Sansui BA 1000 (1975)
A stereo power amplifier from 1975 using vertical power FETs in a pure complementary circuit, capable of BTL mono operation
Overview
The Sansui BA-1000 is a stereo power amplifier released in 1975. The output stage is fully complementary and uses newly developed vertical power FETs running as a source follower. A rear panel switch sets up BTL (Bridge-Tied Load) mono operation, and two types of speakers can be connected. Protection covers current limiting, temperature detection and a protector indicator.
Specifications
| Year of Production | 1975 |
| Effective power (Double-channel operation, 20 Hz to 20 kHz) | 45W + 45W (8 Ω) |
| Effective power (Double-channel operation, 1kHz) | 50W + 50W (4 Ω) |
| Effective power (Double-channel operation, 1kHz) | 55W + 55W (8 Ω) |
| Effective power (BTL connection, 20 Hz to 20 kHz) | 95W (16 Ω) |
| Effective power (BTL connection, 1kHz) | 95W (8 Ω) |
| Effective power (BTL connection, 1kHz) | 95W (16 Ω) |
| Total harmonic distortion factor | 0.08% or Less (Rated Output) |
| Total harmonic distortion factor | 0.05% or Less (at 1/2 Rated Output) |
| Cross modulation distortion factor | 0.03% or less (70 Hz : 7 kHz = 4 : 1, SMPTE) |
| Load impedance | 2 ch : 4 Ω ~ 16 Ω |
| Load impedance | Mono : 8 Ω ~ 16 Ω |
| 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 |
Design
The output stage is a pure complementary circuit with newly developed N- and P-channel vertical power FETs, operating as an ideal source follower. The drive stage is a class A emitter-follower with active followers for both the positive and negative cycles. The first stage uses a PNP low-noise twin transistor. The power supply has a toroidal transformer and two 10,000 μF electrolytic capacitors. A bias stabilizing circuit holds steady through ±20% power supply fluctuations. The heat sink mounts externally on the rear panel and is designed for good air convection. Protection includes a current limiter, temperature detection, and a timing circuit built around a diode switch and a time constant.
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