Kenwood L-A1 & L-D1

L-D1 CD player:

The L series CD player was developed with the aim of the new 90's standard machine.
It is designed with high sound quality, such as the pursuit of stable operation during CD playback, review of all internal signal paths, and emphasis on high margin in all parts of the structure and circuit.

In order to reduce fluttering caused by warpage and deflection of lightweight CD disks, we have adopted a top-loading system in which a turning table is fixed directly to a spindle motor.
In this system, the recording surface is set upward, and the disk is pressed on a smooth φ 130 mm aluminum turntable with a clamper weighing approximately 100g. The moment of inertia is approximately 20 times larger than that of the conventional system, thereby achieving excellent stable operation and improved rigidity.
As a result, the servo amount is minimized, power supply fluctuations due to changes in the servo amount are reduced, and high-purity RF signals are successfully generated.

The pick-up section is designed with a bridge-like structure that spans a disk on a φ 5 mm guide that is robust and very vibration-free.
The bridge structure pickup section made of heavy aluminum die cast drives a coreless motor without cogging with a belt, so it moves extremely smoothly on the guide and enables more accurate reading of pits.

The pickup actuator drive uses a discrete high-performance audio amplifier instead of the conventional operational amplifier IC to enable accurate reading of signals on the disk and clean operation without contaminating the power line and ground line.

The spindle motor that drives the turntable uses the same 3-phase, 8-pole, 12-slot outer rotor brushless spindle motor as high-end LD players.
This motor is a high-torque, low-cogging, powerful motor with a φ 6 mm shaft developed for LD. It has a high ability to rotate an LD disk with 20 times the mass of a CD disk at about 4 to 5 times the rotational speed of a CD. It has a diameter three times that of a conventional spindle motor, so servo response and shaft torsion are greatly improved compared to conventional spindle motors for CDs.

Kenwood L-A1:

This integrated amplifier was announced as the first of the new L series with the aim of becoming a new standard model in the 90's.

Super C with reduced in-phase noise is used in the first stage amplifier.⁴Circuit is mounted.
In general, a differential amplifier circuit is used for the first stage to cancel noise from the power supply circuit by differential operation.⁴The amplifier realizes differential amplification of only signal components by active operation of not mixing but not canceling, and achieves extremely high in-phase component rejection ratio (CMRR). Moreover, the amplifier transistor can always maintain a constant Pc (collector loss), and the element can be kept in an ideal operating state.
In addition, this circuit board is placed close to the volume in order to be completely isolated from the output stage of the power amplifier and the power supply circuit, which are noise sources, to suppress intermodulation of the signal and degradation of S/N.

Quadrive Multiple Final Stage is used for the output stage.
In the conventional model, even in the high-grade model in which the number of final transistors was arranged in parallel in multiple stages, the configuration of the driver stage immediately before was configured by a single connection, and the overall head room was limited.
In the Quad Multiple Final Stage, a dedicated driver is provided for each final transistor to distribute the load of each transistor, improve the linearity of the driver stage, and increase the overall margin, thereby improving the drive performance of low-impedance speakers.
In addition, we pay attention to the radiation of each stage by separating the circuit boards of the final stage, which handles high power, and the driver stage, which handles low power, into the front and back of the heat sink.
The pre-driver stage and driver stage are class A operation to suppress the generation of switching distortion and achieve thermal stability.

The volume uses a fully shielded ultra-low impedance resistor rotating volume. By rotating the slider and rotating the disk-shaped resistor, the number of contacts is reduced and high sound quality is achieved.
The impedance is 1k Ω, which corresponds to 1/100 of the normal impedance, and thermal noise is suppressed to 1/10. In addition, the volume and peripheral circuits are contained in the divided air-chamber frame to eliminate the influence of the output of the power amplifier, power supply circuit and sound pressure.

It is equipped with a VIG circuit (voltage interface gate) to cut out noise components and supply pure energy to the amplifier circuit.
This circuit has a low impedance when viewed from the amplifier side and a high impedance when viewed from the power supply side. This circuit has the property of passing only DC energy from the current and cutting noise components.
This eliminates power supply ripple, signal components, and intermodulation distortion components, enabling pure energy supply.

The power supply section uses a large toroidal transformer with a capacity of 450 VA and a high-quality aluminum electrolytic capacitor.

Instead of the usual gain switching method, discrete amplifiers matching the characteristics of the MC and MM cartridges are mounted on the first stage of the equalizer amplifier.
Dedicated elements with different characteristics are cascode-connected, such as FET elements for the high-output, high-impedance MM type and bipolar elements for the low-output, low-impedance MC type.

The body frame and bottom plate are made of 2 mm thick bottom mm thick bottom plate, which is strong enough to suppress the vibration of the power supply and heat sink. In addition, the selector / equalizer amplifier part, voltage amplification power supply part, power amplification power supply part, volume / Super C⁴The four air chambers of the (main amplifier / first stage amplifier) part are divided by the same 2 mm thick steel plate to prevent mutual interference of each part and to increase rigidity.

It is equipped with a control microcomputer for relay control and electric volume control.
In order to prevent these digital signals for clock control from entering analog circuits and causing deterioration of sound quality, a dedicated small transformer is installed. In addition, all control systems extracted from the microcomputer are isolated using photocouplers (optical coupling).

A high-hardness glass epoxy board is used for the printed circuit board.
In addition, the board is rigidly mounted to a 2 mm thick frame via steel studs to improve reliability.

The panels, volume knobs, input selector knobs and keys are made of either cutting materials or extruded materials with sufficient thickness to improve operability and achieve high rigidity and reliability.
The front panel, which is most exposed to sound pressure, is made of 5 mm thick aluminum extruding.
In addition, the pin jack adopts a high-reliability type with gold-plated brass.

The volume knob made of machined aluminum has an indicator for attenuation level, allowing for delicate volume adjustment.
In addition, there is a high visibility spot light which is easy to check the fine adjustment level.

The Input/Rec out selector is laid out to minimize the inductance component by suppressing the electromagnetic coupling from the output stage that handles high power. It is placed near the pin jack. Transmission loss is reduced by using a high-performance gold contact small inert gas sealed type relay, and crosstalk is completely suppressed by using pure copper bus bar for ground.
The signal selected by the selector is input to the line buffer amplifier at the shortest distance, converted to low impedance, and then input to the volume.

The normally used input selector is indicated by the red LED indicator at the top of the knob.
When it functions as a Rec Out, it turns amber. When the Rec Out is turned off, everything goes out.

Equipped with balanced input terminal.

Remote control unit is included.

Super C developed with the L-A1 integrated amplifier of the L series⁴(Super Constant Current Cascode Circuit) is used for the audio stage.
Audio stage amplification, which used to be composed of operational amplifier ICs, is composed of a full-scale amplifier of discrete design with an emphasis on performance.

Printed circuit boards are made of high-strength glass epoxy boards, which are used as commercial circuit board materials.
In addition, the board is mounted on a rigid 2 mm thick frame via steel studs to improve reliability.

The D/A converter section uses a PDM conversion bit stream 1-bit D/A converter. In addition, an independent switched capacitor on the left and right sides is also installed to reproduce the sound field more finely.
The digital filter is an 8 x oversampling type.

The analog output terminal realizes an ultra-low impedance output of 0.1 Ω, and suppresses external noise signals superimposed on audio cables more than ever before.

In order to prevent interference between the digital and analog systems, separate transformers are installed.
In addition, the microcomputer and display tube are supplied with power from a dedicated transformer, creating an ideal power supply for each system.

To clarify the moving and reference points, the drive mechanism for the large turntable is mounted on a 4-mm-thick aluminum die-cast chassis and is firmly supported by an 8-mm-thick aluminum extruding mechanism frame fixed in a rigid frame.
The front panel is made of 5 mm thick aluminum extruding material. The mechanism, digital control, digital / analog power supply, and power supply / analog demodulation sections are separated by 2 mm thick steel plates on the body frame and bottom plate to prevent interference between each part and improve the rigidity of the housing.
In addition, the top plate is made of 3.8 mm thick aluminum extruding material to divide the air chamber at the front part of the body and the air chamber at the rear part to reduce interference caused by radiation and vibration.

Panels and keys are made of cutting material or extruded material with sufficient thickness to improve rigidity and reliability.
In addition, the pin jack adopts a high-reliability type with gold-plated brass.

In order to prevent accidents such as damage caused by incomplete loading of the CD, a clamper detection mechanism is installed that does not start playback unless a clamper is set.

3-step door position (opening / closing angle) of 45 ° / 60 ° / 80 ° can be selected for cases where upper space is restricted such as installation on a rack.

It has an optical and coaxial digital output with an on/off switch.

Equipped with A/B automatic EDIT function considering tape copy.

Wireless remote control is included.