The Accuphase E-700 sits at the top of the company's E-series integrated amplifier line as a Pure Class-A design, and it is arguably the clearest expression of what Accuphase believes an integrated amplifier should be. It combines the AAVA gain-controlled volume system, a current-feedback power amplifier, and a modular option-slot architecture into a single high-rigidity chassis. What follows is a technically detailed walk through every meaningful part of this amplifier, why each engineering decision was made, and how those decisions translate into what you hear and what you can measure.
Topology and Amplification: How the E-700 Makes Its Sound
What operating class is the Accuphase E-700, and why does that matter?
The E-700 is a Pure Class-A amplifier, meaning its output transistors are biased to conduct continuously and never switch off across the entire audio waveform. In a Class-AB design, each half of the output stage hands off to the other as the signal crosses zero, and that handoff creates crossover distortion, which is most audible at low listening levels where the music lives in the first few watts. By keeping the output devices always conducting, Class-A eliminates that switching artifact entirely, giving extremely linear behavior and low-order harmonic character. The trade-off is heat and efficiency, which is why the E-700 idles at 178 watts and dissipates most of that as warmth even with no music playing. This is also why its rated output is a modest looking 35 watts per channel into 8 ohms rather than a larger Class-AB figure. Those 35 watts are pure Class-A watts, and they behave very differently from AB watts under real musical loads.
Why does the E-700 double its power as impedance halves?
The E-700 delivers 35 watts into 8 ohms, 70 watts into 4 ohms, and 140 watts into 2 ohms, and that clean doubling is the signature of a stiff power supply and a robust output stage acting like a near-ideal voltage source. When an amplifier can double its current delivery each time the load impedance halves, it means the supply rails are not sagging and the output devices are not running out of current headroom. Real loudspeakers are not flat 8 ohm resistors. They dip into the low single digits at certain frequencies, and it is precisely at those dips that a weaker amplifier loses control. The E-700's ability to pour 140 watts into 2 ohms means it retains authority exactly where difficult speakers demand it most.
How does current feedback improve the sound?
Current feedback takes the amplifier's error-correction signal as a current rather than as a voltage, and the practical benefit is that the feedback loop operates at a very low impedance point that resists phase shift across a wide bandwidth. In a conventional voltage-feedback amplifier, the impedance at the feedback node is high, so stray capacitance interacts with it and introduces phase lag as frequency rises, which forces the designer to compromise between bandwidth and stability. Because the current-feedback node is low impedance, that phase shift stays minimal, so the amplifier holds consistent behavior far beyond the audio band and remains stable driving reactive speaker loads. Audibly this shows up as clean high-frequency transients and a sense of ease, because the amplifier is not fighting its own feedback loop at the frequencies where music has the most detail.
What is the output stage made of, and why parallel devices?
The E-700 uses multiple power transistors connected in parallel per channel, sharing the current load between several identical devices rather than asking one pair to do all the work. Paralleling devices lowers the effective output impedance, spreads thermal and electrical stress so each transistor runs well within its safe operating area, and raises the damping factor. It also improves reliability and linearity, because devices operating within a comfortable portion of their range distort less. This is the same philosophy Accuphase applies across its separate P-series power amplifiers, scaled appropriately for an integrated chassis.
What does a damping factor of 1000 mean in practice?
A damping factor of 1000 means the amplifier's output impedance is one thousandth of the 8 ohm load, so it exerts an extremely firm electrical grip on the woofer's motion. When a woofer cone moves, it generates its own back-EMF voltage, and the amplifier needs to absorb and control that energy to stop the cone precisely rather than letting it overshoot. A high damping factor gives the amplifier a very low impedance path to short out that back-EMF, which translates to tighter, more defined bass and cleaner starts and stops on kick drums, plucked bass, and pipe organ notes. In practice, beyond a certain point the gains become subtle, but a figure of 1000 tells you the output stage and speaker cabling connections are engineered to keep the woofer firmly under command.
Volume, Noise and Signal Integrity
What is the AAVA volume control, and how does it work?
AAVA, the Accuphase Analog Vari-gain Amplifier, is Accuphase's replacement for the traditional volume potentiometer, and it changes level by switching weighted current sources rather than by wiping a contact along a resistive track. The incoming music signal is converted into 16 weighted current sources, and volume is set by switching combinations of those currents on and off, which yields 65,536 discrete steps summed back into a voltage. Because there is no variable resistor anywhere in the signal path, there is nothing to wear out, nothing to develop scratchiness over the years, and no mechanical mismatch between the left and right channels. Crucially, the signal is never attenuated by a resistor and then re-amplified, so the signal-to-noise ratio stays essentially constant at every volume setting, whether you are listening quietly at night or filling a room. AAVA is a genuine gain-control system, not a passive divider, and it is central to why the E-700 sounds equally clean and balanced at low levels.
What does the E-700's signal-to-noise ratio of 121 dB tell you?
The 121 dB signal-to-noise ratio at the high level input tells you the noise floor of this amplifier is buried so far below the music that it is effectively inaudible in any normal listening environment. That figure is a direct consequence of the AAVA topology, which does not inject the resistor noise a potentiometer would, combined with careful grounding and a low-noise power supply. In practice, a noise floor this low means the blackness between notes stays black, and quiet passages retain their microdynamic detail rather than being smeared by hiss. It also means the full resolution of high-resolution digital sources can actually reach your ears rather than being masked at the amplifier stage.
What is MCS+ and ANCC, and why are they in this amplifier?
MCS+ (Multiple Circuit Summing) and ANCC (Accuphase Noise and distortion Canceling Circuit) are two complementary techniques Accuphase uses to push distortion and noise lower than a single circuit could manage. MCS+ runs several identical amplifier circuits in parallel and sums their outputs, so the wanted signal adds coherently while the random noise contributions of each circuit partially cancel, improving the signal-to-noise ratio and lowering distortion. ANCC goes a step further by sensing the residual distortion still present in the amplifier and generating a canceling signal to null it out. Together they are the reason the E-700 posts a total harmonic distortion figure of just 0.03 percent into 8 ohms, and hold to 0.05 percent even into the far more demanding 2 to 4 ohm range. Distortion staying that controlled as the load gets harder is exactly what you want, because it confirms the amplifier is not being pushed into nonlinear territory by difficult speakers.
How do the balanced inputs reject noise?
The balanced XLR inputs on the E-700 use an instrumentation-amplifier arrangement, which senses only the difference between the two signal conductors and rejects anything common to both. Any hum or interference picked up along a long cable run appears equally on both conductors, so the instrumentation amp treats it as common-mode signal and cancels it, leaving only the music. This is why a balanced connection to a source or preamp can stay quiet even in electrically noisy rooms or over longer cable runs, and it is a meaningful advantage when the E-700 anchors a larger system.
Power Supply, Chassis and Vibration Control
What kind of power supply does the E-700 use?
The E-700 is built around a large low-noise power transformer feeding substantial filter capacitors, which together form the energy reservoir the Class-A output stage draws on continuously. A Pure Class-A amplifier is constantly pulling current even at idle, so the supply must be both large and quiet, delivering steady rails without sagging when a musical peak demands a sudden burst of current. This stiff supply is what allows the clean power doubling into lower impedances, and its low noise is part of why the noise floor and distortion figures are as good as they are. The 24.9 kg weight of the amplifier is largely accounted for by this transformer and capacitor bank along with the heatsinking needed to shed Class-A heat.
Why is the chassis so heavy and rigid?
The E-700 uses a thick machined-aluminum front panel with the signature Accuphase hairline finish and a high-rigidity chassis, and this mass is functional rather than merely cosmetic. Vibration, whether airborne from the loudspeakers or mechanical from the transformer, can modulate sensitive circuitry and add a subtle blur to the sound, so a rigid, massive chassis resists that vibration and keeps the electronics in a stable mechanical environment. The same mass and careful internal layout also help with electrical noise, because generous spacing and considered grounding keep the power supply and high-current sections away from the low-level signal stages. This construction philosophy is a large part of why Accuphase amplifiers feel the way they do in the hand and why they continue performing to specification for decades.
Connectivity, Expandability and Placement in the Range
Can the Accuphase E-700 be upgraded after purchase?
Yes, the E-700 is a modular design with option slots that accept plug-in boards, so you can add capability as your system evolves rather than being locked into the amplifier's original configuration. Accuphase offers boards such as a DAC option and a phono board, which let you turn the E-700 into the hub of a digital system or add a proper analog front end for a turntable. Because these boards are engineered to Accuphase's standards and integrate directly into the amplifier's signal path and power supply, they are a genuine extension of the design rather than an afterthought. This modularity is a hallmark of the Accuphase approach and means the amplifier can adapt over its long service life.
What do the front-panel analog power meters show?
The two front-panel needle meters display the amplifier's instantaneous output power on a logarithmic scale, giving you a real-time visual sense of how hard the amplifier is working. The logarithmic scale matches the way we perceive loudness and lets the meters show both the small fractions of a watt of quiet passages and the larger swings of dynamic peaks on the same display. They are genuinely useful for understanding how little power most listening actually requires, and they are also an enduring part of the Accuphase visual signature, one that owners tend to appreciate. If you prefer, the metering can typically be switched off for distraction-free listening.
What do the E-700's gain and input sensitivity figures mean for matching?
The E-700 needs 127 mV at its high level input to reach rated output, or 0.617 V at the Main In direct power-amp input, with 28 dB of gain from Main In to output. These figures tell you the amplifier is easy to drive from any normal line-level source, since even modest source outputs will comfortably reach and exceed those sensitivities. The Main In connection is particularly useful because it bypasses the AAVA volume stage and feeds the power amplifier directly, which lets you slot the E-700 into a larger system controlled by an external preamplifier or processor while still using its Class-A output stage. The 28 dB of power-amp gain is a sensible, conventional figure that pairs cleanly with the rest of an Accuphase or mixed system.
How flat is the frequency response, and does it matter?
The E-700's frequency response measures 20 Hz to 20 kHz within +0 and -0.2 dB at rated output, which is essentially ruler-flat across the entire audible band. A deviation of just two tenths of a decibel at the extremes is far below the threshold of audibility, so the amplifier imposes no tonal character of its own, neither warming the bass nor rolling off the treble. This flatness is the intended result of the wide-bandwidth current-feedback topology, and it means what you hear is the source and the loudspeakers, not a coloration added by the amplifier.
Where does the E-700 sit in the Accuphase lineup?
The E-700 sits at the top of Accuphase's E-series integrated amplifiers as its Pure Class-A flagship, above the Class-AB E-series models and below the reference E-800S integrated. Within Accuphase's own range, the E-series integrateds bring the technologies of the separate C-series preamplifiers and P-series and A-series power amplifiers into a single chassis. The E-700 in particular pairs the AAVA volume control from Accuphase's finest preamps with a Class-A current-feedback output stage, so it delivers a large part of the separates experience in one unit. For a listener who values the linearity of Class-A, the reliability and cleanliness of AAVA, and the flexibility of option-slot expandability, the E-700 represents one of the most complete statements Accuphase makes in integrated form.
Taken as a whole, the Accuphase E-700 is an exercise in doing the fundamentals to an exacting standard. Pure Class-A operation removes crossover distortion, current feedback keeps the amplifier wide and stable, AAVA controls level without compromising noise, and a heavy stiff chassis and supply give all of it a solid foundation. The measurements confirm the engineering, and the modular architecture ensures the amplifier can grow with you for many years.