In the mid-1970s, two economists—friends and serious audiophiles—Dr. William Conrad and Dr. Lewis Johnson—were highly dissatisfied with the commercially available equipment of the time and were also perplexed and challenged by the readily apparent sonic differences among components in their own systems. What made these two classic tube systems sound so different? Could the virtues of each be somehow combined? Not content to merely speculate on such issues, Conrad and Johnson decided to systematically investigate by developing and refining a vacuum-tube preamplifier.