Accuphase C-7

Commentary

A stereo head amplifier developed to reproduce the original individuality of the MC cartridge directly.

The circuit is based on the head amplifier section of Accu-phase C-220 and C-240. The input is differential push-pull with four RETs. All stages are push-pull and DC configuration.
RET (Ring Emitter Transistor) was originally developed for power amplification. Its internal configuration is equivalent to that of a large number of small-signal elements arranged in parallel. It is particularly excellent in high-frequency characteristics. The RET used in C-7 was developed specifically for signal amplification. It is excellent in high-frequency characteristics and small-level linearity. Along with these excellent characteristics, the equivalent input noise is extremely small thanks to the multi-element parallel structure, which realizes an ideal input circuit.

The main circuit is modularized. The printed board on which the amplifier and its peripheral elements are mounted is placed in a case and sealed with an epoxy resin. This completely insulates the board from the outside air, improving durability and ensuring stable operation against temperature changes.

The ICL method is used for the input circuit, and the input capacitor is eliminated by the perfect balance of the input differential circuit, so that the small signal of the cartridge is directly led to the RET, enabling high fidelity sound.

By installing a dedicated constant-voltage power supply for each of the left and right channels right next to the module amplifier, impedance is reduced over a wide band.

In consideration of the case of using a cartridge other than MC, it is equipped with a PASS switch which connects input and output directly.

In the C-7, all MC cartridges were actually auditioned and the load impedance was decided to be 100 Ω, and it is suitable for everything from low Orthophone type of 2 ~ 3 Ω to high 40 Ω like EMT.
When the load impedance becomes low, the operation of the cartridge vibration system is over-damped, and there is no sense of volume in the low range, and the sound quality becomes oppressive.

Model Rating

Type	MC head amplifier
Gain	26dB
Frequency characteristic	5 Hz ~ 100 kHz + 0 -0.2 dB
Max Input	35 mVrms (20 Hz to 20 kHz, 0.002% distortion)
Harmonic distortion factor	0.002% (20 Hz to 20 kHz at maximum input)
S/N ratio (IHF-A, RIAA applied)	72 dB (0.1 mV input)
Input conversion noise (IHF-A, RIAA applied)	-152dBV
Input impedance	100 Ω
Output impedance	100 Ω
Semiconductor used	Transistor : 26 FET : 9 IC : 2 Diode : 8 pcs
Power supply voltage	AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption	5W
External dimensions	Width 102x Height 61x Depth 350 mm
Weight	2.5kg