Accuphase P-500 (1985)

Name: Accuphase P-500
Brand: Accuphase

At 33.5 kg, it doesn't just sit on the rack - it stakes a claim.

Overview

The Accuphase P-500 is a 33.5 kg solid-state stereo power amplifier in brushed aluminum and heavy-gauge steel, from Japan's golden era of high-end audio. It was released in May 1985 and built to deliver massive power without losing low-level detail. It's described as a "'Golden Era' power amp with phenomenal performance!" That's a promotional label, but the spec sheet makes it hard to wave away. Accuphase was originally Kensonic Laboratory, Inc. The P-500 carries forward design ideas from earlier flagships like the M-1000 and P-800, balancing big output with careful small-signal handling. At launch it retailed for ¥510,000.

Owners report that the P-500 doesn't just amplify - it controls. The weight hints at the massive toroidal transformer and dense capacitor bank inside. They feed a dual monaural architecture designed to minimize crosstalk and power supply interference. The front panel has an analog pointer meter that tracks output in both dB and wattage. There's no remote power and no digital inputs. It's overbuilt and entirely focused on the signal path.

Specifications

Manufacturer	Accuphase (originally Kensonic Laboratory, Inc.)
Product type	Stereo power amplifier (Solid state)
Production years	Released in May 1985
Original price	¥ 510,000
Country of Manufacture	Japan
Continuous average power (20 Hz to 20 kHz, THD 0.02%)	Stereo: 500W/ch (2 Ω), 420W/ch (4 Ω), 250W/ch (8 Ω), 125W/ch (16 Ω); Monaural (bridge connection): 1000W (4 Ω), 840W (8 Ω), 500W (16 Ω)
Total harmonic distortion	Stereo: 0.02% (2 Ω), 0.01% (4 Ω ~ 16 Ω); Monaural (bridge connection): 0.02% (4 Ω), 0.01% (8 Ω ~ 16 Ω)
IM Distortion Factor (SMPTE-IF)	0.003%
Frequency characteristic	At continuous average output: 20 Hz ~ 20 kHz +0, -0.2 dB (Level Control Maximum); At 1W output: 0.5 Hz ~ 300 kHz +0, -3.0 dB (Level Control Maximum); At 1W output with Level Control -6dB: 0.5 Hz ~ 100 kHz +0, -3.0 dB
Gain	28.0 dB (both stereo and monaural)
Load impedance	Stereo: 2 Ω ~ 16 Ω; Monaural (bridge connection): 4 Ω ~ 16 Ω
Damping factor (50Hz)	Stereo: 500; Monaural (bridge connection): 250
Input Sensitivity (8 Ω)	Stereo: 1.78 V (at continuous average output), 0.12 V (at 1W output); Monaural (bridge connection): 3.26 V (at continuous average output), 0.12 V (at 1W output)
Input impedance	20k Ω (unbalanced), 40k Ω (balanced)
Signal-to-noise ratio (A-weighting)	120 dB (Input Shorted, Continuous Average Output); 100 dB (Input 1k Ω, 1W output)
Subsonic filter	10 Hz, -18dB/oct.
Output meter	Logarithmic compression type -60dB to +3 dB and output direct reading scale
Semiconductor used	Transistor: 82, FET: 10, IC: 8, Diode: 79 pcs
Power supply	AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption	115W (no input), 840W (Electrical Appliance and Material Control Law), 850W (at 8 Ω load rated output)
External dimensions	Width 481 mm x Height 218 mm (including legs) x Depth 445 mm
Weight	33.5 kg

Key Features

Six Parallel Push-Pull Output Transistors per Channel

Each channel uses six parallel push-pull transistors with a collector loss rating of Pc150W, 12 transistors per side. This lets the P-500 deliver 500 watts per channel into 2 ohms without strain, and it stays stable under difficult speaker loads. The design favors current delivery and thermal resilience, which low-impedance or reactive speakers common in high-end systems of the era need.

MOS FET Front Stage with Cascode Push-Pull Configuration

The front stage driving the final output uses a non-switching class A MOS FET setup in a cascode push-pull arrangement. This minimizes crossover distortion and gives a clean, linear signal to the output stage. It avoids the switching artifacts typical of conventional class AB designs, which contributes to the amplifier's exceptionally low distortion figures.

Cascode Bootstrap Push-Pull Input Circuit

The input stage is built around a cascode bootstrap push-pull circuit, which improves bandwidth and linearity. The signal path is direct-coupled, with no capacitors in the signal chain, so it keeps phase coherence and transient detail. Accuphase was clearly set on minimizing passive components that could degrade the signal.

Accuphase Original DC Servo System

A proprietary DC servo system cancels DC offset at the output, so no output coupling capacitors are needed (OCL design). This extends low-frequency response and stabilizes performance across temperature shifts, reducing drift. It also protects connected speakers from potential DC damage.

Dual Monaural Construction with Independent Power Supplies

The P-500 uses a true dual monaural layout, with completely separate power supplies for each channel. The transformer has independent windings for the output and pre-driver stages. The front end gets dedicated rectifiers and filters for left and right. This keeps the channels from contaminating each other and gives each maximum headroom.

Full-Range Balanced Input with 40k Ω XLR

Balanced XLR inputs are standard, rated at 40k Ω. Unbalanced RCA inputs sit at 20k Ω. The balanced circuit includes a 1 dB step double attenuator for precise level matching in professional or high-end home setups. Having both input types was forward-thinking for 1985.

Bridge Connection Switch for Monaural Operation

A front-accessible switch enables bridge mode, which turns the stereo amplifier into a monaural unit delivering 1000 watts into 4 ohms. That suits users running high-efficiency horns or demanding subwoofers, and it saves buying a separate mono block.

Analog Pointer Power Meter with Dual Scale

The front panel has a logarithmic compression-type analog meter that reads from -60 dB to +3 dB, with an additional scale for direct wattage output. Owners note it gives real insight into dynamic headroom and clipping behavior, which was rare in solid-state amps of this period.

Historical Context

The P-500 was developed using technology derived from the M-1000 and P-800, flagship models that established Accuphase's reputation for precision engineering. It was released in Japan in 1985, at the peak of the country's high-fidelity boom, when manufacturers competed on build quality, measured performance, and sonic transparency. Accuphase was founded by former Kenwood engineer Jiro Kasuga in late 1972, and had already built credibility with early models like the P-300, C-200, and T-100. The P-500 was more powerful and more refined than that lineage before it.

Collectibility & Value

The P-500 remains sought after among collectors of Japanese high-end audio. Units appear regularly on the vintage market, typically described as in very good condition with minor cosmetic wear but professionally tested and fully functional. According to recent listings, an auction bid reached ¥298,000 as of July 7, 2024, while asking prices have been listed at $3,700. Its construction and high-quality components contribute to its longevity, though no data exists on common failures or specific maintenance challenges. Given its weight, power demands, and lack of modern connectivity, it's not an amp for casual listeners.