I got a Pioneer Pl-12 turntable from a friend who had it stored away for years. I cleaned it up but have found that some voices have a higher pitch compared to the CD version. I tried the free strobe disks and they verified my fears about the platter turning (I assume) too fast. I also measured similar songs from CDs and albums, and the albums always finish sooner. From some rough time estimates, the turntable is running about 3% too fast.
Looking from the bottom side up on the turntable, there are no adjustments and very little electronics at all. The only electronics are: the motor with a few wires running to it; an enclosed switch to select 115/230 voltable, and a somewhat large capacitor (I think). The "capacitor" has a rating of 0.1 uF and some serial numbers.
I suspect the "capacitor" is old or burnt or whatever. I doubt the voltage switch is the prolem, nor the motor, but who knows?
Any ideas? I have a voltage meter so I can measure the usual volts, ohms, or ampere, but I don't have an oscilloscope to measure frequency.
The turntable is not perfect but it is much better. From several internet searches I found that the original belt was possibly too thick and a tad long. I had great hopes for a new thinner belt and it did slow down the turntable, but not nearly enough.
The next fix was to get out the emery cloth and start sanding down the brass pulley. The pulley is only 3/8" in diameter, so I didn't have to sand it much, but I did manage to sand it down just a tad too much. (Don't ask me how I managed that, cause I was watching and checking like crazy.)
Luckily, the original belt was still handy and now I have a turntable with two options. I can run it a tad slow or a tad fast. Personally, I like the faster option and don't plan to tempt fate any more.
It's wierd, I thought a percent or two change in speed wouldn't make much of a difference, but it does. With the speed-up you get an increase in frequency and also a change in timing. Not only are voices pitched higher, but the music has lots of extra snap to it. If you have a recording that seems dull and lifeless, just speed it up a bit, and man, it'll gain a new life.
Since we like to compare and grade our cables, power cords, and what not, I'll go out on a limb and say the tonal changes from the speed-up is a lot bigger than a cable change. At first I didn't notice the difference so much, but now that I'm keyed onto it, and I notice it immediately.
I have a theory on why musicians have such crappy stereo systems. From watching my violin playing brother-in-law, he uses a stereo like someone would use a hammer. All he wants from a stereo is the pace and tone of the music; mainly so he can play it himself. As such, he sees no need for an expensive system with great imaging and timbre, fast attack, etc. What's funny is that these are the same qualities he expects out of his violin!
Hi fi is usually a bottomless pit - but have you ever noticed that most musicains listen to things with the sonic elegance of a mice powered turntable using a 4" nail hooked up to an old tin can with a bit of string?
It's funny how these threads have a life of their own and don't go in the direction you expect. My initial thought that it was some electrical problem within the turntable, but, most of the talk has been with mechanical issues.
Of all the suggestions, I think the thick belt suggestion is the one I plan to try next. I compared the current belt with a previous worn out one and sure enough it was much thicker. Once I get the speed correct, and get a stable disk strobe pattern, I'll check out if the motor has fast/slow problems. After that, its time to enjoy the thing or drop it off at the nearest thrift shop.
One thing I have learned here is the importance of a second source to compare things. (Now reread the above sentence until you understand it.) I only found the speed problem by comparing the record to a CD copy. After a couple of albums and CDs, something didn't sound right, and that helped me find the problem. In the process of switching the turntable between my main stereo system and the TV surround system, I've found that my much more expensive stereo system has a severe bass problem! Ah yes, this never ends, does it.
This brings back dim, distant memories...!! The PL-12D was a good budget deck and was sold in competition with the Garrard SP-25 (MK whatever..) in the 1970's.
In the past we have worked on some of these decks for clients. Most of the speed problems originated from the motor and usually this was replaced. The original motor is no longer available but there is a motor kit still available that will revive the unit but it costs around £70 (approx US$100) in the UK, so it may not be a cost effective choice for you.
Belts are still available but this is unlikely to cause your fast speed problem.
We have a circuit diagram somewhere in the files and I'll see if I can locate it and double-check if there is anything you can check on, but dim memory tells me that other than reviving the motor there 'aint much else you can do.
You could try wiring an ordinary light bulb in series with the motor - be aware that it needs to be in a safe place as they are reasonably easy to break and of course a broken light bulb is an electric shock hazard - also remember they give off heat. The smaller the wattage of the bulb you use, the more it will slow things down and vice versa. This is in fact simply a current limiting resistor. Used it on my old garrard 401 as the speed control on those is a magnetic brake, which does the sound no good at all. Eventually I got round to machining up a smaller motor drive spindle - didn't sound any better than the lightbulb!
Could it be that one of your parts is a wrong-size replacement that got put in sometime a long time ago? It sounds like the pulley could be a too-big replacement. Or, the belt (which would have been the first thing to wear out and be replaced) could be too fat, making it not fit snugly into the "V" of the pulley, hence to rotate around a slightly larger circle than it should. Good luck.
There is an arm that moves the belt between two different diameters on the pulley. My theory was if it was getting in the way, it would slow down the turntable. Right now, it doesn't look like it affects the belt much.
If I want to physically change the dimensions of the turntable, I have two choices. Make the platter larger or the pulley smaller. Since the pulley is so much smaller, I probably sand it down.
What's weird to me is that the thing runs fast. I didn't expect to run into an old turntable with a hot to trot motor. I'll make sure is has lots of oil and let it run for a day or two. Maybe that will cool its heels.
If your platter turns with the constant speed all you can do is to place arround the platter pulley rubberband making the diameter larger so decreasing the rotations of the platter. Try to "dress" different rubber bands so to get the most precise rotations measured with the strobe disk.
The other question is what is more reasonable to buy the strobe disk or another PL12?
Does the other end of the belt go around the platter? It seems like there is an arm that moves the belt in and out when you change speeds if so, check it also.
The turntable is belt driven where the pulley is connected to the shaft of the motor. I have cleaned the area where the belt rides on the pulley. I don't think the pulley is worn because this would cause the table to turn slower or possibly erratically.
I went back and took a closer look at the belt fit and it looked liked the belt was riding high against a wider shaft. I refitted the belt and made sure it is in the middle of its allotted region, and alas, no change.
You did give me an idea. If all else fails I can sand the pulley/belt area down a bit. This will cause the table to turn slower. Right now, the table runs faster for both speeds (33 1/3 and 45 rpm).
I am close to positively sure the table is running fast. I checked the table with the strobe disk, and the strobe pattern is moving in the same direction the platter is turning. In my book, this means the table is moving a little faster than expected by the strobe disk.
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