The RF energy creating hiss as it is demodulates by the preamplifier seems not to be easy to deal with.
Preliminary external screening experiments with metal lid and some aluminum foil tape aroun inside bare hot conductor of Yamaha RAX200 did not seem to stop the problem.
The induct ant of the pickup around 70H (Henrys)?! Seems to pick io (sic) low frequency RF, long wave band? One can actual hear radio when volum is turned max.
Why not winding the pickup with just a few turns, like the microphone voice coil. Impedance will be low, signal low, signal balanced. And this 50 or 200 ohms impedance can drive a balanced cable of any length like studio or PA microphones. No DI box would be needed as signal is already ready of direct injection to a mic input. Then inside or just outside the preamplifier a step up transformer will step up signal and impedance to drive the electron tube. Added benefit will be control of low cut cutoff frequency by the primary inductance of the transformer attenuating all this nasty muddy bass.
All the many turns will be therefore in the transformer core instead of in the pickup. And if it is a nanoperm toroid like Magnetec's all magnetic field will be contained there and external pickup field will be tending to zero.
Of course the bass signal is high anyway and one can just barely get away with it as the rest of music masks the noise content. But subliminally listening to radio?!, in your favorite rock record?
Preliminary external screening experiments with metal lid and some aluminum foil tape aroun inside bare hot conductor of Yamaha RAX200 did not seem to stop the problem.
The induct ant of the pickup around 70H (Henrys)?! Seems to pick io (sic) low frequency RF, long wave band? One can actual hear radio when volum is turned max.
Why not winding the pickup with just a few turns, like the microphone voice coil. Impedance will be low, signal low, signal balanced. And this 50 or 200 ohms impedance can drive a balanced cable of any length like studio or PA microphones. No DI box would be needed as signal is already ready of direct injection to a mic input. Then inside or just outside the preamplifier a step up transformer will step up signal and impedance to drive the electron tube. Added benefit will be control of low cut cutoff frequency by the primary inductance of the transformer attenuating all this nasty muddy bass.
All the many turns will be therefore in the transformer core instead of in the pickup. And if it is a nanoperm toroid like Magnetec's all magnetic field will be contained there and external pickup field will be tending to zero.
Of course the bass signal is high anyway and one can just barely get away with it as the rest of music masks the noise content. But subliminally listening to radio?!, in your favorite rock record?
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