V3.0 Phono Stage

V3.0 Phono Stage2018-10-07T09:51:08+00:00

Project Description

More than half a century after their introduction, LP records remain audio’s most enduring software format. The Doshi Phono Preamplifier is equally timeless, extracting more information with less artifact than any other phono stage. Now in its third iteration, our Phono Preamplifier has undergone a series of refinements which further elevate its performance.

Engineered to excel with both MC and MM phono cartridges, the Doshi Phono Preamplifier includes a Moving Coil Pre-Preamplifier whose J-Fet transistors provide 26 dB of gain, followed by a pair of monaural, 2:1 step-down transformers which lower gain to 20 dB. Although MC head amps often use step-up transformers (i.e., to increase gain) our novel use of step-down transformers accomplishes three critical benefits:

  • Provides Galvanic Isolation, keeping Pre-Preamplifier grounds separate from the rest of the preamp
  • Converts balanced cartridge input to single ended output, enabling our “Zero-Feedback” tube circuit
  • Impedance is stepped-down 4:1, providing increased bandwidth and a low impedance output to drive the tube MM section.

Driven by our integral MC head amp or directly by a Moving Magnet cartridge, Doshi’s Phono Preamplifier uses three dual triodes per channel to deliver 52 dB of gain (72 dB with head amp), low impedance drive of the passive RIAA EQ circuit and an output impedance of less than 150 Ohms: an impressive specification more typical of transistor circuits. This topology enables our Phono Preamplifier to drive any load. Compatibility with the widest variety of cables and Line Preamplifiers is assured.

Our Phono Preamplifier’s circuit architecture honors the Doshi Design Philosophy. By employing the minimum number of gain stages, we avoid alteration of the delicate audio signal. Just as important, the preamp’s positive and inverting stages are designed to draw equal current which prevents modulation of the power supply for noise-free stability.

The Doshi Phono Preamplifier incorporates our Three Stage Decoupling™ technology to virtually eliminate the influence of both external and internal resonances upon our circuits’ performance. Critical audio circuits are point-to-point wired and mounted on an acoustically isolated sub-chassis. The
entire sub-chassis is suspended from a ½“ thick slab of laser-cut, DuPont Corian which, in turn, floats upon four vibration absorbing feet that are mechanically decoupled from the chassis. Doshi uses extremely strong 14-gauge, powder-coated stainless steel to create a chassis that is mechanically and electrically inert, providing an ideal foundation for performance.

All Doshi Preamplifiers—Line, Tape Head and Phono–include an oversized power supply housed in a separate, resonance-controlled enclosure constructed from the same 14-gauge stainless as our components. Connected to the Preamplifier via a custom-made, heavily damped and shielded cable, our power supply includes a massively oversized transformer and capacitance in excess of 1,500 microfarads: specifications more typical of power amplifiers than preamplifiers. High speed, low noise rectifiers and three levels of resistive-capacitive power filtering provide total isolation of the high voltage supply from the mains, eliminating current modulation and delivering battery-like purity and stability while avoiding the high source impedance of a battery supply. A second,
purpose-engineered power supply for the head amp ensures ultimate circuit performance. In order to extend tube life, all Doshi power supplies feature soft-start circuitry.

To enhance user-friendliness, the Phono Preamplifier provides microprocessor control of input selection, phase and loading functions, all of which are adjustable from a remote handset as well as the front panel. With MC cartridges, loading can be varied from 10 to 250 Ohms in 10 Ohm steps and from 250 to 6K Ohms in 20 Ohm steps. Two loading options can be stored and toggled to allow instantaneous comparison, thereby facilitating fine-tuning
of any MC cartridge. Two MM inputs—47 kOhms and 10 kOhms—are also provided.

Conceived as the definitive component for analog enthusiasts, the Doshi Phono Preamplifier combines purist performance with extreme user-friendliness, exquisite sonics with timeless visual appeal and, of course, build quality and reliability that set the standard for the audio industry.

Specifications:

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Inputs:  Total of 3:  1 MC with adjustable loading. 1 MM input with 10K ohms load and 1 MM input with 47K load

Outputs:  Total of 2 pairs, supplied as RCA , Transformer balanced outputs available as option (additional cost)

Output impedance:  250 Ohms, Capable of driving loads of 10K ohms and higher

Gain:  Total 72db ( MC 22db, MM 50db)

Tubes used:  (2) ECC83/12AX7, (2) ECC81/12AT7, (2) 7247/12DW7

Accessories:  Separate, isolated power supply, umbilical cable with ground wire, and remote control

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