manufacturer in HK to make the PCB. I think it is a powerful layout software. The PCB layout is done by using PADS PowerPCB 5.0. There is a thin trace near C5 connecting them. The signal ground is located in the middle and surrounded by the power ground. 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. 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 220pF C4 and C8 capacitors are used to shot out the high frequency noise at the LM3886 input pins. The 680 ohm and 470pF resistor capacitor filter network is used to filter out the high frequency noise at the RCA input. The LM3886 circuit is in a non-inverted configuration, so the input impedance is determined by the input resistor R1, i.e. This is a stereo amplifier and therefore 4 LM3886s are used.
This amp can deliver about 50W into a 8-ohm speaker and 100W into a 4-ohm speaker. Therefore I designed this amplifier which uses two LM3886 per channel, in parallel circuit. Since my DIY speaker is 4-ohm and somewhat difficult to drive, I want to have a more powerful amplifier to match with it. This is 100W LM3886 power amplifier is based on the PA100 parallel amplifier detailed in National Semiconductor's application note - AN1192.
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