Accuphase P-300X (1980)

Name: Accuphase P-300X
Brand: Accuphase

At 22.5kg, it is not an amplifier for the timid.

Overview

The Accuphase P-300X is a stereo power amplifier released in June 1980. It is a direct evolution of the P-300 and P-300S, with enough refinements to set it apart from both. It was not a minor revision. It was re-engineered with the latest semiconductor technology of its time. It sold for ¥300,000 at launch and targeted serious audiophiles who wanted both power and precision. Owners report a full-bodied sound, and some call it slightly warm, which suits systems that might otherwise sound lean or clinical. It drives difficult loads with composure and has exceptionally low distortion figures, which suggests a design optimized for transparency without giving up musicality.

Engineering came before cost-cutting here. The amplifier uses 42 transistors, 12 FETs, 7 ICs and 61 diodes, so the layout is densely populated. A MOS FET in the drive stage reportedly stabilizes the bias voltage of the output stage and allows the emitter resistors to be removed, which helps signal path cleanliness and thermal stability. The input stage is a cascode bootstrap differential push-pull configuration. The pre-drive stage uses a cascode transistor connection for wide-band stability. The FET-based input also removes the need for an input coupling capacitor. That gives direct coupling, which reduces phase shift and signal degradation at the frequency extremes.

The P-300X has its quirks. The service documentation is scarce. Users note that service manuals and schematics are considered "top secret" and were never officially released. That makes repairs and adjustments hard, especially for anyone unfamiliar with Accuphase's internal design. Common maintenance means replacing the three speaker relays and the small signal relays, which are known to degrade over time. Bias adjustment is another routine job. The brochure specifies 10mV to achieve the rated 80W idle consumption, but some owners report lowering it to 7mV because of excessive heat buildup after extended operation.

Specifications

Manufacturer	Accuphase
Product type	Stereo power amplifier
Production/release	Released in June 1980
Original price	¥ 300,000
Continuous average power (20 Hz to 20 kHz, Distortion Rate 0.01% or Less) Stereo	200W + 200W (4 Ω), 150W + 150W (8 Ω), 75W + 75W (16 Ω)
Continuous average power (20 Hz to 20 kHz, Distortion Rate 0.01% or Less) Bridged	400W (8 Ω), 200W (16 Ω)
Total harmonic distortion factor (0.25W ~ Rated Output, 20 Hz ~ 20 kHz) Stereo	0.01% (4 Ω), 0.005% (8 Ω), 0.005% (16 Ω)
Total harmonic distortion factor (0.25W ~ Rated Output, 20 Hz ~ 20 kHz) Bridged	0.01% (8 Ω), 0.01% (16 Ω)
IM distortion factor (new IHF)	0.003%
Frequency characteristic	20 Hz ~ 20 kHz + 0 -0.2 dB (Rated Output, Level Control Maximum)
Frequency characteristic	0.4 Hz ~ 500 kHz + 0 -3.0 dB (output 1W, level control maximum)
Frequency characteristic	0.4 Hz ~ 150 kHz + 0 -3.0 dB (output 1W, level control -6dB)
Gain Stereo	27.8 dB
Gain Bridge connection	33.8 dB
Load impedance Stereo	4 Ω ~ 16 Ω
Load impedance Bridge connection	8 Ω ~ 16 Ω
Damping factor (new IHF, 50 Hz) Stereo	150
Damping factor (new IHF, 50 Hz) Bridge connected	75
Input Sensitivity / Impedance Stereo	1.4V/50k Ω (Rated Output), 0.11V/50k Ω (New IHF, 1W output)
Input Sensitivity / Impedance Bridged	1.17V/50k Ω (Rated Output), 0.06V/50k Ω (New IHF, 1W output)
S/N (A correction) Stereo	120 dB (Rated Output, Input Short), 100 dB (new IHF, 1W output)
S/N (A correction) Bridged	110 dB (Rated Output, Input Short), 90 dB (new IHF, 1W output)
Subsonic filter	17 Hz, -12dB/oct.
Output meter	Logarithmic Compression Type, With Peak Hold Switching -40dB to + 3 dB and output direct reading scale
Semiconductor used	Transistor: 42, FET: 12, IC: 7, Diode: 61
Power supply voltage	AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption	No input: 80W, 8 Ω load rated output: 550W
External dimensions Normal	445 mm width x 160 mm height (including legs) x 373 mm depth
External dimensions With Wood Case	Width 466x Height 190 (Including Legs) x Depth 385 mm
Weight	22.5kg
Sold Separately Wood Case	A-8 (¥ 16,000)

Key Features

MOS FET Drive Stage with Direct-Coupled FET Input

The P-300X uses a MOS FET in the drive stage. This contributes to stable biasing in the output stage and allows the emitter resistors to be removed, which reduces signal path resistance and improves thermal tracking. Combined with a FET-configured input stage, it eliminates the input coupling capacitor and gives direct coupling from source to amplifier. This reduces low-frequency phase shift and avoids capacitor-induced coloration, a rare feature in early 1980s power amplifiers.

Cascode Bootstrap Differential Push-Pull Input

The input circuit is a cascode bootstrap differential push-pull configuration, which enhances bandwidth and linearity. It minimizes distortion at the first stage of amplification, where signal levels are smallest and most vulnerable to noise and nonlinearity. The cascode pre-drive stage extends high-frequency stability and contributes to the rated bandwidth of up to 500 kHz at 1W output.

DC Servo Feedback for DC Offset Cancellation

DC feedback is applied through a dedicated DC servo amplifier to eliminate DC offset at the output. This protects the connected speakers over the long term. Passive blocking capacitors can degrade sound quality, so this active method keeps signal integrity while safeguarding downstream components.

Isolated Dual Power Supply with Toroidal Transformer

The power supply uses a toroidal transformer wound only on the right and left sides, with separate rectifier and filter circuits for each channel. This layout suppresses crosstalk and interference between channels and improves stereo separation. The amplifier draws a substantial 550W under full 8 Ω load, which gives ample current even during dynamic transients.

Built-In Bridge Mode Circuitry

The P-300X has internal bridging circuitry, so it works as a monoblock amplifier without external adapters. In bridged mode it delivers 400W into 8 Ω or 200W into 16 Ω, which suits high-impedance or inefficient speakers. Input sensitivity adjusts accordingly, and full output in bridged configuration needs 1.17V.

Logarithmic Compression Peak Level Meter with Hold Function

The output meter is a logarithmic compression type. It reads output power directly on an 8 Ω load via a dB scale. A switch activates the peak hold function, which captures and displays peak levels every three seconds. That is useful when matching the amplifier to preamps or checking clipping behavior.

Step-Type Attenuator with 1 dB Increments

A precision step attenuator controls input level in exact 1 dB increments up to -20dB. Potentiometers can wear unevenly and introduce channel imbalance. A step-type attenuator gives consistent, repeatable settings across both channels, which helps with system calibration.

Historical Context

The P-300X came out of the lineage of Kensonic Laboratory's earliest products - the P-300 power amplifier, C-200 preamplifier and T-100 tuner - which received strong critical acclaim on their release in the early 1970s. The original P-300 was a flagship model of that era. The P-300X was developed as a distinct successor, separate from the P-300, P-300S, P-300L and P-300V models. It refined proven concepts with updated semiconductor technology, and it was released as Japanese high-end audio was gaining global recognition for engineering rigor and sonic excellence.

Collectibility & Value

Market prices for the P-300X vary significantly with condition and region. One auction listing recorded a bid of ¥2,500 on September 14, 2023. A November 26, 2025 listing offered a set including the P-300X for €3,100, which suggests strong demand for fully functional or restored units. Restoration often includes recapping with 105°C-rated components, relay replacement and bias adjustment. The lack of officially released service manuals complicates repairs, and users frequently report difficulty sourcing correct documentation even when they own manuals for other P-300 series models. Properly maintained, the P-300X is regarded as a high-value vintage amplifier, especially when paired with contemporaneous Accuphase preamps like the C-200L.

Market Value

┌──────────────────────────────────────────────────────────────────────────┐
│ ACCUPHASE P-300X                                                Nov 2026 │
├──────────────────────────────────────────────────────────────────────────┤
│ High      $1,678                                  Latest          $1,579 │
│ Median    $1,579                                  Trend                — │
│ Low       $1,359                                  Volume           ~2/mo │
├──────────────────────────────────────────────────────────────────────────┤
│ $2,000 ┤                                                                 │
│        │                                                                 │
│        │                                                                 │
│ $1,571 ┤ .                                                        .    ..│
│        │                                                                 │
│        │.                                                                │
│        │                                                                 │
│ $1,000 ┤                                                                 │
│        ├─────────────────────────────────────────────────────────────────│
│    vol │██                                                        █    ██│
│        └─────────────────────────────────────────────────────────────────│
│         2026-03                      2026-05                      2026-06│
└──────────────────────────────────────────────────────────────────────────┘

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