DIY Amplifier
DIY Gainclone

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    After completing several sets of speakers I became interested in how I could apply my electrical engineering skills to the construction of an amplifier.  I began searching the web for ideas.  I came across several amplifier kits and designs.  Some of the most prevalent were the 'Zen' amplifiers found at www.passdiy.com and the amplifiers designed by Rod Elliot, namely the P3A and the DoZ amplifier, both of which have good reputations.  The problem for me was that these amplifiers would cost a considerable amount (200-300), dependant on the parts purchased.  I then found out about the gainclone amplifier from the forums over at www.DIYaudio.com.  The Gainclone is a single chip, integrated circuit amplifier.  It requires very little power filtering (the huge capacitors that you see in most amps), and can be constructed using just a handful of components.  Here is the schematic of one channel of my gainclone, the other channel is of course the same.

 


    I did exclude a few components from this schematic, mainly the .1uF paralleled with the 220K resistor was omitted, as was the 1uF capacitor coupling the v+ to v- lines.  I also left out the coupling capacitor on the input (2.2uF) as it wasn't needed since my DC offset was so low coming from my CD player.

    I used a 500VA transformer with 25-0-25 secondary.  This provides more than enough power to keep two gainclones happy, and would provide more if necessary.  I also used slightly more capacitence than shown here.  I do have the 1000uF capacitors right next to the chips, but I also added filtering capacitors right after the rectifiers, or 3300uF apiece.  This equates to a total of 5300uF per rail, with 1000uF per chip per rail. 

Following are some pictures of the inside of the box:

 This is the inside of the amplifier, you can see the heat sinks bolted to the chips.  The blue caps near the rectifiers are the 3300uF filtering capacitors.  Below the near heat sink are some ventilation holes on the lower part of the chassis. 
This shows the transformer and the potentiometer shaft.  The blue wire is a secondary that I hand-wound to create about 6V for my blue LED mounted on the front
 Here you can see the stepped attenuator used for the volume control, and the 1000uF filtering capacitors.  The tiny pink resistor is the feedback resistor.  The other pins poking through the perf board are the other pins on the amplifier chip

    Here are some pictures of the outside of the amplifier, both the front at the back.  My speaker wires may look puny, but the binding posts are just HUGE, they can accept down to 1AWG wire.  The reason that I chose them is because I had them lying around, they were insulated, and it is easy to get a huge clamping force on the wire.  The interconnect is made from 30AWG magnet wire, and sounds very very good, a definite upgrade from my Dayton microphone cable interconnects

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paul.hilgeman@valpo.edu

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