LUXMAN C-300

Commentary

Stereo control center using duo-beta plusX circuit.

A duo-beta circuit is used to control sound quality while eliminating excess NFB in favor of physical characteristics. This circuit produces an amplifier circuit that is practical even with bare characteristics, and adds an appropriate amount of NFB and b and DC servo as a finishing touch of sound quality.
By doing so, we can suppress the generation of transient distortion such as TIM caused by excessive NFB and suppress the suppression of musical performance by NFB, thereby improving musical performance.

Duo Beta plusX is also used for the feedback circuit of the power supply unit, introducing the concept of appropriate control.
In general stabilized power supplies, the impedance characteristics of the power supply itself, which is not stabilized, rise in the low-frequency range, and sound quality is improved. However, there are problems such as less damping in the low-frequency range and no stability in the DC range.
In plusX, we have created a low-impedance power supply that does not need to rely on excessive feedback, and we have set control that takes advantage of this bare characteristic in the middle and high range, and control that corresponds to the amplifier circuit in the low range.

In the equalizer circuit, cascode bootstrap input by high-Gm low-noise dual FET is adopted at the first stage with current mirror load to obtain low distortion factor and high SN ratio.
High f with a dynamic resistance circuit in the second stage_TA cascode constant current load amplifier circuit using a PNP transistor is constructed, and a high f is supplied to the output stage._TAs a class A push-pull configuration with transistors, current flows, and the output impedance is made low, and the load of the NFB element is also given a margin.

The flat amplifier uses basically the same circuit as the equalizer. Especially, the DC servo circuit is equipped with an operational amplifier with FET input to ensure excellent DC stability.
This eliminates the output capacitor and eliminates sound coloring.

The MC head amplifier consists of a direct-coupled type FET parallel input at the first stage, an A-class pure complimentary service push-pull type at the outputs, and a dedicated constant-voltage circuit placed close to each other to reduce noise and source impedance.

The power supply section is completely independent on the left and right sides from the transformer winding, and includes the rectifier circuit and constant voltage circuit to constitute a twin monaural power supply.
As a result, interference between the left and right channels is suppressed, and at the same time, the winding direction is aligned for both the primary and secondary sides of the transformer, for thorough sound quality control.
The transformer and capacitor of this power supply are large in size and large in capacity to reduce impedance.

High-quality film capacitors are used for the coupling capacitors of each stage and the capacitor of the power supply, and small-capacity Styrofoam capacitors are connected in parallel.
All of these film capacitors and most of Styrofoam capacitors have the same polarity for sound quality control.
In addition, it uses continuously variable precision class detent volume with aluminum die cast case, oxygen-free copper 500 core shielded cable, etc.

It is equipped with necessary and sufficient functions, and the wiring route is arranged according to the signal flow to simplify it.

Equipped with a turnover shift tone control that achieves the desired balance with simple operation.
The two conventional operations are simplified because the turnover frequency moves continuously according to the amount of change.

It is equipped with a line-phase sensor that can detect the polarity of home AC outlets and unify the polarity of devices.

Equipped with a twin T-type subsonic circuit composed only of passive elements.

Various measures have been taken to improve the sound quality.
We have completely eliminated magnetic distortion by designing the chassis so that magnetic materials do not come close to the substrate facing surface.
The input / output terminal is gold-plated, and the secondary fuse of the transformer is soldered to the fuse holder to reduce contact resistance.
In addition, the Tape system employs a remote switch to simplify the wiring.

A natural wood cabinet is adopted, and aluminum foil is attached on the back side to obtain shielding effect.

Model Rating

Type	Duo Beta plusX Stereo Control Center
Output voltage	Pre Out : standard 1 v, up to 20 v Rec Out : Standard 140 mv, Max 20 v
Output impedance	Pre Out : 47 Ω Rec Out : 100 Ω
Harmonic distortion factor (20 Hz to 20 kHz)	Phono MM/MC : 0.005% or less (Rec Out : 140 mV) Tuner, AUX : 0.005% or less (Pre Out : 1 v) Monitor1, 2 : 0.005% or less (Rec Out : 1 v)
Intermodulation distortion factor (60 hz : 7 khz = 4 : 1)	Phono MM/MC : 0.002% or less (Rec Out : 140 mV) Tuner, AUX : 0.002% or less (Pre Out : 1 v) Monitor1, 2 : 0.002% or less (Pre Out : 1 v)
Frequency characteristic	Phono : 20 Hz to 20 kHz ± 0.2 dB Tuner, AUX : 0.5 hz to 140 khz -0.5 db Monitor1 and 2 : 0.5 Hz to 140 kHz -0.5 dB
Input Sensitivity (Pre Out : 1 v)	Phono MC:0.09mV Phono MM:2.0mV Tuner, AUX : 140 mv Monitor1 and 2 : 140 mv
Input impedance	Phono MC : high 100 Ω, low 50 Ω Phono MM : MM50k Ω, MC100 Ω Tuner, AUX : 55k Ω Monitor1, 2 : 55k Ω
SN ratio (IHF-A correction, input short)	Phono MC : -148dB/V (input equivalent noise) Phono MM:80dB Tuner, AUX : 100 dB Monitor1, 2 : 100 dB
Tone control	Turnover frequency shift type (for high and low frequencies)
Subsonic filter	7 Hz (Twin T Type)
Attachment	MC impedance switching (high, low) MM/MCdirect impedance switching Tone bypass switch Rec Out switch Tape monitor 2 systems (1, 2) Tape Dubbing (1 → 2, 2 → 1) Line phase sensor
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption	25W (Electrical Appliance and Material Control Law)
AC outlet	Switched : 2 systems, total450W Unswitched : 1 line, 500W
External dimensions	Width 478x Height 163x Depth 384 mm
Weight	9kg