Amplificator Final Denon POA 3000

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Amplificator Denon POA 3000: solid state, 2 etaje finale, transformator toroidal, vumetre mari, luminate, fata argintie, nu detin laterale de lemn, suna foarte bine, detalii tehnice mai jos.



350,000yen(1979 release)

Stereo power amplifier which carries DENON class A which studied Class-A operation thoroughly and was born.

DENON class A by a real bias circuit original with DENON is carried, and high output-ization is realized though it is operation of Class-A amplifier as it is.
The newly developed high-speed power transistor (fT: 100MHz, Pc:150W) that was excellent in the high region characteristic is adopted especially as an output transistor. This transistor has a good linearity of hFE also at the time of high output, and has the good characteristic that at least 100Hz of Output powers are maintainable by low distortion.
While making this high-speed power transistor push pull connection of 5 parallel per single-sided channel and aiming at improvement in a linearity by leaps and bounds, the low distortion characteristic covering a broadband is acquired.

In order to solve the lowness of efficiency and the problem of generation of heat and enlargement which were the faults of Class-A amplifier, the real bias circuit is adopted.
In order to carry out Class-A magnification linearly using the linear region of the magnification characteristic of a transistor, without a signal ripple changing, it is controlling by this circuit to send direct-current bias current equal to the peak value of the signal current which flows into a transistor. The suitable direct-current bias current always stabilized from the minute signal to the Taishin number according to the magnitude of a signal ripple by this could be supplied, the futility of power consumption could be excluded, and generation of heat has also decreased. Furthermore, since bias current is stably controlled by a control function irrespective of the temperature state of an output transistor, the operating state of best condition is always maintained.

Moreover, it is controlling to make bias current recover from signal current early, and in order to prevent the standup of the bias in this case cutting off behind time, he precedes one step to the standup of a signal, and is trying to send some fixed bias current at the time of a non-signal, and to rise. Since bias rises previously and increases even if the musical tone signal of high frequency with a quick standup comes by this, it is controlled to become Class-A operation certainly.
Furthermore, also to the nonlinear characteristic in the very small current domain which a transistor has, fixed bias current acts effectively, and it is controlled so that an output transistor does not enter this domain.
This real bias circuit has realized about 1/of efficiency of the power consumption of 5 as compared with the conventional system.

A driver circuit has high fT and it constitutes it from a cascode emitter-follower driver who carried out 4 parallel connection of the small signal transistor (fT:400MHz, Pc: 400mW) of the high linearity characteristic per single-sided channel.
Cascode connection of this transistor with a 4 times as many broadband transmission characteristic as fT of a putter transistor is made,Degradation of the high region characteristic is prevented by preventing the influence of Cob (collector-base junction capacity), such as a power transistor, while raising a high region linearity further, and driving an output stage by a broadband and low impedance.
Moreover, with the last output stage, electric power was supplied from the independent power supply circuit, and the mutual intervention is prevented.

A pre-driver stage carries out a balanced drive by a twin complimentary differential circuit, and is carrying out the push pull drive of the power stage with the cascode pre driver.
The high-speed transistor of the same fT400MHz as a driver stage is adopted, an electric power drive also constitutes a possible drive circuit, and the use transistor is carrying out a broadband and low impedance magnification.
Moreover, in order to maintain the stability of the operating point of differential circuits, such as a pre driver, an operation stabilizer circuit is prepared and the influence by a temperature drift is suppressed.

The direct direct-current servo system by low-noise FET differential amplifier and its parallel operation is adopted as the first rank.
The direct direct-current servo system by low-noise FET differential amplifier and its parallel operation is adopted as the first rank.
This has the completely same composition as control amplifier PRA-2000, removed the coupling capacitor of the input unit and has eliminated the unnecessary colorization. Moreover, the increase in a noise level is suppressed by it not only acquiring super-low-pass stability, but this servo circuit shutting out a direct-current middle point drift, and not adding servo amplifier to a return system.
By the parallel connection of differential amplification, and direct-current servo through which it passes, respectively, noise is reduced by 3 moredB and the distortion is stopped to one half.

The power-source part is taken as the output stage and another power transformer system which divided others.
The power source for output stages consists of a large-sized toroidal transformer of the volume according to right and left, and a 100,000-micro F mass capacitor which attained low impedance-ization to the high region. This transformer had a twice [ about ] as many capacity (1000VA) as a 200W+200W B class amplifier power transformer, and magnetostriction is prevented by floating this with the aluminum chassis of nonmagnetic 2mm thickness.
Moreover, it applies to a drive stage from the first rank, and EI type power transformer is formed independently, the influence of load fluctuation with an intense output stage is avoided, it has a constant-voltage stable circuit, and stabilization of a power-source part and low impedance-ization are attained.

According to the very big in rushes current at the time of power switch ON (inrush current), in order for the life of a power switch to prevent becoming short or affecting other electrical appliances, the prevention circuit from in rushes was established in the power-source part, and the trouble is prevented.

The large-sized power meter which can carry out the Direct reading of the Output voltage on either side in dB and W display is carried.

The speaker and the transistor are protected by the high-speed protection circuit which served as the muting circuit which prevents the pop noise generated at the time of ON-OFF operation of a power switch.
At the time of abnormalities, LED of the protection display in a front glass blinks.

The core of amplifier is considered as the layout of a symmetrical form, and separating from a first rank circuit to the maximum also position-wise [ a power-source part ] and electrically etc. has become the construction which gave priority to the characteristic.
Moreover, the heavy effect and Miller effect of thick sheet glass are used for the meter part of the front panel, a 5 - 6 second DENON mark is first displayed at the time of the power source ON, and it has structure which illuminates back large-sized peak meter.
Specular surface finishing is given to pleuron.

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