Accuphase E-406 (1993)
Twenty-eight kilograms of champagne-gold integrated amplifier, built around a 9 kg transformer and a promise that the preamp and power amp never have to share a power supply.
Overview
The Accuphase E-406 weighs 25 kg. It was released in June 1993, and it was Accuphase's attempt at a question the company had circled for two decades: can you take the engineering from a separate preamplifier and a separate power amplifier and put both in one chassis without compromising either? According to the documentation that survives, the answer was to give each section its own transformer, its own rectification, and its own regulated supply. That makes it effectively two components sharing a faceplate.
The headline numbers are 170W per channel into 8 Ω and 250W per channel into 4 Ω, with total harmonic distortion held to 0.02% across a 4 Ω to 16 Ω load from 20 Hz to 20 kHz. Intermodulation distortion is spec'd at 0.01%. Those figures were conservative by Accuphase's usual standards. The rated load impedance range of 4 Ω to 16 Ω and the four parallel output devices per channel suggest the E-406 was built to drive difficult speakers without complaint. The damping factor of 120 into 8 Ω at 50 Hz points the same way: enough grip to keep a woofer under control, without being so extreme that the amplifier looks like it's fighting itself.
No single specification makes the E-406 interesting. It's the pile of decisions that only make sense if you've spent years building separate components and then decided to do it all in one box. The preamp section can be separated from the power amp section with a rear-panel switch, with dedicated input and output terminals, so the E-406 works as two independent components or as a conventional integrated. Nobody adds that casually. You add it because your customers already own separate components and might want to use them alongside the E-406 rather than instead of it.
Accuphase was founded in late 1972 by former Kenwood engineer Jiro Kasuga, with Kenwood as a partial owner until the mid-1990s. The E-406 arrived twenty-one years into that run, when the company had a deep catalogue of separate amplifiers and a reputation for build quality that bordered on the obsessive. The ¥380,000 asking price at release put it firmly in flagship integrated territory. Audio (October 1993, p.114) listed the E-406 in its amplifiers directory, positioning it well above the E-306 and the budget E-211 in the company's own lineup.
Key Features
Separate Transformers for Preamp and Power Amp Sections
The power supply explains most of the E-406's other characteristics. The preamp and power amp sections each get their own transformer and their own dedicated power supply, which Accuphase's documentation describes as a way to "completely prevent mutual interference between amplifiers." The power transformer for the amplifier section alone is in the 9 kg weight class, and smoothing is handled by two 33,000 μF block capacitors. A local active ripple filter compensates for crosstalk from the main supply. This isn't a shared-supply design with extra filtering tacked on. It's two power supplies in one chassis, which is why the E-406 weighs what it does.
The documentation also notes that the preamp section and power amplifier section are separated, with a changeover switch for use as an independent amplifier and its own input and output terminals. Owners can use the power amp section with an external preamp, or the preamp section with external power amps, without modification.
Differential Pure Complementary Push-Pull Circuit with Current Feedback
The E-406 uses Accuphase's original differential pure complementary push-pull topology with current feedback in both the line and power amplifier stages. The input circuit is a Darlington-connected, emitter-grounded differential amplifier, which the documentation describes as achieving high CMRR (common-mode rejection ratio). In plain terms, the input stage is designed to reject noise that appears equally on both halves of a balanced signal, the kind of noise long cable runs pick up. The line amplifier section is built from discrete parts, with a single-ended push-pull emitter-follower output stage.
Triple Parallel Push-Pull Output Stage
The power amplifier output stage uses four parallel output devices per channel, mounted on a large heatsink. The documentation describes this as a triple parallel push-pull configuration, with high-current audio-specific power transistors. The stated goal is stable operation under low-impedance loads, the kind of speakers that dip below 4 Ω at certain frequencies and cause lesser amplifiers to current-limit or shut down. Accuphase's original DC servo amplifier is used in the feedback circuit, which the documentation says prevents any DC component from appearing at the speaker outputs. That protects as much as it performs: no DC offset means no thump through the woofers at power-on, and no slow voice-coil damage over time.
Balanced Inputs and Gold-Plated Signal Path
The E-406 includes balanced inputs alongside its single-ended connections. Input sensitivity for the balanced input is 147mV for rated output, with an input impedance of 40k Ω. The high-level single-ended input has the same 147mV sensitivity but a 20k Ω impedance. The main input, intended for use with an external preamp, is 1.47V for rated output at 20k Ω. Gain from main input to output is 28 dB; from high-level input to pre-out it's 20 dB.
The main signal path uses a gold-plated printed circuit board over high-purity copper. The documentation explains this as reducing the influence of skin effect and improving conductivity. Signal switching is handled by nitrogen-filled, gold-plated cross-bar twin relays under microcomputer control, with switching timing managed on the order of milliseconds to eliminate switching noise. The relays are sealed units originally intended for the communications industry, which is not a part you specify if you're building to a price.
MM/MC Phono Stage with Dedicated Input Circuits
The equalizer section has separate input circuits for moving-magnet and moving-coil cartridges. The MM input uses FET elements to maintain high input impedance across the band - 47k Ω, with a sensitivity of 4.65mV for rated output. The MC input uses a differential circuit built from low-noise elements, with the NFB loop impedance kept low; sensitivity is 0.15mV for rated output at 100 Ω. Maximum input before 0.005% distortion is 300mVrms for MM and 8.0mVrms for MC. Signal-to-noise ratios are 90dB for MM and 75dB for MC, both A-weighted with input shorted.
Tone Controls, Filters, and Metering
The tone control section uses an add-on active filter design, the same approach found in full-scale graphic equalizers. Bass is adjustable ±10 dB at 50 Hz (300 Hz turnover), treble ±10 dB at 20 kHz (3 kHz turnover). A loudness compensator adds +6 dB at 100 Hz when the volume is set to -30dB. A subsonic filter rolls off at 17 Hz, 12 dB per octave. The front panel has large dual analog power meters with peak hold, using logarithmic compression for direct reading of output in dB into an 8 Ω load. The meters are calibrated to indicate peak level, and the amplifier's documentation notes they're set for 170W into 8 Ω.
Headphone Amplifier and Remote Control
The E-406 has a dedicated headphone amplifier rather than a simple resistor pad off the main output. The documentation describes it as "a special amplifier for headphones installed to give consideration to sound quality." The headphone jack accepts impedances from 4 Ω to 100 Ω. The included remote commander, the RC-10, uses an infrared pulse system and runs on two R03 batteries. It controls input selection and volume, the latter via a motor-driven potentiometer. The motor is covered with a silicon steel magnetic shield to reduce noise. The RC-10 is also compatible with the C-250 preamplifier, which is why used examples show up listed for both models.
Chassis and Construction
The chassis is non-magnetic and vibration-resistant, with Accuphase's signature champagne-gold faceplate. The speaker terminals are large solid-brass posts that accept very thick cables and banana plugs. Selecting the A+B position allows bi-wiring. The E-406 also supports optional input boards via two rear-panel slots compliant with the AAB interface standard, though the fact sheet doesn't specify which boards were available.
Dimensions are 475 mm wide, 180 mm high, and 423 mm deep. Power requirements cover AC100V, 117V, 220V, and 240V at 50 or 60 Hz. Power consumption is 65W with no input, 390W under the Japanese Electrical Appliance and Material Control Law standard, and 620W at 8 Ω rated output.
Historical Context
The E-406 was released in June 1993 at ¥380,000. Accuphase positioned it as the ideal integrated amplifier, a component that combined the development technology built up over years in the company's separate amplifier group, with the preamplifier and power amplifier sections made completely independent despite sharing a chassis. The company's own documentation describes it as "a pre-main amplifier developed by Accuphase as the ideal form of an integrated amplifier."
In Accuphase's lineup, the E-406 sat at the top of the integrated range. The E-306 and E-306V were positioned below it, with the budget E-211 further down. The E-406 was the flagship integrated, the one that got the 9 kg transformer, the balanced inputs, the full relay-switched signal path, and the ¥380,000 price tag. HiFi-Stereo (1996, p.61) listed it at $6,995 in the U.S. market, with 170W per channel into 8 Ω from 20 Hz to 20,000 Hz at 0.02% THD, six line-level inputs including two balanced, two tape loops, and an MM/MC phono input.
Accuphase was founded in late 1972 by Jiro Kasuga, a former Kenwood engineer. Kenwood held a partial ownership stake in the company until the mid-1990s, so the E-406 was developed and released during the final years of that relationship. The E-406's production end year isn't documented in available sources.
Collectibility & Value
Documented market data for the E-406 itself is thin. An eBay listing for the RC-10 remote controller, compatible with both the E-406 and the C-250 preamplifier, was priced at $239. Another listing noted the amplifier as "Operation Confirmed" with 100V power. TMR Audio quoted a flat $85 shipping rate within the contiguous United States, including packaging and insurance. A European retailer listed a champagne-coloured example with remote control as no longer available.
No collector market prices for the amplifier itself, no common failure points, and no maintenance or repair information appear in the available research. The E-406's 25 kg weight makes shipping expensive. The RC-10 remote is shared with the C-250, so replacements are findable, but they don't turn up constantly. Beyond that, the usual advice applies: buy on condition, confirm the meters and relay switching work, and budget for the possibility that a 1993 amplifier may need service.
User reviews on audioreview.com number eleven, and the amplifier has sixty reviews noted on one retailer's site, but the content of those reviews isn't available in the research. What can be said is that the E-406 occupies a specific place in Accuphase's history — the flagship integrated of the early 1990s, built to a standard that explains both its weight and its enduring appeal among collectors who want one box that does what two boxes used to.
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