The Kenwood L-07D offers a host of performance features. Each of these is designed as a means to achieve the designer's goals. The subsystems of the deck are carefully integrated into a solid unit which forms a rigid 35kg structure. In this deck, form and function are mutual.
The plinth is the "base" of the deck. It is the structural attachment point of all other components of the deck. One main function of the plinth is to rigidly position the platter and tonearm in relation to each other, among other important tasks. Another of the plinth's main functions is to prevent internal and external vibrations from affecting the interface of the point of contact between the cantilevered stylus and the record groove.
The L-07D plinth achieves a super-rigid positioning of the critical components by using a massive aerospace aluminum subframe. On one side of this massive structure is the attachment point for the direct drive motor. The motor bolts to the aluminum subframe of the plinth with six massive hex head bolts. On the other side of the aluminum subframe is the attachment point for the massive 3 kg VTA-adjustable Collet chuck tonearm base, which bolts down with four bolts inside a deep well. The massive metal structure of the motor-subframe-tonearm base results in extreme rigidity of the entire structure which supports and contains all moving parts of the deck. Four massive feet at the corners of the plinth are height-adjustable. Each footer weighs about 1.4 kg/3.0 pounds. A spirit level is built into the top surface of the platter. The adjustable footers and spirit level are used to level the deck.
The Motor and Electronic Engineering
The motor is the heart of the deck's performance and amazing -94db rumble figure. A constant current DC Servo motor was chosen for its ability to maintain a constant torque, and provide speed feedback information to the controller, which regulates platter speed via a Phase Lock Loop (PLL). A coreless, brushless, slotless motor was chosen to eliminate torque ripple. A brushless motor was chosen to eliminate brush wear and brush-related rumble. The main bearing is integral to the motor. A self-lubricating Teflon thrust bushing runs inside a true oil bath bearing well. The bearing shaft is 12 mm thick and made from hardened steel, as is the captured ball bearing. The massive and rigidly supported bearing sleeve is made of solid bronze. A layer of oil between all moving parts assures long life and smooth operation of the bearing. The motor housing contains aircraft-style rigid reinforcements within the motor casing. The motor contains not only the required rotor and stator for rotational movement, but also a magnetic levitation function that puts an upward force on the spinning platter to unload the bearing and reduce rumble.
The main criticism of less well designed PLL systems is that they don't react fast enough to correct speed variations, and the corrections overshoot the mark. The result is audible wow and flutter. The L-07D completely avoids this pitfall by yet another innovative design. The massive platter and high motor torque establish an extremely high moment of inertia to fight stylus drag and prevent transient load variations from affecting platter speed. The PLL system plays backup, only being activated when platter speed varies by +/- 3.7% at 33.33 rpm or +/- 5.0% at 45 rpm. Within that range, PLL is maintained and the controller makes no speed corrections. Motor speed is regulated by a quartz crystal (vibrating at 5.5296 MHz) to precisely 33.33 or 45 rpm with zero tolerance.
Two brakes are provided, one electronic the other mechanical. As soon as the Operation Button is pressed when the platter is turning, the electronic brake will slow the platter very quickly and smoothly. Once the platter slows to one fifth of operational speed, the solenoid operated mechanical brake is applied. The mechanical brake employs a felt brake shoe which engages the platter to bring it to a quick, smooth, complete stop. The entire operation of stopping the platter takes only two seconds. The mechanical brake is released when the Operation Button is pressed again to start play. There are only two buttons on the top of the deck, the Operation Button for start/stop and the Speed Button to select 33.33 or 45 rpm.
The Tonearm Base and Tonearm
The tonearm base is a massive 3 kg structure that contains a Vernier-type geared mechanism to adjust Vertical Tracking Angle (VTA.) A four jaw Collet chuck, similar to the type used on drills, rigidly secures the tonearm to the tonearm base. The chuck is opened to adjust VTA and locked once VTA is adjusted. VTA can be adjusted "on-the-fly", while listening to the record. A calibrated rod and arrow mechanism is used as a reference to record VTA setting. This is a useful feature when using multiple cartridge/headshell combinations. The EIA standard headshell collar allows use of any removable headshell with the L-07D tonearm. The tonearm itself uses resonance-canceling composite design. The tonearm tube is made from aluminum covered with layers of carbon and boron. Tonearm bearings are oversize hardened roller bearings with no play. The headshell is made from seven layers of carbon and boron. Litz wiring is used in the tonearm and headshell. The anti-skate mechanism uses a weight and string mechanism with no springs to wear out. The cueing is hydraulically damped. The tonearm cable is massive and has a screw on collar that secures the DIN connector to the tonearm. RCA male ends are heavily gold plated.
The Platter and Platter Sheet
The L-07D platter is a resonance-canceling composite, just like the rest of the deck. The main sub-platter is a three layer sandwich of Aluminum and Duralumin. The platter sheet is a sheet of precision machined stainless steel. The platter sheet is non-resonant and non-magnetic. The platter and sheet combination will neither vibrate nor ring. The 5mm thick platter sheet is made from non-magnetic stainless steel. This thick disc shields the pickup cartridge from the magnetism of the motor below. Total rotating mass of the platter and sheet is 5.5 kg/ 12.1 pounds. Add the weight of the rotor and the total rotating mass becomes in the range of about 6.8 kg/15 pounds. Add the optional DS-20 Outer Disk Stabilizer (1.4 kg/ 3.0 pounds) and the optional DS-21 Inner Disk Stabilizer (0.5 kg/1.1 pounds) and the total rotating mass goes up to 8.7 kg/ 19.0 pounds. Also, the optional TS-10 Ceramic Platter Sheet can be used on top of the standard stainless steel platter sheet with the stabilizers, adding an additional 1.2kg/2.7 pounds to bring the total rotating mass up to 9.9 kg/ 21.7 pounds.
External Control Unit
The electronic controls and power supply are contained within a separate Control Unit. The Control Unit contains the main transformer, a switch for external voltage adjustment (120V or 220V), a power supply PCB that supplies separate voltage feeds of +15.1, -15.1, +25.7, -26.7, and +8.0 VDC. A small PCB contains multiple diodes and a switch that is used to alter the dynamic compensation parameter when the DS-20 Outer Disk Stabilizer is used. The main PCB is the logic control PCB. The independently supplied + and - voltages available to the logic card are used in a circuit design that allows, via trim pots, independent adjustment of the positive and negative voltages of the sine wave that is sent to the motor. Another trim pot allows adjustment of the shape of sine wave that is sent to the motor. Using an oscilloscope, a wow/flutter meter, and the service manual, the electronics can be adjusted to optimize the sound of the deck to phenomenal specifications. Periodic adjustments are recommended, as electronics components values change over time. When the motor is re-lubricated, the electronics rebuilt with new capacitors, and adjustments are set with oscilloscope and meters, the deck is optimized and playback is stunning. A 20 wire umbilical connects the Control Unit to the deck. An aircraft quality JAE (Japan Aviation Electronics, Industry, Ltd.) connector mates the Control Unit cable to the deck.
Motor and Turntable:
Drive System - Quartz Pll Direct Drive
Motor - Coreless and slotless DC servo motor
Platter - 13 inch diameter (330mm) aluminum alloy diecast laminated with Duralumin with stainless turntable sheet
Speeds - 33-1/3 and 45 rpm
Wow and flutter - less than 0.02% (WRMS)
Rumble - better than -94dB DIN weighted
Load fluctuation - 0% (within 120g of tracking force0
Transient Load fluctuation - less than 0.00015% (at 33-1/3 rpm, 400Hz, 20g.cm load)
Transient Load fluctuation - less than 0.00008% (at 33-1/3 rpm, 1000Hz, 20g.cm load)
Type - Static balance type, J-shaped pipe arm, EIA connector
Effective length - 9-5/8 inch (245mm)
Overhang - 9/16 inch (15mm)
Tracking error - +2 deg 26 minutes at 150mm; -1 deg 11 minutes at 85mm; +1 deg 48 minutes at 50mm
Usable cartridge weight - 1 to 9 grams or 9 to 22 grams with supplied weight
Adjustable height range - Within 1/4 inch (7mm) by helicoid fixture (0.1mm steps)
Arm base - Collet chuck type, weight 3.3lbs (1.5Kg)
Headshell - Compression molded carbon and boron fiber, weight 12g
Turntable Dimensions - 21-7/8 x 6-5/8 x 18-1/2 inches (W x H x D)
Control Unit Dimensions - 5-1/8 x 4-11/32 x 14 inches (W x H x D)
Turntable Weight - 68.2lbs (31Kg)
Control Unit Weight - 9-1/2lbs (4.3Kg)
The L-07D instruction manual states:
Your choice of this product indicates that you are a devotee of excellence in sound reproduction. We appreciate your patronage and take pride in the long tradition of quality components that the name Kenwood represents.
So that you can get the most out of your L-07D, we suggest that you take the time to read through this manual before you hook up and operate your system. This will acquaint you with operating features, and system-connection considerations, so that your listening pleasure will be enhanced right from the start. You will notice that in all aspects of planning, engineering, styling, operating convenience and adaptability, we have sought to anticipate your needs and desires.
In the more than 100 years since Edison invented the phonograph, a lot of progress has been made. The L-07D was designed and developed with a view to making an ultimate record playing system, which converts the music information cut in the record with 100% accuracy into an electrical signal; in other words, it achieves "perfect conversion" from the engraved groove into the reproduced signal.
Various new techniques have been developed and applied in the L-07D to achieve this "perfect conversion". However, any one of these techniques cannot exhibit its full effect on its own: they work together to make a total system effective. Kenwood's engineers are proud of the L-07D; it is a high precision turntable which will give a new appreciation of the capabilities of records.
The L-07D was designed giving priority to the following:
High rigidity and good anti-vibration properties.
The three supporting points in the pickup loop are extremely accurate.
High transient load characteristics.
High fidelity electrical signal transmission.
Super-heavy, metal-inserted cabinet with complex structure providing high rigidity and good anti-vibration properties.
The cabinet has a complex structure which is basically a double-layer structure and metal is inserted into important parts, so that the center of gravity is lowered, the tonearm and the phono-motor are completely supported and anti-vibration properties are greatly improved.
The upper layer of the cabinet is made of the new ARCB material which can be precisely molded and has outstanding rigidity. Further, diecast aluminum is inserted into important parts of the upper layer. The lower layer of the cabinet is made from mahogany complite which has superior rigidity and anti-vibration properties. Thus, the cabinet has very high rigidity and is almost perfectly vibration-free.
Dynamic compensated motor
The most important point in improving the phono-motor is to remove cogging and torque ripple. Theoretically, it is possible to build a motor without torque ripple, but in practice such a motor is impossible because of machining accuracy and viscous resistance. The motor coil was formerly driven at constant voltage. In the L-07D, however, the motor coil is driven at constant current. Therefore, counter-electromotive force in the coil can be ignored and control can be more precise.
The L-07D uses double servo coupling, which automatically switches the control method when the speed differs by +/-3% from the rated speed. When the speed difference is beyond +/-3%, the speed is controlled to obtain a large torque and, when it is less than +/-3%, the phase is controlled to obtain a wide lock range and large phase gain.
Further, at a speed of +/-3%, the circuit coupling is changed from DC to AC to reduce influences from the motor drive circuit and the motor offset.
If the moment of inertia varies to a great extent (e.g. if KENWOOD's disc stabilizer DS-20/DS-21 are used), the dynamic parameter (time constant) can be changed.
Anti-vibration, complex structure turntable platter with high transient load characteristics and large moment of inertia
A moment of inertia of 1,025kg/cm2 is obtained (when the turntable sheet is attached), resulting in high kinetic energy of rotation. Therefore, the platter rotates stably even if the transient load from the stylus varies. The mechanical impedance supporting the record is kept high, so that signals cut in the record can be traced exactly by the stylus.
The turntable platter is made of diecast aluminum inside of which there is Duralumin 4mm thick. The top surface of the platter is finished accurately.
Further, a non-magnetic stainless steel turntable sheet is mounted on the platter so that good anti-vibration properties are obtained.
Non-resonant boron laminated pipe tonearm with high stiffness
Light and rigid materials must be used for the tonearm to raise the resonant frequency of the tonearm. In the L-07D, super-hard aluminum as used in air frames together with carbon and boron fibers are used for the tonearm. This 3-layer structured tonearm has high stiffness and, because of the combination of different materials, resonance is suppressed and influences degrading stylus performance are eliminated.
The head shell attached is a 7-layer carbon-boron laminated structure, therefore it is light as well as extremely stiff.
Highly accurate and rigid pickup loop
The pickup loop, which is the signal conversion system of the turntable and picks up the signal cut in the record, includes "3 fulcra" - the platter support point (center shaft), the tonearm support point (pivot) and the cantilever supporting point. These are most important in any turntable system. The accuracy of the positions of these "3 fulcra" is generally accepted as determining the performance of the turntable. The most important requirement of "ideal conversion" is that the locations of these "3 fulcra" relative to the groove of the record do not change.
In the L-07D, 12mm (15/32in.) diameter hard stainless steel is used for the precision finished center shaft so that performance is improved. To support the heavy turntable platter, a floating magnet is used, so that viscous resistance of the thrust pad, etc. is reduced and the cutoff frequency of the motor is lowered.
Carbon tool steel is used for the tonearm pivot and stainless steel is used for the rotating shaft together with over-sized bearings. Therefore, the tonearm turns smoothly around the supporting point and all other motions are eliminated. The cantilever supporting point must be 100% stationary. If not, unnecessary signals will be picked up or the music signal will be modulated, resulting in degraded sound.
The tonearm shaft is fixed by means of a Collet chuck to the tonearm base which is made of brass and stainless steel. The tonearm base is equipped with the helicoid height adjustment mechanism which enables highly accurate height adjustment at a rate of 0.1mm per turn for a total height of 7mm. The tonearm shaft is also made of BSBM material and has a diameter of 27.6mm (1-3/32in.)
Whatever the force from the Collet chuck the tonearm shaft is never deformed. The tonearm base and tonearm shaft weigh a total of 3kg. This mass-concentration design improves strength and resistance to external mechanical interference.
Carefully selected inner wires transmitting electrical signals faithfully
Pure copper Litz wire is used throughout the electrical transmission system. Our unique penta-structure and two core shielded cable gives optimum performance. In the output cord + and - signal lines are arranged symmetrically and they are completely shielded. Each conductor is a Litz wire consisting of 168 wires of 80 udia, thus DC resistance is reduced to the limit. For the inner cord in the tonearm, a penta Litz wire each conductor of which consists of 56 wires of 50 u dia.is used. For the head shell wires, silk-covered Litz wires of 12 milli-ohm are used.
New type connector of the output cord can be locked giving a contact area several times as great as that formerly used in KENWOOD turntables. All terminals are gold plated to assure low contact resistance for years of operation.
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