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High-output, high-performance integrated amplifier with MCS topology in
preamplifier and power amplifier stages. Current feedback ensures optimum
phase characteristics in high frequency range. Wide-band power transistors
in triple push-pull configuration and high-efficiency R-toroidal power
transformer deliver plenty of quality power: 260 watts per channel into 4
ohms or 180 watts into 8 ohms. Option boards can be used to implement
digital input or analog record playback with impeccable quality.
Q11 Q13 Q15
Q12 Q14 Q16 Q10
Q8 Q6
Q5
Q7
Q9
+-“
OUTPUT INPUT
-“ B1
+B1
-“ B2
+B2
REGULA-
TOR
REGULA-
TOR
NFB
NETWORK
Q1a
Q3a
Q2a Q4a
Q1b
Q3b
Q2b Q4b
BIAS STABILIZER
CIRCUIT
Triple parallel push-pull power unit delivers 260
watts/ch into 4 ohms, 220 watts/ch into 6 ohms,
and 180 watts/ch into 8 ohms
The power transistors used in the output stage are
multi-emitter devices designed for audio applications,
with optimum frequency response, forward-current
transfer ratio linearity, and switching performance
characteristics. By arranging these devices in a triple
parallel configuration (Figure 1), low impedance is
The E-408 is a further refined and enhanced
version of the highly popular and successful
E-407. Incorporating latest technology and
using only top quality parts, the E-408 is an
integrated amplifier that stands out through
sheer excellence. S/N ratio in the preamplifier
and power amplifier sections has been further
improved by the adoption of MCS (Multiple
Circuit Summing). Musical dynamics never
sounded so impressive, with every nuance
clearly outlined. The E-408 is the yardstick by
which integrated amplifiers will be measured
from now on.
Because an integrated amplifier has very high
overall gain, even the slightest interference or
crosstalk at the input can have a considerable
effect on the signal provided at the output. To
preclude this possibility, the E-408 is built with
totally separate preamplifier and power
amplifier sections. Both electrically and
structurally, these two parts operate completely
autonomously. Each has its own power supply
and dedicated regulator circuitry. A separate
set of inputs and outputs even allows using
the preamplifier and power amplifier as if they
were stand-alone components.
The circuits in the preamplifier and power
amplifier stages both use the MCS principle
as well as current feedback. MCS is a
sophisticated technique developed by
Accuphase for connecting multiple circuits in
parallel. The overall result of combining these
circuit topologies are improved performance
specs as well as superior sound quality. The
output stage of the power amplifier is
constructed as a triple parallel push-pull
configuration of multi-emitter type power
transistors designed for high-current audio
applications. The efficient R-toroidal power
transformer in the power supply and plenty of
filtering capacity support 260 watts per channel
(4 ohms) or 180 watts (8 ohms). The preamplifier
section features tone controls and a loudness
compensator designed to retain the purity of
the music signal. Functions such as recordermonitoring and copying provide welcome
flexibility. All major parts were selected by strict
listening evaluation to assure a high all-round
standard of quality.
A Digital Input Board using a high-precision
MDS (Multiple Delta Sigma) D/A converter is
available as an option, allowing the digital signal
of a CD player or similar to be directly supplied
to the E-408. Another option is an Analog Disc
Input Board for high-grade reproduction of
analog records.
achieved. The transistors are mounted to a large
heat sink for efficient dissipiation of thermal energy.
As a result, the E-408 provides plenty of high-quality
output power.
Parallel connection MCS topology in preamplifier
and power amplifier stages
Both the power amplifier (Figure 1) and preamplifier
(Figure 2) employ the MCS (Multiple Circuit Summing)
topology developed by Accuphase. This design
results in significantly improved performance
characteristics such as higher S/N ratio and lower
OUTPUT
Q8
Q5
Q7
Q6
+B
-B
Q4a
Q3a
Q2a
Q1a
Q4b
INPUT
Q3b
Q2b
Q1b
distortion. In the E-408, two separate amplification
circuits are fed the same signal, as well as the
feedback signal, and the output of the circuits is
combined, which is equivalent to parallel operation
of the overall circuit. Mathematically, when two
parallel circuits are employed, the improvement in
S/N ratio is 3 dB.
Current feedback circuit topology in power
amplifier and preamplifier sections prevents phase
shifts
In the E-408, the signal current rather than the more
conventionally used voltage is used for feedback.
Because there is almost no phase shift, phase
compensation can be kept to a minimum, resulting in
excellent
transient
response and
superb sonic
transparency.
Figure 4 shows
frequency
response for
different gain
settings of the
current
feedback amplifier. The graphs demonstrate that
response remains uniform over a wide range.
Fig. 2 Line amplifier circuit diagram
Fig. 1 Power amplifier circuit diagram (one channel)
BufferCurrent
adder
I-V
converter
Trans-impedance
amplifier
Amplifier Output
Current NFB
network Input
Fig. 3 Current feedback amplifier principle diagram
Fig. 4 Frequency response with current feedback
(response remains uniform even when gain changes)
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Logic-controlled relays for signal switching assure
high sound quality and long-term reliability
All signal switching is performed by logic-controlled
relays which are arranged so as to permit the shortest High-efficiency toroidal power transformer and high
filtering capacity
The power supply
section is a critical
aspect of any power
amplifier. The E-408
features a large to-
roidal power trans-
former with a rating
of 600 VA. The trans-
former is housed in
a non-resonant alu-
minum enclosure
filled with damping
material that has
excellent heat
transfer character-
istics. Two large
33,000 µF capaci-
tors smooth out any
current irregulari-
ties. This no-holds-
barred approach
manifests itself in
rock-solid, powerful sound even at ultra-deep fre-
quencies.
Tone controls with summing active filters for
best sound
The tone control circuitry in the E-408 was specially
designed
with sum-
ming active
filters such
as found in
high-quality
graphic
equalizers.
Figure 5 il-
lustrates the
operation
principle of
F1
-“A1 -“A2
VR1
F2
VR2
Input
Output
Fig. 5 Tone control principle
(Summing active filter type)
Two sets of large size speaker terminals
The speaker terminals are made of extruded high-
purity brass
material which
accept also
heavy-gauge
speaker cable.
Two sets of
outputs with a
speaker selector
are provided, and
bi-wiring
(supplying the
same signal via
dual leads to speakers with separate high-frequency
and low-frequency inputs) is also possible.
this circuit. The flat signal is passed straight through,
and only when an adjustment is required, the charac-
teristics are created at F
1 and F 2 and added to the
signal, thereby producing the desired change. This
design provides efficient control without diluting sig-
nal purity.possible signal paths. The hermetically sealed relays
are high-quality types developed specifically for
demanding communication applications. The contacts
are twin crossbar types plated with gold for minimum
contact resistance and outstanding long-term
reliability.
Output stage with triple parallel push-pull
arrangement, MCS, and current feedback
circuitry mounted to large heat sink
Supplied remote
commander RC-20
allows volume
adjustment and input
source switching
