Kenwood L 07 M Brochure

Page 2

7 Electronic Technology and Audio
__ Techniques

Recent amplifier design techniques have made remarkable progress
in line with the development of superior audio parts and elements.

Distortion and Signal to Noise (S/N) ratio ratings, considered
to be the basic criteria of amplifier performance, have shown impressive
measurement gains of one and even two digits in the past two or three
years. Dedicated sound engineers, however, have been looking beyond
such technical measurement data in their challenging work to uncover
audio techniques that may further improve what is actually heard
(aural sound).

This has focused attention on the dynamic characteristics of am-
plifiers, and is resulting in certain new concepts of theory, as well as new
audio products.

Here at Kenwood, we have attached great importance to aural
sound and we have maintained for years a group of sound engineers
who specialize in wide ranging R & D work, completely separate from
our design and engineering staff.

This separate task force first discovered the relation between the
dynamic characteristics of an amplifiers power supply and its reproduc-
ed sound, and advanced the epoch-making Dynamic Crosstalk theory
in the fall of 1975. Our introduction of the popular KA-7300 In-
tegrated Amplifier followed, with its independent left and right channel
power supplies for its power amplifier section which solved the problem
of Dynamic Crosstalk distortion. Its clear, powerful, distortion-free
sound, thanks to the dual power supply system, confirmed their theory
and caused much favorable comment in the audio world.

Another breakthrough was the Model 600 Integrated Amplifier
introduced in the spring of 1976 with its greatly improved characteristics
for phase distortion and transient response, and which featured DC
power amplifiers that significantly upgraded sound quality.

In this way we have been developing and adapting new techniques
in amplifier design. This is done only after very careful consideration,
and not merely because they are new. The decisive factor is always
whether the new technique will improve the basic function of an
amplifier as a part of an audio system.

Page 35

1. INPUT SELECTOR SWITCH, TAPE SWITCH and TWO EQUALIZERS

The Input Selector Switch which selects signal sources is a must"
function that is provided. However, the source selection is limited to
TUNER, AUX and PHONO, the amplified phono signal at the
equalizer circuits outputs, as too many switch positions make wiring
complex and are liable to invite space coupling, and consequent dis-
tortion.

A switching position is not provided for low level phono signals at
the equalizers' inputs because switching at such low levels would
adversely affect sound quality. Instead, two independent equalizer
circuits are provided for PHONO 1 and PHONO 2. Direct connection
of MC (moving coil) cartridges can be made to PHONO 2.

Phono cartridge load impedance selection, likewise, has been
eliminated to avoid circuit characteristic variations that may affect
performance deterioration.

@ Fig. 9 - Tape Switch Functions and Positions.

S\\"l'l("lI POSI lION SIGNAL

(l) DUBBING (B ->A) SOURCE 38° 2 ° SPEAKER
A

(3) B - PLAY SOURCE 885 o o SPEAKER
A

(3) REC SOURCE 3 0 So SPEAKER
B A

(4) RE(' OFF SOURCE 0A0 080 fiPEAKER

(5) RFC SOURCE 3 0 g 0 SPEAKER
A I}

((1) A- PLAY SOURCE 2) (E 0 0 SPF/\KFR
A l}

(7) DUBBING (A -~ ll) SOURCE 2R3 8R5 SPEAKER

I .

A separate rotary Tape Switch which accommodates two tape
decks to permit dubbing is employed. At its normal midpoint position.
the REC (recording) terminals are cut off from the signal circuit, so
that the tape recording circuit, even if non linear, will not affect the
signal that is being reproduced.

34