Leak varislope 3 mono owners manual

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H. j. LEAK a CQhLTD.
April. 1957

VARISLOPE; 111 l PIKE-AMPLIFIER
INSTALLATION, gPERATI " and MAINTENANCE

NOTES ON A3300 TED APPARATUS

The Varislope III pre-amplifier is designed for use spec 'with Leak power amplifiers TL/ 12 Plus. TL/25 Plus and
TL/SO. It will also operate perfectly with any previous wer amplifier, though the facility of a socket for picking
up heater and anode supplies for a tuner will not be ava unless an 'tioaal octal socket is fitted to the power
amplifier. Instructions for carrying out this modifiCationgw .M

CONNECTING THE VARISLOPEJ Ill FIRE-K .

4. This unit may be used free-standing on a table, or it

. . be mounted on a panel of any thickness, through a cut-out
I of 10% x 31- (27 cms. x9-85 ems.) To mount on a » -

» I: remove the rubber feet by pulling smartly out of their
h the cut-out until the front plate butts against the panel.
then pass the U-shaped bracket over the back of the > i » plifier and fix it by passing the wing screw through the
hole in the bracket and into the threaded hank-bush .p «e centre of the rear panel on the [ire-amplifier. Tighten
the vlvrng screw just enough to prevent the metal boc :oruhe' front plate of the pre-amplifier from slipping on the
pane .

2. A multiple cable of 4ft. (1-22 metres) is supplied 1 .
The male plug on this cable fits the socket on the - . .
cable fits the male socket on the Varislo III rn
u. r: upto» uvunum of 16 .(5 met

retaining holes ; pass the body of the pre-amplifier tl .

unnecting the Varislope III to the Leak power amplifier.
mplifier marked PRE-AMP. The female plug on the
_FROM AMPLIFIER. Longer cables can be supplied

- .. . . _ . u . . . - : .- ulifler from arislope III, a switch is incorporated in the VOLUME
. a. J. (i make use of this facrlity a --L 41mm- cable is s 'ed with. , ,_ ' .111; one end of the
ea-le is fitted with a plug which inserts into thl sookc marked 3 . flaw III; the
r other end of the cable must be passed through the ru ber We! 11! " ,K ' at the m, of
aim associated Lealgpower amplifier. thhmu n-f grommet. and the two burc'l cntls connectedtn thejqnunuls
with the Leak power amplifier not earthed igroufi this can be reducet oymfifigw A
the power amplifier. Reversing the SWITCH co _ tions will not be tfective. We strongly/deprecat-L '
earthing the power amplifier. ' 'A , , . "

:3. THE CONNECTION 0F HCKUPS 4., _.

,7

Two pickups can be connected to the co-axial .
Varislope III. Below these sockets are the assoc"

selector switch marked PICKUP."
The greatest care has been taken in the design of f,
in the world can be connected to give optimum re '
of pickup. Our prime aim is for you to. obtain

-amplifier to ensure that any pickup generally available
. .. the highest quality obtainable from the chosen make

timum results from the pickup of your choice. Please
follow our instructions very carefully, even if they to conflict with other advice.

We know from experience that the main troubles . ~ - . red by that!!- er at home are with the reproduction
of records. There are five major reasons for these! bles 2-- " \

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

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

(6) Hum. This often arises because insufficient a n is given during the design of a pickup to the commonly-
found circumstances in which rt wrll operate. unear an electric motor and near a power amplifier. Hum

' can also arise from incorrect connection of t ,3: p by the user.
(:1) Rumble. Vibration from the motor is t_ itted to the pickup stylus and appears in the sound output
as a rumbling or humming norse. Rumble wars when the pickup is lifted from the record.
4
(e) Acoustic feedback. If a loudspeaker is pieced ' e same cabinet as a pickup, then vibration from the move-

ment of the loudspeaker can be transmitted to .' lus of the pickup. As the volume is increased a stage is
reached where a sustained roaring norse rs set . At volume levels considerably below this point distortion
is noticeable. Acoustic feedback dssappears Wlfinflie pickup is lifted from the W. 1

l

A /

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(fl Connecting pickups having a single wire withlrl

Er),__._ _______ THEINNER
1, r v ' fi WIRE TAKEN
. fl_ 4 __________ - ________ .t \ THROUGH
" SHORTEsT possua E HOLES): 25'6
p L scaeen .
lCKUP LENGTH or .: somenao ro PR5 AM PLUG SOLDERED AT
UNSCREENED WIRE. oureu SHELL. THE rip.

If hum is to be kept to a minimum the out ng should either have an insulated covering. or it should
be prevented from touching any metal on th motor-board or anywhere else. The outer screening must
not be used for earthing any part of the motor and {turntable lisscmbl). which should be earthed by a separate
wire taken to the (in terminal on the Look power .melilicr. 11 the lune-211111 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 ,3. 1.
connected to the body of the motor lilttmllllé.
very likely to cause hum, particularly when u
are most strongly urged to replace it with the

Relianperx are wired as shown above, the screen then being
late. This is bad practice on the part of the makers, and is
a low output pickup. If you have this type of wiring, you
. Lem (g) below.

(g) Connecting pickups having two wires within I: screen.

_ ._ _. _ . - - - r\ , '- ONE INNER
"vwh L of" 1 9* , " , t) WIRE TAKEN
_______________ m o co - rfi \ THROUGH

7' w cam :
plump . i- new AND one PRE-AMP. PLUG. misfit AND R-
suomasr possuBLE moan WIRE soLDERED AT
LENGTHS OF SOLDLRr'I TO THE TIP.

UNSCREENED WIRES. OUTER SHELL.

Again. as in (f) above, the outer screen should :ither lune an insulated covering. or it should be prevented
from touching: the motor. ummr-lumrd or anywhere 8153- If. howcvg; the/(screening does touch, then hum 15
loss [itch to be caused than by using the sing "Mt" ->>>Wm 0f (94

(1) Connecting low impedance pickups using a trait-mett.

c _ ..._ , pgwmbifi " 7 7 :Jl- SECONan

PICKUP L _ J
NOTE WELL.

The transformer must be enclosed in a stl'cclllng, can of high-permeability metal, i.e., mu-metal or permendur.
The primary winding must be balanced, thc cer re-uip being taken to the chassis.

The primary terminals are to be as small as pti'xlblt and m be as close together as is practiceable, in order
to obviate a loop in the wiring. The primary i ids to be tightly twisted for the same reason. The live"
secondary terminal to be screened and to he as mull il\ pitwlblfi. Ideally all terminals should be inside the
can. The above precautions are not yet LiniwrJll) followed, though they have been standard practice on
Leak pickups for ten years. These precautim. rc essential if the lowest hum level is desired.

(1') HIIIII- as:

The Varislope Ill pie-amplifier has an cm-rmnmurily low hum level, which can be checked by removing
the pickup plug and turning up the " VOLITh E control. The connection of any input device to the
pickup socket will lower the input impedance mt would, therefore. reduce the bum level. If the hum level
increases on connecting the pickup, the cause d-ilt'rltum must lie outside the pre-amplifier, and our instructions
on the choice and connection of pickups should it: arefully read in an attempt to locate the cause of the bum.

Hisn.

With the input control switched to a pickup pm [inn and the VOLUME " control at maximum, a certain
amount of hiss will be heard. This hlSS is a It \ as is possrble 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 piEkLTpithoving-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 variable-reluctamwng-lrop) pickups the output will be so low, for reasons
explained later (see 6c (2), p5), that hiss will he more noticeable. This is the price that the user has to
pay in return for a modest outlay with reasonaw good results!