Accuphase P-266

Commentary

This is a stereo power amplifier using MOS FET, which was created by the development technology of AccuPhase cultivated over many years.
Four types of power amplifiers are available : stereo power amplifier, class A stereo power amplifier, monaural power amplifier and class A monaural power amplifier.

Unlike bipolar transistors, Power MOS FET (Metal-Oxide Semiconductor Field Effect Transistor) has no charge storage, so it has excellent high-speed switching characteristics. It does not generate notching distortion even in high frequencies, and it can obtain excellent distortion characteristics over a wide band.
Since it is a voltage-controlled device, power amplification can be performed only by applying a signal voltage to the input gate. Compared with bipolar transistors, which require a large signal power, a low-power device is sufficient for the drive stage at the front stage, and excellent devices can be selected.
Moreover, since it is a high-gain element, the number of amplification stages can be reduced, and stability can be improved by simplifying the signal path.
Since the temperature coefficient of the high-current region is negative, if the current of the element increases abnormally for some reason, the temperature of the pellet will rise sharply, and the negative temperature coefficient acts in the direction of reducing the current, and the temperature will decrease to prevent the destruction of the element. There is a self-defense function.
It also has excellent high-frequency characteristics and linearity.

It is composed of a strong output stage and a power supply part so that it can sufficiently withstand a low impedance load. The output stage is composed of triple push-pull of MOS FET, and P_DA margin of 600W (maximum drain loss power) is provided.

Equipped with an operation changeover switch, it can operate even in a full-scale pure A class system in which the operation area of the push-pull element completely overlaps.
Switching to class A operation is performed by a bias switching circuit. An optocoupler is incorporated in the circuit, and a light emitting diode is turned on and off to change the bias current to switch between normal operation and class A operation.

Equipped with a bridge drive switch, it can also be used as a large output power amplifier.
The principle of operation is that by inputting a signal of the same waveform and opposite phase to each amplifier and connecting the speaker to the outputs of both amplifiers, the voltage applied to the speaker is doubled, and in principle the output is four times as large as when one amplifier is operated.
This method has the advantage that even harmonic distortion is canceled due to the reverse phase drive, and the characteristics are improved. In addition, since the energy flowing from the power supply flows alternately in positive and negative directions and the energy in only one direction does not flow to both amplifiers, the apparent power fluctuation factor is improved, and energy with good linearity can be sent to the speakers.

The pre-drive stage uses the cascode connection push-pull configuration used in the P-300X and M-100.
Cascode is a circuit used for high frequencies such as the front end of a tuner. It has excellent high-frequency characteristics without mirror effect, good linearity up to the limit value of the element, and greatly improved element characteristics before applying NFB.

FET input is used, and the input coupling capacitor is removed for direct connection.
In order to prevent this, the P-266 uses a DC servo amplifier to perform DC feedback to cut off DC and stabilize the DC drift generated in the circuit.

In order to strengthen the power supply for the preamp section, the rectifying circuits for the left and right channels are separated and installed in each printed circuit board.
In addition, it is strengthened by a power regulator to realize low impedance over a wide range.

A subsonic filter is installed to remove ultra-low frequency noise.

Equipped with an attenuator that changes in 1 db steps up to -20dB.

It is equipped with a logarithmic compression type peak level meter with a hold switch. It can directly read dB value and output power of 8 Ω addition, and peak hold is also possible by switching.
In peak hold mode, the peak value is held at a sampling period of every 3 seconds.

Equipped with speaker switching mechanism by output relay.

A cabinet with natural rosewood finish is sold separately.

Model Rating

Type	Stereo power amplifier
Continuous average power (20 Hz to 20 kHz, Distortion Factor 0.01%)	Stereo specification Normal: 200W/ch (4 Ω) 130W/ch (8 Ω) 65W/ch (16 Ω) Class-A: 55W/ch (4 Ω) 30W/ch (8 Ω) 18W/ch (16 Ω) Monaural specification (bridge connection) Normal: 400W (8 Ω) 180W (16 Ω) Class-A: 110W (8 Ω) 55W (16 Ω)
Total harmonic distortion rate (20 Hz to 20 kHz 0.25W ~ continuous average output)	Stereo : 0.01% (4 Ω Load) 0.005% (8 Ω ~ 16 Ω Load) Monaural specification (bridge connection) : 0.01% (8 Ω Load) 0.005% (16 Ω Load)
IM Distortion Factor (IHF)	0.003%
Frequency characteristic	20 Hz ~ 20 kHz + 0 -0.2 dB (Continuous Average Output, Level Control MAX) 0.5 Hz ~ 300 kHz + 0 -3dB (at 1W Output, Level Control MAX) 0.5 Hz ~ 150 kHz + 0 -3dB (Level Control -6dB at 1W Output)
Gain	Stereo : 27.8 dB Monaural specification : 33.7 dB
Load impedance	Stereo specification : 2 Ω ~ 16 Ω Monaural specification : 4 Ω ~ 16 Ω
Damping factor	Stereo specification : 120 Monaural specification : 60
Input Sensitivity / Impedance (at 8 Ω load)	Stereo : 1.3V/20k Ω (at continuous average output) 0.12V/20k Ω (IHF at 1W output) Monaural specification : 1.1V/20k Ω (at continuous average output) 0.06V/20k Ω (IHF at 1W output)
S/N (A correction)	Stereo : 120 dB (Input Short, Continuous Average Output) 100 dB (Input 1k Ω, 1W output, IHF) Monaural specification : 110 dB (Input Short, Continuous Average Output) 90 dB (Input 1k Ω, 1W output, IHF)
Stereo headphone	Low output impedance type
Subsonic filter	17 Hz, -12dB/oct.
Output meter	Logarithmic compression peak indication type, -40dB to + 3 dB and output direct reading scale With Peak Hold Switching
Semiconductor used	Transistor : 34 FET : 18 IC : 7 Diode : 68 Pieces Opto-coupler : 2 pcs
Power supply voltage	AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption	Normal: 120W (no input) 500W (at 8 Ω load rated output) Class-A: 150W (no input) 190W (at 8 Ω load rated output)
External dimensions	Width 445x Height 160 (Including Legs) x Depth 373 mm Wood Cabinet : Width 466x Height 190x Depth 385 mm
Weight	20kg
Sold Separately	Wood Cabinet A-8 (¥ 16,000)