Audio Database


NEC A-700
79,800yen(1985 release)

The Integrated Amplifier which aimed at the improvement in the operationality corresponding to audio-video age supplying the original technology of NEC, such as a reserve IBM-PCN-II power source.

A push pull type amplifying circuit is adopted as all the amplification stages, and the last amplification stage has become circuitry with the parallel push pull stream composition. By carrying out the parallel using of the output transistor for the substantial reduction by half by the emitter resistor which goes into an output current circuitry in series, stability was not spoiled but it has realized.
Furthermore, it is made the setups in which the limiter which spoils the linearity of output power does not operate in a 2-ohm load intensity by the output circuit development which does not need the protection by an ASO limiter.

The original reserve IBM-PCN-II power source of NEC is carried in the power-source part.
Another power source with which time for the charging time of a capacitor input type rectifier circuit not to flow is compensated was used for this, and it delayed the phase of the output 90 degrees, is a flume detour way scheme by which the valley of a ripple is filled, and, thereby, has strengthened the stability.
Even if it is going to acquire the Oide power by this at the time of the capacitor electric discharge generated with the conventional capacitor input type power source, the hangup that supply voltage will fall is solved.
Moreover, the line filter which cuts a power-source noise into an AC outlet is carried.

The mechanical ground construction is adopted as a vibration-proof rigid structure design.
This is stopping the ill effect which mechanical vibration has on an electrical circuit by review of the chassis structure of clarifying the ground point of not only the ground potential that is an electric reference point but mechanical vibration.
In A-700, the opportunity reference point of the set itself is made into the structure which responds to all the mechanical vibration on foot as a foot of a main unit, and the product made from a sintered alloy 50mm in diameter and 22mm in height is adopted as a sole plate.
Moreover, in order to connect a structure division article and a power transformer to a foot certainly, the 2.0mm griddle in thickness is adopted as a sole plate,Furthermore, a cloth beam is connected with adoption of the cloth beam which solid-construction-izes sub- metal fittings on either side, rear panel, and heat sink, and a sole plate with two beams, and the core of a power transformer is certainly fixed to a beam.
This has gained the bass by variation of the stray capacity on a signal line, and a floating inductance which pressed down the failure of distortion, a crosstalk, and a phase response etc. and sat on the waist, and sharp loud sound.

Although it1 circuitries, such as a tone defeat, were established in the tone circuitry and it was coped with by switchpoint changeover in the former in it, in order that a signal might pass a switchpoint contact even in this case, the tone-quality failure was received.
In order to cope with this, excessive amplifier and a switchpoint contact were not passed, and the main direct tone circuitry which controls the property of direct sending and a main amplifier themselves for a signal directly to a main amplifier is developed and adopted.
Moreover, its attention is paid to the delay characteristics at the time of a music play, especially the variation of right-and-left both channels,The group delay by a computer simulation, a phase, a setups of the optimum value of each property of a swing,Adoption of the audio peculiar part selected carefully for the impedance of a bus / treble both volumes and the mandatory of a correction curve, and the mandatory of the allowable error of a circuit constant etc. has realized the tone circuitry excellent in a feeling of a lateralization.

In order to correspond also to an analog play, the high gain equalizer amplifier is carried.
Low-noise Hi-GmFET which was excellent in the tone quality is used for the differential amplifier, and also the shunt type power source for exclusive use is carried.

Two input terminals and one output-terminal for visual equipments are carried.

Rating of a mode
Form High-quality integrated amplifier
<Power amplifier part>
Circuit system Whole page direct DC servo circuitry
Effective output (both channel drive)
They are 20Hz - 20kHz at the time of a sinusoidal consecutive output.
100W+100W (4ohm)
50W+50W (8ohm)
THD 0.006% or less (at the time of an effective output)
Cross modulation distortion 0.006% or less (at the time of an effective output)
Frequency characteristic 5Hz - 300kHz
Tone control High-Precision tone circuitry (±3dB)
<Preamplifier part>
Circuit system High-Gm FET direct input EQ circuitry
Input sensitivity/impedance Phono(man month/MC): 2.0mV / 20kohm
compact disk, Tuner, Tape1/2 (Video), Tape3/4 (Audio), AUX:150mV /, 20kohm
(Picture signal: 1 Vp-p/75ohms)
An Output voltage/impedance Tape1, 2 and 3, 4 Rec:140mV /, 2.2kohm
Monitor: 1.0 Vp-p/75ohms
SN ratio Phono(MM/MC):90dB(-142dBV)
compact disk, Tuner, Tape1, 2, 3 and 4, AUX: 110dB (-126dBV)
RIAA deflection Less than (10Hz - 40kHz) ±0.2dB
Phono maximum permissible input MM:150mV
Subsonic Filter 5Hz (-3dB, 6dB / oct, phone equalizer inclusion)
Input/output phase Inphase
<A power-source part, others>
Circuit system Shunt power-source scheme + reserve IBM-PCN-II power source
Power consumption 190W
Dimensions The width 430x height 120x depth of 380mm
Weight 14.0kg