ALEKS Maestro Silver TUBE PHONO preamplifier MM/MC

The circuit of the phono preamplifier  without negative feedback loop.

The input stage is built on a 6N23P-EV vacuum tube (E88SS; 6922;6DJ8 etc.) using a cascade structure to reduce the input capacitance.

RIAA correction is performed by a frequency-dependent divider between the 1st and 2nd stages.

The 2nd stage allows installation of the tubes 6P14P-EV (EL84); 6P18P (EL82) without additional adjustment of the components.

Although installation of these alternative tubes might affect the sensitivity of the corrector and the perceived audio-tone balance.

A 6P18P tube is installed in the device (service life >= 5000h). If the tubes 6P14P-EV are used instead,

the output signal level increases one and a half times.

A direct connection between the 1st and 2nd stages is implemented. The DC-blocking capacitor is installed only at the output of the device.

The rectifier of the anode power supply is made on a tube rectifier 6C4P-EV (circa 1970’s).

The MS section is built on N-channel MOSFET transistors 2SK170BL (Toshiba).

In MS mode the circuitry is connected directly to the MM circuitry using a signal relay (gold-plated contacts).