Leak stereo 30 service manual

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'STEREO 36'

INTEGRATED TRANSISTORISED
AMPLIFIER

M"'W"|""W"W" INSTALLATION ' OPERATION ' MAINTENANCE

IMPORTANT

Do not connect any A.C./D.C. device (TV, Tape or Radio) to the Stereo 30 amplifier. These sets can
have high A.C. potentials on their chassis, and this can cause serious damage to the Stereo 30 amplifier.

CONNECTING THE 'STERED 30'

1.

This unit may be used free-standing on a table, or it may be mounted on a panel of any thickness, through
a cut-out of 121% X3? (31-8 X95 cms.). To mount on a panel: take off the cover by removing the wing-
screw which passes through a hole in the cover fixing bracket and threads into a hank-bush iu the centre
of the rear panel of the amplifier. Pass the body of the amplifier through the cut-out until the front plate
butts against the panel, replace the cover and wing-screw and tighten just enough to prevent the front plate
on the amplifier from slipping on the panel.

The mains transformer primary is wound for voltages of 110, 117, 130, 210, 230, 250 (40-60 c/s). The
circular voltage selector (situated at the back of the amplifier) should be withdrawn to its fullest extent,
rotated so that the arrow indicates the voltage nearest to your supply and then reinserted.

The amplifier is fitted with a l3-ft. (4~metre) power cable, either Z-core or 3-core according to the practice
of the country to which it is shipped. This cable should be connected to the domestic power supply as
follows:

(a) 3-core cable. If the power supply socket has a third (earth) contact, the green wire should be connected
to the corresponding pin on the power supply plug and the red and black wires should be connected
to the live and neutral pins respectively, usually marked L and N.

If the socket has only two contacts then connect the red and black wires to the pins of the plug fitting

this socket. Cut oh the green lead and run a separate earth (ground) lead from the EARTH' terminal

on the rear of the chassis to the water system or to the steel conduit encasing the house wiring, providing '
that these systems themselves are properly grounded.

(b) Z-core cable. The plug fitted to the power cable should be connected to the domestic power supply
socket. A separate earth (ground) lead should be run from the EARTH terminal on the rear of the
chassis to the water system or to the steel conduit encasing the house wiring, providing that these
systems themselves are properly grounded. ~

It is very bad practice to omit this earth connection, and to ensure freedom from hum (caused by earth

loops) no other earth connection should be made.

The amplifier is switched on by turning the volume control.

A double socket marked A.C. OUTLETS is fitted as a convenient source of power supply for turntables,
self-powered radio tuners, etc. The power taken from this socket should be limited to 100 watts or there-
abouts. This socket is not fused but is controlled by the amplifier switch.

The amplifier has been designed to operate under domestic conditions for the reproduction of speech and
music anywhere in the world-it will perform in accordance with the specification in ambient temperatures
up to 45°C (112°F). Due to the very small amount of heat generated by the amplifier it is possible to mount
the amplifier in a small cabinet and it is only necessary to ensure that the slots in the cover are uncovered.
Sinewave testing at full power output must be of short duration, particularly at high frequencies, otherwise
the 1 amp D.C. fuse will blow.

Fusing. In order to give the amplifier maximum protection against abuse we have fitted a DC. fuse of
1 amp rating. Care should be taken to avoid shorting the loudspeaker leads as this may blow the fuse.

When using a low impedance (4 ohms) ineflicient loudspeaker system it may happen that excessive overload
ing of the amplifier on transients will cause the fuse to blow (the distortion under these conditions would be
severe and audibly very objectionable). It is permitted under these conditions to increase the fuse rating

to 1-5 amps.

Loudspeakers of any impedance from 4-15 ohms may be used and they should be connected by twisted
pairs of wires to the plugs fitting the dual socket marked LOUDSPEAKERS 4-15 OHMS R and L. It
will be seen from the circuit drawing that one side of the loudspeaker winding is connected to the chassis,
and no part of the loudspeaker wiring should be earthed elsewhere. The DC. resistance of the connecting
wires should be as low as possible, and not more than one-tenth the DC. resistance of the loudspeaker. It is
bad practice to operate any amplifier without a loudspeaker, and if it is desired to mute either loudspeaker by
switching it out of circuit this should be accomplished by use of a changeover switch which replaces it with
a resistor of corresponding value and rating. If for any reason only one loudspeaker is to be used then a
similar resistor should be connected across the loudspeaker socket of the amplifier channel not in use.

1 For Servloo Manual:
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8.

Phasing. it is vitally important that the diaphragms of your two loudspeakers move in phase, i.e. in the
same direction at the same instant. To make sure of this note very carefully the following:

If you are using identical loudspeakers (as you certainly should if you want true stereo) the manu
facturer will doubtless have kept to a convention when marking the terminals, very often simply red and
black. In this case the loudspeakers will be in phase when connected as shown below.

c RED wme- R/ED
L ..
/ BUCK wme Eats LOUDSPEAKER L
LOUDSPEAKERS
"'5 °HM5\ RED ere RED
/ 1 o
a 0 BLACK WM E374 LOUDSPEAKER a

If your loudspeaker terminals are unmarked or you are using dissimilar loudspeakers you can check the
phase as follows: place the two loudspeakers as close together as possible; set the function switch
to INPUT R and the input selector to PICKUP. Connect an unscreened length of wire (about l ft.) to
the PICKUP R socket. Turn BASS control to maximum and then turn up VOLUME control until
the hum picked up by the unscreened lead is fairly loud. Then reverse the leads to one loudspeaker; the
condition which gives you noticeably more bass hum is the correct connection, i.e. the loudspeakers are
in phase.

Do not insert the input plugs into the input sockets unless an input device is connected to the plug via
a screened cable. Failure to observe this instruction will result in high noise levels when the selector switch
is turned to MIC, PlCKUP or TAPE HEAD.

DPERATING_THE lSTEREO 30

10.

ll.

12.

13.

BALANCE CONTROL

The BALANCE control allows you to compensate for difi'erences in sensitivity between loudspeakers, or
the L and R sides of any stereo input device. The gain in each channel is identical when the pointer on the
BALANCE control knob is at 12 oclock. A further function of the 'BALANCE control is mentioned in
para. 20.

VOLUME CONTROL

The input attenuators on the rear panel of the STEREO 30 should be set so that a normal level of repro-
duction is obtained with the main VOLUME' control set to 10 oclock or higher. It is better not to listen
with the VOLUME control below 10 oclock, as the channel balance below this setting may vary by more
than ldB. '

FUNCTION SELECTOR

A four position switch allows the choice of:

(a) MONO. This parallels that L and R circuits, enabling a stereo pickup to play mono LP records.

(1;) STEREO.

(c) INPUT R (mono, connects both amplifier channels to the R input device).

(d) INPUT L (mono. connects both amplifier channels to the L input device).

Positions 3 and 4 enable you to reproduce mono signals through both the loudspeakers connected to the
Stereo 30. See para. 20.

NOISE (Hum and Hiss)

The STEREO 30' has a very low noise level which can be checked by removing all the input plugs and
turning up the VOLUME control. The high-pitched hiss associated with vacuum tube amplifiers is less
noticeable with transistors, the irreducible noise being lower in .pitch and unobtrusive,

N.B. When connecting an input plug to the STEREO 30 ensure that the screening of the co-axial lead does
not touch the chassis of the amplifier as this may cause excessive hum.

CONNECTING STEREO PICKUPS

14.

(a) The greatest care has been taken in the design of this amplifier to ensure that any pickup generally
available in the world can be connected to give optimum results, i.e. the highest quality obtainable from
the chosen make of pickup. Our prime aim is for you to obtain optimum results from the pickup of your
choice.