Accuphase / Kensonic C-230 MOSFET stereo preamplifier


Accuphase C-230High fidelity preamplifier Accuphase / Kensonic C-230. Class A circuit, World’s first MOSFET preamplifier. The C-230 was produced 5 years long in the audio’s golden age, from 1979 until 1984, of course in Japan. Built like a tank, heavy 10kg construction with a massive brushed aluminium face plate, aluminium side attachments and rigid chassis. Obviously all 4 knobs are made out of aluminium and are precisely milled and shaped. It’s a pleasure to play with them, whilst adjusting the sound. The ability to choose the crossover frequency makes it even more enjoyable. The balance knob is a mix of plastic and aluminium and has a different shape from the other four ones. Briefly speaking the preamp is a pure perfection in assembly and quality of used materials. Well, no wonder – it’s exactly what Accuphase is about, of course besides the outstanding sound
quality. The gear has basically the same features as the preamp section of the well appreciated E-303 (X).

Accuphase C-230Let’s take a short look inside the machine. In order to do so, the top and the bottom covers need to be unscrewed. Looking from the top, the first thing, that stands out, are the thick parallel mounted input selection bars. They look very interesting. The preamp has a very modular construction. Each electronic section has it’s own PCB. The power supply consists of a fair-sized shielded power transformer supported by a bunch of ELNA power caps (2 x 10000uF, 4 x 2200uF). It’s possible to make an easy input voltage adjustment using the voltage selector that is situated underneath the power transformer. Available values are 100V, 117V, 220V, 240V 50/60Hz. What I like about this generation of Accuphase gear are the tone potentiometers, which are very reliable, precise and easy to maintain. What is also worth mentioning is the fact, that this preamp is especially hunted by record player users. The extremely well equipped phono section is a real masterpiece.

Retail price in Japan in year 1979: 170000¥
Relative price in in Japan in year 2011 using the retail price index: 236000¥


Manufacturer's description

The Accuphase C-230 is a high gain control preamplifier which symbolizes the combined aggregation of Accuphase audio technology. It employs the basic Accuphase design of complementary-symmetry push-pull driven circuitry, features Class-A operated DC amplification and utilizes a newly innovated DC Servo Control system in its high level amplifier. By using a push-pull drive in every stage of circuitry, it has the low distortion and high stability. The DC amplifier system eliminates sound colouration and assures high quality sound reproduction. MOSFETs are utilized in a control centre with no notching distortion. The unit amplifiers are equipped with exclusive voltage power supplies to alleviate the inefficiency of high frequency range in wideband amplifiers. The DC Servo Control System allows the system to operate as a DC amplifier without blocking capacitors which cause sound colouration and prevents shock noise. The Accuphase C-230 has a thoroughly designed equalizer, using Class-A operated MOSFETs to achieve large current drive and low output impedance to obtain highest signal to noise ratio. It also has a feedback canceller circuit to prevent sound quality to deteriorate from the capacitive feedback. The push-pull head amplifier is connected to moving-coil cartridges to realize a clearer, richer and more detailed sound reproduction character.

The Accuphase C-230’s tone control function is expanded to provide a smooth control over a selection of turnover frequencies for bass and treble. It has a rotary switch that allows tonal variation and on/off switching of tone control circuit. The preamplifier has three-step loudness compensator to provide a choice of sound energy balancing curves to help human ears detect certain audio frequencies during low-level reproduction, as well as balancing out listening room characteristics. The subsonic filter cuts off frequencies below 17Hz that sometimes cause intermodulation distortion in the audible frequency range. The C-230 allows two tape recorders to be connected. There is an independent copy switch that permits copying while enjoying a different program source. The output can be cut off by the switch at any occasion. The Accuphase C-230 is a remarkable preamplifier engineered by Accuphase after extensive tests with the best inherent characteristics. With the extravagant circuitry and effective components, it elevates the preamplifier to be among the best. Accuphase is confident that they have perfected a control centre of the highest order in the C-230 with which the inner world of musical reproduction can be enjoyed to the full extent.

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Technical specification

Form Stereo control center
Frequency response (new IHF) High-level input: It is +0 20Hz – 20000Hz. -0.2 dB
Disc input: 20Hz-20000Hz±0.2dB
THD (new IHF, THD+N) 0.005% or less (20Hz – 20000Hz)
Input sensitivity/input impedance
(Rating / new IHF)
DISC(HEAD AMP:OFF): 2.5mV/0.96mV/100, 47k and 82k, 150kohm
DISC (HEAD AMP:ON): 0.125mV/0.05 mV/100 ohms
AUX, Tuner, Tape, and Play:160mV/62mV/47kohm
An Output power/Output load impedance Output: 1.3V/20 ohm
Tape Rec: 160mV/200 ohms
Headphone Output load impedance: 0.3ohm
Output (8ohm load): 0.25W, 1kHz
Distortion (THD+N): 0.01%
S/N (A-compensation) / input conversion noise
It is input short-circuit at the time of a rated input.
Tuner, AUX, Tape Play : 112dB -128dBV
Tuner, AUX, Tape Play : 92dB
Maximum-except-take-off level More than 8.0V
Distortion (THD+N): 0.005% (20Hz – 20000Hz)
The disc maximum input
HEAD AMP OFF: 300mVrms, 1kHz
Distortion (THD+N): 0.005%
HEAD AMP ON: 15mVrms, 1kHz
Distortion (THD+N): 0.005%
Minimum load impedance Outputs: 1kohm
Tape Rec: 10kohm
Tuner, AUX, and Tape Play
Tape Rec: 0dB
Outputs: 18dB
HeadPhones: 18dB
Tape Rec: 36dB
Outputs: 54dB
HeadPhones: 54dB

(It is +26dB at the time of the DISC input HEAD AMP ON)

Tone control The step type by 11 contact rotary switch

Low-pitched sound 500Hz : ±10dB (100Hz)
200Hz : ±10dB (50Hz)
2dB step
2dB step
Loud sound 2kHz : ±10dB (10kHz)
7kHz : ±10dB (50kHz)
2dB step
2dB step
Loudness Compensation COMP1:+6dB(50Hz)
COMP of 3:+10dB (50Hz), +6dB (20kHz)
(with Volume control and -30dB)
Subsonic Filter 17Hz, -12 dB/oct
Attenuator -20dB
The semiconductor used 85Tr, 16FET, 5IC, 22Di
Power source 100V, 117V, 220V, 240V/50Hz, 60Hz
Power consumption 35W
Dimensions the width 445x height 128(piece — it includeds) x depth of 370mm
Weight 10.0kg
Option Wood cabinet A-9 (15,000yen)


“Control amplifier which concentrated and completed the technology which the Accuphase has cultivated for years. The head amplifier for MC cartridges and full-scale headphone amplifier are built in, and the tone control function is also carried abundantly.”

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