| DENON POA-3000 |
|
| 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.
|
| Form |
Stereo power amplifier |
| Music power |
250W+250W (8ohms) |
Output power
(both channel drive, a sine wave output, 20Hz - 20kHz) |
180W+180W (8ohms) |
| THD |
0.002% or less (20Hz - 10kHz)
0.003% or less (20Hz - 20kHz) |
Cross modulation distortion
(60Hz:7kHz=4:1, Output power) |
0.003% or less (at the time of 180W equivalent) |
| Output bandwidth (IHF, both ch(es) drive) |
5Hz - 100kHz (THD 0.02%) |
| Input sensitivity/input impedance |
1V/50kohm |
| Output load impedance |
0.04%(1kHz) |
| Dumping factor |
200 (8 ohms, 1kHz) |
| S/N ratio (IHF-A) |
122dB or more |
| Transmission characteristic |
1Hz-350kHz+0dB-3dB |
| Separation |
100dB or more (20Hz - 1kHz)
85dB or more (- 20kHz) |
| Slew rate |
More than ±300v/microsec |
| Frequency response |
10Hz-100kHz±3dB |
| Subsonic-Filter characteristic |
16Hz, 6 dB/oct |
| Level meter characteristic |
Indicating type: Peak value indicating type output level
meter
Indicating range: -50dB-+5dB and 0dB=200W/8 ohm |
| Power supply voltage |
AC100V, 50Hz/60Hz |
| Power consumption |
At the time of a non-signal: 220W
At the time of the Arinobu number: 730W (Electrical Appliance and
Material Control Law) |
| Dimensions (a knob, a base included) |
Width 495x height 188x depth of 459mm |
| Weight |
34kg |
|
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