Accuphase P-550 (1994)

A high-power stereo amplifier released in April 1994, with a current feedback topology and gold-plated, high-purity parts all through the signal path.

Overview

The Accuphase P-550 is a stereo power amplifier from Accuphase Laboratory, Inc., released in April 1994. It puts out 550W per channel into 2 Ω, 420W into 4 Ω, and 270W into 8 Ω. Bridged mono output is 1100W into 4 Ω and 840W into 8 Ω. It cost ¥580,000 at launch. The design uses a current feedback circuit and has balanced and unbalanced inputs. The build is heavy, with a 15-mm-thick front panel and gold-plated internal signal paths.

Specifications

Production Year	April 1994
Output Power (stereo)	550W/ch (2 Ω), 420W/ch (4 Ω), 270W/ch (8 Ω)
Output Power (monaural, bridged)	1100W (4 Ω), 840W (8 Ω)
Total Harmonic Distortion	0.05% (2 Ω), 0.02% (4 Ω–16 Ω)
IM Distortion	0.003%
Frequency Response	20 Hz – 20 kHz (+0, -0.2 dB) at rated output; 0.5 Hz – 160 kHz (+0, -3.0 dB) at 1W
Gain	28.0 dB (stereo and monaural)
Damping Factor	500 (stereo), 250 (monaural)
Input Sensitivity (8 Ω)	1.85 V (stereo, full output), 3.26 V (monaural, full output)
Input Impedance	20k Ω (unbalanced), 40k Ω (balanced)
S/N Ratio	123 dB (A-weighted, input shorted)
Power Supply	100 VAC, 50/60 Hz
Power Consumption	200W (idle), 980W (max, per Electrical Appliance Law), 920W (8 Ω rated output)
Dimensions	475 mm (W) × 211 mm (H) × 444 mm (D)
Weight	33.0 kg

Design

The P-550 uses a current feedback amplifier circuit, with the output signal fed back as current. The output stage has ten parallel audio power transistors in a high-output multi-emitter structure (130W collector loss, 15A collector current). The drive stage uses power MOS FETs with negative thermal characteristics. Power comes from a 1200 VA toroidal transformer and dual 47,000 μF/100WV electrolytic capacitors. Signal paths use high-purity copper with gold plating. That covers the PCB copper foil, grounding board, bus bars, input terminals, and speaker terminals. The input terminals are about ten times thicker than standard. Balanced inputs work by direct signal injection to the non-inverting and inverting inputs. There are two sets of gold-plated speaker binding posts for bi-wiring, cross-drilled for banana plugs, and both balanced and unbalanced gold-plated inputs. A rotary switch selects input type and stereo or bridged mono mode. The front panel is 15-mm-thick champagne-anodized aluminum with large illuminated analog power meters and a back-lit blue Accuphase logo. The top panel is recessed and holds buttons to turn off the meters and switch speaker outputs. The heat sinks are fully enclosed and the rear handles are large. The amp runs silently, with no thumps at turn-on or turn-off, and stays only slightly warm after extended use.

Reception

Reviewer David Spear described the P-550 as having "extremely pure and transparent sound, precise imaging, a wide and deep soundstage, excellent micro- and macrodynamic contrast, and absolutely no hardness, harshness, congestion, or grundge." The presentation is "crystal clear and highly refined," leaning "analytical" or "cool" rather than "lush" or "warm." Bass is "very well controlled and quite extended," midrange is "agile, nimble, fluid, delicate, effortless, open, pristine, unsullied," and treble offers "excellent air, shimmer, and extension" with a "soft, organic, natural sound." It avoids the harshness often associated with high-powered solid-state amplifiers. The amp performs well even when cold, though 20 minutes of warm-up is typical. It is considered a state-of-the-art component with excellent sound, trouble-free operation, uncompromising build quality, intelligent design, and elegant styling, "well worth its asking price."

Market

Listings for the Accuphase P-550 include a unit at €4,600 (Audio-markt, Jan 26, 2025), one at PLN 29,000 (OLX Poland, Mar 17, 2024), and brochures at €6 (Kleinanzeigen, Jan 27, 2026 and Jan 7, 2023). An original English information folder exists.