Vintage Pioneer turntable speed issue--advice wanted

Discussion in 'Audio Hardware' started by drh, Sep 4, 2007.

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  1. drh

    drh Talking Machine Thread Starter

    Today, using a KAB Speedstrobe, I checked a recently-acquired Pioneer PL A-45D turntable and was surprised to find that both speeds are steady but noticeably too fast. The table has no pitch control. It has no evidence of trim pots, either; all I could find was the board pictured below, which I presume is a speed control circuit, since the power mains go directly into it and leads on the other side go directly to the motor. (Note: the slider switch is to select between 120 and 240 volts; it's set to 120.) I have not replaced the belt, but I would have expected belt problems to manifest as wobbly or slow rotation. Any suggestions about how to reset the speed?

    Oh, I should add that the automatic start/reject/shutoff mechanism seems to be working OK--it isn't interfering with the rotation, as far as I can tell.
     

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  2. crooner

    crooner Tube Marantzed

    Location:
    San Diego, CA
    The belt drive Pioneers use synchronous AC motors, so the speed is dependent on the condition of the belt and of course, the line frequency. Have you checked the main bearing? The motor might also need lubricating.

    The board in your picture looks too simple to be a frequency generator servo.
     
  3. Rolf Erickson

    Rolf Erickson New Member

    Location:
    Los Angeles, CA
    Hmmmm...

    Seems to me if you have a single speed motor locked to 60 Hz... (We have established that you have no table generated oscillator frequency controlled motor drive, Yes? Just an AC syncro motor, Yes?) It can only run FASTER than normal if... The AC line frequency is somehow higher than 60Hz.. (highly unlikely) The motor or pulley is a 50 Hz unit? (not probable unless intended for use in Europe) .. Or, if the belt has slipped off the pulley area it should ride on, and has started to ride on the rim or other portion of the pulley that is not correct. Slipping would not run faster, poor lubrication would not run faster. Check to see if the belt is running EXACTLY on the correct pulley area and not riding elsewhere. Clean it also, perhaps some build-up of residue is changing the diameter of the pulley. Hope this helps. R.E.
     
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  4. drh

    drh Talking Machine Thread Starter

    Indeed it did! I checked again this evening and tried playing with the speed lever. I noticed that when I swithed from 45 to 33, the platter would run "on speed" for maybe a second or so and then speed up; further investigation revealed that moving the lever about halfway between the marked "33" and "45" would yield a pretty good 33. Apparently, the belt is indeed running in a slightly "wrong" area of the pulley (assuming that the slowing wasn't from friction between the belt and the "derailleur" that throws it between speeds). I guess I need to see whether I can adjust the "derailleur." Or could this be a "worn out belt" issue?
     
  5. Using something like a q-tip with a dab of alcohol to clean the pulley could help. I've done that and been suprised at the amount of gunk that came off.
    Replacing the belt would also be par for the course. Just have to make sure you get one that's an exact match for your TT model.
     
  6. Rolf Erickson

    Rolf Erickson New Member

    Location:
    Los Angeles, CA
    Go for a new belt and thourogh cleaning of all running surfaces.

    Yes, I suspected something like this. Your belt may have stretched enough to ride, "wrongly" on the rim or incorrect areas of the pulley. It will harm nothing to replace it with a new proper sized belt. This alone may solve the problem. But also clean the entire running surface of any foreign residue. This will not harm anything, and may, even by itself, solve the problem. Otherwise, do check the "De-railer" alignment. Good luck. Rolf.
     
  7. I have the answer!!!!! Two years ago, I had a Pioneer PL-A35 turntable that I gave to a friend, and encountered the same exact problem. Because I knew to expect this, I ordered belts from two different sources. The first brand-new belt (a bit less elastic) caused it to play too fast (as mentioned above). The second brand-new belt (a bit more pliable) was installed, and guess what? Perfect speed! I had the same issue with a Sansui SR-4050C turntable, tried 3 different belts and the closest belt caused it to play "ever-so-slightly" slow. To correct this, I was able to do a tweak that was mentioned a few times. I did the "fingernail polish" (or touch up pen) trick - simply touch a small amount onto the spinning pulley, let it dry, and reinstall the belt. Too much, it'll run too fast (use lacquer thinner to remove a little, if there is too much) - it may take a few tries. Other than an expensive VPI SDS, Clearaudio Synchro, or Pro-Ject Speedbox, the aforementioned solutions mentioned the cheapest and easiest ways to go.
     
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  8. oops, I didn't quite read the whole story ....if the problem is occuring with the old belt, it is likely slipping down and riding on the 45 rpm part as mentioned in the other responses (but I often replace the belt before it even gets to this point). Still, I felt it was necessary to mention my encounter with a fast speed issue after installing a brand-new belt(because some of the aftermarket belts, though they'll fit, are not the same composition and have a different "grip", causing it to be off-speed). Unfortunately, finding a replacement belt for a turntable where the original belt is unavailable can sometimes be a game of "trial and error" to get it right. Hope my advice helps in respect to getting the speed correct with a replacement belt. Best wishes.
     
  9. drh

    drh Talking Machine Thread Starter

    Thanks for the insights! I picked the table up at our local thrift store for $6 a couple of weeks back, so this was my first checkout with any care. I think it was so cheap because the belt was not installed on the pulley in the store and the clerks thought the table didn't work. Aside from lacking a headshell (and I already have a cheap spare headshell that will fit), the thing is in absolutely beautiful condition--not even any scratches on the dust cover (albeit plenty of dust *under* it! ;) ).
     

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  10. keith65

    keith65 Forum Resident

    Location:
    Denmark
    Didn't want to start a new thread. I have the same problem with my Pioneer PL-10 and PL-15d. They both run a tad too fast, just so much that it doesn't feel quite right to me, probably 2-3 seconds off for a standard track. Would a speedbox fix this problem? Or is it just how these belt Pioneer turntables are? I would really like these turntables to run perfect speed, and have tried 3-4 different belts, cleaned all parts etc...:cry:
     
  11. Nate

    Nate Forum Resident

    Once had a pl15d which ran fine once I had a good belt on it. A speed of would allow you to tweek speed
     
  12. Antares

    Antares Forum Resident

    Location:
    Flanders
    Too fast is easy. Just put one or more layers of (non-shiny) electricians tape on the belt path under the platter to enlarge the diameter. You can also try Dymo labeler style stock which is a bit thicker, so one layer may suffice. Be sure to make clean seams, no overlaps.
     
  13. keith65

    keith65 Forum Resident

    Location:
    Denmark
    Thanks Antares, I will try to experiment, but shouldn't there be a better solution, or were these Pioneers designed to run a bit on the fast side? Seems a bit odd if they were, cause they were widely popular and some of the best selling turntables ever.
     
  14. Antares

    Antares Forum Resident

    Location:
    Flanders
    Possible that manufacturers erred a bit on the fast side as that will always sound better than slow (just look at all the posts and threads about (even expensive) Rega tables here). If you're looking for an electronically regulated solution, it will get expensive quick (unless you're a DIY specialist maybe), and probably not warranted for a simple vintage table. I use the electrical tape trick on my Sansui too and can only recommend it.
     
    keith65 likes this.
  15. Robin L

    Robin L Musical Omnivore

    Location:
    Fresno, California
    I got the speed down on my Strathclyde 305-m by carefully cleaning the pulley attached to the motor. Though the residue on the pulley was nearly invisible, using a 'magic eraser' and narrow strips of fine sandpaper did the trick.
     
  16. keith65

    keith65 Forum Resident

    Location:
    Denmark
    Interesting, thanks. I have cleaned the pulley with a swamp and mild water/soap, not much difference. Maybe I should try magic eraser or some isopropyl.
     
  17. keith65

    keith65 Forum Resident

    Location:
    Denmark
    I find it a bit strange that a lot of these vintage belt-driven turntables don't have pitch control, especially the more expensive ones like Thorens, Sansui, Pioneer etc. My old cheap mid 60s beogram has pitch control, it just makes everything easier and more listenable at the correct speed.
     
  18. keith65

    keith65 Forum Resident

    Location:
    Denmark
    Update, cleaned the pulley shaft and the inner platter where the belt runs. I thought I had cleaned it all but this time I decided to clean it extra good, and guess what it helped. The speed is within listenable limit now. Not sure if it runs perfect, but defintely more like it should. So if any of you have trouble getting the right speed on your old Pioneers, try cleaning all surfaces where the belt runs really good, as Robin L also suggested, it might be the solution. :)
     
  19. The Pinhead

    The Pinhead SLEAZY SOUTHAMERICAN CAVEMAN

    My Pioneer belt driven TT made me so mad I sold it and bought a direct drive one.
     
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  20. McLover

    McLover Forum Resident

    Location:
    East TN
    Pioneer belt drives need clean pulleys and inner platter surfaces. And are more than a bit picky about belts being correct length, width, and thickness. Follow those guidelines and have the speed lever linkages adjusted correctly and good non-sagging motor mounts, you will have a better relationship with your Pioneer. And really, my advice applies to all belt drive turntable owners old and new.
     
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  21. quadjoe

    quadjoe Forum Resident

    I bought a Pioneer PL-10 new in February of 1975, and I never had a speed issue with it. I don't think that Pioneer tables of that vintage ran fast, as I never heard anyone complain of it back then, nor did I read that in any reviews in audio magazines. However, as these tables are now approaching 40+ years of age, I'm not surprised that there could be issues, though in all likelihood, the problem is that there is a problem with the belt, as others have suggested. I no longer have the PL-10 as I sold it in 1990 because I couldn't get a belt for it (that was pre-internet days for me.)
     
  22. quadjoe

    quadjoe Forum Resident

    I had an early '80s Pioneer direct drive table that couldn't keep a steady speed (bad electronic control module) that was repaired 3 times under warranty. I believe it was a model PL-5, and it ended up in the trash. I bought a new belt for my PL-10, and kept using it for another 7 years. It's interesting that different people have different experiences. I did really like how the PL-5 sounded when it worked. It's a shame, really. The repair guy said that he worked on a lot of that particular model for the same complaint. You'd have thought that it would be the automatic functions that would cause issues.
     
  23. The FRiNgE

    The FRiNgE Forum Resident

    About the belts, the thickness and pliability do make a difference. The width of the belt also makes a difference. Not all replacement belts are exactly the same width, give or take a small amount of tolerance. The +/- tolerance makes a difference. Also as a belt becomes stretched, the speed will change.

    I will attempt to explain the reason why. The synchronous motor runs at constant speed, so the type of belt does not change the motor speed. (your speed problem has nothing to do with the motor) The platter speed changes occur as the belt centers on the small pulley, and encounters a small amount of friction and slippage. The typical pulley is machined on an arc to center the belt. A flat pulley would theoretically turn the platter at speed always, regardless of belt tension and size, but would not center. So in the real world application, the belt would not self center, so it would ride to one of the rims and drag, causing terrible speed fluctuations.

    The curved arc centers the belt. BUT the design requires the belt to wrap somewhat on the smaller part of the pulley, which slows the speed. A belt too loose will not apply enough tension to contact the smaller (flanks) part of the pulley, which it must do to turn the platter at the correct speed. Again, there is some inherent self slippage and friction as the belt wraps around the arc of the pulley (I should draw a diagram to illustrate this) The slippage and friction is normal, and must be just right for the platter to turn at the correct speed. (The belt does not slip around the pulley per se, the slippage is localized on the pulley, the physics involved in self centering and turning the platter at correct speed)

    http://ww2.justanswer.com/uploads/benimur/2010-06-21_151959_Turntable_Belt.jpg

    The speed will increase when:
    1) the belt becomes stretched
    2) the belt is too narrow
    3) the belt is too thick

    I apologize if I am not clear on the physics involved. Belt TT's are finicky. It's important to replace with exactly the right belt. Plus as mentioned by our fellow hifi enthusiasts in this discussion, the pulley must be clean, and can accumulate invisible deposits and/or petina.
     
    Last edited: Dec 11, 2014
  24. The Pinhead

    The Pinhead SLEAZY SOUTHAMERICAN CAVEMAN

    Don't recall what model mine was but the friggin' belt WOULD not stay where it was suppossed to on the platter pulley, causing audible speed variations. Direct drive has been the only way to go for me ever since.
     
  25. quadjoe

    quadjoe Forum Resident

    There is a definite life span for turntable drive belts, and when they get just a little stretched that's exactly what happens. If the motor or platter pulleys or the belt have even the slightest trace of oil it could also cause that problem. I remember when I first got my PL-10, the owner's manual was very clear on not touching the pulleys or the belt with your bare hands, they actually included a ribbon to use to place the belt on the motor pulley. Radio Shack in those days sold a product called belt dressing, that conditioned the rubber, gave it more "grip", and extended its life. You could also use it on the drive belts in tape decks as well, and I used it for years. In the 15 years I owned that turntable, I only had to replace the belt twice.

    I can see how speed variations could cause you to switch to direct drive. I've had two Technics DD tables, and both have rock steady speeds. I had a Sony belt drive table that had such inaccurate speed it was completely unsuitable for classical music, or any slow music with sustained notes for that matter. That said, most better quality belt drive tables have very good to excellent speed stability (below the threshold of audibility), so if you ever decide to try one out, I doubt you'd be disappointed.
     
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