Audio Database

The

LUXMAN L-58A
149,000yen(September, 1979 release)

Description
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The Integrated Amplifier which aimed at improvement of physical condition of the amplifier for the tone-quality modification instead of a mere property modification by the original Duo beta circuit.

A Duo beta circuit means it as the circuitry which combined two NFB.
In this circuitry, many properties are improved by completing the good amplifier of genius (nakedness property) rather than not applying a lot of NFB and improving many properties of amplifier, and combining a little NFB and DC servoes with this.

In the power amplifier part, the pure complimentary differential push-pull circuit by FET 2SK163 for N channels and for P channels (2SJ44) is adopted as an input stage, and the naked distorted property is improved as a DC amplifier stream composition.
Moreover, from an input stage to an output stage, all were constituted from a push-pull circuit, and simultaneously, ft (high region cut-off frequency) was high, adopted the small transistor and FET of Cob (collector output capacitance), and has reduced distortion.
And while adopting as an output stage MOS FET (2SK134 and 2SJ49) whose ft is about 500MHz and sending 300mA or more of bias currents, the "notchless class A" to which the amplifier which does not carry out a switching operation was made is made combining the high-speed driver circuitry.
Moreover, by circuitry devices, such as adoption of an element, adoption of local NFB, etc. which were excellent in the high region property, open loop gain (naked gain) was lowered and the single figure naked frequency characteristic is improved.
In these results, the distortion of the nakedness of a power amplifier part improves to 0.4% (it is 2 to 5% conventionally), and the slew rate has improved at 300v/sec sec (it is 10v/microsec conventionally).

In the equalizer part, the cascode input type bootstrap circuit by FET4 stone adoption s Is in the input stage, a dynamic-resistance circuitry with a transistor is combined, and distortion of nakedness is suppressed.
Moreover, in order to stop an Output load impedance low as much as possible, the SEPP circuit (single ended push-pull circuit) by transistor 4 stone is adopted, and distortion of nakedness is reduced.
In these results, the distortion of the nakedness of a preamplifier part (equalizer stage) improves to 0.2% (2 to 5% of the former), and the slew rate has improved at 150v/sec sec (it is 10v/microsec conventionally).

In the Duo beta circuit, 1/100 or less conventional NFB is applied to this amplifier circuitry. This reduced TIM distortion and the tone quality of a mid-high range is improved.

In order that the firm low-pass play, the fall of the dumping factor generated by having reduced the amount of NFB, the cone excursion of a speaker, etc. may prevent cross modulation distortion and an SN ratio from getting worse, original DC servo circuitry is adopted in the Duo beta circuit.
A little these DC servo circuitries are parallel combined with the NFB circuitry, since they have adopted low-noise FET amplifier, can use a good film capacitor for a filter circuit, and are enabling the firm low-pass play.

Since priority is given to a tone quality, many FETs of the input were not connected but it has been dared to adopt DC amplifier stream composition by the parallel connection of FET with the head amplifier for MC.
While connecting parallel FET for N channels which was excellent in the Noise Figure, it has DC amplifier composition which has improved the high region property especially combining a constant current circuit. Although this is disadvantageous somewhat by the SN ratio substantially, if the impedance of MC cartridge which connects changes, the gain automatic-regulation scheme which adjusts amplification degree automatically would be adopted, and this problem will be solved.

It has composition which banishes the flat amplifier leading to a tone-quality failure, and covers the amplification degree running short in a power amplifier circuitry. For this reason, in order for a tone control circuit to prevent receiving influence in other circuitries, buffer amplifier is formed in the preceding paragraph of the tone control.
The source follower circuitry of the cascode interconnection by an FET input is used for a buffer circuit and a tone control circuit. Moreover, the circuitry which can change a curving point with NF type of a LUX scheme is adopted as a tone control circuit.
Moreover, since it is at the time which does not need a tone control, it enables it to bypass these circuitries.

In the power circuit of a power part, while adopting a measure against tone quality type mass block capacitor, the film capacitor was combined parallel and the high region property is improved.
Moreover, the transistor for power with a quick switching speed was used for the constant-voltage regulated power supply for preamplifier parts, and it has fully lowered the circuit impedance.
Furthermore, a constant-voltage regulated power supply is adopted as the pre-driver stages of a power amplifier part, and the stabilization of operation is attained.

In order to suppress to the minimum that the metals chassis inside amplifier interferes in a product-line circuitry, it is made the structure which hollowed the chassis corresponding to the printed circuit board.
Moreover, eddy current distortion is eliminated thoroughly, such as adopting the wooden box of real wood as a cabinet, also extracting the shielding to necessary minimum, and using ultra-thin aluminum foil.


Rating of a mode
Form Stereo integrated amplifier
Succession effective output 80W+80W (8 ohms, both ch operation, 1kHz)
THD 0.009% or less (8 ohms, Output-power-3dB, 20Hz - 20kHz)
Cross modulation distortion 0.009% or less (8 ohms, Output-power-3dB, 60Hz:7kHz=4:1)
Frequency characteristic Phono man month: 20Hz-20kHz}0.3dB
Tuner, AUX, Monitor1, 2:10Hz - -100kHz three dB
Input sensitivity/impedance Phono man month: 1.6mV/50kohm
Phono MC-1:1.6mV/100 ohms
Phono MC-2:0.25mV/100 ohms
Tuner, AUX, Monitor1, 2:200mV/40kohm
SN ratio (IHF-A) Phono man month: 80dB or more
Tuner, AUX, Monitor1, 2:110dB or more
Tone control The point curving [ low-pass ]: 200Hz, 400Hz (defeat is possible)
The point curving [ high region ]: 2kHz, 4kHz (defeat is possible)
Filter Subsonic speed: 15Hz, off, 30Hz
A high cut: 9kHz, off, 15kHz
A low boost 70Hz, off, 150Hz
Attachment Phone straight switchpoint
Mono-switchpoint
Signal-off switchpoint
Warmup indicator
Speaker selector
Headset jack
Supply voltage AC100V, 50Hz/60Hz
AC outlet Power-switch interlock: 100W
Power-switch un-interlocking.: 100W
Power consumption 180W (Electrical Appliance and Material Control Law)
Dimensions Width 464x height 156x depth of 332mm
Weight 11.0kg