Accuphase F-15

Commentary

Channel divider with interchangeable crossover board.

The F-15 consists of a combination of an active filter and a buffer amplifier. All unit amplifiers have the same configuration with a gain of 1. The active filter amplifier that creates crossover characteristics is combined with a CR element to create the characteristics.

A push-pull circuit is used for the unit amplifier. The input is a source follower of low noise and high gmFET complimentary service, and the complimentary service is a push-pull circuit with wide-band transistors.
This circuit has no loop feedback, and excellent performance is obtained by the push-pull system and local period system as well as the careful selection of elements.

The DC servo system is used for the output unit amplifier in order to prevent the generation of DC component and to stabilize it.
Since the gain of the unit amplifier is 1, if the servo time constant is set at one point, the time constant becomes larger and the lowering characteristic of the low-frequency range becomes broader and the distortion increases. To solve this problem, the F-15 uses a series connection of the mirror integration circuit and sets the time constant in 3-stage configuration to reduce the CR per stage and improve the low-frequency distortion characteristics.

The front panel is equipped with low, mid and high level control with independent left and right channels.
The attenuator is a precision 1 dB step type, but it can be controlled in 0.5 dB steps by a combination of 0.5 dB shift switches. The adjustment range is 41 points of 0 to -20.5 dB and - ∞.

You can change the crossover frequency by changing the crossover board for each frequency.
Each crossover board is equipped with left and right channel CR elements. These elements, which have a significant effect on sound quality, are mainly composed of precision metal film resistors and high-quality silbird mica capacitors to minimize degradation and colorization of sound quality.
The crossover board opens the sub-panel at the bottom of the front panel and inserts it into a socket.

Two types of cutoff attenuation slope characteristics can be selected : -12dB/oct. and -18dB/oct.
This can be done with the changeover switch on the crossover board.

A protective circuit is mounted to prevent damage to the speakers due to shock noise when the crossover board is replaced in the operating state. In this protective circuit, the muting is activated just before the board is removed from the socket electrode and the output is cut off.

For 2-way use, insert a 2-way board (sold separately) into the middle and high area board socket.
When using it as 4-5-way, add another F-15.

There was a special rosewood cabinet sold separately.

Model Rating

Type	Channel divider
Maximum Input Level (Distortion Factor 0.01% or less, 20 Hz to 20 kHz)	Balanced : 7.0 v, XLR type Unbalanced : 7.0 v, RCA
Total Harmonic Distortion Factor (20 Hz to 20 kHz, 2.0 V output)	0.003%
Frequency Response (Single Channel Equivalent Band)	20 Hz ~ 20 kHz + 0 -0.2 dB 0.5 Hz ~ 300 kHz + 0 -3.0 dB
Gain	0dB
Crossover frequency	Change by replacement of crossover board Standard frequency : 21 points
Crossover characteristic	-3.0 dB + / - 5%
Slope characteristic	-12dB/oct., -18dB/oct., -24dB/oct. Switch-over type
Input impedance	Balanced : 40k Ω (20k Ω / 20k Ω) Unbalanced : 20k Ω
Output impedance	Balanced : 50 Ω (25 Ω / 25 Ω) Unbalanced : 50 Ω
S/N (output 0.5 v, IHF-A corrected)	100dB
Minimum load impedance	Balanced : 600 Ω Unbalanced : 600 Ω
Level adjustment	0 dB to -20.5 dB, 1 dB step and ∞ Each band is left and right independent
Power supply voltage	AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption	32W
Maximum external dimensions	Width 475x Height 170x Depth 380 mm
Weight	16.0kg
Sold Separately	Wood Cabinet A-12 (¥ 16,000) Frequency board Model number Crossover frequency Price CB-70 70Hz ¥15,000 CB-100 100Hz ¥15,000 CB-130 130Hz ¥15,000 CB-180 180Hz ¥15,000 CB-250 250Hz ¥15,000 CB-290 290Hz ¥15,000 CB-300 300Hz ¥15,000 CB-350 350Hz ¥15,000 CB-500 500Hz ¥13,000 CB-650 650Hz ¥13,000 CB-800 800Hz ¥13,000 CB-1000 1kHz ¥13,000 CB-1200 1.2kHz ¥11,000 CB-1800 1.8kHz ¥11,000 CB-2500 2.5kHz ¥11,000 CB-3500 3.5kHz ¥11,000 CB-5000 5.0kHz ¥11,000 CB-7000 7.0kHz ¥11,000 CB-8000 8.0kHz ¥11,000 CB-10000 10kHz ¥11,000 CB-12500 12.5kHz ¥11,000 CB-2way Two way board ¥2,000

　

Since 2-way has a single crossover frequency, set a board with that frequency for LOW/MID, and use a 2-way board (which jumps the circuit inside) for MID/HIGH.	In the case of 3 way, it is the most standard usage.
In case of 4-way, 2 F-15s are used. The output from the preamp is input to both terminals simultaneously for parallel connection, using the same crossover board for the first LOW/MID and the second MID/HIGH.	For 5-way, two F-15s are connected in series. In this case, to prevent S/N deterioration, the output of the preamplifier is connected to the input of the F-15 for the mid - and high-frequency range, and the output of the first LOW OUTPUT is connected to the second unit. The output goes from the top of the first unit to high and middle and low, and from the top of the second unit to middle, middle and low.