LUXMAN C-05

Commentary

A preamplifier that uses a single-stage amplifier along with the M-05.

The C-05 employs a class A symmetrical push-pull operation in all stages of the head amplifier, equalizer amplifier and flat amplifier, making it an amplifier circuit with extremely stable open-loop characteristics.

The C-05 uses a single-stage amplifier developed from duo-beta technology.
Luxman's original duo-beta circuit combines an appropriate amount of NFB for sound quality with a DC servo that tightens the sound image from outside the audible band. In addition to improving performance in the open loop before applying NFB, a small amount of NFB is applied to improve the performance not only in pursuit of characteristics but also in music reproduction performance.
This duo-beta circuit eliminates the need for high open-loop gain, which is required when applying a large amount of NFB, and realizes a single-stage amplifier configuration without the second stage amplifier, thereby simplifying the circuit.

The adoption of a single-stage amplifier realizes two epoch-making improvements.
In conventional amplifiers, the second amplifier stage is an amplifier circuit with a reference to the power supply. Therefore, the power supply used as the reference for amplification fluctuates due to changes in the input signal, and the music signal is modulated. In addition, noise is induced from the power supply to amplify and reproduce the music signal. In the single-stage amplifier, this problem is solved completely by realizing an amplifier circuit with only a ground reference, and amplification with only a ground reference is realized.
In addition, in the amplifier circuit, a high frequency correction stagger is provided for each amplification stage. In the case of two stage amplification, the two staggers interfere with each other, which significantly deteriorates the freshness of music. However, this can be eliminated by one stage amplification.

In order to make the reference potential = 0 absolute, the common power supply and theoretical mid-point grounding are not left unattended, and the ground is thoroughly grounded. Moreover, since the impedance becomes high when grounding the wiring board, the chassis ground is directly grounded. In addition to simply grounding the chassis, the ground line for each stage is concentrated at one point to make it more perfect. This point is also the center point of the left and right channels.
The oxygen-free copper wire is used for the tumor part.

The head amplifier is a single-stage amplifier with a differential cascode using carefully selected low-noise transistors. The output section is also a Class A SEPP with a small power transistor with a heat sink. As well as a high S/N, high drive performance is achieved.

The equalizer amplifier employs a symmetrical differential double-cascode push-pull circuit using a low-noise dual FET with the highest Gm at that time, and achieves both low distortion rate and high S/N by performing one step amplification with minimum load resistance.
The C-05 equalizer amplifier has exactly the same circuit structure as the flat amplifier in the circuit diagram. It is designed with the idea of combining the NFB circuit that performs RIAA correction with the amplifier that allows complete faithful reproduction as a base. In addition, the load of the NFB element is given a sufficient margin so that the nuance and atmosphere of the music intended by the recording side can be reproduced with a sufficient margin, and the output impedance is low.
In addition, by removing the output capacitor, coloring of sound between stages is eliminated.

The flat amplifier section uses a symmetrical differential double-cascode push-pull single-stage amplifier circuit using a low-noise dual FET with the highest Gm at that time as well as the equalizer amplifier. The DC servo circuit is equipped with an operational amplifier with FET input.

The power supply section is equipped with a large power transformer with a well-controlled winding. This transformer employs a compact and highly regulated circular transformer. We also select electrolytic capacitors for signals with extremely low leakage and distortion. Both the primary and secondary sides of the power transformer are subject to strict polarity control, and together with the line phase sensor, the transformer achieves perfect polarity control.
For the power supply, the head amplifier and servo circuit are equipped with an independent power supply.

In order to eliminate the adverse effect of electro-striction, the chassis itself is made of aluminum and the structure is composed of two layers of copper plates at important points. The copper plates and chassis are firmly fixed to prevent slight vibration.

An extension shaft is used to install a changeover switch at a required point on the circuit to minimize the wiring itself.

Carefully selected parts are used. Even non-polar film capacitors are used with the same polarity. oxygen-free copper wires and gold-plated pin jacks are also used.

The input attenuator uses a precision continuously variable detent volume with excellent linearity and sound quality.

There were an adapter for rack mounting and a wood case sold separately.

Model Rating

Type	Control amplifier
Output voltage	Pre out : 1 V (rated), 12 V or more (maximum)
Output impedance	Pre out : 47 Ω
Total harmonic distortion factor	Phono1, 2 : 0.03% or less (Rec out : 2 V, 1 kHz) DAD, Monitor1, 2 : 0.05% or less (Pre out : 2 v, 1 kHz) Tuner, Line : 0.002% or less (Pre out : 2 v, 1 khz)
Frequency characteristic	Phono1, 2 : 20 Hz to 20 kHz ± 0.2 dB DAD, Monitor1, 2 : 1 Hz to 50 kHz ± 0.5 dB Tuner, Line1, 2 : 1 Hz to 50 kHz ± 0.5 dB
Input Sensitivity (Output 1 v)	Phono MM:2mV Phono MC : 100 μ V DAD, Monitor1, 2 : 150 mV Tuner : 150 mv (with input level set) Line:150mV
Input impedance	Phono1, 2 : 50k Ω, 100k Ω DAD, Monitor1, 2 : 100k Ω Tuner : 50k Ω Line : 100k Ω
Signal-to-noise ratio (IHF-A corrected)	Phono1, 2 : 90 dB or more DAD, Monitor1, 2 : 110 dB or higher Tuner, Line : 110 dB or higher
Attachment	Monitor switches (Tape1, Tape2) Tape dubbing switch (1to2, 2to1) Recording switch Phono function switches (Phono1, Phono2) Signal off switch Line phase sensor
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption	40W (Electrical Appliance and Material Control Law)
External dimensions	Width 460x Height 135x Depth 442 mm
Weight	11.0kg
Sold Separately	Dedicated Wood Case W-05C (¥ 50,000) Rack Mount Adapter LM-05C (¥ 15,000)