Accuphase F-15L (1981)

Name: Accuphase F-15
Brand: Accuphase

Active multi-channel crossover with switchable slopes and modular frequency boards, released August 1981.

Overview

The Accuphase F-15L is an active crossover (multi-channel divider) manufactured by Accuphase Laboratory, Inc., originally known as Kensonic Laboratory, Inc. It was released in August 1981 with balanced and unbalanced input/output circuits. The unit supports 2-way to 5-way speaker systems, using interchangeable crossover boards to set frequency points—21 standard options available. For 2-way operation, a separately sold CB-2way board is installed in the mid/high socket; additional F-15L units can be added for 4-way or 5-way configurations. The front panel features independent left/right level controls for low, mid, and high bands, with 1 dB step adjustment and a 0.5 dB shift switch for finer control.

Specifications

Production Year	August 1981
Original Price	¥200,000
Input Level (Max, <0.01% THD)	Balanced: 8.0V (XLR), Unbalanced: 8.0V (RCA)
Total Harmonic Distortion	0.003% (20Hz–20kHz, 2.0V output)
Frequency Response	20Hz–20kHz ±0.2dB; 0.5Hz–300kHz ±3.0dB
Gain	0dB
Crossover Slope	-12dB/oct, -18dB/oct, -24dB/oct (switchable)
Input Impedance	Balanced: 40kΩ (20kΩ/20kΩ), Unbalanced: 20kΩ
Output Impedance	Balanced: 50Ω (25Ω/25Ω), Unbalanced: 50Ω
Minimum Load Impedance	600Ω (balanced and unbalanced)
S/N Ratio	100dB (0.5V output, IHF-A weighted)
Power Supply	AC100V/117V/220V/240V, 50Hz/60Hz
Power Consumption	32W
Dimensions	475mm (W) × 170mm (H) × 380mm (D)
Weight	16.0kg
Semiconductors	100 transistors, 56 FETs, 22 ICs, 58 diodes

Design

The F-15L combines active filters with buffer amplifiers, using seven buffer stages to isolate circuit sections and prevent interference. All unit amplifiers are configured identically with a gain of 1, using push-pull circuits with low-noise, high-gm FET source followers at the input and wide-band transistors in the output stage. The design employs no loop feedback; instead, performance is achieved through precise component selection, push-pull topology, and local feedback. A DC servo system in the output stage prevents DC offset, and all amplifiers operate as DC-coupled stages without coupling capacitors. The active filter uses CR elements combined with amplifier stages, with crossover frequency set by replacing modular boards containing precision metal film resistors and silver mica capacitors. Each board allows selection of -12dB/oct or -18dB/oct slopes via onboard switch, with -24dB/oct also listed in specs. A protective circuit mutes output during board removal to prevent speaker damage. Balanced transmission is supported throughout, and the unit is compatible with the 3D method via a rear-panel switch.

Context

The F-15L is an upgraded version of the F-15, adding balanced input/output capability. Crossover boards are compatible with the earlier F-5 and F-15 models. Frequency boards such as CB-70 and CB-100 were sold separately, as was the 2-way conversion board. A matching wood cabinet, Model A-12, was available for ¥16,000. Related models include the F-5, F-20, and F-25 active crossovers.

Market

Original crossover boards were priced between ¥11,000 and ¥15,000. Original brochures and used units occasionally appear on auction and classifieds sites.