![]() ![]() You don't have to overdrive a triode to generate harmonic content. Ken Moon wrote:And don't worry about losing any 2nd harmonics - the signal just doesn't get big enough on an input stage to see that effect. This also has the benefit of producing lower output impedance, which will mean less loss if a tone stack immediately follows the parallel triode stage. The lower noise (higher SNR) comes from using smaller resistor values in the circuit. So a center-biased 12AX7 parallel input stage (in typical range of preamp B+ values) might use a 10k grid stopper, 51k plate resistor and 750R cathode resistor, and would be fully bypassed with a 44uF cathode bypass cap. If you have a typical input stage, want to keep the same frequency response and voltage swing on the output, and just get the advantage of lower noise, you'd need to:ġ) Cut value of grid stopper in half (since input capacitance doubles with dual triodes, halving resistance keeps same freq response).Ģ) Cut values of plate resistor and cathode resistor in half. ![]() ![]() Whether or not a parallel triode stage has more gain than a single triode stage depends on the rest of the circuit.Īnd don't worry about losing any 2nd harmonics - the signal just doesn't get big enough on an input stage to see that effect. ![]()
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