Figured out the speed problem for Pioneer PL-41 & PL-50 tables

Metalownz

Audiophile? Getting there
We all know a thicker belt will make it run faster correct? When i say thicker i dont mean top to bottom. I mean the thickness of the belt itself. Obviously a thicker belt will make these tables run faster. Its unfortunate that all ebayers sell the thicker belt only. Ive bought them all, so i know. So, you think you have the right belt, and you test speed, to find out it usually runs at a constant 34.0 RPM's. Or, you can move the capstan down and let it sit at the top of the lip and it'll usually slow speed down, but you'll get noise due to the belt rubbing the selector switch. There is also the shaving of the capstan (which ruins it). You can also put tape around the platter. These to me are all just band aids. I searched high and low for the right belt, and finally i found it. Sits on the middle of the capstan, speed is dead on 33 1/3. By the way, your table isn't supposed to run fast by design like some have said in the past. The PL-41 & PL-50 are supposed to have a belt thats supposed to be the correct thickness and it'll run on perfect speed. Im now fully enjoying my PL-41 & 50 tables.
 

Attachments

  • 20141021_204540.jpg
    20141021_204540.jpg
    45.2 KB · Views: 155
  • 20141015_222707.jpg
    20141015_222707.jpg
    42.2 KB · Views: 149
  • 20141020_191256.jpg
    20141020_191256.jpg
    40 KB · Views: 160
We all know a thicker belt will make it run faster correct? When i say thicker i dont mean top to bottom. I mean the thickness of the belt itself. Obviously a thicker belt will make these tables run faster. Its unfortunate that all ebayers sell the thicker belt only. Ive bought them all, so i know. So, you think you have the right belt, and you test speed, to find out it usually runs at a constant 34.0 RPM's. Or, you can move the capstan down and let it sit at the top of the lip and it'll usually slow speed down, but you'll get noise due to the belt rubbing the selector switch. There is also the shaving of the capstan (which ruins it). You can also put tape around the platter. These to me are all just band aids. I searched high and low for the right belt, and finally i found it. Sits on the middle of the capstan, speed is dead on 33 1/3. By the way, your table isn't supposed to run fast by design like some have said in the past. The PL-41 & PL-50 are supposed to have a belt thats supposed to be the correct thickness and it'll run on perfect speed. Im now fully enjoying my PL-41 & 50 tables.

So, it's a secret, right? :)

John
 
No lol. I just didnt post the link because i wasnt sure i was allowed to.

As long as you're not affiliated with the vendor, you're good. If you're still uncomfortable, just give the brand and description or simply the vendor name instead of a link.
 
As long as you're not affiliated with the vendor, you're good. If you're still uncomfortable, just give the brand and description or simply the vendor name instead of a link.

Will do. Im not affiliated with the seller.
 
I usually have a pretty good grasp of mechanical action, but I cannot figure out how the thickness of a rubber belt matters when the motor pulley and platter are both on the inside.
 
Same thing is true for the Thorens tables that don't have speed adjust. One MUST buy the real Thorens belt for dead on balls accurate speed. Otherwise, all bets are off and money keeps pouring out the door for 10 dollar belt after ten dollar belt. Getting the Thorens belt, expensive to some (ah most) at about 33 from Qaudio in the US provides a good few/many years of accurate speed.

I just check pioneer parts and the belt of the PL-41 was 37 and change and shipping, another ouch but again years of accurate speed.

Now where is it the OP is getting his belts?
 
Last edited:
I usually have a pretty good grasp of mechanical action, but I cannot figure out how the thickness of a rubber belt matters when the motor pulley and platter are both on the inside.

A belt driven by a syncro motor has to slip on the drive pulley. depending upon how many poles are in the motor determines how fast the pulley face is accelerating to latch. Under acceleration the pulley surface must slip past the belt. between the poles in the motor is the "stall" time. during stall the belt must slip past the pulley (being driven forward by the main platter).

regarding belt thickness, the belt has to "average", not only slip, but average itself due to its material makeup. the thicker belt averages itself to a larger diameter. take the inside circumference of the belt and then the outside circumference, "average" that number, vs a proper thickness belt "average, and that is how much larger the pulley surface becomes.

If one measures a drive pulley circumference, and multiplies that number by its RPM, and then measure the circumference of the driven platter and multiplied by 33.33 the table, if the belt was in pure static friction during play, it would run slow. The numbers for an AR are as follows. The distance traveled in 1 minute at pulley surface is 768.12". The distance traveled at subplatter surface in 1 minute is 787.32" Now to further complicate this, I'll add half the belt thickness to the pulley dimentions and that distance the center thickness has traveled in 1 minute is 782.25" The outside of the belt will travel 796.40". As you can see, the center of the belt is running very near the same distance as the subplatter.
 
A belt driven by a syncro motor has to slip on the drive pulley. depending upon how many poles are in the motor determines how fast the pulley face is accelerating to latch. Under acceleration the pulley surface must slip past the belt. between the poles in the motor is the "stall" time. during stall the belt must slip past the pulley (being driven forward by the main platter).

regarding belt thickness, the belt has to "average", not only slip, but average itself due to its material makeup. the thicker belt averages itself to a larger diameter. take the inside circumference of the belt and then the outside circumference, "average" that numb
er, vs a proper thickness belt "average, and that is how much larger the pulley surface becomes.

If one measures a drive pulley circumference, and multiplies that number by its RPM, and then measure the circumference of the driven platter and multiplied by 33.33 the table, if the belt was in pure static friction during play, it would run slow. The numbers for an AR are as follows. The distance traveled in 1 minute at pulley surface is 768.12". The distance traveled at subplatter surface in 1 minute is 787.32" Now to further complicate this, I'll add half the belt thickness to the pulley dimentions and that distance the center thickness has traveled in 1 minute is 782.25" The outside of the belt will travel 796.40". As you can see, the center of the belt is running very near the same distance as the subplatter.

Better than i ever could have explained it. Lol
 
I was glad to help. I just knew that PL-41 tables can play spot-on, with no need for shaved/machined capstains or tape on things to do it. You did a lot of the figuring as to the 'why' behind the reason yours weren't behaving.
I had simply gotten lucky and blundered onto the correct belt long ago.
 
PRB specifies their FRX-35.1 belt for both tables, the PL-41A/D and PL-50.

The FRX belt this length is .184 thick so it should be the right belt. There are a few other 35.1 belts of other thicknesses. I don't know if the FRX will work or not. My thorens has the right belt as should your table.
 
Last edited:
A belt driven by a syncro motor has to slip on the drive pulley. depending upon how many poles are in the motor determines how fast the pulley face is accelerating to latch. Under acceleration the pulley surface must slip past the belt. between the poles in the motor is the "stall" time. during stall the belt must slip past the pulley (being driven forward by the main platter).

regarding belt thickness, the belt has to "average", not only slip, but average itself due to its material makeup. the thicker belt averages itself to a larger diameter. take the inside circumference of the belt and then the outside circumference, "average" that number, vs a proper thickness belt "average, and that is how much larger the pulley surface becomes.

If one measures a drive pulley circumference, and multiplies that number by its RPM, and then measure the circumference of the driven platter and multiplied by 33.33 the table, if the belt was in pure static friction during play, it would run slow. The numbers for an AR are as follows. The distance traveled in 1 minute at pulley surface is 768.12". The distance traveled at subplatter surface in 1 minute is 787.32" Now to further complicate this, I'll add half the belt thickness to the pulley dimentions and that distance the center thickness has traveled in 1 minute is 782.25" The outside of the belt will travel 796.40". As you can see, the center of the belt is running very near the same distance as the subplatter.

Thank you for the technical explanation! :thmbsp:

Usually my brain grabs this stuff quickly, without over-thinking it. This one just had me stumped.
 
I was glad to help. I just knew that PL-41 tables can play spot-on, with no need for shaved/machined capstains or tape on things to do it. You did a lot of the figuring as to the 'why' behind the reason yours weren't behaving.
I had simply gotten lucky and blundered onto the correct belt long ago.

Yeah, major process of elimination. Im just glad that its all sorted out. I knew that the right belt would eliminate the speed issue as well.
 
Back
Top Bottom