Turntable New Belt Speed Error

I ordered new belts for my 2 Pioneer PL-50's off the famous auction site.

Immediately I noted a marked change in the pitch and speed of my music.

I had read about these happenings before upon belt replacement and had found a profuse number of possible reasons for this. Some said motor bearing load. Others say dirt on the capstan. And one stab said something about belt width or thickness. I really didn't know anything but I was definitely disappointed.

Research time.... :yes:

OLD BELT -- 0.2 inches wide, 0.025 thick, I assume slightly stretched in length.
NEW BELT -- 0.2 inches wide, 0.035 thick, I assume like new at 35.1 in length. Supposedly an original FRX35.1

Speed check: 100 revolutions on the stopwatch (should take 180 seconds)

TT 1:

NEW BELT -- 173.3/180 seconds = 3.72% error
OLD BELT -- 176.5/180 seconds = 1.94% error

3.72% - 1.94% = 1.78% induced error by new belt.

TT 2:

NEW BELT -- 172.0/180 seconds = 4.22% error
OLD BELT -- 175.3/180 seconds = 2.61% error

4.22% - 2.61% = 1.83% induced error by new belt.

My measurements show a difference of a mere 0.05% between the two turntables measuring both of the two belts (old vs new) on two different turntables of the same make/model.

SO.....

Does the effective addition of the belt thickness (.010) give me THIS much error?

No one will ever convince me thickness of the belt doesn't matter at this point.

I had a similar problem with my Dual a few years ago. The new belt was something like 0.025 or 0.028 inches thick, and the platter spun fast enough that even cranking the pitch control fully negative still wasn't slow enough. Installing the proper belt (0.019 inches thick) restored proper operation.

Hello.

I noted the same effect when, years ago, I replaced the belt on my Pioneer PL-514 for the first time. Obtained a PRB belt from a local electronics outlet, installed it, placed Elvis Costello on the platter, and immediately noticed that the pitch was higher.

I initially thought that the tightness of the belt was the issue, but, after obtaining a second replacement belt from another source (same tightness but thinner) the Pioneer's speed returned to normal. A friend once told me that it had to do with an average of the inner and outer rotational speeds of the belt, but I'm not enough of a physics major to qualify that.

Good luck!

I'm totally convinced that thickness is an issue to be reckoned with....

These belts being sold on e*ay are probably an issue. Supposedly, this is an original FRX35.1. I'm not sure what that thickness is supposed to be, but it's definitely different than my old one and has increased my speed by 2%.

Not good. :scratch2:

If the belt is thicker the speed should increase. But, what is causing it to be slow is too much friction. Your motor is syncronous, it will not run slow. It will run at speed or it doesn't run. Your drive pulley circumference X (motor) RPM will be a shorter distance than the driven circumference X 33.33 rpm. The belt "latches" onto the acceleration of the drive pulley as it launches from pole to pole. That "average acceleration" speed is higher than actual motor speed. If the belt doesn't have enough slip in it, it will run slow.

Clean the belt of mold release agents, clean the drive pulley of all old belt material, clean the driven surface. Put your new belt into a baggie with a little baby power (the type with talc, not corn starch) and shake it up until the belt is coated. Use gloves to install the belt. The speed should be more correct.

marcmorin said:

If the belt is thicker the speed should increase. But, what is causing it to be slow is too much friction. Your motor is syncronous, it will not run slow. It will run at speed or it doesn't run. Your drive pulley circumference X (motor) RPM will be a shorter distance than the driven circumference X 33.33 rpm. The belt "latches" onto the acceleration of the drive pulley as it launches from pole to pole. That "average acceleration" speed is higher than actual motor speed. If the belt doesn't have enough slip in it, it will run slow.

Clean the belt of mold release agents, clean the drive pulley of all old belt material, clean the driven surface. Put your new belt into a baggie with a little baby power (the type with talc, not corn starch) and shake it up until the belt is coated. Use gloves to install the belt. The speed should be more correct.

Click to expand...

Nothing about the motor is running slow. The platter RPM is running fast apparently by the increased effective pulley diameter created by the thicker belt (I assume). Am I missing something?

ukfan4sure! said:

Nothing about the motor is running slow. The platter RPM is running fast apparently by the increased effective pulley diameter created by the thicker belt (I assume). Am I missing something?

Click to expand...

No, I mis-read your speed calc's. I agreed with you in my opening statement about belt thickness should increase speed. And for the reason you state.

My PL-50 also ran fast. There are two screws on the capstan, what i did was loosen the screws so the capstan can be pushed down a bit. I pushed it down till the belt runs at the top of the capstan. It cured my 33 1/3 problem, but still runs a tad fast on 45. I may try the baby powder solution. I think what also happens are these new belts need time to wear a tad before speed slows down. Try running the tt for about 3 hours while your doing something else. I love my PL-50, and wouldnt give up on this speed issue.

Metalownz said:

My PL-50 also ran fast. There are two screws on the capstan, what i did was loosen the screws so the capstan can be pushed down a bit.... Try running the tt for about 3 hours while your doing something else. I love my PL-50, and wouldnt give up on this speed issue.

Click to expand...

Thanks, I'll give both of those a shot. :thmbsp:

marcmorin said:

If the belt is thicker the speed should increase. But, what is causing it to be slow is too much friction. Your motor is syncronous, it will not run slow. It will run at speed or it doesn't run. Your drive pulley circumference X (motor) RPM will be a shorter distance than the driven circumference X 33.33 rpm. The belt "latches" onto the acceleration of the drive pulley as it launches from pole to pole. That "average acceleration" speed is higher than actual motor speed. If the belt doesn't have enough slip in it, it will run slow.

Clean the belt of mold release agents, clean the drive pulley of all old belt material, clean the driven surface. Put your new belt into a baggie with a little baby power (the type with talc, not corn starch) and shake it up until the belt is coated. Use gloves to install the belt. The speed should be more correct.

Click to expand...

I am also having an issue with a new belt on a PL-50 (too slow), and I am going to try the talc because other interventions have failed, but I have a question. It seems counter-intuitive that, when a platter is going too slow, one would want more slip in the belt. I would think that the slip would interfere in the energy transfer from the pulley to the platter.

I just replaced the spindle bearing and sprayed a little WD-40 down the spindle. Is there another type of lubricant that I should use around the spindle?

Regards,

D-Ray

It would seem to me that even if the belt was thicker if it's just a 2 pulley system how can belt thickness possibly make a difference?

The motor and platter drive contact the inside of the belt.

Weather it's paper thin, or an inch thick the effective distance the belt travels on the "Inside " of it's loop has to be the same. The inside of the belt is the only part that touches the pulleys.

When I put a new belt on my old Rega there was Crud built up on the motor and platter drive contacts. This crud effectively increased the size of those "pulleys " . Pulley size affects speed. I cleaned them well and was amazed how much gunk had built up over the years. ( Dust, smoke residue, crumbled belt material, etc )

Could it be that using a table with an old slipping belt playing just slightly slower than it should makes the new belt which doesn't slip seem "Fast" ?

Or am I totaly out to lunch?

d-ray657 said:

I am also having an issue with a new belt on a PL-50 (too slow), and I am going to try the talc because other interventions have failed, but I have a question. It seems counter-intuitive that, when a platter is going too slow, one would want more slip in the belt. I would think that the slip would interfere in the energy transfer from the pulley to the platter.

I just replaced the spindle bearing and sprayed a little WD-40 down the spindle. Is there another type of lubricant that I should use around the spindle?

Regards,

D-Ray

Click to expand...

Hey, Don!

I'd probably want to clean all the WD-40 out of there. I and others have had good luck on these and the similar brg. ass'y on the PL-41 using a 30 wt. synthetic motor oil like Mobil 1.

Enjoy the PL-50!

John

Have you used a strobe disk to check it? Several free for the printing out there...

Chip

Chip Chester said:

Have you used a strobe disk to check it? Several free for the printing out there...

Chip

Click to expand...

A strobe disk isn't really very precise. It tells you whether your table is fast or slow, by a little or a lot. The stopwatch method the OP used allows you to quantify the degree of error rather than simply observing it.

John

The Lenline disk over at vinylengine has some direct-reading speed error ring patterns. A disk with many direct-reading error rings for 33 1/3 would make a good quick project for someone... and could be hosted here for d/l as required.

There's always this: http://platterspeed.com/#top
and probably several others.

Note that the stylus should be engaged in the groove while using a strobe disk to verify speed. The "drag", such as it is, is greatest when the stylus is at the outer edge of the program material.

Keep in mind that an FRX31.5 although an original FRX35.1 is a replacement belt from a rubber belt vendor, NOT A PIONEER BELT for this turntable. That can make a big difference.

noise gate said:

It would seem to me that even if the belt was thicker if it's just a 2 pulley system how can belt thickness possibly make a difference?

The motor and platter drive contact the inside of the belt.

Weather it's paper thin, or an inch thick the effective distance the belt travels on the "Inside " of it's loop has to be the same. The inside of the belt is the only part that touches the pulleys.

When I put a new belt on my old Rega there was Crud built up on the motor and platter drive contacts. This crud effectively increased the size of those "pulleys " . Pulley size affects speed. I cleaned them well and was amazed how much gunk had built up over the years. ( Dust, smoke residue, crumbled belt material, etc )

Could it be that using a table with an old slipping belt playing just slightly slower than it should makes the new belt which doesn't slip seem "Fast" ?

Or am I totaly out to lunch?

Click to expand...

As the belt wraps around the pulley it creates an effective diameter that is not equal to the surface diameter. It does the same as it wraps around the platter. If you increase the belt thickness, you increase that effective diameter by a higher ratio at the pulley than at the platter and therefore speed up the turntable.

OK, I disassembled the spindle again and got all of the WD40 cleaned out. Replaced it with turbine oil (Too damn cold to get out to get Mobile 1). When I put the platter back on the spindle and gave it a manual spin, it spun freely for several minutes. I thoroughly cleaned the platter and the belt. Reattached the belt and the platter was running about two seconds long for 33.3 revolutions. I timed 100 revolutions at 3:06. Let it spin for awhile, and after 20 minutes or so, it was running 33.3 spot on at 1:00. Confirmed it with my ears playing some Stevie Guitar Miller.

I figured that there might be some old lubricant in the motor, but also figured that it might not be a good idea for a klutz to disassemble the pulley motor to clean it out, so I tried a drop of oil right under the base of the pulley. It's still running at the correct speed, so I'll let it get cold overnight and see how it starts up tomorrow. Thanks for the ideas so far.

Regards,

D-Ray

That's great, Don!

John

Belt width is more the factor here. Although, if a belt is thicker than the original, it may not decrease in width slightly when stretched like the original.

Most motor pulleys on vintage tables are larger in diameter at the center. So, the wider a belt is, the more it extends to the larger part of the motor pulley, making the speed faster. If the table's running fast, the belt may be a bit too wide. Or, a slightly thinner or shorter belt may stretch a bit and cause the belt to become a bit narrower and ride at the correct point on the motor pulley.