Accuphase E-307 Brochure

m Parallel push-pull output stage delivers 2 × 100 watts of quality po wer

into 8 ohms m Current feedback topology assures superb phase stability
in the upper frequency range m Logic-controlled relays for shortest signal
paths m Separ ate switch allows independent use of preamplifier and power
amplifier m Large , high-efficiency power transformer m Digital input possible
with option board m Analog record playback possible with option board

Witness another rev olution in sound. Integrated amplifier realizes digital input
via option board with high-precision MDS (Multiple Delta Sigma) D/A
conv erter . Current feedback topology assures superb high-range phase fidelity .
Wide-band power transistors in parallel push-pull configuration and large
power transformer deliver 140 watts/channel into 4 ohms and 100 watts/
channel into 8 ohms.

Based on the highly successful Accuphase E-306V
which has become a mainstay in the category of
integrated amplifiers, the E-307 is a further
enhanced and accomplished product for totally
faithful music reproduction. It reflects the extensive
experience Accuphase has gained in building
superb separate-type amplifiers. Ev ery single aspect
has been honed to deliver optimum performance.
An integrated amplifier provides various advantages
such as convenient operation and modest space
requirements. However, because its overall gain is
very high, even the slightest interf erence or crosstalk
at the input can have a considerable effect on the
signal provided at the output. To preclude this
possibility, the E-307 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 dedicated
set of inputs and outputs even allows using the
preamplifier and power amplifier as if they were
stand-alone components.
Accuphase's highly acclaimed current feedback
topology is used in both the preamplifier and power
amplifier. This innovative principle eliminates phase
shifts in the upper frequency range and assures
stable operation and uniform frequency response
which does not change with gain. Phase
compensation can be kept at a minimum, and high
amounts of negative feedback with their associated
disadvantages are no longer required, resulting in
excellent transient response, with superb sonic
transparency and detail.
A total of six input positions are provided, including
two balanced inputs for professional-quality noise­free signal transmission. The tape enthusiast will
welcome connectors for two tape recorders, with
easy dubbing in both directions. Tone controls,
loudness compensation, and other convenient
features come in handy. Flexibility is further
enhanced by the option to install a Digital Input
Board with a high-precision MDS (Multiple Delta
Sigma) D/A converter that directly accepts the digital
signal from a CD player or similar, for un­compromiing reproduction quality. An analog disc
input board is also available, allowing high-grade
reproduction of analog records.

Parallel push-pull output stage delivers quality
power: 140 watts/channel into 4 ohms, 100 watts/
channel into 8 ohms

Figure 1 shows a circuit diagram of the power
amplification stage. The power transistors are multi­emitter types designed for audio applications. They
have been selected for optimum frequency
response, forward-current transfer ratio linear ity , and
switching performance characteristics. Arranged to
achieve low impedance, the de vices are connected
in parallel and
mounted directly
on a large heat
sink for efficient
dissipation of
thermal energy.
This allows the E­307 to deliver
ample power
output, amounting to 140 watts into 4 ohms, 120
watts into 6 ohms, or 100 watts into 8 ohms per
channel.

Current feedback circuit topology in power
amplifier and preamplifier sections prevents
phase shifts

In the E-307, the signal current rather than the more
conventionally used 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 impedance-con verting amplifier then
converts the current into a voltage to be used as
the feedback signal. Since the impedance at the
current feedback point (current adder in Figure 2) is
very low, there is almost no phase shift. Phase

Figure 2 Principle of current feedback amplifier

High-current power transiters

compensation
can be kept to a
minimum,
resulting in
excellent
transient
response and
superb sonic
transparency.
Figure 3 shows
frequency response for different gain settings of the
current feedback amplifier. The graphs demonstrate
that response remains uniform over a wide range.

Discrete-type line amplifier for superior sonic
purity

To assure optimum performance, the line amplifier
is built entirely from discrete parts. A pure
complementary push-pull circuit is used, and current
feedback topology enhances circuit operation. This
reduces the need for phase compensation, resulting
in effortless, utterly natural and transparent sound.

Highly reliable logic-controlled relays

Program source switching is performed by logic­controlled relays which are arranged to permit the
shortest 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.

Fig. 3 Frequency response with current feedbac k

(response remains uniform also when gain changes)

Figure 1 Circuit diagram of power amplifier section (one channel)

Relays connected directly to
gold-plated input/output jacks

Tone controls use summing active filters for
pure sound

The tone control circuitry in the E-307 was specially
designed with summing active filters such as found
in high-quality graphic equalizers. Figure 4 illustrates
the operation principle of this circuit. The flat signal
is passed straight through, and only when an
adjustment is required, the characteristics are
created at F1 and F2 and added to the signal,