Pioneer PL 50 runs too fast

[boreas]

The aluminum tape I have is very thin -- 0.0025", as opposed to 0.0065" for the electrical tape. The electrical tape is also very shiny and smooth, but maybe less so than the aluminum. However the subplatter on my tt is pretty smooth and polished as well. I haven't tried either though, so I don't know.

I didn't realize the stuff you were working with was that thin. If it's not too slippery it should work well. It'll also look a lot better than black electrical tape.

John

 

[keithpgdrb]

A followup post -- after installing a bathroom vent last year, I have a roll of high quality aluminum tape left over. Wouldn't that be better than electrical tape? Ie, the platter is aluminum, therefore at least the belt's contact surface is the same material. Also, the aluminum tape would potentially flatten better, being metal and all. Thoughts?

I may try it this weekend. Any idea how thick a layer it requires?

been out of the loop for a little bit here. I think that the aluminum tape sounds fine. If there is any slipping, it would be on startup and wind down. There shouldnt be much actual pulling after it gets started.

I also think the aluminum tape may be the way to go, because of consistent thickness. it shouldnt stretch like electrical tape.

I was actually thinking about aluminum tape. Although, I dont think its the material that is a possible issue, its the adhesive. I am afraid the stuff will ooze over time.

as far as how much. the ONE person who mentioned using tape says he ended up putting on about 3mm of tape. that sounds like a lot, but who knows. anything is worth a shot.

 

[boreas]

as far as how much. the ONE person who mentioned using tape says he ended up putting on about 3mm of tape. that sounds like a lot, but who knows.

It does. We're talking about a 4% speed error here so it seems to me (without doing any calculations or testing at all) that changing the circumference of the inner platter by 4% would at least get you very close.

• So, you'd take the diameter of the inner platter and multiply by Pi (3.1416) to give you the circumference.
  
• Then multiply that figure by 1.04.
  
• Divide that figure by Pi to get your new diameter.
  
• Subtract the "old" diameter from the new.
  
• Divide by two and that gives you the necessary thickness of tape.

I think.

John

 

[keithpgdrb]

It does. We're talking about a 4% speed error here so it seems to me (without doing any calculations or testing at all) that changing the circumference of the inner platter by 4% would at least get you very close.

• So, you'd take the diameter of the inner platter and multiply by Pi (3.1416) to give you the circumference.
  
• Then multiply that figure by 1.04.
  
• Divide that figure by Pi to get your new diameter.
  
• Subtract the "old" diameter from the new.
  
• Divide by two and that gives you the necessary thickness of tape.

I think.

John

wow, thats a lot of math.

 

[keithpgdrb]

Just an update, and interesting results. I ended up just giving up on the idea of changing the cap. Pretty much everyone said it wouldn't do anything, and I got really busy. I may change it later.

So, I taped the platter with electrical tape. Not thrilled, but it did work. I actually have a play along record where the first track is a tuning note. I fed the audio into my digital chromatic tuner. Pretty much sits dead in tune now.

Interestingly enough, I did this with the old wider thinner belt. When I installed the newer belt, the table went way too fast. By a half step almost. Very interesting because they are both supposed to be pl50 belts, and are the same length. So it seems the wider belt made the change with the tape, while the newer narrower thicker belt pretty much hardly changed the pitch at all. The new belt also fits tighter.

So anyway, I'm going to try to return the new belt, and then I'll struggle when this one wears out. I can see why some people hate belt drives.

One side note. It is indeed amazing how much the sound opens up when it's at the correct speed. Everything is fuller and richer. This is what I was hoping for.

 

[Metalownz]

I had this issue with my newly owned PL-50 running too fast, and i just unscrewed the pulley that the belt wraps around, pushed it down till the belt was close to the top, then tightened the screws, problem solved.

 

[jimbofish]

It does. We're talking about a 4% speed error here so it seems to me (without doing any calculations or testing at all) that changing the circumference of the inner platter by 4% would at least get you very close.

• So, you'd take the diameter of the inner platter and multiply by Pi (3.1416) to give you the circumference.
  
• Then multiply that figure by 1.04.
  
• Divide that figure by Pi to get your new diameter.
  
• Subtract the "old" diameter from the new.
  
• Divide by two and that gives you the necessary thickness of tape.

I think.

John

Your geometry is right. :yes:

Math-wise, though, I believe you can simplify the calculations by just multiplying the original diameter by .04 and dividing by 2. :scratch2: Some of the calculations can be canceled out algebraically.

 

[SoundsRight]

When needing to measure RPMs accurately I would recommend getting an RPM meter (tachometer). They can be very cheaply purchased on Ebay and work well. There are non contact types using a laser diode and read RPM by placing a small piece of reflective tape on the platter or disc and pointing the laser at it.

Here is one similar to the one I got:

Digital Tachometer

Just search Ebay for "Digital Tachometer" there are many suppliers. They work well and are cheap.

What I did was get an old LP I did not like and on one side I put a single reflector piece to measure RPM, and on the other side of the LP I put 10 reflectors precisely spaced at 36 degrees. Using the 10 reflector side the meter reads the RPMx10, so just divide by 10 for an improved average and double digit accuracy.

Maybe I can post some pictures later.

SoundBound

 

[ukfan4sure!]

Change the belt. I've worked on a lot of turntable and, in my experience, 9 times out of 10 changing the belt will correct the speed problem. Small variations in belt diameter, width or thickness can cause the speed to be off. It helps to have a stock of belts available to try to find the one which works right. I have to do this on a regular basis. How wide is your replacement belt? Most Pioneer turntables want narrow belts (around 0.185") but many vendors sell ones of 0.2"-0.25" width and claim they are the right ones.
Rick

For everyone out there buying replacement belts off of that famous auction site, this bit of advice is spot on. I have also experienced this problem with belts purchased.

When I told the seller of the belts about the THICKNESS (not width in my case as Rick reports above) problem, he told me basically I was nuts, but did a refund to avoid a conflict. I wasn't even asking for that. I was simply telling him his belts didn't meet spec and would cause it's intended turntable to run fast. He needed to be aware of that. His belts measured at 0.032 inches and spec on the old belt (the original) showed 0.024 inches.

The problem is, the platter speed is based on the effective diameter of the pulley/belt combo. If the belt is thicker, it adds to the total ratios. Trust me, it's true! Here is an exerpt from a posting on Audio Asylum from a while back.

"...As I understand it the rotational speed is a function of the size of the pulleys and the belt thickness. This is because, contrary to what you might think is logical, the length of the belt has to be measured at its center of thickness. Think of bending a rubber tube around something round. The inner diameter will compress and the outer diameter will stretch.

There's a name for this phenomenon, but I can't think of it. I think that when mechanical engineers are spec'ing pulley's there is a formula that takes into account the belt thickness and compensates. That little bit of compression will affect the turning ratio of the pulleys.

Think that if you have two pulleys of the same size it would not matter what the thickness of the belt is. But if two different size pulleys their different diameters will affect the amount the amount of compensation that has to be calculated...."
.

 

[Sprague]

just bought one of these (4,000 yen I couldnt very well just leave it in the shop)