6SJ7/EBC33 Hyperlinear Preamp

The term "Hyperlinear" referes to the feedback loop from the cathode follower back to the input pentode’s screen grid (g2). Due to this feedback loop the input pentode is more or less working in triode mode, but the connection between plate and g2 is extended to include the cathode follower. This reduces the overall distortion and lowers the output resistance of the CF.

Some measurements with 6SJ7G and EBC33:

• THD: 0.05% at 1V rms output.
• THD: 0.5% at 10V rms output.
• Output impedance: 200ohm.
• Frequency response: 10Hz – 100kHz (+0/-3dB, 50k load)
• S/N: ~78dB ref 1Vrms output.
• Max gain 24dB.
• Max output level: 25V rms.