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An alternative circuit is shown at the right. It uses a mono-polar power supply and only 12AU7s. No feedback is used and total idle current equals 15 mA per channel. The power supply noise that makes to the output is nulled out by adjusting the amount of power supply noise at the second triode's grid. This signal is phase inverted at the plate where it then cancels. The heater power supply should be reference to +75 volts. To avoid having the front-end adding too much distortion to this amplifier, the common cathode resistor can be replaced with a current source.
The next circuit to the right also uses only 12AU7s and uses a White cathode follower at its output. The circuit below it uses a 12AX7 as an input tube configured as a cathode follower. While probably unnecessary, the cathode follower will extend the bandwidth of the line-stage amplifier.
Both of these circuits invert the output phase. This will upset some audiophiles unnecessarily, as all that is required to set thing straight is to invert the wires leading to the speakers. Yet, some audiophiles balk at the suggestion. Let's imagine a comparable situation. A man walks up to a saleswoman at a bookstore and displays a book held upside down in his hand. He says that this book is the last of its type in the store and he would gladly buy if the printers hadn't printed it upside down. The saleswomen asks why he doesn't turn the book around. He snootily replies that he does buy misprinted books period. She informs that the manager has one copy of the same book in the backroom and that she is willing to swap the books if he wishes. She returns with the righted book and the customer is happy.
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