The Doshi Line Preamplifier V3.0

The Doshi Line Preamplifier V3.02018-11-20T12:31:04+00:00

Project Description

The Doshi philosophy can be expressed in one word: balance. A balance of classical and cutting-edge technologies, of measured and musical performance, of professional and residential design advantages. Nowhere is this sense of balance more evident than in the Doshi Line Preamplifier.

Designed for residential use, the Doshi Line Preamplifier takes its inspiration from sophisticated techniques developed for the recording industry. Based upon legendary studio hardware including Pultec EQs and Universal Audio Compressors, Doshi has developed a transformer-coupled volume control, a technology which offers performance advantages not possible with any other design. Offering both a fully differential signal path and Galvanic Isolation, the Doshi Volume Control handles all inputs—XLR or RCA—as fully balanced and provides isolated, floating outputs, thereby eliminating the possibility of ground loops at either input or output, assuring absolute freedom from ground noise: an especially important consideration with digital sources.

Doshi’s Purist Pathway™ doctrine of circuit simplicity reaches its full potential in our Line Preamplifier due to its single gain stage, which employs one ECC99 Dual-Triode Vacuum Tube per channel: the first triode provides gain while the second—a “Follower”—minimizes output impedance. Thanks to our elegant circuit design, the Doshi Line Preamplifier offers zero negative feedback, low output impedance and the ability to drive any cable and amplifier load.

The Doshi Linestage includes four differential inputs, each of which can be outfitted with either XLR or RCA connectors, tailored to its owner’s needs (Two XLR and Two RCA are standard).  Inputs are relay-switched into a transformer which provides 31 high-precision, relay-switched volume steps. Home Theater Bypass is also included, further augmenting versatility. Two sets of differential isolated outputs—also specified as RCA or XLR to the customer’s desires—and a 12V on/off Trigger complete our preamp’s comprehensive connectivity. Naturally, all functions of the Doshi Line Preamplifier have been placed under the control of an elegantly styled, machined aluminum remote control.

Behind its sculpted aluminum faceplate, the chassis of our Line Preamplifier incorporates Doshi’s 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. While our competitors build their enclosures from mild steel and aluminum, Doshi uses extremely strong 14-gauge stainless steel to create a chassis that is mechanically and electrically inert; as a result, our components provide an ideal foundation for performance.

As befits a state-of-the-art component, the Doshi Line Preamplifier includes an oversized power supply housed in a separate, resonance-controlled chassis. Connected to the Preamplifier via a custom-made, heavily damped and shielded cable, our power supply includes a purpose-built transformer. Manufactured by Toroid, this transformer is massively over-specified to prevent resonances that occur when a transformer is run at full capacity. Power Supply capacitance in excess of 1,500 microfarads is 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. In order to extend tube life, all Doshi power supplies feature soft-start circuitry.

The Doshi Line Preamplifier represents the highest level of audio performance ever achieved in a linestage. The realization of timeless circuit designs, executed with the finest component parts, uncompromising build quality and inspiring aesthetic beauty, the Doshi Line Preamplifier represents a lifetime investment in musical pleasure.

Specifications:

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Gain: 12db gain

S/N Ratio: over 100db

Tube Complement: 2 ea ECC99 long life driver tubes (one per channel)

Input Impedance: 10 kOhm

Output Impedance: 50 Ohm Typical

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