Sansui AU 7700 Brochure

Page 2

The Ultimate Amp-dual power supply for all stages
and a differential amp for each.

PREAMPLIFIER SECTION

Phono Equalizer With 300mV RMS
Overload Capacity

The 4-transistor phono equalizer
features a differential amplifier in its initial
stage to ensure clear. transparent sound.
Sound clarity is also enhanced by the use
of a direct-coupled amplifier system. A
high overload capacity of 300mV RMS
(1kHz) is attained by careful selection of
precision parts. The deviation from the
standard RlAA equalization curve is kept
within 0.5dB over the range from 30Hz
to 15kHz.

7-Positlon Tape Play/Dubbing Switch

You can connect two tape decks to the
AU-7700. Then, with a flick of a linger.
you can play either deck and also dub
one onto the other while monitoring either
lie. the deck in record mode or the
deck in playback mode)

Versatile Tone Control System

The AU-7700 gives you the Sansui-
exclusive inductonless Midrange tone
control, in addition to the usual Bass and
Treble tone controls. which adds impor-
tant presence to all midrange frequencies
to which our ears are most sensitive.

The Midrange control adjusts in idB
nominal steps to a total of +5dB and
-5dB The circuit is constructed around
SIX transrslors. with a differential amplifier
Circuit employed in its initial stage The
AU-7700 actually tailors" the color of

reproduced sound. and in a highly
professional way, for its low-noise type
transistors and the detent-type printed
variable resistors are as precise and
critical as those employed in any superior

professional studio mixer/equalizer console.
. Each tone control is provided with click-stop

positions for accuracy and convenience.

Turnover Frequency Selectors for Bass
and Treble

The tone selector switches select the
frequency over or below that which the
tone control affects 150Hz. 300Hz or
600Hz for Bass. and 2kHz. 4kHz or
8kHz for treble. (The midrange turnover
frequency is fixed at kaz.) The system
thus permits subtle adjustments (as many
as 10.571 different tonal combinations)
and completely flat response that conven-
tional Bass/Treble tone controls simply
can't offer.

2-Step Low/High Filters

Used in the low and high filter circuits
of the AU-77OO are expensive NF active-
type filters with amplifiers of their own.
The cut-off characteristic of each filter is
selectable. 12dB/oct. at 60Hz or 12dB/oct.
at 20Hz for Bass; 6dB/oct. at 7kHz or
12dB/oct. at 12kHz for Treble. The 20Hz
filter is to eliminate such low-frequency
noise such as caused by warped records;
the 60Hz filter cuts motor rumble. etc. if
tape hiss is present. use the 7kHz filter.
and for noises such as record scratches
or electric-appliance hum. use the 12kHz
filter which has a sharper cutoff slope.
Choosing the most suitable filters lets you
enjoy noise-free music all the time.

Tone & Filter Defeat Switch

To obtain a completely flat and uncolor»
ed response. set this switch to DEFEAT.
The tone control and filter circuits are
completely bypassed and the phono
equalizer is directly connected to the
power amplifier It will turn the AU-77OO
into a "straight wire with gain " When set
to FILTER ONLY. the high and low filters
will be activated. but not the tone controls.

2-Step Loudness Switch

Use this to compensate for both lows
and highs. or. if you prefer according to
your room acoustics. only the lows.

2-Step Audio Muting Level

This switch selects either -15dB or
-30dB muting. Use it to fine-adjust the
volume during the low-level listening. or
to temporarily reduce the sound volume.

POWER AMPLIFIER AND

PROTECTION CIRCUITS

Dual Power Supply

We begin by introducing one of the
less obvious but highly meaningful des
sophistications of the AU-7700- its
independent plus/minus dual power
supply. In some integrated amplifiers. the
equalizer amplifier is adversely affected by
the high-current power amplifier to the
extent that tonal quality suffers or, worse.
oscillation results. A solidly-constructed
power supply assures clear definition and
clean sonority of reproduced signals.
which is what you can expect from the
AU-7700. The supply consists of a jumbo
power transformer and two large
10.000pF capacitors. Indeed. even the
preamplifier is regulated by a stabilized
plus/ minus dual power supply via a
separate winding on the transformer.
zener diodes and transistors.

Differential Amps for Each Stage

Another often-overlooked aspect of r
electronics is the assurance that negative
feedback. when applied to reduce noise
and distortion, does not become unstable
The AU-77OO utilizes a direct-coupled
differential amplifier in the initial stage of
the phono. tone control and power
amplifier circuits so that negative feedbaCK
remains stable over the entire audio
range. Noise is lessened. distortion almost
eliminated entirely. and superior transient
characteristics are assured. The plus/
minus dual power supply provides a high
voltage to each circuit. enabling a wide
dynamic range to be achieved together
with reduced distortion, And then. since
the input and output ends have no elec-
trical DC potential anywhere in the amplifi-
cation stage. transient response is excel
lent and you hear virtually no click noises
or scratching. even when controls are
operated at maxrmum.

Direct-Coupled Parallel Push-Pull Circuit
The AU-7700's power amp is a master-
piece of advanced solid-state electronics