There’s a mystique in audiophile circles about tube amplifiers ... and the high impedance of its output is brought down to speaker impedance with that mains transformer. Best of all it doesn ...

The K2-W vacuum-tube op amp has an LTspice-simulated open loop gain of 27,000. The modeled K2-W input impedance is >100 MΩ. The LTspice modeled result shows 1.00 nA of input current. Early SPICE ...