The phono preamp uses three triodes per channel: one half of two 6N1P-EB type tubes for gain, and one half of a 12BH7 for cathode follower output. The 6N1P is a current production Russian tube; its high performance specs and sound quality have made it a favorite alternative to pricey NOS valves.
The RIAA equalization is split; the first EQ constant is implemented between the two 6N1P gain stages, and the second EQ constant between the second gain stage and the cathode follower. The cathode follower is direct coupled, with an output impedance of roughly 500 ohms, so the circuit can easily drive long interconnects.
Constant Current Sources (CCS) are used for loads on all the tubes, and LEDs are used within the CCS for cathode bias. The LEDs are selected for their low noise, dynamic impedance, and RF stability in the circuit.
If you’re not an engineer, don’t worry if this all sounds
complicated. The simple result of the circuit is rich, smooth, detailed
analog sound in all its glory.
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