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State-of-the-art integrated amplifier features current feedback topology
for superb high-range phase fidelity. Wide-range power transistors in
triple parallel push-pull configuration and massive toroidal transformer
deliver ample power: 260 watts × 2 into 4 ohms, 180 watts × 2 into 8
ohms. Option board enables analog record reproduction in top-notch
quality.
The E-407 represents a new pinnacle of ampli-
fier design. Featuring latest technology and us-
ing only the highest quality materials, this inte-
grated stereo amplifier is destined to become a
new reference. Frequency response, S/N ratio,
and all other performance aspects make the
E-407 perfectly suited for the new generation
of ultra high quality program sources such as
SACD and DVD-Audio.
An integrated amplifier provides various advan-
tages such as convenient operation and modest
space requirements. However, because its over-
all gain is very high, even the slightest interfer-
ence or crosstalk at the input can have a consid-
erable effect on the sonic result. To preclude this
possibility, the E-407 is designed to achieve total
electrical and structural separation of the
preamplifier and power amplifier sections. These
two parts operate as if they were entirely sepa-
rate components. A switch even allows using the
preamplifier and power amplifier independently.
Accuphase's highly acclaimed current feedback
topology virtually eliminates phase shifts in the
upper frequency range and assures outstanding
performance and sound quality. The power am-
plifier output stage employs a triple parallel push-
pull configuration, using multi-emitter power tran-
sistors designed for high-power audio applica-
tions. Ample muscle is provided by the power
supply section which features a massive, highly
efficient toroidal power transformer housed in a
diecast enclosure equipped with heat fins.
In the standard configuration, the E-407 has six
inputs, two of which employ the balanced princi-
ple that assures ideal signal transmission char-
acteristics. Provisions for two tape recorders, with
easy dubbing in both directions, tone controls, and
loudness compensation are further attractive fea-
tures. An optional analog disc input board allows
reproduction of analog records with outstanding
sonic quality.
The external design of the E-407 continues the
Accuphase tradition, featuring a champagne gold
brushed front panel. Two large power meters in
the center are flanked by the input selector sec-
tion and the volume control. Not only by virtue ofits excellent sound, from its looks as well the
E-407 is a great addition to any living room.
Triple parallel push-pull output stage delivers
quality power: 260 watts/channel into 4 ohms,
220 watts/channel into 6 ohms or 180 watts/
channel into 8 ohms
The output devices are multi-emitter power tran-
sistors designed for high-power audio applica-
tions. These devices have excellent frequency re-
sponse, forward-current transfer ratio linearity, and
switching performance characteristics. They are
connected in a triple parallel configuration (Fig-
ure 1) for low impedance and mounted directly
on a large heat
sink to assure ef-
ficient dissipation
of thermal energy.
This allows the E-
407 to deliver am-
ple power output,
amounting to 260
watts into 4 ohms,
220 watts into 6 ohms, or 180 watts into 8 ohms
per channel.
Current feedback topology in power amplifier
and preamplifier sections guarantees top-
level performance
In the E-407, the signal current rather than the
voltage is used for feedback. Figure 2 shows the
operating principle of this circuit. At the sensing
point of the feedback loop, the impedance is kept
low and current detection is performed. An im-
pedance-converting amplifier then converts the
current into a voltage to be used as the feedback
signal. Since the impedance at the current feed-back point (current adder in Figure 2) is very low,
there is almost no phase shift. Phase compensa-
tion can be kept to a minimum, resulting in excel-
lent transient
response and
superb sonic
transparency.
Figure 3 shows
frequency re-
sponse for dif-
ferent gain set-
tings of the cur-
rent feedback
amplifier. The graphs demonstrate that response
remains uniform over a wide range.
Discrete-type line amplifier for superior sonic
purity
The line amplifier is entirely built from discrete
par ts, to assure optimum performance. Using a
principle developed by Accuphase, a differential
pure complementary push-pull circuit is combined
with a single-ended push-pull emitter follower
output stage. This comparatively simple topology
reduces the need for phase compensation, re-
sulting in effortless, utterly natural and transpar-
ent sound.
Highly reliable logic-controlled relays
Program source switching is performed by logic-
controlled relays which are arranged so as to
permit the
shortest possi-
ble signal
paths. The
her metically
sealed relays
are high-qual-
ity types devel-
oped specifi-
cally for de-
manding com-
munication ap-
plications. The contacts are twin crossbar types
plated with gold for minimum contact resistance
and outstanding long-term reliability.
Tone controls use summing active filters for
pure sound
The tone control circuitr y in the E-407 was spe-
cially designed with summing active filters. Fig-
ure 4 illustrates the operation principle of this cir-
High-current power transistors
Relays connected directly to
gold-plated input/output jacks Figure 2 Principle of current feedback amplifier
Figure 1 Circuit diagram of power amplifier section (one channel)
Figure 3 Frequency response with current feedback
(Response remains unifor m also when gain changes)
Line amplifier assembly with
current feedback circuitry
Bias
stabilizer
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cuit. The flat signal is passed
straight through, and only when
an adjustment is required, the
characteris-
tics created
at F1 and F2
are added to
the signal,
thereby pro-
ducing the
desired
change. This
design pro-
vides efficient
control with-
out degrading signal purity.
Large toroidal power transformer and high fil-
tering capacity
The power supply section is a critical aspect of
any power amplifier. The E-407 features a large
toroidal power transformer with a rating of 600
VA. The transformer is housed in a non-resonant
aluminum enclosure filled with damping material
that has excellent heat transfer characteristics.
Toroidal transformers which use heavy-gauge
copper wiring on a ring-shaped core have vari-
ous advantages, such as very low impedance,
small size, and high conversion efficiency. The
toroidal type transformer used by Accuphase is
ideally suited for audio applications. It has the fol-
lowing characteristics:
aNear-circular core caliber allows near-circular
coil windings with high packing density, result-
ing in low leakage flux and minimum vibrations.
bSmaller ferrite core diameter and copper
windings with high specific gravity mean lowferrite losses and low inrush current.
Two massive electrolytic capacitors, each rated
for 33,000 uF assure ample reserves also for re-
production of the most demanding passages.
Dedicated headphone amplifier for best sound
The E-407 provides a separate
amplifier for the phone jack de-
signed to provide superior sonic
performance. The speaker out-
put can be cut off by a switch,
and the main volume control
can be used to adjust the
headphone listening level.
Two sets of heavy-duty
speaker terminals
The oversize speaker
terminals are made of
extruded high-purity
brass material whichaccept also heavy-gauge speaker cable. Two sets
of outputs with a
speaker selector
are provided, and
bi-wiring (supply-
ing the same sig-
nal via dual leads
to speakers with
separate high-fre-
quency and low-
frequency inputs)
is also possible.
Large analog peak power meters
The power meters use logarithmic compression
to cover a wide dynamic range, letting you easily
monitor the output level of the rapidly fluctuating
music signal. Meter illumination can be switched
off, which is conven-
ient for example in
a home theater
setup.
nSupplied remote commander RC-20
Allows volume control and source
switching
Power amplifier
assembly with tri-
ple parallel push-
pull output devices
mounted to large
heat sink and cur-
rent feedback am-
plifier circuitry
Heavy-duty speaker terminals
Figure 4 Tone control circuit principle
(Summing active filter type)
Massive filtering capacitors and
large toroidal power transformer