Doshi Audio Evolution Stereo Amplifier - Hybrid Valve/J-FET Design

The Evolution Stereo Amplifier builds on the successful V3 design, combining solid-state precision with valve musicality in an innovative hybrid topology. Utilising a J-FET differential input stage driving an EL-34/6CA7 valve output section, this amplifier delivers 65 watts per channel of real-world speaker drive capability whilst employing only two gain stages and approximately 7dB of feedback. The result is a sweet, effervescent sound that preserves musical beauty through minimal signal path complexity and carefully managed thermal design.

Reserve your Evolution Stereo Amplifier today to experience the perfect marriage of solid-state control and valve harmonics.

Key Features

• Hybrid topology: J-FET differential input with EL-34/6CA7 valve output stage
• 65 watts per channel into real-world speaker loads
• Only two gain stages for maximum signal purity
• Minimal feedback design (approximately 7dB) for natural sound
• Custom-designed power transformer with regulated supplies
• Innovative output transformer with separate screen windings
• Single-ended/direct or XLR balanced inputs via differential converter

Innovative Hybrid Architecture

The Evolution's unusual topology represents a carefully considered approach to amplifier design. By employing a solid-state J-FET differential amplifier at the input stage, the Evolution achieves exceptional linearity and low noise whilst maintaining the harmonic richness of its valve-based output section. The EL-34/6CA7 output valves, renowned for their musical character, benefit from the precision control of the J-FET input stage. This hybrid approach delivers the best of both technologies - the accuracy and stability of solid-state combined with the dimensional soundstage and tonal beauty of valves.

Minimalist Signal Path Philosophy

Following Nick Doshi's recording engineering principles, the Evolution employs only two gain stages - a remarkably simple topology for an amplifier of this capability. This minimalist approach, combined with approximately 7dB of feedback, ensures maximum preservation of musical detail and dynamics. Where many amplifiers rely on complex circuits and heavy feedback to achieve measured performance, the Evolution prioritises musical realism through elegant simplicity. The result is a level of directness and immediacy that connects listeners to the emotional core of their music.

Advanced Transformer Design

The Evolution features a custom-designed power transformer working in conjunction with regulated power supplies to ensure stable, noise-free operation. The innovative output transformer incorporates separate screen windings - a sophisticated design element that contributes to the amplifier's sweet, effervescent sound character. This careful attention to transformer design reflects Doshi's understanding that these critical components fundamentally shape an amplifier's sonic signature.

Thermal Management Excellence

Every passive component in the Evolution is rated for many times its actual dissipation, resulting in low thermal stress and minimal heat modulation. This over-engineering ensures that components operate well within their comfort zone, maintaining consistent performance regardless of dynamic demands or extended listening sessions. The reduced thermal stress also contributes to long-term reliability, ensuring the Evolution delivers consistent performance for decades to come.

Flexible Input Configuration

The Evolution accommodates both single-ended and balanced sources with equal finesse. Single-ended sources connect directly to the amplifier's input stage, maintaining the shortest possible signal path. Balanced XLR inputs are handled via a high-quality differential to single-ended converter, ensuring that balanced sources benefit from noise rejection whilst maintaining the amplifier's inherently simple topology. This flexibility allows the Evolution to integrate seamlessly with any high-end system configuration.

Real-World Performance

Delivering 65 watts per channel, the Evolution provides ample power for driving a wide range of loudspeakers in real-world conditions. Unlike specifications measured into simple resistive loads, this power rating reflects the amplifier's ability to drive actual loudspeakers with their complex impedance characteristics. The combination of valve output stage and robust power supply ensures that the Evolution maintains its composure with demanding speaker loads whilst preserving the delicate nuances that bring music to life.

Technical Specifications

• Power Output: 65 watts per channel
• Topology: Hybrid - J-FET differential input, EL-34/6CA7 valve output
• Gain Stages: 2 stages only
• Feedback: Approximately 7dB
• Output Valves: EL-34/6CA7 type
• Inputs: Single-ended/direct or XLR balanced (via differential to SE converter)
• Power Transformer: Custom-designed with regulated supplies
• Output Transformer: Innovative design with separate screen windings

Design Philosophy

The Evolution Stereo Amplifier embodies Doshi Audio's commitment to preserving musical beauty through intelligent engineering. By using the minimum number of gain stages and carefully managed feedback, the Evolution maintains a level of realism that serves the music rather than the specification sheet. This approach, informed by Nick Doshi's years of recording live performances, ensures that the excitement and emotional impact of the original performance reaches the listener intact.

Experience the Evolution Stereo Amplifier - contact Martins Hi-Fi to arrange a demonstration of this exceptional hybrid amplifier in our dedicated listening rooms.