Accuphase P-300V
¥ 350,000 (released in July 1987)
Commentary
This pre-main amplifier is based on the push-pull drive of all amplification stages and is composed entirely of cascode connection with excellent high-frequency characteristics up to the drive stage.
Following the original P-300, the model has been changed to P-300S, P-300X, P-300L, and P-300V. In the fifth generation, an ultra-low impedance drive capable of withstanding 1 Ω load and a more complete balanced input circuit have been realized.
The output stage consists of 10 parallel wide-band transistors with collector loss Pc of 130W for a total of 20 transistors.
As a result, the total Pc is 2600W per channel, and when the power efficiency of the output stage is assumed to be 70%, the theoretical limit output reaches 3700W. This structure allows linear high-quality power to be sent even at low load impedance.
Since 20 transistors are configured in 10 parallel, it can cope with a large current under a low impedance load and can drive even at a low impedance of 1 Ω.
Bridge connection is enabled.
Bridge connection is a method in which signals of the same magnitude but opposite phase (reversed phase) are input to the same amplifier, and a speaker is connected to the output terminals of both amplifiers to obtain double output at the 4 Ω load in stereo driving.
Normally, when a bridge connection is made, a phase inversion circuit is inserted into one amplifier. However, in the case of P-300V, the polarity of the differential input circuit of the two amplifiers is utilized, and the connection is changed so that the opposite phase signals are input to each other. This is a pure switching circuit.
Equipped with a full-scale 40k Ω balanced input. International standard 3P-XLR-type connector allows balanced outputs of any impedance to be connected.
The balance input circuit of the P-300V is configured to inject the signal directly to the positive and negative inputs of the differential input circuit, making it an ideal configuration.
In this method, a level control must be inserted into each of the positive and negative inputs. However, a 1-dB step attenuator is used to reduce the interlocking error.
The operating point is set strictly so that each PNP/NPN element is not cut off by the input signal in order to suppress the switching distortion at the small output which occurs at the output stage.
The previous stage driving the final stage consists of MOS FET cascode push-pull, which is equivalent to a non-switching class A drive, and the previous stage is also composed of class A cascode push-pull. This realizes a stable output stage with little distortion from small output in the noise region to large output in the rated output.
The input circuit constitutes a cascode bootstrap push-pull circuit.
The cascode bootstrap circuit satisfies the requirements of the input stage : high gain, excellent frequency and phase characteristics in the ultra-high frequency range, and no deterioration of the distortion factor due to changes in input impedance.
The push-pull configuration of this circuit, together with the wide-band drive stage, improves the element characteristics in the NF loop.
The power supply section is supplied through a filter circuit with a winding dedicated to the pre-stage amplifier circuit in the transformer for independent rectification of the left and right.
The input signal is directly input to the Input terminal.
For this reason, when a pre-amplifier with large DC drift is connected, it is amplified and appears on the output, which may damage the speaker. Therefore, DC is cut off by AccuPhase original DC servo system and DC drift of the amplifier itself due to temperature change is also stabilized.
Equipped with an output meter convenient for monitoring.
Logarithmic compression type peak power meter allows direct reading of output power at 8 Ω load along with dB.
Equipped with Route 3 inputs for one balanced system and two unbalanced systems, it can be switched with a switch on the front panel.
One of the unbalanced inputs is located in the front panel sub-panel.
Two types of speakers, A and B, can be connected.
The speaker that is not in use receives vibration and resonates, which may impair sound quality. Therefore, the speaker that is not in use is automatically short-circuited to prevent resonance.
The top panel is gold-tone scratch hairline finish, and the bottom sub-panel is black hairline finish.
In addition, natural Persimmon sideboards are installed on both sides.
.JPG)
.JPG)
.JPG)
.JPG)
Model Rating
| Type | Stereo power amplifier |
| Rated output (20 Hz to 20 kHz, Distortion Factor 0.01%) |
Stereo type (both channels operate simultaneously) 2 Ω load : 350W/ch 4 Ω load : 280W/ch 8 Ω load : 180W/ch 16 Ω load : 90W/ch Monaural specification (bridge connection) 4 Ω load : 700W 8 Ω load : 560W 16 Ω load : 360W |
| Total harmonic distortion factor | Stereo Specifications : 0.01% (Simultaneous Operation of Both Channels, 2 Ω ~ 16 Ω Load) Monaural specification : 0.01% (bridge connection, 4 Ω ~ 16 Ω load) |
| IM distortion factor | 0.003% |
| Frequency characteristic | 20 Hz ~ 20 kHz + 0 -0.2 dB (Continuous Average Output, Level Control MAX) |
| Gain | 28.0 dB (both for stereo and monaural specifications) |
| Load impedance | Stereo specification : 2 Ω ~ 16 Ω Monaural specification (bridge connection) : 4 Ω ~ 16 Ω |
| Damping factor | Stereo specification : 300 Monaural specification (bridge connection) : 150 |
| Input sensitivity (8 Ω load) | Stereo specification Continuous average output : 1.5 V 0.12 V at 1W output Monaural specification (bridge connection) Continuous average output : 2.7 V 0.12 V at 1W output |
| Input impedance | Unbalanced : 20k Ω Balance : 40k Ω |
| S/N (A correction Stereo / Mono) |
120 dB (Input Short, Continuous Average Output) 100 dB (Input 1k Ω, 1W output) |
| Stereo headphone | Applicable Impedance : 4 Ω ~ 100 Ω |
| Output meter | Logarithmic compression type -40dB to + 3 dB and output direct reading scale |
| Transistors and diodes used | Transistor : 90 FeT : 16 IC : 8 Diode : 73 Pieces |
| Pwer | AC100V/117V/220V/240V, 50Hz/60Hz |
| Power consumption | No input : 130W Electrical Appliance and Material Control Law : 630W 8 Ω load rated output : 600W |
| External dimensions | Width 475x Height 170 (Including Legs) x Depth 408 mm |
| Weight | 24.8kg |