advertisement


Turntable Drift

P

Polycotton

Member
Hi

The only issue after 10 years of ownership of my TT is that when I set the speed with the strobe disc and the black box with the led in it the black marks drift. I can get the marks to stand still with ref to my cartridge but by the next LP they have drifted one way or another. The knob on the speed control only seems to give course control, the slightest touch of the knob and the black marks drift.
The frequency of writing this is 49.979Hz.
 
I am not familiar with the Palmer control electrics/electronics at all, however, (according to Google results) in the UK "the National Grid is obliged by its licence commitments to control the frequency within ±1% of 50Hz so it can fluctuate between 49.5Hz to 50.5Hz. However the normal operational limits are 49.8Hz to 50.2Hz." Turntable manufacturers that use AC synchronous motors take this into account with some going so far as to synthesize a perfect 50Hz sine wave within their power supplies. Regardless, even a standard resistor/capacitor network circuit feeding a basic Premotec AC synchronous motor isn't going to go far off speed due to such variation, nor would the frequency of minor mains frequency drifts necessarily be detectable as audible 'wow'.

Your mention of the extreme sensitivity of the speed control suggests that the issue is local to this device. The 'Any Palmer turntable owners on PFM?' thread suggests that the motor is a standard 9904 111 32311 low torque AC synchronous type which suggests that the control electrics would not normally be speed adjustable without a more sophisticated circuit than the typical resistor/capacitor or capacitor/capacitor type.

Question: Does the (presumed to have come with) user manual discuss the motor drive system and/or boast of any particular control circuit tech?

UPDATE: Further investigation (Stereophile) reveals that Palmer used Martin Bastin's Wave Mechanic AC wave-regenerator power supply in a customized box. Suspect the potentiometer is in need of a good cleaning after 10 years of (presumably) less than regular usage.
 
You haven't mentioned which TT this is. I guess it's a direct-drive Japanese-made (Technics ?) - these are prone to losing contact in the knobs and switches after a long while. Open it up, and use a Deoxit-type of contact cleaner on all switches and potentiometers. Then use compressed air very gently to blow away the remains (do not blow air near the tonearm wiring).
If this doesn't do the trick, you are looking at a recap job for the speed control section.
 
Fellow Palmer turntable here. The problem you have could be down to a few things.

1. When did you last change the battery in the little black box strobe unit supplied with the Palmer turntable? I recently discovered that when the battery voltage in the strobe gets a bit low the frequency of the unit fluctuates quite wildly as the operating button is pressed, giving the impression that the speed of the platter is changing.

2. When did you last oil the spindle bearing? If the bearing gets too dry, even a small amount of extra drag in the bearing will cause the platter speed to be quite unstable. The drive motor of the Palmer has only just got enough torque to overcome the drag of the bearing and the stylus drag to keep the platter spinning at a stable speed,

3. Is the drive belt still in good condition?

4. If you have dismantled the spindle to check or replace the oil its possible for the ball bearing to become dislodged from it's location in the base of the spindle when re-assembled which will also cause the speed to vary.

It could be a problem with the Wave Mechanic power supply, but its more likely to be one of the above problems. The wave mechanic power supply uses a Wien bridge oscillator to generate a stable clean 60Hz sine wave using an RC time constant. The speed control potentiometer is part of the resistance in the RC time constant, and is a good quality plastic film type. However the full travel of the knob will only vary the output frequency by about 2.5Hz.

The output from the Wien bridge oscillator drives an audio frequency amplifier, the output of which drives the primary of a toroidal transformer which steps up the output from the audio amplifier to around 135 volts AC for the drive motor. In my experience the output frequency of the wave mechanic is very stable indeed.

If you still suspect the Wave Mechanic you could contact Martin Bastin who is very helpful and will check it out for you. I have Martin's contact details.
 
If there is a speed control it'll likely need cleaning. There may be a second set under the deck that also needs to be sprayed with contact cleaner as well.

I've done a few old Technics and Pioneers for friends and the speed is usually way more stable after cleaning the speed controls.
 
Disarmamant said:
Fellow Palmer turntable here. The problem you have could be down to a few things.

1. When did you last change the battery in the little black box strobe unit supplied with the Palmer turntable? I recently discovered that when the battery voltage in the strobe gets a bit low the frequency of the unit fluctuates quite wildly as the operating button is pressed, giving the impression that the speed of the platter is changing.

2. When did you last oil the spindle bearing? If the bearing gets too dry, even a small amount of extra drag in the bearing will cause the platter speed to be quite unstable. The drive motor of the Palmer has only just got enough torque to overcome the drag of the bearing and the stylus drag to keep the platter spinning at a stable speed,

3. Is the drive belt still in good condition?

4. If you have dismantled the spindle to check or replace the oil its possible for the ball bearing to become dislodged from it's location in the base of the spindle when re-assembled which will also cause the speed to vary.

It could be a problem with the Wave Mechanic power supply, but its more likely to be one of the above problems. The wave mechanic power supply uses a Wien bridge oscillator to generate a stable clean 60Hz sine wave using an RC time constant. The speed control potentiometer is part of the resistance in the RC time constant, and is a good quality plastic film type. However the full travel of the knob will only vary the output frequency by about 2.5Hz.

The output from the Wien bridge oscillator drives an audio frequency amplifier, the output of which drives the primary of a toroidal transformer which steps up the output from the audio amplifier to around 135 volts AC for the drive motor. In my experience the output frequency of the wave mechanic is very stable indeed.

If you still suspect the Wave Mechanic you could contact Martin Bastin who is very helpful and will check it out for you. I have Martin's contact details.
Click to expand...

Hi @Disarmamant

I never thought to check the batteries.
I have never oiled the spindle bearing, I do not know how to do that.
Drive belt is brand new.
Ask this question from a point of ignorance. The paper disc with the black marks on says 50hz on it, does it matter that the output of the PSU is 60Hz?
Thank you.
Kind Regards.
 
Polycotton said:
Hi @Disarmamant

I never thought to check the batteries.
I have never oiled the spindle bearing, I do not know how to do that.
Ask this question from a point of ignorance. The paper disc with the black marks on says 50hz on it, does it matter that the output of the PSU is 60Hz?
Click to expand...

If I were you I'd change the battery in the strobe anyway after ten years.

Oiling the spindle bearing is quite easy, but you have to check the ball in the base of the spindle is put back correctly. You will need a few drops of ISO VG 32 slideway oil, and small blob of grease. Remove the drive belt and carefully lift the platter off the top of the spindle.

Then you can slowly lift up the spindle and remove it from the bronze bearing outer, this is the point where its easy to dislodge the ball from the base of the spindle. You might find the ball will fall out anyway and remain in the base of the bearing. If that happens then a small bit of grease on the end of a pencil will enable you to retrieve the ball from the base of the spindle.

Add a few drops oil into the base of the spindle and a smear of oil onto the spindle shaft. If the ball has dropped out of the base of the spindle then you can put a very small bit of grease in the hole at the bottom of the spindle and push the ball back in place, the grease should hold the ball in place whilst you replace the spindle back in the bronze bearing outer. As the fit between spindle and the bearing outer is very close you will find the spindle will resist dropping back down in the bearing due to the air pressure inside the bearing.

If your bearing has a 'well' machined in the bronze outer top face, like mine does, I'd add a few drops the slideway oil into the recess well while the bearing spindle is being refitted so it can lubricate the top of the bearing. You might find it takes a little while for the spindle to drop down fully in the bearing out as the air can only escape very slowly.

Don't be tempted to buy some 'super duper 'spindle bearing oil advertised on the internet. Jon Palmer told me to use only ISO VG 32 slideway oil for good reasons.

If you need some of the correct oil send me a PM with your address and I will put a small bottle of it in the post for you.

The PSU for the motor outputs at 60Hz to drive the motor at 300rpm. The strobe disk you have is to check the platter rotation at 33.33rpm using a 50Hz strobe, so no it does not matter that the PSU is 60Hz.
 
Hi
@Disarmamant

Thank you for your detailed responce.
I have tried new batteries in the strobe and it has made no difference.
I use the knob on the psu to get the black marks to stand still, with reference to my cartridge looking from above, then the marks will start moving to the left. So I then adjust it again and the marks start to drift to the right. It seems that there is not enough fine adjustment in the speed control knob. It seems you have to only sneeze on the speed control and the black marks drift one way or the other. However at the end of the day, to my ears, it makes no difference to the sound. Iam probably being concerned over nothing.
 
You must log in or register to reply here.


advertisement


Back
Top