Accuphase F-15L (1987)
Active crossover with balanced input/output, released June 1987
Overview
The Accuphase F-15L is an active crossover, also known as a frequency dividing network, manufactured by Accuphase Laboratory, Inc. (originally Kensonic Laboratory, Inc.). It was released in June 1987 as an improved version of the F-15, adding balanced input and output circuits. The unit supports 2-way to 5-way speaker systems and allows crossover frequency selection via interchangeable boards, with 21 standard frequencies available. It includes seven buffer amplifiers to prevent circuit interference and operates as a DC amplifier without coupling capacitors. The front panel features independent left/right level controls for low, mid, and high frequencies, with 0.5 dB step adjustment using a precision attenuator.
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 uses an active filter and buffer amplifier design, with seven buffer amplifiers isolating circuit stages to prevent interference. All unit amplifiers have a gain of 1 and use a push-pull circuit topology without loop feedback. The input stage uses low-noise, high-gm FETs in a source follower configuration, followed by wide-band transistors in a complementary push-pull arrangement. Each amplifier ensures low distortion through careful component selection, local feedback, and push-pull operation. Output stages include DC servo control to eliminate DC offset, with all amplifiers operating as DC-coupled amplifiers. The signal path uses precision metal film resistors and high-quality silbird mica capacitors. Balanced transmission uses a 3-core cable to send equal but opposite-phase signals. The unit includes a protection circuit that mutes output when a crossover board is removed. It supports 3D audio via a rear-panel switch and allows 2-way operation using the included 2-way adapter board. Additional F-15L units can be added for 4-way or 5-way configurations. 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, with prices such as ¥15,000 for the CB-70, ¥13,000 for the CB-1000, and ¥11,000 for the CB-12500. A historical listing from approximately five years ago priced the unit at $1,484.01, noting it in excellent operational and cosmetic condition (9/10), including the 70Hz, 100Hz, and 250Hz crossover boards and the 2-way adapter board. Shipping within the contiguous US was a flat $55.
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