So, you need power, real pure audio power, not to annoy your neighbors with your psy trance collection of CDs or gigabytes of digital music in your computer that you carefully selected, but just to know that, by just turning your volume control a notch, you are able to unleash a monstrous sound prone to create envy to your audiophile friend.He just bought his (perfect) tube amplifier, but not you. You want to enjoy the master pieces of classical composers, your favorite jazz groove or that north European head-banging heavy metal band without needing a second mortgage for your house.
Well, I thought the same, and like others ended up knowing the now (in)famous GainClone, which is a simple audio amplifier based on a single chip, in this case the National Semiconductor LM3886, which can provide you with 68W mono power into a 4 ohm speaker system.
I bought a set of these chips long ago and they were gathering dust in one of my electronic part cabinet drawers, until a friend of mine got a gainclone kit for himself. Not feeling to be left behind, I decided to put my hands into the dirt, literally: I had a bunch of non-working 20 year old transistor based amplifiers that I got at a yard sale, along with a nice pair of Technics SB-LX7 8ohm 3-way 200W speakers.
The good thing about keeping junk around is that you can always make use of it, and so I did: scavenged all the parts from one of the old amplifiers, which has markings on the left of “Realtime Processed DC power Amplifier – LUXMAN 5M20″ and “Laboratory Reference Series : Customed by Lux Corporation” on the right.
I could make use of one of the power supply transformers and the rectifying circuitry (the original amplifier has two independent power units), which saved me a lot of dough. I also took out some resistors and capacitors from the old circuits to use them around the LM3886 chip.
The schematic doesn’t go much farther than the bare application circuit shown within the LM3886 datasheet, has you can see from figure 1. Using the available parts recovered from the junk, I designed the board shown in figure 2, which is larger than you usually see from kit vendors, but since I was using old parts, this technology tends to have capacitors which take more area on the PCB. Call me nuts by using 20 year old electrolytic capacitors…You can get both the schematic and pcb design in Eagle format from here.
After printing out the PCB drawing into the Staples Photo Basic Paper SKU 471861 / SKU471865 and going through the normal procedure of using the GBC H200 laminator, hot water for peeling out the paper and etching with heated and bubbling Sodium Persulphate, I got the nice looking bare PCB boards shown in figure 3.
Having the PCB boards, and after drilling and populating it with the parts, I just needed to prepare myself to hear for the first time the oh so famous gainclone sound coming out from one of the Technics speakers.I plugged one of the boards to the power supply of the old amplifier, which gives around 30-0-30V of DC voltage and using a makeshift rca to 3.5mm jack cable to connect the input to my 1GB i-River MP3/OGG player, I could finally appreciate the excellent sound produced by this seemingly simple audio system.