SANSUI BA-1000
¥ 89,800 (released in 1975)
Commentary
A stereo power amplifier using a vertical power FET for audio as an amplifying element.
A newly developed vertical power FET is used for the output stage.
Since the vertical power FET has excellent linearity especially in a large current region, the input and output signals are proportional to each other even when a large amplitude signal is added to the gate. In addition, the BA-1000 operates as a source follower, which further reduces distortion and enables amplification with excellent linearity.
It also has a self-controlling function against heat generation, has no temperature drift, and is resistant to thermal destruction. Moreover, it is suitable for driving a reactance load such as a speaker with a wide safe operation range.
In addition, since the slope of the maximum output curve with respect to the load impedance is gentle, a large output can be obtained even at high impedance. In addition, considering the characteristics of a speaker in which the impedance rises near the lowest resonance frequency, this element is suitable for driving.
This vertical power FET is available in N-channel and P-channel types, making it possible to construct a pure complimentary service circuit with low distortion and excellent characteristics.
A pure complimentary service circuit using newly developed N - and P-channel vertical power p-channel vertical power FETs. The final stage is an ideal source follower to further reduce the distortion factor. In addition, in order to stably obtain excellent characteristics, FETs with the same characteristics are operated by push-pull to minimize distortion components.
In order to drive the vertical power FET with low impedance and improve the high-frequency characteristics, a newly developed emitter-follower circuit with an active follower circuit is used in the drive stage. This circuit is provided with low output impedance and good operation against capacitance load. In the BA-1000, this circuit is used independently for + cycle and - cycle, and class A operation is adopted.
Since this circuit uses a bipolar transistor with a small collector capacity and excellent linearity, the vertical power FET at the last stage has a + cycle and - cycle waveform perfectly symmetrical, and the speaker can be driven with high linearity and low impedance.
Since the vertical power FET has a non-saturated static characteristic, even if the bias voltage between the gate and source is constant, the operating point moves according to the fluctuation of the power supply voltage, and the bias fluctuates, causing crossover distortion. Therefore, it is necessary to control the gate potential so that a constant bias current can be maintained against the fluctuation of the power supply voltage.
The BA-1000 uses a bias stabilizing circuit that can stabilize the power supply voltage against ± 20% power supply voltage fluctuations.
A PNP low-noise twin transistor is used in the first stage to improve the S / N ratio and stabilize the output midpoint potential.
The power supply section uses a toroidal transformer with good regulation and low leakage flux, and the electrolytic capacitor uses a large capacity type of 10,000 μ Fx2 for a stable power supply.
It can be used as a monaural power amplifier via BTL connection by switching the switch on the rear panel.
In order to effectively dissipate heat, a heat sinker with a shape that physically calculates air convection is directly attached to the rear panel and installed externally to stabilize the vertical power FET.
The vertical power FET is ON when no bias is applied between the gate and the source. Therefore, a large current flows between the drain and the source when the power is turned on, and the FET may be destroyed.
The BA-1000 uses a timing circuit that combines a diode switch and a time constant circuit to apply a voltage that turns CUT OFF to the gate as soon as the power is turned on. When the driver stabilizes, the timing circuit is disconnected and a normal bias is applied to the gate.
The protector indicator blinks while the timing circuit is operating.
As a protective circuit, it is equipped with a current limiter and temperature detection circuit that can cope with overload.
The current limiter detects the current in the final stage, the temperature detection circuit detects the temperature of the radiator with a positive star, and the load is disconnected with a relay. The speaker is also isolated from the amplifier when direct current appears in the output to protect the speaker.
Equipped with a protector indicator, it blinks to indicate an error during operation of the protection circuit.
When the abnormal operation is finished, all operations are recovered and the protector indicator becomes the power indicator and the normal lighting condition is achieved.
Two types of speakers can be connected.
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Model Rating
| Type | Stereo power amplifier | ||
| Effective power |
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| Total harmonic distortion factor | 0.08% or Less (Rated Output) 0.05% or Less (at 1/2 Rated Output) |
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| Cross modulation distortion factor | 0.03% or less (70 Hz : 7 kHz = 4 : 1, SMPTE) | ||
| Load impedance | 2 ch : 4 Ω ~ 16 Ω Mono : 8 Ω ~ 16 Ω |
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| Power Band With (IHF) | 5 Hz ~ 30 kHz (8 Ω) | ||
| Frequency response (1 kHz) | 5 Hz to 80 kHz + 0 -1dB | ||
| Damping factor | 70 (8 Ω) | ||
| Channel separation | 85 dB or More (1 kHz) | ||
| Hum and noise (IHF) | 105 dB or more | ||
| Input Sensitivity / Impedance | 700mV/50k Ω | ||
| Rated power consumption | 117W | ||
| External dimensions | Width 482x Height 88x Depth 338 mm | ||
| Weight | 10kg |