Input facilities for ceramic pick-up cartridges.
Following the introduction of ceramic pick-up cartridges, a requirement has arisen for a valve pre-amplifier input circuit having an input impedance of 2MΩ, and sensitivity of approximately 350 mV for full output. Constructors wishing to use such pick-up cartridges with the three pre-amplifier designs described in Mullard Circuits for Audio Amplifiers, Chapters 9 and 14, should alter the circuitry of one of the input positions to the arrangement shown in the diagram. Only relevant component values are shown, and the switching arrangements have been simplified for clarity.
The values given are applicable to the three pre-amplifier circuits, but it should be remembered that the alteration must be made to the same switch position on both channels of the stereophonic pre-amplifier.