6 X 12AU7 tube Grounded Grid preamp
This circuit is a truly minimalist line stage amplifier. It derives its name from the fact that the triode that provides the gain for the circuit receives its input from its cathode being coupled to a Cathode Follower rather than its grid. Still, I prefer to use the name "Common Cathode amplifier" asthat is how the circuit is described in many of my beloved electronic books from the 40's and 50's. (Two articles on this circuit topology and it modification are available at the GlassWare site.) Furthermore, "Grounded Grid amplifier" is usually used to describe an amplifier with only one triode that receives its signal directly at its cathode and hence has both a very low input impedance and low input capacitance.Mr. Rozenblit seems to have a penchant for full-wave voltage doublers. Two are used in this preamp, one for the positive rail voltage and one for the negative rail voltage. Contrary to some of the buzz going around today, there is nothing wrong with these power supply configurations. This power supply circuit doubles the voltage that a full-wave bridge rectifier circuit would provide, but with only half the output current capability. The ripple is at the same 120 Hz frequency as in the full-wave bridge rectifier circuit and the transformer core is not partially magnetized as it is in the half-wave voltage doubler circuit. Shunt
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