MASS-kobo Model 491 twin-balanced monoblock headphone amplifier, hero product shot
MASS-kobo

MASS-kobo Model 491

Sale price$20,000.00

The MASS-kobo Model 491 is the successor to the flagship Model 465, a twin-balanced monoblock headphone amplifier with four high-performance amplifier stages and fully independent left and right power supplies, a topology more commonly found in high-end loudspeaker amplifiers than in headphone designs. Delivers over 3.5 W + 3.5 W into 32 Ω balanced, enough to drive the HIFIMAN Susvara at reference quality. Made-to-order in Japan.

Type and Technology

Twin-balanced monoblock headphone amplifier. Four high-performance amplifier stages (two per channel) with fully independent left and right power supplies. Lead-free solder throughout. Inputs: balanced XLR (electronically balanced, switchable reference input level +4 dBm / -10 dBm) × 2, unbalanced RCA × 2. Outputs: XLR 4-pin balanced stereo × 1, XLR 3-pin balanced L/R × 2, new 4.4 mm balanced × 1, and 1/4-inch TRS single-ended × 1. Three-stage gain selector (LOW / MID / HI). Universal AC 100-240 V power supply.

Sound Character

A clean, stress-free presentation that the manufacturer describes as making the listener "forget the amplifier is even there." The independent dual-mono power supplies and twin-balanced topology contribute to a vanishingly low noise floor and exceptional channel separation: the conditions under which low-efficiency planar magnetic headphones reveal their full dynamic and tonal range without the amplifier imposing its own character.

Build and Connectivity

Compact desktop chassis at 330 × 247 × 104 mm, weighing 6.1 kg without power cable. Front-panel headphone outputs cover every common balanced and single-ended standard so the Model 491 partners with virtually any modern headphone cable terminations. Designed and hand-built by MASS-kobo in Shizuoka, Japan. Each unit is made to order and typical lead time is one to four months depending on parts availability.

Best For

Reference-system listeners pairing the most demanding low-efficiency planar magnetic headphones: including the Dan Clark Audio Stealth, HiFiMan Susvara Unveiled, and similar, with a dedicated headphone amplifier engineered to the standards of a high-end speaker amplifier. The dual XLR 3-pin outputs also make the Model 491 directly suitable for cables that split into separate left/right balanced runs.

What's in the Box

  • MASS-kobo Model 491 headphone amplifier
  • Power cable (standard accessory)
  • Dedicated Pelican case for transport and storage
  • Pelican shipping carton

Specifications

Specification Value
Type Twin-balanced monoblock stereo headphone amplifier
Inputs XLR 3-pin balanced (electronically balanced) × 2; RCA unbalanced × 2
Outputs XLR 4-pin balanced × 1; XLR 3-pin balanced L/R × 2; 4.4mm balanced × 1; 1/4-inch TRS × 1
Input impedance 3.7 kΩ (XLR balanced) / 20 kΩ (RCA unbalanced)
Reference input level Balanced: +4 dBm / -10 dBm (switchable); Unbalanced: -10 dBm
Maximum input level Balanced: +30 dBm (XLR); Unbalanced: +20 dBm (RCA)
Maximum output (P-P) Unbalanced 22 V P-P; Balanced 32 V P-P (32 Ω, 1 kHz, THD+N 0.05%)
Maximum output (RMS) Unbalanced 7.4 V; Balanced 10.7 V (32 Ω, 1 kHz, THD+N 0.05%)
Maximum undistorted output Balanced ≥ 3.5 W + 3.5 W; Unbalanced 1.8 W + 1.8 W (32 Ω, 1 kHz, THD+N 0.05%)
Residual noise (Bal. out) 90 μV (Gain LOW, Vol MIN) to 490 μV (Gain HI, Vol MAX)
Frequency response 10 Hz - 100 kHz (-0.5 dB); 17 Hz - 50 kHz (-0.2 dB)
Gain settings LOW / MID / HI
Power supply AC 100-240 V, 50 / 60 Hz; 0.9 A at AC 100 V
Dimensions 330 × 247 × 104 mm (excluding protrusions)
Weight 6.1 kg (unit only); 11.2 kg packed
Construction Hand-built, made-to-order, lead-free solder
Made in Shizuoka, Japan

Options

The Model 491 is a hand-built, made-to-order product with a one-to-four-month lead time depending on parts availability. Pricing reflects the international MASS-kobo USD list price and is subject to revision in line with the manufacturer's pricing.

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