L0-9M
Technical Discription

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DC POWER AMPLIFIER
In many ways the direct current (DC) amplifier is the ideal amplifier for audio use. Kenwood audio engineers have taken up the challenge of producing this ideal amplifier. The result has been success in producing a power amplifier which makes this dream come true.

Characteristics of DC Amplifiers
They make reproduction of low frequencies down to subsonic and DC levels possible. The result is to give a greater sense of power in the audio reproduction which greatly increases enjoyment of music and reproduces the low-frequency high-energy sounds of a live performance as only a DC amplifier can.

There is zero phase difference between input and output. Because there are no capacitors in the signal path to cause phase rotation, phase distortion is absent.

Output waveform is a faithful duplication of the input waveform.
Although this would seem to be a natural prerequisite for a hi-fi amplifier, it is a fact that only a DC amplifier makes faithful duplication possible.

The performance of a DC amplifier depends upon the stability of each individual circuit within it. In the input stage, special dual FETs are used, intended for the most demanding electronic computer applications (in packs of perfectly balanced pairs). This is followed by a three-stage differential amplifier operating in Class A, in which the open loop gain is high, and in which a fully adequate degree of negative feedback is applied with a predriver load circuit in which the power transistor bias is stabilized by a constant current supply circuit. This circuit configuration gives excellent stability and extremely wide frequency response.

Features

SINGLE CHANNEL "DIRECT-DRIVE" APPROACH
The L-09M is a single channel amplifier designed to operate next to the speaker in "a new approach to sound perfection" of the Kenwood Direct-Drive System. Power switching can be done by remote control at the L-07C Control Amplifier which is an integral part of this system. This new departure marks another significant step forward in the great strides Kenwood has made in eliminating dynamic crosstalk distortion and improving DC amplifier techniques.

DC POWER AMPLIFIER WITH LOW DISTORTION
The circuitry features three stages of differential amplification. FET's used in the first stage enables L-09M to amplify down to zero frequency (DC) and completely eliminates the phase distortion normally encountered with AC amplifiers. Incorporation of pure complementary circuitry assures amplification of signal throughout audible range with negligible distortion.

SEPARATION OF LEFT AND RIGHT CHANNEL
In Kenwood's Direct-Drive System completely eliminates dynamircrosstalk distortion, a distortion encountered when left and right channels are powered by same power source. Incorporation of heavy duty transformer and large electrolytic capacitor in power supply are few reasons why L-09M amplifier provides "fullness" of sound at low bass frequencies.

POWER METER AND CLIPPING LEVEL INDICATOR
The L-09M is equipped with a Power Meter which permits direct reading of power output in watts (RMS), and a Clipping Level Indicator Lamp which lights up in red to warn if overloading should ever cause output waveform clipping and sound quality deterioration. A Meter Range Selector Switch is provided which permits reading of three ranges for 8-ohm speaker, impedance, namely: 0.03 to 4 watts, 0.3 to 40 watts, and 3 to 400 watts, and also three ranges for 4-ohm speakers.

SIX-STEP ATTENUATOR
The L-09M is provided with a 6-step Input Level Attenuator that enables precision 0 dB, —3 dB, —6 dB, —9 dB, —12 dB and — ∞ attenuation. It is ideal for accurate adjustments of power amplifier sensitivity, improvement of aural S/N ratio characteristics, and level control in multi-channel systems.

NEW TYPE RADIATOR
The 2-speed ventilation fan works automatically, and a rise in temperature will turn it faster.

DIRECT DRIVE SYSTEM
The KENWOOD "direct-drive" amplifier system is based on having the L-07C, control amplifier, close at hand and the L-09M next to the speaker where it can drive it directly for best performance. The 15-meter Remote Cord that is supplied eliminates the need of extra power cord between L-09M and L-07C. Connect power cord to the closest wall outlet that is available. This Remote Cord is used to carry a small DC control current between the two components so that AC power on-off switching of the L-09M can be done at the L-07C side.

In the KENWOOD "direct-drive" amplifier system, the control and power amplifier units which are separated are connected through special audio cables. Therefore, these cables are naturally somewhat longer than those used in conventional systems. They are equipped with screw-lock type pin plugs (patent pending) to absolutely prevent them from working loose and possible causing damage to expensive speaker systems.

A 1-meter Speaker Cable and a 15-meter Remote Power Cord are supplied with this amplifier.Two 12-meter long Audio Cables with gold plated connectors are supplied with the L-07C for connection to the L-09Ms.

KENWOOD MULTI-AMPLIFIER SYSTEM

Owners of the Kenwood Direct-Drive System comprising the L-07C Control Amplifier and two L-09M Power Amplifiers can easily build it into a very high grade tri-amplification, 3-way system by adding an Electronic Crossover Network and an L-07M Power Amplifier, and making the necessary connections as follows:

Connect each component as shown in the block diagram.

Notice that the L-09M is used for the low frequency audio passband because of the relative low efficiency of woofers, while the L-07M is used for the high frequency passband to meet the lesser power requirements of the higher efficiency tweeters.

AC Power switching of the three power amplifiers can be done at the L-07C Control Amplifier, if the Remote Cords that are supplied with them are connected to the L-07C.

The output levels of the MID and LOW pass-bands can be accurately set at first with the respective L-09M ATTENUATOR knobs.

Thereafter, the volume level of all three audio passbands can be adjusted simultaneously with the Master Volume control of the L-07C.

REMOTE OPERATION
For tri-amplification or other multi-channel operations, the remote power connection lineup can be as follows:

and AC power ON-OFF switching can be done simultaneously by remote control from the Control Amplifier for as many Power Amplifiers as are involved.