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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