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Sophisticated MCS topology assures outstanding S/N ratio Enjoy crystal
clear sound emerging from a background of utter silence. Current feedback
amplification, wide-band power transistors in parallel push-pull configuration,
and potent power supply deliver plenty of quality power: 140 watts per channel
into 4 ohms or 100 watts into 8 ohms. Option boards allows digital signal
input or analog record playback with impeccable quality.
Parallel connection MCS topology in
preamplifier and power amplifier stages
Both the preamplifier (Figure 1) and power
amplifier (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 distortion. In the
E-308, the same signal is supplied to two
separate amplification circuits, which also
receive the feedback signal. The output of the
circuits is combined, which is equivalent to
parallel operation of the overall circuit.
Mathematically, when using two parallel circuits,
the improvement in S/N ratio is 3 dB. The circuit
BIAS
STABILIZER
components of the line amplifier input stage
and output stage are also driven in parallel,
which further minimizes noise that could arise
in the various amplification stages.
Current feedback circuit topology in power
amplifier and preamplifier sections prevents
phase shifts and assures excellent sound
quality
In the E-308, the signal current rather than the
The E-300 series has always played a central
role in the Accuphase integrated amplifier lineup.
Drawing from a wealth of know-how and
experience, the E-308 incorporates the latest
advances in circuit technology and materials
research. It has been designed to deliver
onehundred percent of musical enjoyment.
Specially noteworthy is the MCS (Multiple Circuit
Summing) topology implemented in the
preamplifier and power amplifier sections. It
drastically improves S/N ratio, allowing utterly
natural sound to emerge from a background of
deep silence.
An integrated amplifier offers various advantages
such as convenient operation and modest space
requirements. However, because its overall gain
is very high, even the slightest interference or
crosstalk at the input can have a considerable
effect on the sonic result. To preclude this
possibility, the E-308 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
separate components. An EXT PRE switch and
dedicated inputs and outputs allow independent
use of the preamplifier and power amplifier.
Both the preamplifier and power amplifier use
the MCS principle developed by Accuphase, with
multiple input circuits connected in parallel.
Together with the current feedback topology,
this results in a significant enhancement of all
vital performance parameters. The power
amplifier output stage adopts a parallel push-
pull configuration of multi-emitter power transistors
designed for high-power audio applications. The
large power transformer in the power supply and
plenty of filtering capacity sustain ample high-
quality output power.
The preamplifier section comprises features such
as tone controls, loudness compensator, and
facilities for recorder monitoring and copying.
Each circuit component has been carefully
selected after extensive tests. The end result is
an integrated amplifier that clearly stands out
from the rest. Option boards can be used to
implement digital inputs and high-quality analog
record playback. 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. Also,
frequency
response
remains
uniform over
a wide gain
range. This is
evident from
Figure 4
which shows
frequency
response for
different gain settings of the current feedback
amplifier.
Parallel push-pull output stage delivers
quality power: 140 watts/channel into 4 ohms,
120 watts/channel into 6 ohms or 100 watts/
channel into 8 ohms
The output devices are multi-emitter power
transistors designed for high power audio
applications. These devices have excellent
frequency response, forward-current transfer
ratio linearity, and switching performance
characteristics. They are connected in a triple
parallel configuration (Figure 2) for low
impedance and mounted directly on a large
heat sink to assure efficient dissipation of
thermal energy. A generous design margin
allows the E-308 to deliver ample power
output.
BufferCurrent
adder
I-V
converter
Trans-impedance
amplifier
Amplifier Output
Current NFB
network Input
Gain
(High) Frequency
(Large)
Fig. 1 Circuit diagram of line amplifier (one channel)Fig. 2 Circuit diagram of power amplifier (one channel) Fig. 3 Principle of current feedback amplifier
Fig. 4 Frequency response with current feedback(Response remains uniform also when gain changes)
High-power transistors
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Highly reliable logic-controlled relays for
best sound quality
Program source switching is performed by logic-
controlled relays which are arranged so as to
permit straight and short signal paths for
enhanced sonic purity. 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.
Two sets of heavy-duty speaker terminals
Two sets of
oversize
speaker
terminals are
provided which
accept also
heavy-gauge
speaker cable.Large power transformer and high filtering
capacity
The power supply section is a critical aspect of
any power amplifier.
The E-308 features a
large power trans-
former with a rating of
500 VA. The trans-
former is mounted in
an enclosure filled
with damping material
that has excellent
heat transfer charac-
teristics. This design
prevents unwanted
interaction with the
rest of the amplifier.
Two massive electro-
lytic capacitors, each
rated for 22,000 µF,
are used to filter the
current. This ampleperformance margin of the power supply en-
sures dynamic sound down to very deep fre-
quencies.
Tone controls use summing active filters for
pure sound
The tone control circuitry in the E-308 features
summing active filters. Figure 5 illustrates the
operation
principle of
this circuit.
The flat sig-
nal is
passed
straight
through,
and only
when an ad-
justment is
required, the characteristics created at F
1 and
F 2 are added to the signal, thereby producing
the desired change. This design provides effi-
cient control without degrading signal purity.
Input Output
Fig. 5 Tone control circuit principle
(Summing active filter type)
Power amplifier assembly with parallel
push-pull output devices mounted to large
heat sink, MCS circuit, and current
feedback amplifier circuitry.
n nn n
nSupplied remote
commander RC-20
Allows volume
adjustment and
input source
switching
Gold-plated
input/output jacks with
directly connected relays