A Pleiades transformers was made using Magnetec's 388 Nanoperm core. Primary turns were 6 and secondary turns were 110. Primary inductance was 0.6mH which was previously found to be a good value to compensate the Grampian ribbon for proximity of about 1 inch. Assuming a mic output impedance of 50 Ohms this gives a low cut turnover of 20KHz! Pop behaviour was very good due to the electromagnetic damping of the ribbon from the short circuit offered by the Pleiades filter at close to 0Hz.
The secondary was capacitor coupled to a Pleiades input amplifier made of a EF183 electron tube triode connected and 4MOhms from plate to grid!, and a bit more than 3V at plate, Vb being 4,5V!
Voice was extremely natural with excellent transparent detailed and soft sibilants, possibly due to the resonance of the ribbon being at sub low frequency giving very low displacements at HF and the excellent transient response of the very lightweight ribbon. Some apparent hiss may be improved if the step up ratio is increased from 1:18 to 1:30. I am pleased after less than 20 years of experiments to hear such a nice and natural voice reproduction from the excellent ribbon mic. The Grampian mic had its 25-50Ohms output connected to the 0.6mH Pleiades primary winding.
The secondary was capacitor coupled to a Pleiades input amplifier made of a EF183 electron tube triode connected and 4MOhms from plate to grid!, and a bit more than 3V at plate, Vb being 4,5V!
Voice was extremely natural with excellent transparent detailed and soft sibilants, possibly due to the resonance of the ribbon being at sub low frequency giving very low displacements at HF and the excellent transient response of the very lightweight ribbon. Some apparent hiss may be improved if the step up ratio is increased from 1:18 to 1:30. I am pleased after less than 20 years of experiments to hear such a nice and natural voice reproduction from the excellent ribbon mic. The Grampian mic had its 25-50Ohms output connected to the 0.6mH Pleiades primary winding.
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