I've been meaning to build my own amplifier for a while now. My old tube amp is on its last leg and I need something that can withstand a little more damage to bring back to school with me in the fall. Based on an example circuit from the Audio IC Users' Handbook and my interest in gain clone-type amplifiers, I decided to design myself an amplifier board based on the LM3886 IC.
The schematic I used is similar to the main example of the datasheet, with a little more added circuitry. Unfortunately, I won't be able to post a picture of the schematic due to copyright. The board that I designed functions as a one channel 68w amplifier, running off of +/- 28V. In my finished amp, I'll be using two of this board [one for each channel] , as well as a power supply circuit board and a transformer.
I started off with searching Digikey for all the components I plan on using. I'm using all through-hole components in order to keep the board as simple as possible. After finding all the parts I needed to produce two circuit boards, I began to focus on the board design itself. I used the dimensions of the parts I ordered to design a small circuit board that holds just the amplifier IC and the components needed to run it. I wanted the board to be as small as possible in order to minimize noise from circuit board traces, as well as to keep the PCB costs down.
My end result was what you see above. Note that IC1 is not labeled for the LM3886 because I used a different IC with the same footprint to design the board rather than creating a custom component. Designing the board was quite the learning process, it was my first time using EAGLE to create a circuit board, as well as my first time ordering custom circuit boards. I'm happy with the end result.
As a side note, I found that seed studio will produce custom PCB's for a very low cost, and ended up ordering 5 copies of my board for 9.99 - not bad at all! If you'd like a copy of the EAGLE schematic/board files I created I'd be happy to email them to you.
Strange experienced.. Everyone kept telling me not to go over 84 volt or else the chip would die. I have many of these little LM3886T, so I took the risk in testing one of them. I have a power supply that can produce +-36ct or +-48ct at 4amp. I am using the same size heatsink as in the picture without the fan. I first tested with +-36 parallel of 6 speakers, probably some loss through the wires but this brought it down to 2ohm. It sounds great playing "AC/DC Who made Who". Pretty loud with lots of punch. The heatsink was warm but nothing hot. I then switched it to the +-48, this is 96v total exceeded 12v, thinking it will die or not produce any sound because of the SPIKE. Well, it played the same "Who made Who" louder with stronger punches. I left it playing for days, thinking it could only max out for a short amount of time. It didn't give up. The heatsink was hot, but wasn't melting crayon hot. I measured the voltage at the chip's pins, taking in 96volt. when I turned it up full power, the voltage dropped a bit, but it was still 94volt. Has anyone tried higher volts?
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