Kenwood KA-7002 (1971)

A far higher grade stereo amplifier than any previous Kenwood model, the KA-7002 is a tribute to Kenwood's philosophy  that only the purest sound satisfies listener's ears.  By use of the direct coupling circuitry with pure complementary-symmetry driver stage, which means all interstage coupling capacitors are eliminated, its sound quality is purified to ensure ideal frequency response, very lowest Im distortion and improved damping factor characteristics. The KA-7002's superiority has been finally verified and guaranteed through the series of listening tests as well as through the technical measuring and simulations. That means every figure, every feature of KA-7002 is hundred percent alive. 

 Special FEATURES

All stages direct coupling circuitry and pure complementary symmetry driver stage ensure superb frequency response, ultra-wide power bandwidth, large damping factor, lowest IM distortion, etc.

Improved NF type equalizeer stage for wide dynamic range.

2dB step type accurate tone controls with 2 step turnover switches and complete defeat switches.

Low filter either at 40 Hz or 80 Hz with  sharp 18dB/oct cutoff.

Impedance selector for phono input (30 or 50 Kohms)

Low level phono input (0,06mV).

Exclusive Null Balancer brings perfect stereo balance.

3 pairs speaker outputs and front panel selector switch.

Tape monitor and dubbing switch for 2 tape decks.

4 channel input, output terminals and volume control.

Pre-amplifier output jacks and main amplifier input jacks.

 Excellent Frequency Response

Since KA-7002 employs full stage direct coupled circuit in the main amplifier unit, without coupling capacitors, DC amplification becomes almost possible. Frequency response is, therefore, largely improved and other various characteristics are enhanced with sufficient feedback. The output impedance is always flat, from ultra-low frequency to high-frequency, and has no boost in low frequency range due to output capacitor.

Stable Output & Low Distortion Factor

In an asymmetrical power supply using output capacitors, the maximum output decreases in the ultra-low path range due to limited capacitance. The power supply in KA-7002 is symmetrical on both upper and lower sides. The output in the ultra-low path range will not decrease and the output is always stable. Since transistor functions are the same in the upper and lower half cycle of the input signal, cross-over distortion and switching pulse components can be eliminated, which has been inevitable in conventional semi-complementary circuits. Consequently, distortion at the low output level becomes very small.

High Damping Factor

In order to enhance DC stability, the differential amplifier circuit is composed of high temperature characteristic transistors in the first and pre-drive stage and by use of zener diode the supply voltage in the first stage circuit is stabilized with 100% DC feedback applied. This eliminates deterioration of mechanicalstatic due to a direct current flowing in the voice coil  of the speaker. Also, this differential amplification is done in the direct coupled circuit, good phase characteristics are attained. And damping factor with reference to the speaker is improved up to 45 (at 8 ohms) without descending down at lower frequency range.

Three Stage Direct Coupled NF-Type Equalizer

The equalizer circuitry is made up of 3-stage direct coupled, NF-type having a wide dynamic range. This was developed from the circuitry in the KA-6000 whose excellent characteristics and power voltage, a wide dynamic range is obtained.

Precise Tone Controls

Tone control is variable in 2dB steps. Turn over roll off is switchable into 2 stages, 150 or 300 Hz in Bass and 2 kHz or 6 kHz in Treble. In order to eliminate slight osoillation at flat position, the cancellation can be operated by both level control knob and the independent defeat switches.

Protection Circuit

Asthe main unit consists of direct coupled circuits, the protection circuit differs from conventional layouts in which the first stage power supply is disconnected. This type system suppresses current to the output transistors by PC detection system using a current limiter through which no input signal is applied in the driver stage when large current flows to the output transistor. When this protection circuit operates, no DC voltage is produced at the output terminal.

Sharp Cut Filter

In order to eliminate noise due to resonance of arm, motor noise wow and flutter, scratch, etc., without deterioration of tone quality an 18 dB/oct filter is built-in. Also, in order to prevent schock noise created during switch operation, strictly selected tantal solid capacitor with a leak current below 1 mA is used.

Mode Switch For 4-channel Reproduction

Besides the conventional 2-channel use, the mode switch circuit has input/output terminals and control volume for 4-channel stereo and functions as a 4-channel control amplifier.

Perfect Balance Control System

In order to obtain left and right output balance, a sound source has been conventionally set to the center of the right and left speakers by setting Mode to Mix. In the KA-7002 a null balance system has been adopted so that sound is disappeared when right and left levels become even, as a result, total balance from the cartridge to the amplifier can be fully obtained by manipulation of the Null Balance while playing monaural disc.

 Unlimited Capability and Usability of KA-7002

The concentrated terminals on the rear panel show the KA-7002 is capable for all the program sources and has wide usability which meets any of the critical audiophile' requirements.

The KA-7002 is able to play the leading role of the highest music system.

Phono 1 - Connect moving magnet type cartridge. Load impedance is switchable (30 or 50 kohms)

Phono 2 - Input sensitivity of 0,06 mV. Low output moving coil type cartridge can be dirctly connected.

Mic - By 2 microphones, stereophonic reproduction is enjoyable. In case one mike is used, the sound is made monaurally from both speakers.

4-Channel - Input and output terminals for 4-channel reproduction. With Mode Switch equipped on the front panel, KA-7002 can control 4-channel music system.

Normal/Separate Switch - At normal side, pre-amplifier and main-amplifier are combined. At separate side, they are individually separated.

Tape Recorder - 2 pairs of tape-play and tape-rec jacks and 2 DIN connectors. Dubbing and monitoring of A→B, B→A decks are available.

Speakers - 3 pairs of speaker system are connectable. Selector switch on the front panel offers 5 varietes of thier combinations.

AC Outlets - 3 switched outlets for total 300 watts and 1 unswitched for 100 watts.

Specifications

Total Dynamic Power (both channel, IHF):

196 watts at 4 ohms

170 watts at 8 ohms

Continuous Power Output (each channel driven):

80/80 watts at 4 ohms

70/70 watts at 8 ohms

Continuous Power Output (both channel driven):

68/68 watts at 4 ohms

50/50 watts at 8 ohms

Harmonic Distortion:  less than 0,5% at rated output from 20 Hz to 20,000 Hz

Intermodulation Distortion (60 Hz & 7,000 Hz ; 4 : 1):

At rated output : Less than 0,3%

At -3 dB rated output : less than 0,1%

Frequency Response:  20 Hz to 50,000 Hz ±1 dB

Sensitivity (for tared output at 8 ohms load):

Phono 1 : 2,5 mV

Phono 2 : 0,06 mV  or  2,5 mV

Mic : 2,5 mV

Tuner, Aux 1, 2 :  200 mV

Tape A, B : 200 mV

Main amp input : 1 V

Input Impedance (at 1 kHz):

Phono 1 : 30 or 50 kohms

Phono 2 : 200 ohms (0,06 mV);  50 kohms (2,5 mV)

Mic : 50 kohms

Aux 1, 2 : 100 kohms

Tape A, B : 100 kohms

Main amp input : 50kohms

Signal-to-Noise Ratio (below rated output):

Phono 1 : 65 dB

Phono 2 : 45 dB (0,06 mV);  65 dB (2,5 mV)

Mic : 67 dB

Aux,  Tuner, Tape  : 77 dB

Noise at minimum volume control 0,5 mV at 8 ohms or 0,0003 milliwatts

Damping Factor:  90 at 16 ohms load;  45 at 8 ohms load

Low Filter (for rumble):  80 Hz and 40 Hz cutt-off, 12 dB per octave

High Filter (for scratch):  7,000 Hz cut-off, 12 dB per octave

Bass Control:  ±10 dB at 100 Hz with 2 dB step switch (tone control switch at 300 Hz)

Treble Control:  ±10 dB at 10,000 Hz with 2 dB step switch (tone control switch at 2 kHz)

Turnover roll off freq: 

Bass : 150 Hz, 300 Hz, defeat

Treble : 2 kHz, 6 kHz, defeat

Input:

Pair of Phono 1, Phono 2; Mic, Aux 1-2; Tape Play A, B; 4 channel and main amp.inputs

Output:  3 pairs of stereo speaker outputs (4 to 16 ohms); pre-amplifier  outputs;  headphone jack; low level mono output; Tape recording outputs A and B, DIN standard tape Rec/Play connector A and B; switched and unswitched AC outlets and 4 channel output

Power Requirement:  AC  110 - 120 V, 220 - 240 V, 50/60 Hz

Power Consumption:  15 watts at no signals , 275 watts at full power

AC Outlets:  3 switched, 1 unswitched

Dimensions (W x H x D):  408 x 134 x 280 mm (16-15/16'' x 5-5/32'' x 11-1/32'')

Weight:  10 kg  (22,1 lbs)