The Fascinating KT170
The Tung-Sol KT170 is an octal-based beam tetrode vacuum tube, introduced in 2021 as the flagship model of the KT (kinkless tetrode) series.
The KT family has long been revered by audiophiles, with the KT88 at its heart since 1956. Over the years, many have tried to create a new vacuum tube for high-end audio that delivers more power while matching or exceeding the KT88’s sonic quality.
The KT170, Tung-Sol’s latest and most refined creation, represents the culmination of Cayin’s extensive expertise with all available KT vacuum tubes.
With its highly efficient external power supply circuit and substantial power reserves, the KT170 offers a commanding headphone output of up to 18W per channel, elevating the personal listening experience to new heights.
Immersive Listening Experience
The driver tubes amplify the signal voltage, ensuring that the amplification circuit operates with exceptional linearity.
The KT170 output tubes, operating in single-ended Class A, provide a fully amplified signal without splitting the musical information, preserving the purity of the sound.
Cayin’s engineers have carefully designed the gain circuit, independently adjusting the working current at each vacuum tube stage, allowing the Soul 170HA to deliver the full, rich tones unique to single-ended Class A amplification.
The Soul 170HA offers users a truly immersive audio experience, balancing musicality with technical precision.
Single-ended Voltage Amplification
After evaluating various options, Cayin chose two indirectly heated dual triode JJ 6SN7 tubes for voltage amplification due to their medium amplification factor and low internal resistance.
The JJ 6SN7 is renowned for its low noise, balanced tonal output, and dynamic, detailed sound that offers exceptional musical expressiveness.
Outboard Power Supply Design for Ample Power
With a physically separated, two-box design, the outboard power supply delivers clean, low-noise power to the amplification circuit, ensuring independent operation. This design also provides superior heat dissipation, even when stacked, offering flexibility in amplifier placement.
Dual power supply transformers deliver both high and low voltage separately, minimizing electrical interference and ensuring clean power to the amplifier.
A multi-stage tube-regulated power supply feeds different stages of the amplification independently, reducing ripple effects and improving both voltage and current amplification performance.
The high-rigidity chassis and damping mounts effectively absorb shock and vibration, isolating noise caused by transformer vibrations and magnetic leakage to achieve a higher signal-to-noise ratio (SNR).
Indispensable Power Supply Link
Heavy-duty Umbilical Cable
Custom-designed, silver-plated 6N copper wires connect the outboard power supply to the main chassis. These cables feature separate high- and low-voltage transmission, with two cables in total.
6N copper ensures excellent electrical conductivity, minimizes impurities that could interfere with signal transmission, and guarantees long-term performance and durability.
The cables are independently shielded to minimize external interference as well as interference between the multi-stage power supply circuits.
Foolproof Quick-Release Connections
Aviation-grade quick-release connectors are used on both ends of the cables for a seamless connection. The 8-pin connector is for high-voltage power transmission, while the 12-pin is for low voltage, ensuring the independent feeding of power from the multi-stage supply to various amplification stages.
These connectors allow for quick, reliable connections and disconnections, with no risk of error.
Tube-Regulated Power Supply
The Soul 170HA uses a multi-stage tube-regulated power supply, feeding power to various amplification stages independently.
Two JJ GZ34S rectifier tubes manage the high-voltage supply to the driver stage, ensuring a tube presentation that is euphonic and nuanced.
The rectifier tubes convert incoming power to DC, providing clean power with minimal interference for the circuit. Unlike output or driver tubes, rectifier tubes last for years without deterioration and do not require matching, making them easy to replace individually.
The Essence of Tube Amplification
Transformer-Coupled Balanced Output
The Soul 170HA is a transformer-coupled, single-ended Class A amplifier. The KT170’s output drives a pair of transformers that support both headphone and speaker outputs.
The vacuum tube amplification operates in single-ended mode, with the output transformers providing an alternative phase to create a balanced output, allowing for a balanced drive from a single-ended circuit.
Custom-Designed Audio-Grade Transformers
Transformers are crucial in Cayin’s amplifiers. The choice of core material, winding specifications, and copper wire quality all affect the performance and sound signature of the amplifier.
Cayin designs and manufactures all power supply and output transformers in-house, allowing full control over the design to achieve the desired sound.
They use high-purity copper enameled wire in toroidal power supply transformers to minimize magnetic noise.
Custom-designed EI-type output transformers, using a Z11 silicon steel core, ensure minimal signal loss and enhanced fidelity.
Cayin’s shielding packaging and circuit protection measures prevent noise interference and extend the lifespan of the product.
Dual Operation Modes
Triode Mode
In Triode mode, the KT170’s screen grid is directly connected to the anode. This configuration produces a tender, smooth, and elegant sound with a holographic image, ideal for vocals, strings, and mid-range focused genres.
Ultralinear Mode
In Ultralinear mode, a tap on the primary winding of the output transformers connects to the KT170 screen grid, increasing the voltage and changing the power tube’s operating state. This results in a bold, open sound with great momentum, making it perfect for orchestral music and compositions with a wide dynamic range.
Dual Tonality
By adjusting the operating current of the two KT170 tubes simultaneously, users can choose between:
- Dynamic: Dense, fast, and powerful, with prominent contrast and an exciting, forceful quality.
- Soft: Relaxing, delicate, and peaceful, revealing low-level details with an engaging and immersive quality.
Impedance-Matched Headphone Output
The in-house designed output transformers provide three sets of impedance-matched outputs for different headphone impedances:
- Low (L): 8Ω-64Ω
- Mid (M): 65Ω-250Ω
- High (H): 251Ω-600Ω
Properly matched impedance ensures natural sound with well-defined bass, particularly for planar headphones, which are more sensitive to impedance matching than dynamic headphones. Users can experiment with different settings once they become familiar with the sound signature of each output.
Application-Oriented Output
The 4-pin XLR output provides a fully balanced output, while the 4.4mm headphone output is optimized for a broader range of applications, including high-sensitivity portable headphones and IEMs.
- 4-pin XLR (Balanced): 12WPC–18WPC
- 4.4mm (Balanced): 2WPC–4WPC
- 6.35mm (Single-ended): 7WPC–17WPC
The 4.4mm output is optimized for low-impedance, high-sensitivity headphones and IEMs, ensuring minimal noise and excellent sound quality. It can also serve as a fallback when dealing with hum or interference.
Dynamic Auto Bias
The Soul 170HA features a Dynamic Auto Bias servo circuit that automatically adjusts the bias when vacuum tubes are replaced, ensuring optimal compatibility with the amplifier. This circuit enhances safety and extends tube life.
0dB Gain Difference
The volume control system includes a custom ALPS carbon film potentiometer and low-noise, low-distortion JRC MUSES72320V electronic volume chips, providing 128 precise volume steps for stable and reliable control. The system guarantees a 0dB gain difference between the two channels, ensuring balanced audio output.
Comprehensive Protection for Ideal Performance
The Soul 170HA is equipped with an MCU that manages multiple protection circuits and startup sequences to safeguard the amplifier’s performance and ensure the safety of the vacuum tubes.
Performance-Driven Design, Top-of-the-Line Configuration
Hand-Matched Vacuum Tubes
Each vacuum tube used in the Soul 170HA is hand-tested and matched. They undergo stringent performance tests, including a 48-hour aging process, final measurements, and a listening test to ensure uniformity and high-quality sound.
Classic Point-to-Point Wiring
The entire circuitry is hand-wired using point-to-point soldering, ensuring the shortest signal path and minimal signal loss. This design isolates audio signals, grounding, and high-voltage power, preventing interference and enhancing reliability.
High-End AudioCapX PPFXS Coupling Capacitors
These capacitors isolate DC, improve audio transmission accuracy, and enhance the overall sound quality.
Elegant and Majestic Design
The Soul 170HA’s front panel is made of aerospace-grade aluminum with a matte black anodized finish, while the side panels are crafted from North American black walnut wood, polished by hand for a refined aesthetic. The luxurious VU meter design combines functionality with visual appeal, and the protective tube cage prevents accidental contact with the hot tubes during operation.
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