interesting read translated from japanese
YAMAHA
B-2 NATURAL SOUND POWER AMPLIFIER ¥ 200,000
stereo power amplifier that Yamaha was released in 1976. 1973 equipped with its own development of the SIT (V-FET) crossbow class power amplifier of all FET B-1 was released the company, V-FET Anne was developed and launched in a more realistic form was a flop. In the B-2, the power FET · 2SK-77 that has been developed in the B-1 one size to small, was complimentary of, Shinkai of onset power FET · 2SK-76 (Nch), mounted 2SJ-26 (Pch) It had been. V-FET is, the three-pole vacuum tube by the voltage control element that operates similar also, it was element with a different again appeal to the MOS FET. However, at that time in the technology of mass production, it was what produced of the combined pair characteristic is difficult.
Yamaha, Pch, Nch of device chip size of the impurity concentration, the fully discussed in the gate mesh structure addition, strictly control the production process it is possible that, combined pair characteristics over a wide operating range, still own a pair of sorting in a way, it was selected "Yamahasu was using as Papea FET ". As a result, in the B-2, the first FET complimentary push Yamaha pull configuration has been taken. Excellent linearity of the newly developed, by using a sufficiently high FET gain, can be driven with low power, the driver simple circuit configuration of the stage previously stable NFB is applied two-stage amplification had been taken. Also, Karentomi distortion generated such as by being a whole page except the combination sulfonate and the first stage of the color circuits in a push-pull configuration, lower can be suppressed, excellent bare properties and by being implemented and superior while applying the least the NFB distortion rate characteristic is secured had been. In addition, eliminating the capacitor from the NFB loop, complete DC was also removed to the capacitor of the input it had become an amplifier configuration. The output stage, pure complimentary parallel push using two Yamaha original super pair FET was configured with pull OCL circuit. The power FET is a drain loss 100W, linearity is well pairs especially the ones that have all of the well, a wide output range, had obtained a low distortion in the frequency band. By the this is excellent FET Ri, it had been operating at low idling current to break the common sense of it until the FET amplifier. The heat sink large to also be used for the Lch, respectively Rch, the power FET is mounted directly to a heat sink which has been subjected to special processing, heat by lowering the resistance effective heat radiation is performed, with a sufficient margin even at full power It was possible the operation of. This drive circuit to drive power FET, Symmetrical push-pull drive scheme has been adopted directly below. This is, of the power stage Nch, Dora in the Pch of FET each pure complementary push-pull circuit in a luxury circuit that Eve, had contributed to the excellent characteristics. As described above, the rising, the pairing with the excellent power FET to linearity, Symmetrical push-pull times by the road, and high slew rate, we have realized a low distortion. The voltage amplification stage, the first stage in the cascode bootstrap with FET differential amplifier, current mirror differential in thepre-drive stage and had adopted a push-pull amplifier. In the first stage, the super-low-noise FET which precisely align the
pair characteristic, and coupled to a thermal and a differential amplifier had been. Using the high-gm FET, is multiplied by a constant current bias in which the temperature correction to the source side, common mode rejection suppress the drift of the midpoint potential to a minimum by taking very large ratio (CMRR), also, of the power supply shadow of slight ripple sound also been canceled, it has secured a high SN ratio. The differential amplifier stage, is equipped with a cascode
bootstrap circuit, a drain in the change of the input signal - voltage between the gate and so does not change the input impedance strain were not to deteriorate vary. Puridorai parts and to the class A operation in the differential push-pull of a combination of current mirror circuits, enough gain in the low distortion had been. Power supply circuit, in the same manner as the B-1, is equipped with a power transformer in the left and right independent, was to avoid the mutual interference between channels.
Use the large capacity Chemi-Con of 18,000μF × 2 per one channel, it had to achieve a richbass characteristics. Further, the drive stage before a complete constant-voltage power source, to suppress the deterioration of S / N due to external noise and ripple, amplifiers times it was to ensure the stable operation of the circuit. The bias circuit of the power FET, a change in the bias voltage caused by fluctuations in the power supply voltage automatically corrected to
it had always adopted the automatic stabilization bias circuit to keep constant. Also, by using a diode matrix, POWER I was so prevent damage to the FET by preventing rush current flowing to the switches turned ON FET. Peak level meters, the same as the UC-1 adapter for the B-1, -50dB from (1mW) + 5dB (300W) Madere can be displayed without Nji switching, instruction within -2dB also a sine wave 1 wave of 10kHz high-precision logarithmic compression type Pikume entering the
error Ta had been installed. This meter, "EXTERNAL" so that it can be used in other applications as well as power display switching between "INTERNAL" is provided, in the "EXTERNAL", had also become possible use of the meter alone. Other Me, such as when the multi-amplifier, you can look at the output level of the other power amplifier, that you can see the input voltage of the preamplifier I can also be used to. Speaker output A, provided two systems of B, not only can be switched at
the front panel, the level of A, B2 system left and right had become can be adjusted at the level volume independently. Input There is also a 2 system, which is also the front panel had become can be switched in. As described above, B-2 is, as FET power amplifier next to Chodokyu machine B-1, I met only new, care about in all FET is such as using a bipolar transistor and a hybrid not, has become a balanced design, as at the time of the amplifier physical properties also had what was very good. Also towards the sound, but strength is not enough B-1, the unique V-FET was delicate and amplifier of nuance rich attractive sound.