Leak point one plus owners manual

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Page 1

H. I. LEAK & CO. LTD.
June. 1957

POINT - ONE PLUS PRE-AMPLIFIER

INSTALLATION, OPERATION and MAINTENANCE

NOTES ON ASSOCIATED APPARATUS V /

a a a

The Point-One Plus pre-ampliﬁer is designed for use speciﬁcally with Leak power ampliﬁers TL/ 12 Plus, TL/25 Plus and
TL/50. It will also operate perfectly with any previous Leak power ampliﬁer, though the facility of a socket for picking
up heater and anode supplies for a tuner will not be available unless an additional octal socket is ﬁtted to the power
ampliﬁer. Instructions for carrying out this modiﬁcation will be sent on request.

CONNECTING THE POINT-ONE PLUS PRE-AMPLIFIER

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 10% x 3% (27 cms. x9-85 ems.) To mount on a panel : remove the rubber feet by pulling smartly out of their
retaining holes 1 pass the body of the pre-ampliﬁer through the cut-out until the front plate butts against the panel,
then pass the U-shaped bracket over the back of the pre-ampliﬁer and ﬁx it by passing the wing screw through the
hole in the bracket and into the threaded hank-bush in the centre of the rear panel on the pre-ampliﬁer. Tighten
the wing screw just enough to prevent the metal backing on the front plate of the pre-ampliﬁer from slipping on the
panel. 1

A multiple cable of 4 ft. (1-22 metres) is supplied for connecting the Point-One Plus" to the Leak power ampliﬁer.
The male plug on this cable ﬁts the socket on the power ampliﬁer marked PRE-AMP. The female plug on the
cable ﬁts the male socket on the Point-One Plus marked FROM AMPLIFIER. Longer cables can be supplied
to special order, up to a maximum of 16 ft. (5 metres).

To enable you to control the power ampliﬁer from the Point-One Plus, a switch is incorporated in the

VOLUME control. To make use of this facility a Z-core ﬂexible cable is supplied with the "I 4.410ch

Plus; one end of the cable is ﬁtted with a plug which inserts into the socket marked SWITCH on the rear of
the Point-One Plus"; the other end of the cable must be passed through the rubber grommet marked SWITCH
CABLE at the rear of the associated Leak power ampliﬁer. knotted behind the grommet, and the two bared
ends connected to the terminals marked SWITCH situated underneath the mains transformer. If excessive
hum is experienced, particularly with the Leak power ampliﬁer not earthed (grounded). this can be reduced by
reversing the mains input leads to the power ampliﬁer. Reversing the SWITCH connections will not be
effective. We strongly deprecate NOT earthing the power ampliﬁer.

THE CONNECTION 0F PICKUPS

The pickup is connected to the co-axial socket marked PICKUP at the rear of the Point-One Plus." Below
this socket is the associated input volume control.

The greatest care has been taken in the design of this pre-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 the optimum results from the pickup of your choice. Please
follow our instructions very carefully, even if they appear to conﬂict with other advice.

We know from experience that the main troubles encountered by the music-lover at home are with the reproduction
of records. There are ﬁve major reasons for these troubles :-

(a) No record can possibly give perfect reproduction, and many records (perhaps the majority) contain noticeable
distortions due to imperfections in recording and/or processing. These imperfections may show up as rattle,
high surface noise, recorded hum and rumble, and recorded wow. Shrill treble may be due to a poor
record, and/or due to a pickup having its high-frequency resonance within the audible range.

(1)) No pickup is perfect and the majority have performances very much below those which are attainable.

(0) Hum. This often arises because insuﬁicient attention is given during the design of a pickup to the commonly-
found circumstances in which it will operate, i.e., near an electric motor and near a power ampliﬁer. Hum
can also arise from incorrect connection of the pickup by the user.

(d) Rumble". Vibration from the motor is transmitted to the pickup stylus and appears in the sound output
as a rumbling or humming noise. Rumble disappears when the pickup is lifted from the record.

(9) Acoustic feedback. If a loudspeaker is placed in the same cabinet as a pickup, then vibration from the move-
ment of the loudspeaker can be transmitted to the stylus of the pickup. As the volume is increased a stage is
reached where a sustained roaring noise is set up. At volume levels considerably below this point distortion
is noticeable. Acoustic feedback disappeari when the pickup is lifted from the record.

Page 2

PICK UP

(f) Connecting pickups having a single wire within a screen.

For Service Manuals Contact
WHOM TECHNICAL SERVICES
6 Cherry Tree Rd. Chinnor
Oxon OX9 4OY
sz-olW-351694 Fax; 018443525

ries@mauvitronm.ut
{* ______________________ T HE INNER

I l 3\ WIRE TAKEN

V---~--------~- THROUGH
/ HOLLOW CENTRE

SHORTEST POSSIBLE . SCREEN MEAN, pLUe PIN AND
LENGTH OF SOLDERED TO SOLDERED AT

UNSCREENED WIRE. OUTER WELL. THE TIR

If hum is to be kept to a minimum the outer screening should either have an insulated covering, or it should
be prevented from touching any metal on the motor, motor-board or anywhere else. The outer screening must
not be used for earthing any part of the motor and turntable assembly, which should be earthed by a separate
wire taken to the A terminal on the Leak power ampliﬁer. If the tone-arm is of metal and the outer
screening is connected to it. then the arm must not make metallic contact through its bearings with the metal
turntable and motor assembly.

Unfortunately, some record-players and record-changers are wired as shown above, the screen then being
connected to the body of the motor mounting-plate. This is bad practice on the part of the makers, and is
very likely to cause hum, particularly when using a low output pickup. If you have this type of wiring, you
are most strongly urged to replace it with the system (g) below.

(g) Connecting pickups having two wires within a screen.

i "T - 7? -ﬁ ONE INNER
' _______________________ i . I WIRE TAKEN

PICKUP

\ THROUGH

SHORTEST POSSIBLE SCREEN AND ONE / PRE-AMP. PLUG. OH-F8; i337
LENGrHs or - NNER WRE SOLDERED AT
SOLDERED TO THE Tm
UNSCREENED WIRES. OUTER SHELL.

Again, as in (f) above, the outer screen should either have an insulated covering, or it should be prevented
from touching the motor, motor-board or anywhere else. If, however, the screening does touch them hum 13
less likely to be caused than by using the single-wine system of (f).

(iﬁ'wimecting low impedance pickups using a transformer.

I. _ _ _ _ _ _ _
PRIMARY (If/Ll SECONDARY
T I

PICKUP L _ _

NOTE WELL.

(1')

The transformer must be enclosed in a screening can of high~permeability metal, i.e., mu-metal or permendur.
The primary winding must be balanced, the centre-tap being taken to the chassis.

The primary terminals are to be as small as possible and to be as close together as is practiceable. in order
to obviate a loop in the wiring. The primary leads to be tightly twisted for the same reason. The live"
secondary terminal to be screened and to be as small as possible. Ideally all terminals should be inside the
can. The above precautions are not yet universally followed, though they have been standard practice on
Leak pickups for ten years. These precautions are essential if the lowest hum level is desired.

Hum.

The Point-One Plus" pre-ampliﬁer has an extraordinarily low hum level, which can be checked by removing
pickup plug and turning up the VOLUME" control. The connection of any input device to the pickup
socket will lower the input impedance and should, therefore, reduce the hum level. If the hum level increases
on connecting the pickup. the cause of the hum must lie outside the pre-ampliﬁer, and our instructions on
the choice and connection of pickups should be carefully read in an attempt to locate the cause of the hum.

Hiss.

With the input control switched to a pickup position and the VOLUME control at maximum, a certain
amount of hiss will be heard. This hiss is as low as is possible to obtain at the present day, and it is inherent
in high-gain vacuum tube ampliﬁers.

It is a fact that with the highest quality pickups (moving-coil types used with a transformer) the VOLUME
control will not need to be anywhere near the maximum position. and therefore the hiss will be unobtrusive:
but with competitively-priced variablereluctance (moving-iron) pickups the output will be so low, for reasons
explained later (see 60 (2), p5), that hiss will be more noticeable. This is the price that the user has to
pay in return for a modest outlay with reasonably good results !