Accuphase C-240 (1978)

Fifty-seven push switches, a rosewood cabinet, and a fully symmetrical Class A DC circuit in every stage - Accuphase's control center from the late seventies.

Overview

The C-240's front panel has four rotary knobs, a single lever switch, and fifty-seven push switches. It looks more like laboratory equipment than consumer hi-fi. The Accuphase C-240 is a stereo control amplifier built by Accuphase Laboratory, Inc. in Japan and released in September 1978. Sources call it a "Stereo Control Center Preamplifier," a "Precision Stereo Control Center Preamplifier," or simply a preamplifier. The name shifts, but the machine underneath doesn't. It is a line-stage and phono preamp.

The headline number is the signal-to-noise ratio: 110 dB on the high-level inputs. That is a very low noise floor. Switch in the moving-coil head amplifier and the S/N drops to 72 dB, because the extra gain needed for low-output cartridges always costs something in noise. With the head amp off, the figure sits at 85 dB for moving-magnet cartridges.

Frequency response is quoted at 20 Hz to 20,000 Hz with a +0/-0.2 dB tolerance on the high-level inputs and ±0.2 dB on the disc inputs. Harmonic distortion is rated at 0.005% across the same bandwidth at rated output. Those are single-source manufacturer figures, not independent laboratory measurements, so treat them as the design target rather than a verified result. They are consistent with what a well-executed Class A DC circuit should deliver.

The circuit is the story. Every amplification stage - head amplifier, equalizer, high-level, and headphone - runs in Class A with symmetrical push-pull drive. That is an extravagant choice. Class A runs hot, draws current continuously, and wastes power in exchange for linearity. Most designs would do it only in the line amp. The high-level amplifier uses a DC servo method (patent pending) to eliminate the DC blocking capacitors that would otherwise color the sound. The head amplifier uses specially developed ring emitter transistors for small signals, while the equalizer stage combines FET buffers with RETs for high-frequency power amplification.

Inside the chassis are 159 transistors, 10 FETs, and 102 diodes. It is a discrete design with no op-amps. The unit measures 466 mm wide by 188 mm tall by 391 mm deep and weighs approximately 18 kg according to the available documentation, though that weight appears in only one source and should be treated as approximate. Power supply options cover 100 V, 117 V, 220 V, and 240 V at 50/60 Hz, so units turn up wired for different markets depending on where they were originally sold.

Key Features

Fully Symmetrical Class A DC Circuitry

The C-240 uses a fully symmetrical push-pull Class A DC design through every amplification stage, from the head amplifier input to the headphone output. Symmetry here means the positive and negative halves of the waveform are amplified by matched circuit halves, which cancels even-order distortion and improves linearity. Class A operation means the output devices conduct continuously rather than switching on and off, eliminating crossover distortion entirely. Combining both in a DC-coupled design, with no capacitors in the signal path, was a serious engineering commitment in 1978. It is the reason the C-240 has held its reputation among collectors.

Dual Phono Inputs with Switchable Head Amplifier

Two disc inputs are provided, each switchable between moving-magnet and moving-coil operation via the built-in head amplifier. With the head amp off, input sensitivity is 2.0 mV with switchable impedance of 100Ω, 47kΩ, 82kΩ, or 150kΩ, enough to match a wide range of MM cartridges. With the head amp on, sensitivity rises to 0.1 mV at a fixed 100Ω, suitable for low-output MC designs. Two phono inputs were unusual even then, and they reflect a period when serious listeners often ran two turntables with different cartridges.

Feather-Touch Relay Switching

Input selection is handled electronically via relays rather than mechanical switches. Each of the fifty-seven push switches on the front panel activates a relay using a dual-circuit arrangement designed to reduce contact resistance. This keeps the audio from running through long runs of switch contacts.

18-Brush Volume Control

The volume potentiometer uses 18-brush sliding elements running against mirror-finished conductive plastic resistor tracks. More brushes mean more contact points, which distributes wear and maintains consistent tracking between channels. Conductive plastic resistors were chosen over carbon for their lower noise and better long-term stability. None of this shows up in a spec sheet, but a cheap volume pot develops dead spots and channel imbalance after twenty years of use, and a well-made one doesn't.

Tone Controls and Loudness Compensation

The tone controls are 8-step push switches rather than continuous rotary pots, with ±8 dB of adjustment at 50 Hz and 20 Hz for bass, and at 20 kHz and 50 kHz for treble, in 2 dB steps. Loudness compensation offers three settings - +6 dB, +9 dB, or +10 dB at 50 Hz - with the COMP3 setting also adding +6 dB at 20 kHz, active below -30 dB volume. These aren't audiophile-purist features, but the stepped implementation means settings are repeatable.

PureCon Headphone Amplifier

The headphone output isn't a tap off the line stage. It is a dedicated amplifier using Accuphase's PureCon circuit. Output impedance is 0.3Ω, and the amp delivers 0.25 W into 8Ω at 1 kHz with 0.01% distortion. The low output impedance means the amp can drive a wide range of headphone impedances without frequency response deviations. Most preamps of the era treated headphone outputs as an afterthought. The C-240 didn't.

Natural Rosewood Cabinet

The C-240 is housed in a natural rosewood cabinet, a material Accuphase used across its better components of the period. The wood damps resonance and gives the chassis a warmth that metal cases lack. Surviving units often show minor scratches and coloration in the finish, which is normal aging for a forty-plus-year-old wooden cabinet.

Historical Context

The C-240 was released in September 1978, during what's often called the "Golden Era" of Japanese high-fidelity audio equipment. Contemporary coverage of high-end audio in the early 1980s noted that moderate-price integrated amps, receivers, and systems were among the new entries from major manufacturers, even as the era's premium designs pushed discrete circuit engineering to new extremes (High-Fidelity, September 1982, p.29). One 1982 HiFi-Stereo piece observed that claimed sonic differences between esoteric components are often the product of reviewer imagination and psychological bias rather than genuine audible distinctions (HiFi-Stereo, October 1982, p.67). Japanese manufacturers were investing heavily in discrete circuit design, premium materials, and build quality that rivaled or exceeded anything coming out of Europe or America. Accuphase Laboratory, Inc. positioned itself at the top of that market.

The C-240 was designed to pair with the Accuphase P-400 power amplifier, which contemporary sources describe as forming a perfect combination with the preamp. The P-400 has been described as a highly regarded stereo power amplifier, and the C-240 as a highly regarded preamp. That suggests the two were conceived as a system rather than as standalone components. No production end year is documented in available sources, so it's unclear how long the C-240 remained in the lineup.

Collectibility & Value

The C-240 is not one of Accuphase's flagship models, but it has developed a following among collectors who appreciate the Golden Era designs. An example unit was listed at $1,350 approximately five years ago, described as in excellent condition with only minor aging such as scratches and coloration, and confirmed by a professional technician to be in flawless working order. More recent eBay listings show asking prices of $1,750 and $2,150 for units described as "Precision Stereo Control Center Preamplifier" and "Stereo Control Center Preamplifier USED JAPA" respectively.

A current listing on a Korean audio site shows an asking price of 1,300,000 (currency not explicitly stated in the source), with the unit noted as 220/230V. Units wired for 100V require a step-down transformer in most markets, while 220/240V units can be plugged in directly in Europe and many other regions.

No common failures or repair notes are documented in available sources. The volume potentiometer and the relay switching system are the most likely candidates for service based on the design, but that's inference rather than documented experience. A schematic is available for the C-240. The original retail price is not documented - the $1,350 figure is a used-market listing, not an MSRP.