STEREO/MONO POWER AMPLIFIER
Separating what you do want in fine musical reproduction from what you don't want is a job that calls for power-lots of it. Distortion, noise and unwanted tonal coloration must go. That's why every circuit in the BA-5000 is designed with more than enough power headroom to eliminate everything but the music each step of the way along the circuit chain. Abundant power reserve also enables transients, dynamics and range to be preserved without strain and without the slightest hint of coloration oraudible noise. The meaning of power becomes clear asyou enjoy the musical resolution, transparency and definition of the BA-5000. Here are the facts about its construction and design.
The differential amplifier at the input stage of the BA-5000 uses a dual-transistor formed on one semiconductor wafer. Since it offers a high input/low output impedancecharacteristic, the circuit operates with unwavering stability at all times, regardless of the input level control settings.
Next,the pre-driver circuit is a 2-stage differential amplifier using a dual-transistor stage for balanced zero voltage, followed by an active-loaded driver stage for high-gain Class-A amplification. This allows the application of optimum and stable negative feedback to drastically reduce all types of distortion.
Three Darlington-connected amplifier stages for high current gain are found in the final output stage, terminated by eight large power transistors, for each channel. The power transistors are arranged in an elaborate "four-in-parallel" OCL complementary symmetry push-pull configuration. This means that linearity is maintained throughout to reduce distortionand further extend power headroom. Results: per channels power output of 300 watts, min. RMS, both channels driven into 8 ohms over a 20 to 20,000 Hz bandwith with no more than 0,1% total harmonic distortion. It is here that the proof of the BA-5000's overall integrity is heard - a very wide dymanic range, and a realistic bass reproduction with virtually no distortion at rated output.
A high-efficiency transformer couples the final stage of the output power circuit to the speaker terminals. This allows the BA-5000 to deliver its rated output at loads of 8 ohms, 4 ohms or 2 ohms in 2-channel operation; in mono the total of 600 watts, min. RMS over a 20 to 20,000 Hz bandwidth, with no more than 0,1% total harmonic distortion, is available across loads of 16 ohms, available for professional studio work or for PA use at live rock concerts, etc.
The transformer also functions as a bandpass filter to cut subsonic signals, such as are generated by warper or offcentered records. Speaker cones are thus protected against exessive excursion and resulting breakdowns.
If temperatures or electrical conditions warrant the triple protection circuit operates and the front panel Power/Protector indicator changes fromgreen to red; the LED lamp will continue to glow red until safe conditions are restored. It also illuminates in red for moments after power-on, then turns green to indicate that power issafely available to speaker terminals.
The BA-5000 has three thoroughly dependable protection circuits:
An ASO detection circuit monitors teh current flow in power transistors and limits the current entering the final stage instantly if the latter semiconductors are forced to work beyond thier Area of Safe Operation (ASO);
A self-restoring temperature detection circuit with a thermistor cuts off the incoming signals from the driver stage if heat rises as the result of overloads or other abnormalities;
An overload detection circuit with quick-acting fuses is also included.
Accurate metering, a touchy point in amplifiers of this size and quality is assured by the use of two very responsive meters calibrated on the logarithmically compresses scale in steps from 0,01 to 300 watts (8 ohms); scales in decibeles are also provided ( -50 to +5 dB). Pulsive inputs are shown accurately and more quickly than in even the best VUs for correct output power indication.
Less magnetic leakage flux. A highly concentrated magnetic field. Less heat generation. Smaller size and improved power regulation. These are some of teh advantages of the special power transformae which add up to improved transient response, allowing the BA-5000 to respond to pulsive musical signals instantaneously regardless of level. Sansui has used toroidal coil windings on a seamless ring and a twin positive/negative dual power supply format with separate windings for left and right channels to prevent potentially harmful channelinteraction. This transformer also has special provisions for eliminating the audible "thump" of power-on switching.
The four oversized electrolityc capacitors (each 22,000µF for a total of 88,000µF) regulate power evenly whether input levels are high or low.
Low-level circuits such as the input and driver stages are fedbalanced negative/positive current fron an independent dual power supply.
CONTROLS,CONNECTIONS AND MOUNTING
Individual left and right input controls on the front panel, and one stereo set of speaker terminals on the rear panel are provided. The solid chassis uses thick 2 mm steel plates; it is sized and designed forprofessional rack mounting. The chassis cover is an attractive vintage claret color, with jet-black alumite face plate and aluminum trim. The top panel carries the block diagram of the amplifier inside for the benefit of engineering-oriented enthusiasts.Voltage outputs of 70V MONO and 25V STEREO areindicated on the rear panel for convenience in professional applications.
STEREO; Min.RMS both channels driven from 20 -20000 Hz,with no more than 0,1% THD
300 watts per channel into 2, 4, 8 ohms
24,5 volts into 2 ohms
34,6 volts into 4 ohms
49,0 volts into 8 ohms
MONO; Min. RMS from 20 - 20000 Hz,with no more than 0,1% THD
600 watts into 4, 8, 16 ohms
49,0 volts into 4 ohms
69,3 volts into 8 ohms
98,0 volts into 16 ohms
STEREO; 2, 4, 8 ohms
MONO; 4, 8, 16 ohms
OUTPUT VOLTAGE: 25 volts stereo; 70 volts mono
POWER BANDWIDTH: 20 - 20000 Hz at or below rated min. RMS power output and THD
TOTAL HARMONIC DISTORTION: less than 0,1% at or below rated min. RMS power output
INTERMODULATION DISTORTION: (70 Hz; 7000 Hz = 4:1 SMPTE method) less than 0,1%
FREQUENCY RESPONSE: 15 - 30000 Hz, +0dB, -2dB (at 1 watt)
DAMPING FACTOR: approx. 10 at 8 ohm load
HUM AND NOISE (IHF): better than 100 dB
INPUT SENSITIVITY AND IMPEDANCE: 700 mV, 50 kohms (1000 Hz for rated output)
AC OUTLET: unswitched total 150 watts
SEMICONDUCTORS: 59 Transistors, 34 Diodes, 5 Zener Diodes, 2 ICs, 1 LED
Power Voltage; 100, 120, 220, 240 V, 50/60 Hz
Power Consumption; 490 watts (rated) 1350 watts (max.)
DIMENSIONS: 482 x 222 x 466 mm (19 x 8¾ x 18 inch)
WEIGHT: 49 kg (108,0 lbs) Net.