Posted on Feb 6, 2014

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 LM3886 circui

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t 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 PowerPCB 5. 0. I think it is a powerful layout software. The equalizer used is a regulated power supply. I used 10000uF per rail before the LT1083 regulator. After the regulator, I have 100uF on the regulator board. The advantage of using regulator is that the equalizer ripple voltage is removed. If power regulation is not used, I can hear very little 50/100Hz hum from the speaker. The high current MUR860 diode is used to ensure high current flow. The voltage regulator used is LT1083, it can provide about 8A of current. Transformer used here is a 500VA 2x 25V. The equalizer is then regulated by 2 LT1083, after the regulation, the...

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