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The DC Motor
and PSU (Power Supply Unit)
When
to Set the Speed
The motor and PSU should be
left ‘on’ so that they can be ‘burned in’ for around 24
hours the speed should be set using the following
conditions: -
a. The deck
should be stopped and then restarted 10 minutes after
‘switch on’,
You can now set the speed.
This will then remain more or less steady for the average
record playing session of around 2 - 3 hours.
b. The speed
should be set with a record playing so that stylus drag is
taken into account.
c. Speed drift
whilst playing the side of an LP should not occur unless
something is amiss.
d. Subsequent use
should not need adjustment of the speed; if it does it
should be only very minimal.
Trouble Shooting the DC
Motor and PSU
The following notes are
courtesy of Origin Live’s observations of DC motors, and are
a good general guide for all turntables with a DC motor
drive.
• Excessive Motor Noise
The motor needs a run in time
of around 2 - 3 days continuous running under load before
the bearings ‘bed in’.
The motor is sometimes a
little noisy to start with. It is best to run in the motor
on full power with the belt off for the first 5 hours. Most
importantly you can ‘tune in’ the motor to give minimum
noise by slackening off all 3 mounting plate screws next to
the pulley then tightening one screw in turn. Find out which
screw reduces motor noise when lightly tightened and then
adjust the other two to give minimum noise. It may be
necessary to use thread lock or similar to stop the screws
vibrating loose. If it continues to be very noisy please get
back to us and we may check it out but the DC motor is never
silent as a/c motors are - this is because they are cogless
and rely on a different type of brush. Having said this, DC
motors still sound a much better in terms of musical
performance.
• Speed stability
introduction
The speed stability of the
deck is excellent once everything has settled down in a
listening session. Bear in mind that the ear detects when
something is running slightly slow much more easily than if
the deck is running slightly fast. For this reason most
manufacturers set their decks to run slightly fast. You can
expect a bit of speed variation when the motor is first
switched on - it takes about 1 to 2 min’s to warm up
properly and then the motor should run at its correct speed.
If you move the position of
the motor pod it alters the belt tension - this changes the
friction on the motor bearings and the height that the belt
rides on the pulley so you will need to re-adjust the speed.
Increasing belt tension has the effect of slowing the motor
down - excessive belt tension can introduce speed variation.
Tension is best set at the minimum required to produce speed
stability.
• If you keep switching the
deck on and off you can get a little speed variation as it
can take a few minutes to warm up the circuit each time even
if it’s only switched off for 3 seconds. This is unavoidable
although we have tried to design it out but is fairly
inaudible anyway.
• If you measure the speed
without a needle on the record, the speed will not be
perfect as the speed should only be set with the stylus
tracking the record.
• If you measure the speed
within 1 minute of putting the needle on the record, the
speed will not be perfect as it can take a good 2 minutes to
really settle down.
• Some people make the mistake
of constantly watching the speed before the deck has settled
down and the needle has been on the record for a good 2
minutes. Strobes are very accurate and the slightest speed
variation is picked up.
0.1% variation is observable
but practically inaudible.
Speed variation causes can be due to the
following:
• Belt tension too tight -
this can increase friction on the motor bearings
sufficiently to cause a small heating effect that may cause
motors with tight tolerances to vary their speed. As long as
a flat drive belt is riding clear of the bottom flange of
the pulley it should be tight enough, so reduce belt tension
as much as possible - listening for the best sound with a
record playing is a sure fire way of getting this correct as
it affects the sound quality. As you change the belt tension
the platter speed may change slightly and need resetting.
• Lack of belt tension -
increase tension 2mm at a time until speed is stable.
• If the 3 small cross 3 small
cross-head screws head screws next to the pulley are
tensioned too tightly, the mo next to the pulley are
tensioned too tightly, the motor bearings can be
fractionally distorted and cause speed variation.
• For the short pulley - The 3
small cross head screws can be oriented incorrectly such
that the drive belt rubs on them as it rotates - to solve
this, rotate the motor pod if this is the type of motor
mounting. Alternatively if the motor is on a plate then turn
the plate through half a turn and re-fix.
• Pulley rubbing on side of
top plate or rubber washers under screw heads (rubber
washers are not always fitted). This is usually
characterised by the pulley speeding up gradually over time
as it wears away the surface it is rubbing against. Carry
out a careful visual inspection of the area around the
pulley as it rotates to check it has clearance.
• Dirt or oil on running
surfaces - Clean motor pulley and belt running surfaces with
alcohol (surgical Spirit) or methylated spirit.
• Slipping pulley - The pulley
is a taper fit on the shaft. If it becomes loose or falls
off, simply replace it and give it a tap down using your
fingers only - do not force it down or tap it with a hard
object. Very occasionally the pulley can lose its "grip" on
the motor shaft - this causes slipping which is easily
observed as sudden speed variations especially on heavy
passages of music. The easy solution is to glue the pulley
onto the motor spindle using fairly slow setting superglue
or preferably clear nail varnish - place a tiny drop of glue
inside the PULLEY hole. Do not place glue on the spindle in
case it drops down into the motor bearings. Fit the pulley
onto the spindle and hold till set. If you make a mistake do
not try and remove the pulley too forcefully or you can
wreck the motor. Superglue is softened by heat so use a
soldering iron to heat the pulley and then pull it off
gently with a pair of pliers. Do not try heating the whole
motor with a hot air gun as this will cause speed
instability due to bearing distortion. (Using clear nail
varnish rather than Super glue is less risky).
• See if the sub-platter is
fouling on anything - on certain decks it can rub against
one of the spring covers - The sub-platter has also been
known to ‘bottom’ against the top of the bearing house -
there should be about 1 to 3mm clearance between the top of
the bearing house and the bottom of the sub-platter.
• A dirty bearing that
exhibits too much friction - The sub-platter should drift
round effortlessly with the slightest of nudges and go on
spinning. If you suspect the bearing friction is a little
high, return the bearing to us for checking
• A worn thrust bearing - this
may occur on a small run of bearings which were too soft.
• Faulty transistors that have
developed temperature instability.
• A belt that is running right
on the bottom edge of the sub-platter - this is rectified by
re-adjusting the height of the main bearing thus lowering
the sub-platter.
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