Pioneer PL41 runs fast and a potential solution

Jim Creek

Jazz, Wine, Electronics
After listening to my Pioneer PL41 for a while it became clear that the pitch was slightly higher than normal. I put a 60hz strobe disc on the platter. Shure enough, the table is running fast.

I checked the capstan. It has the groove that indicates it's for 60hz.

I'm not sure if it's the belt. I understand a thicker belt can make the platter run fast.

Then I found this post on Youtube:

"The problem is not a Mechanical one-do not waste working pulleys by filing them down-the reason that the Turntable is running too fast, apart from a slightly slack Drive belt through age is that the Load resistor in the rectifier panel to the Motor unit is tired and has gone "high", therefore, when these age, they start to carbon- break due to long-term heating effect of current over years and they start to "push" towards going open-circuit, but on the way there,they become tired and so the Voltage across them rises and hence the motor is pushed harder and runs fast. "

The PL41 uses an AC driven Hysteresis motor. There is no rectifier panel. However, there is a 300 ohm resister between the motor and transformer.

I am going to replace that resister, suspecting it may have gone "high" due to age.

What do you guys think?
 
After thinking the problem through I decided not to replace that 300 ohm resister. The speed of the motor has to be determined by AC frequency.

It has to be a belt issue somehow. The capstan is correct for 60 hz and is clean. The belt rides on the capstan correctly for each speed as I have observed.

Belt must be too thick or stiff or something.
 
The thickness of the belt would make no difference as the speed is the relationship of the circumference of the spindle vs the circumference of the platter. Try putting one or two thicknesses of masking tape around the platter. That should slow it a little.
 
There has been much discussion on the effects of belt thickness. To thick a belt will cause it to run at the wrong speed. And yes, the motor speed is set by the hertz of the incoming line, not the voltage.

BillWojo
 
There has been much discussion on the effects of belt thickness. To thick a belt will cause it to run at the wrong speed. And yes, the motor speed is set by the hertz of the incoming line, not the voltage.

BillWojo

True words. I went through several different belts for my Sansui FR4060 before I got one that ran at the right speed. It is spot on now. My PL-50 runs just a hair fast but not enough to hear it.
 
Buy a belt from LP Gear and your problem will be solved. Trust me when i tell you its the belt thickness. I own a PL-41 & PL-50. Bought a belt for each, raised the capstan so the belt rides in the middle (fat part) and speed is dead on 33.3.
 
Buy a belt from LP Gear and your problem will be solved. Trust me when i tell you its the belt thickness. I own a PL-41 & PL-50. Bought a belt for each, raised the capstan so the belt rides in the middle (fat part) and speed is dead on 33.3.

I trust you! Those $10 belts on eb#y were awfully tempting. But I bit the bullet and bought one from LP Gear.
 
Belts! Belts! Belts!

I have had a dozen or more of these Pioneer 4-pole synchronous motor turntables. And every one of them ran too fast with the wrong belt.
 
Simple geometry will tell you that thickness SHOULD make no difference as only the inside of the belt touches the spindle and the platter. Now, if the spindle is slightly tapered and the belt does not ride in the proper place, belt thickness, width or tension may affect speed as it may cause the belt to move out of the proper place.
 
Ive done alot of experimenting, and its a fact that belt thickness matters for the PL-41 and PL-50. HTHMAN, have you ever owned a PL-41 or PL-50?
 
I ran across this picture on the somewhere one the internet, credit give to the source.

Think of it this way. On the part of the belt that is moving a straight line, the inside and the outside of the belt move at the same speed.

When the belt is bent around a radius, the outside, by definition will have to travel farther than the inside of the belt. It is a slight difference, but there is a difference.

From the center of the pulley, the radius to the outside of the belt is greater than the radius of the inside of the belt. So the belt stretches on the outside and compresses on the inside. So the actual affective radius is greater than the radius of the pulley. The thicker the belt the greater the affective radius. Again it is just a small amount, but it may be enough to affect the speed of rotation of the platter.

Just as an example, if and this is not usually the case, the radius of the motor pulley and the platter were the same, then this would not be an issue. The greater the difference in the radius of the pulley and platter the greater the affect, although small, of the thickness of the belt.

There is more to what happens as the belt moves around the pulley than meets the eye.
 

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Simple geometry will tell you that thickness SHOULD make no difference as only the inside of the belt touches the spindle and the platter. Now, if the spindle is slightly tapered and the belt does not ride in the proper place, belt thickness, width or tension may affect speed as it may cause the belt to move out of the proper place.

At first I thought as you do, simple geometry. But now, it is possible there is more complexity to the belt thickness issue. A thinner belt may have more elasticity and rebound. A 4 pole motor will have 4 acceleration points which may strech the belt slightly at the 4 points. This may play into the speed issue somehow.Who knows?

I am putting my faith into the experience of the AKers that achieved success with the LP belts.

I will find the truth when the LP Gear belt arrives and post my experience here.
 
I bought 8 belts from different sites before i went the LP Gear route. My capstan is clean, and the LP Gear belt is perfect.
 

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I ran across this picture on the somewhere one the internet, credit give to the source.

Think of it this way. On the part of the belt that is moving a straight line, the inside and the outside of the belt move at the same speed.

When the belt is bent around a radius, the outside, by definition will have to travel farther than the inside of the belt. It is a slight difference, but there is a difference.

From the center of the pulley, the radius to the outside of the belt is greater than the radius of the inside of the belt. So the belt stretches on the outside and compresses on the inside. So the actual affective radius is greater than the radius of the pulley. The thicker the belt the greater the affective radius. Again it is just a small amount, but it may be enough to affect the speed of rotation of the platter.

Just as an example, if and this is not usually the case, the radius of the motor pulley and the platter were the same, then this would not be an issue. The greater the difference in the radius of the pulley and platter the greater the affect, although small, of the thickness of the belt.

There is more to what happens as the belt moves around the pulley than meets the eye.

Yes, I created this illustration and posted it on VinylEngine a couple of years ago.

Your explanation of the phenomenon is spot on.

Les.
 
Les, I am sorry that I could not remember where I found the picture and give you the credit.

Your picture is spot on for giving a visual explanation of this.
 
Ive done alot of experimenting, and its a fact that belt thickness matters for the PL-41 and PL-50. HTHMAN, have you ever owned a PL-41 or PL-50?

I have a PL-41 that runs true to speed. I bought a PRB FRX35 belt on eBay for a whopping $12.95 and it works perfectly.
 
Seems to me that belt thickness could matter only inasmuch as it might affect the ability of the belt to flex or bend. Too thin won't work, regardless of the geometry.

In my brief experience replacing belts, what mattered in my case was the width of the belt. My Technics SL-23 didn't run correctly with a belt that was too narrow, despite it being the correct length.
 
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