Leak Stereo 70 Brochure

Page 1

Stereo Reproduction

Over the past ten years stereo sound reproduction
has become as much a part of our lives as the
motor car and jet travel. In View of the astonishing
sense of realism and the lack of listening fatigue it is
not surprising that stereo should have attained

such great popularity.

What may surprise many people is how long stereo
has been known to communication engineers

H. J. Leak carried out his first stereo microphone
transmission (with D. W, Turpin) in 1931 and
subsequent experiments proved the feasibility of
stereo sound as we know it today.

What is relatively new about stereo is its availability
to the general public by high-quality records and
the increasing use of stereo radio.

Old or new. H. J. Leak 8 Company has always been
acknowledged as the leader in the field, And our
products prove it.

Stereo 70 _
This brand new unit from the world's best known

amplifier manufacturer is simply bristling with
exciting new features.
To start with there's the power output - a genuine
35 watts per channel. Furthermore. there's the
distortion (or the lack of it) - a mere 01% at
1000 Hz for all power outputs up to 25 watts per
channel.
And, what's more, in addition to the features the
discerning audiophile expects on a LEAK
amplifier we have made provision for the
following :-
The use of two turntables and pickups. selection
between the two being made by the input
switch on the front panel.
The use of a pair of loudspeakers in a location
other than the main listening room.
The use of stereo headphones for personal
listening as an alternative to loudspeakers.
The use of a portable tape recorder which can
be pllugged into the DIN socket on the front
pane.
All this, backed by the famous LEAK craftsmanship
and reliability. makes the Stereo 70 the most
technically advanced amplifier available.
And it sounds it.

Ease of Installation _ . . .
The compactness of the Stereo 70 and its availability

in either chassis form or in a teak case solve any
problems about location. The chassis model can be
fitted into a panel of any thickness and the special
design makes this easier than with any other
amplifier. The case model can be used

freestanding on a shelf. on a table. or in a bookcase.
We have taken a great deal of care over the electrical
connections to the Stereo 70. All LEAK Tuners. and
Loudspeakers. and most auxiliary equipment
(pickups. etc.) are now supplied with standard
cables and plu s which are simply plugged into the
Stereo 70. Int is way it is possible to set up a
complete stereo system and have music within

ten minutes.

Function . V .

The function of an ordinary mono amplifier is to
accept the tiny electrical si nals from the input
device (pickup. tape ampli ier. tuner or
microphone) andto build them up to a magnitude
capable of operating a loudspeaker system. and to
ac ieve this with negligible distortions.

The LEAK Stereo 70 amplifier is simply two identical
mono amplifiers electronically separate. but
physically combined. This amplifier reproduces
stereophonically and monophonically from records.
tape, radio and microphone. using any pickup, any
tape amplifier. any tuner and any microphone
available in the world. This com rehensiveness
gives the important advantage 0 compatibility With
the finest pickups and microphones available in the
world: this is not the case with cheaper low-gain
amplifiers.

The Stereo 70 functions electronically to the highest
standards obtainable by present techniques - to
the performance standards demanded by
communications engineers for broadcasting and
recording. There is nothing we can add to the
circuitry or the price to improve the fidelity of
reproduction obtainable from the Stereo 70.

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Ease of Operation

You don't have to be a skilled electronic engineer to
get the best lrom your Stereo 70. Though
comprehensive and flexible. it has been created by
the world's best~known amplifier designer
specifically for the use and enjoyment of the
music-lover at home, for his wife and for his
children. Simple-to-follow operating instructions
are enclosed with the amplifier. and five minutes
practice will give you easy mastery.

All controls are of the single knob. dual-ganged,
close-tolerance type which gives much greater ease
of handling than the cheaper twin knob. dual-
concentric. unganged type.

Appearance

The appearance is of elegant and functional
simplicity whether the unit is used free-standing in
its teak case or whether it is cabinet mounted when
the front panel will blend with any wood. The front
panel decor is black and silver.

Circuitry

The two identical circuits are designated " L " (for
the left-hand input signal) and " Ft " (for the right-
hand input signal). Each circuit uses a low-noise,
low-distortion 2 stage (5 transistors) feedback
tone control ore-amplifier section.

The first stage (3 transistors) provides low-noise
amplification and frequency selective negative
feedback equalisation for record reproduction

The second stage (2 transistors) embodies
feedback tone control circuits which give
continuously variable control of both bass and
treble frequencies

The circuitry of this tone control stage and power
amplifier input stage is arranged to incorporate a
high-pass filter which sharply attenuates the low
frequency response below 20 Hz. This removes all
unwanted signals which do not contribute any
useful information and may cause audible
interference or amplifier overload at sub-sonic
frequencies (the turn-overfrequency is 17 Hz and
the attenuation rate is 18 dB per octave).

The power amplifier section has been designed in a
4 stage (6 transistors) directly coupled transformer-
less. push-pull configuration with over 60 dB of
negative feedback, thus reducing all forms of
distortion to inaudibility.

Heavy DC negative feedback in conjunction with
diode temperature and voltage stabilisation ensure

that the high specifications are always maintained at
extremely low and high temperatures.

Specification and Performance
Transistors and Diodes

4 - BC1-49, 4- BC148 or BC115. 2- BC107 or

BC115, 2 - BC154. 4 - 2N2102, 2 ~- 2N4036.

4 - 2N3055, 4 -1N3754. 1 - USDl 399Y.

Power Output (Both Channels Sine Wave Driven):

35 watts r.m.s.. each channel into 8 ohm
loudspeakers.

28 watts r.m.s, each channel into 15 ohm
loudspeakers.

Music Power Output

45 watts r.m.s.. each channel into 8 ohm
loudspeakers.

30 watts r.m.s.. each channel into 15 ohm
loudspeakers.

Total Harmonic Distortion:

0-1 % for ALL power levels up to 25 watts r.m.s..
each channel at 1 kHz into an 8 ohm or 1 5 ohm
loudspeaker.

Total Intermodulation Distortion'

Input- 70 Hz and 7 kHz in ratio of 4 : 1.

Less than 0-3% for ALL power levels up to 28 watts
into 15 ohm loudspeakers.

Less than 0.5% for ALL power levels up to 35 watts
into 8 ohm loudspeakers.

Overload distortion less than 0-1% for input signals

up to 20 dB above stated sensitivities from 30 Hz

to 15 kHz.

Damping Factor:

40 measured at 1 kHz for 1 5 ohm loudspeakers.

20 measured at 1 kHz for 8 ohm loudspeakers.

Crosstalk.

Between" L " and " R " channels-50 dB up to
1 kHz and -30 dB at 10 kHz.

Hum and Noise:

66 dB below 30 watts output on " Tuner " and

" Tape Amp and 56 dB below full output on

other inputs with tone controls at 12 o'clock and

volume control at maximum. With the volume
control turned to minimum, the residual hum and
noise is 90 d8 below 30 watts power output.

Power Supply:

110V. 117V.130V.210V.230V.25OV:40-60 Hz.

Consumption:

150 volt-amps.