Section 2-29 of:<p><a href="http:&#x2F;&#x2F;nwavguy.blogspot.com&#x2F;2011&#x2F;07&#x2F;o2-design-process.html" rel="nofollow">http:&#x2F;&#x2F;nwavguy.blogspot.com&#x2F;2011&#x2F;07&#x2F;o2-design-process.html</a><p>And the entire article at:<p><a href="http:&#x2F;&#x2F;nwavguy.blogspot.com&#x2F;2011&#x2F;05&#x2F;virtual-grounds-3-channel-amps.html" rel="nofollow">http:&#x2F;&#x2F;nwavguy.blogspot.com&#x2F;2011&#x2F;05&#x2F;virtual-grounds-3-channe...</a><p>Its easy to make something that amplifies, but he&#x27;s trying to make something that provides specs maybe 10x to 10000x better than human hearing can detect, which is much harder.  You can build something that outputs 0.1% THD and you won&#x27;t be able to hear it, but he wants (wanted?) to build to 0.001% THD and he&#x27;s got the rather expensive test equipment required to prove it.<p>JDS labs sells a PCB for less than the cost of shipping (you&#x27;ll spend more on UPS than on the board) or a full parts kit for $60.  This has been around for years and I&#x27;ve been tempted but haven&#x27;t built one.  I just checked JDS and its still in production and in stock.  Being CC- licensed there are probably other places to get PCBs and kits.