Accuphase F-15L (1987)

Name: Accuphase F-15L
Brand: Accuphase

Active crossover with balanced input/output, released June 1987

Overview

The Accuphase F-15L is an active crossover, also called a frequency dividing network. Accuphase Laboratory, Inc. made it (the company was originally Kensonic Laboratory, Inc.). It came out in June 1987 as an improved F-15, with balanced input and output circuits added. It handles 2-way to 5-way speaker systems. Crossover frequency is set by swapping in interchangeable boards, and 21 standard frequencies are available. Seven buffer amplifiers keep the circuits from interfering with each other, and the whole thing is a DC amplifier with no coupling capacitors. On the front panel, the low, mid and high levels each get independent left and right controls. They use a precision attenuator with 0.5 dB steps.

Specifications

Gain	0dB
Maximum Input (Distortion Factor 0.01% or Less, 20 Hz to 20 kHz)	Unbalanced: 8.0V, Balanced: 8.0V
Total Harmonic Distortion Factor	0.003% (20 Hz ~ 20 kHz, Output 2.0 V)
Frequency Characteristic	20 Hz ~ 20 kHz + 0 -0.2 dB; 0.17 Hz to 1000 kHz + 0 -3.0 dB Single Channel Equivalent Bandwidth
Crossover Frequency	Change by replacement of crossover board; Standard frequency: 21 points
Crossover Characteristic	-3.0 dB +/- 5%
Slope Characteristic	-12dB/oct, -18dB/oct switching type
Input Impedance	Unbalanced: 20k Ω; Balanced: 40k Ω
Output Impedance	Unbalanced: 100 Ω (both Low/Mid/High); Balanced: 50 Ω (both Low/Mid/High)
Minimum Load Impedance	Unbalanced: 1k Ω; Balanced: 600 Ω
S/N Ratio	100 dB (output 0.5 V, A-corrected)
Level Adjustment	0 dB ~ -20.5 dB, 0.5 dB step
Semiconductor Count	Transistor: 100 units; FET: 56; IC: 22; Diode: 58 pcs
Power Supply Voltage	AC100V/117V/220V/240V, 50Hz/60Hz
Power Consumption	20W
Dimensions	Width 445 x Height 109 x Depth 373 mm
Weight	9.1kg

Design

The F-15L is built from active filters and buffer amplifiers. Seven buffers isolate the circuit stages from each other. Every amplifier has a gain of 1 and uses a push-pull topology with no loop feedback. The input stage is low-noise, high-gm FETs wired as source followers. Wide-band transistors follow in a complementary push-pull arrangement. Each amplifier gets its low distortion from careful component selection, local feedback and push-pull operation. The output stages have DC servo control to remove DC offset, and all the amplifiers are DC-coupled. The signal path uses precision metal film resistors and high-quality silbird mica capacitors. Balanced transmission runs over a 3-core cable and sends equal signals in opposite phase. A protection circuit mutes the output when a crossover board is removed. A rear-panel switch gives 3D audio. For 2-way operation, use the included 2-way adapter board. Add more F-15L units for 4-way or 5-way setups. The crossover board is compatible with the F-5 and F-15 models.

Market

The Accuphase F-15L had an original price of ¥230,000. A dedicated wood cabinet, model A-12, was sold separately for ¥16,000. Crossover boards were also sold individually. The CB-70 was ¥15,000, the CB-1000 was ¥13,000, and the CB-12500 was ¥11,000. A listing from approximately five years ago priced the unit at $1,484.01. It was described as excellent in operation and cosmetics (9/10), and it came with the 70Hz, 100Hz, and 250Hz crossover boards and the 2-way adapter board. Shipping within the contiguous US was a flat $55.