Leak stereo 20 owners manual

Page 1

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STEnED 20'
power: AMPLIFIER

m""""""""" INSTALLATION ' OPERATION ° MAINTENANCE

OPERATION

The STEREO 20 may be fed from the 'VARISLOPE 2 STEREO preamplifier or from any other suitable
source. The LEAK pre-amplifier is supplied with a grey or brown multiple cable terminating in an octal
plug which fits the socket on the 'STEREO 20 marked PRE-AMP and automatically makes the input
connections.

When the 'VARISLOPE 2 STEREO pre-amplitier is not used the input connections should be taken via
two screened co-axial cables to the plugs titling the sockets marked "INPUT L and INPUT R'. Source
impedances higher than 25.000 ohms will tend to raise the hum level above the advertised figure of 80dh
below It watts. An input of l25mV r.m.s. will give a power output of II watts.

INSTALLATION

3.

*1.

Check that all valves (tubes) are correctly seated in their holders and that the markings on the valves corres-
pond with those on the chassis adjacent to the holders. The amplifier will work equally well with any of the
alternative valves.

The amplifier should stand on its base in a well-ventilated position. lfplaced in a case or cabinet, ventilation
must be provided. Four fixing feet are fitted to the amplifier. and these raise the bottom of the amplifier
and allow air to circulate freely.

On the British model the mains transformer is tapped for voltages of 205. 225 and 245 and the voltage
selector plug on top of the mains transformer (see TOI CHASSIS' drawing) should be set appropriately.
On the U.S.A. model the mains transformer is tapped for voltages of HO. 7 and l24 and the voltage
nearest the guide key on the removable plug portion of the rain connector marked A! POWER'. In
order that the amplifier may be remotely controlled we have provided two terminals marked-SWI'I'LH'
underneath the mains transformer (see UNDER CHASSIS drawing). The amplifiers leave our factory
with a wire link joining the terminals. A remote switch may be run from the switch terminals. the switch
flex being passed through the adjacent grommet marked SWlTCH CABLE'. This flex should be knotted
behind the grommet and the wire ends connected to the switch terminals-rafter removing the wire link.
Most users will wish to employ the switch incorporated in the volume control of the VARISLOPE 2
STEREO~ pre-amplifier. which is supplied with a plug and twin flex for this purpose. Full details are gi\ en
on the installation sheets which accompany every pre-amplifier.

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

A connection to earth (ground) should be taken from the third terminal on the removable plug portion of
the 'A.(. POWER' connector. This terminal is the one furthest away from the guide key and its corres-
ponding terminal on the fixed portion ofthe connector is marked on the chassis by the symbol .1... It is very
bad practice to omit this connection. which may be made to the water system or to the steel conduit
encasing the house wiring. providing that these systems themselves are properly grounded. To ensure
freedom from hum (caused by earth loops") no other earth connection should be made

The loudspeakers should be connected by twisted pairs ofwires to the terminals marked 'LOUDSPEAKER
I. and LOUDSPEAKER R. 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
D.(. resistance ofthe connecting wires should be as low as possible. and not more than one-tenth the DC.
res .tance ofthe loudspeaker. It is a bad practice to operate any power amplifier v\ ithout a loudspeaker. and
i It is desired to mute either loudspeaker by switching it out ofcircuit this should be accomplished by use of
a changeover switch which replaces it with a resistor of corresponding value and rating. lffor any reason
only one loudspeaker is to be used then a similar resistor should be connected across the loudspeaker
terminals of the amplifier channel not in use. The selector plugs on top of the output transformers (see
'TOP CHASSIS drawing) should be adjusted for the nearest match to the advertised impedance of the
loudspeakers.

Some users may wish to connect (as a temporary measure) a single channel LEAK pre-amplifier to the
STEREO 20'. Under these circumstances. the standard black multiple cable (supplied with the pre-
amplifier) should be connected to the PRE-AMP socket. The left-hand channel will be driven by this
pre-amplifier and the right-hand channel should have a resistor olapproximately 16 ohms watt) connected
across its loudspeaker terminals.