Product Features: Mid-frequency richness, warm sound, smooth elasticity, strong sense of air, and long-lasting listening pleasure without fatigue. The effects vary noticeably when switching between different brands of vacuum tubes, making it ideal for novice DIY enthusiasts who enjoy experimenting. The included vacuum tubes are as described in the text; images are for reference only.
The Charm of Vacuum Tubes: Vacuum tube amplifiers pair well with digital audio sources (such as CD, VCD, DVD, etc.), using the "tube warmth" to mellow or eliminate digital harshness. This results in a warm, musical, and airy sound, delivering a sweet and smooth musical quality (often referred to as "tube sound"). In contrast, standard transistor amplifiers may produce a piercing, less enjoyable sound due to digital artifacts, commonly known as "transistor sound" or "solid-state harshness."
The 6N8P (interchangeable with international models 6SN7/6H8C/CV181) is a classic low-frequency dual triode. Unlike high-frequency dual triodes (e.g., 6N3) or general-purpose dual triodes (e.g., 6N1), its key characteristics include moderate amplification, low transconductance, and high plate dissipation and plate voltage. Widely regarded for its rich sound and affordability, it is an excellent choice for voltage amplification. Additionally, its high grid bias makes it well-suited for dynamic signal sources like the McIntosh MCD301, which outputs up to 6V.
Common preamplifier circuits include cascode amplification and common-cathode amplification. Most designs feature two amplification stages and one cathode follower. Some units employ a common-plate input stage for improved input characteristics. Critical to any preamplifier are signal-to-noise ratio and distortion. For tube amplifiers, it’s important not to set excessively high expectations for distortion and noise. To achieve optimal performance, using a line amplifier is often necessary. Its key feature is the omission of a volume potentiometer, typically providing around 20dB of voltage gain. High-quality stepped attenuators are expensive and can introduce microphonic effects when adjusted, making their exclusion a practical choice.
While many preamplifiers use pentodes like the EF86 or 6AC7, their high internal impedance can hinder synergy with power amplifiers. We believe that a two-stage amplification design is not always essential. The key lies in increasing the plate voltage to extend the characteristic curve and enhance dynamic output. Inspired by this principle, we adopted a single-tube, single-stage amplification circuit, achieving outstanding results in our final build. The underlying theory is as follows:
[Brief Introduction to Components]
◆ Standard configuration includes one Linlai 5U4G rectifier tube and one GE or RCA 6SN7 amplification tube.
◆ 60W power transformer with pure copper winding (code: 763801) and a 10H 80MA high-inductance choke (EI48x30). Made with high magnetic flux core, both choke and power transformer are fully shielded to minimize magnetic leakage. Finished with baked paint for rust resistance and aesthetic appeal.
◆ Tube rectification using 5U4G or 5Z4P (compatible with various imported 5V rectifier tubes such as 5AR4, 5Z3P, 274B, etc. The transformer filament current is rated at 3A). Filtering circuit consists of two 33μF Rubycon Japan capacitors, two 100μF Rubycon Japan low-impedance capacitors, one 0.1μF film safety capacitor, and a 10H choke in a CLRC configuration. This ensures minimal ripple and a quiet background. Tube rectification delivers finer high-frequency detail and a smoother, more rounded sound compared to solid-state rectification.
◆ Dual 160V 150MA high-voltage supply. 6SN7 operates on 6.3V 1A AC, with two filament balancing resistors grounded to effectively reduce noise. This filament wiring preserves the musical richness of AC heating while eliminating hum. The 5U4G uses 5V AC supply for lively and dynamic sound quality.
◆ No input coupling capacitor. Output coupling utilizes a 2μF Tokyo Electronics TE MKP film capacitor in parallel with a 0.01μF Fairchild USA capacitor, delivering excellent performance across both high and low frequencies.
◆ High-quality metal film resistors with copper leads combined with carbon film resistors for warm sound, enhancing the classic tube character.
◆ Japanese ALPS 16-type potentiometer.
◆ PCB made from 1.6mm thick double-sided copper-clad board with star grounding design. Background noise is exceptionally low, below 2mV. Dimensions: 130mm x 75mm.
◆ Silver-plated copper pin tube sockets. Upgrade to gold-plated sockets for an additional 10 yuan.
◆ Gold-plated pure copper RCA jacks, durable and secure.
Sound Performance: This unit delivers rich, full-bodied audio with an exceptionally quiet background and wide dynamic range.
◆ Weight: 3.7kg
◆ Chassis styled after Western Electric design, constructed from 1.2mm thick steel with spray-coated finish. Dimensions: Depth 220mm (including knobs and RCA connectors), Height 200mm (from chassis feet to top of 5U4G tube), Width 160mm.
