Kenwood L 07 C Brochure

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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.

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speaker cone causing a very slight feedback phenomena in the am-
plifier.

To avoid this, care should be taken to position the Power and
Control Amplifiers away from the direct path of speaker excursion
pressures and vibrations. This is especially important in the case of
the L-O7M which must be located within a meter from the speaker. A
cushion should be placed under it if it is to be placed on top of the
speaker. It may also be set up on a solid table next to the speaker.

Check to see if the arrangement is satisfactory as follows. Operate
the speaker at a high volume level, and place your hand on top of the
amplifier. It will be satisfactory if you do not feel any vibration
through your hands. Make the same check for the Control Amplifier.

Be sure that you do not block the air vent holes, especially those
beneath the chimney heat sink, when you put a cushion under the
power amplifier.

The same precautionary measures against vibration are, of course,
necessary for the turntable which is liable to be affected even more
than amplifiers.

Avoid Direct Draft 0f Air Conditioners

All amplifiers originate heat, although the degree of heat created
may differ. Thus the internal temperature of the amplifier which rises
soon after power is switched on. will vary when used for long periods.
Generally the temperature stabilizes after about one hour, and changes
very little after that. Therefore. an amplifier is usually designed to
perform best after it reaches this normal operating temperature.

it would be ideal, of course, if an amplifier could deliver best
performance as soon as it is switched on, and continue so unchanged,
until it is switched off. It is a fact, however, that in the present state
of the art, some variation in performance cannot be helped during the
initial warm up period.

One way to get the most out of your amplifier is to get it warmed
up as fast as possible. For instance, operate it at a high volume level
initially: prevent room temperature from dropping rapidly; or keep it
away from the direct draft of an air conditioner in the summer.

The direct draft of a cooler may even prevent an amplifier from
ever reaching its best performance temperature. At least it will cause
wide variations of the amplifiers internal temperature and, thus, affect
its performance capability.

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3 Always Use REC-OFF Position
__ Except When Recording

A REC-OFF position is available as a normal position on the
TAPE switch of the Control Amplifier. Always keep the TAPE switch
at this position, except when making a recording with the Tape Deck.

This will mean that the tape recorder will be cut off when it is not
used and its input resistance and capacitance, as well as the capacity of
the recording cable will not constitute a load to the equalizer, which
would affect sound reproduction. Thus, this REC-OFF Tape Switch
position ensures that reproduction always occurs under ideal conditions.

Use Separate Tonearm For Moving Coil Cartridges

This unit has a standard equalizer for MM cartridges, and an
independent high gain equalizer for MC cartridges. This means a
significant improvement in sound quality over the conventional built-in
head amplifier system which involves switching at very low phono in-
put levels. It is recommended that your system installation include
separate MM and MC tonearms to take full advantage of the two
separate equalizer circuits.

If only one tonearm is used there will be some inconvenience when
changing from one type cartridge to another as it would necessitate
reconnections to PHONO 1 or PHONO 2 inputs. However, if two
turntables are used, it will be very convenient since they can be
respectively connected directly to their respective equalizers.

It is also better from the sound quality viewpoint to equip these
cartridges with different tonearms. MM type cartridges are generally
high compliance and match lightweight and good tracking tonearms.
MC cartridges generally are low compliance and so a heavier, sturdily
built tonearm is better.

How To Use The GND Terminals

The power amplifier has one GND terminal, while the Control
Amplifier has two. The latter two are not common, one connecting
directly to the common ground of the circuit, and the other to the

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