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Post by monkumonku on Jul 23, 2015 14:39:25 GMT -5
There's a thread over in the Steve Hoffman forum about what is your turntable speed. There is an app that is able to measure the speed, so the OP asked people to download it and post their results. No one seems to be THAT far off but I'm thinking, with the cost of turntables - most seem to be hundreds if not thousands of dollars, wouldn't you expect the speed to be dead on 33.33 rpm? Perhaps in practical terms being exactly 33.333333333 isn't necessary unless you have perfect pitch and are OCD is something is not a true A or whatever, but given that you spend all that money on turntables, shouldn't the speed be precise? forums.stevehoffman.tv/threads/whats-the-speed-of-your-turntable.448310/Possible explanation - lets say it measures 33.2 instead. Maybe the friction from your needle is causing the platter to slow down. So shouldn't manufacturers implement drag adjustment to correct for that?  |
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klinemj
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Post by klinemj on Jul 23, 2015 17:00:22 GMT -5
It's all Emotiva's fault...their amps cause a magnetic loop due to low quality power cords that cause this. It's well known on "other forums" and clearly shows on test LP's of random noises. Switching to a special power cord on all Emo products typically solves the problem. Seriously, though...I had an old TT that had a handy way to adjust the speed to exactly the right speed. I can't recall if that was a Dual or Technix, but as I recall it involved a light (strobe?) that lit up the side of the platter. Or, maybe the...uh...medicines...I was on at the time are affecting my memory. It was college, after all... Mark |
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Post by novisnick on Jul 23, 2015 17:01:40 GMT -5
It's all Emotiva's fault...their amps cause a magnetic loop due to low quality power cords that cause this. It's well known on "other forums" and clearly shows on test LP's of random noises. Switching to a special power cord on all Emo products typically solves the problem. Seriously, though...I had an old TT that had a handy way to adjust the speed to exactly the right speed. I can't recall if that was a Dual or Technix, but as I recall it involved a light (strobe?) that lit up the side of the platter. Or, maybe the...uh...medicines...I was on at the time are affecting my memory. It was college, after all... Mark Technics! heres a shot of the model I own.  |
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Post by garbulky on Jul 23, 2015 17:02:31 GMT -5
My speed was 10 but then I turned it up to 11. Much better.  |
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Post by klinemj on Jul 23, 2015 17:05:32 GMT -5
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klinemj
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Post by klinemj on Jul 23, 2015 17:07:30 GMT -5
Yes Nick! Indeed! Something like that. Mine was pretty old, and I can't recall but I think I also had a Dual with a similar system. Or, I may be mis-remembering...had my Thorens SOOOOO long....
Mark
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Post by novisnick on Jul 23, 2015 17:10:52 GMT -5
I purchased that TT new in ,,,,,,,,,wait for it,,,,,,,,,,,,,,wait for it,,,,,,,,,,,,,,,,,,,,, 1976!!!
Still sounds pretty good !!
Edit; it is belt driven
new belt and cartridge, sounds good but it's not my Rega. Great entry level TT though.
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Post by klinemj on Jul 24, 2015 9:01:05 GMT -5
I need a new belt for my Thorens...bought it in '83 or '84?
It still works, but it's so worn...
Mark
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Post by audiobill on Jul 24, 2015 9:16:05 GMT -5
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Post by vneal on Jul 24, 2015 10:28:23 GMT -5
My Project is
33.31
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Post by chaosrv on Jul 24, 2015 11:25:24 GMT -5
I just hooked my Scoutmaster to a Phoenix Engineering Eagle power supply/speed controller and their Road Runner tachometer. A perfect 33.3333 rpm
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Post by KeithL on Jul 24, 2015 11:41:20 GMT -5
In theory, a turntable should be rotating at 33-1/3 RPM (33.3333 - and so on forever).
In practice, there are a lot of things which can affect that number.
Even the cheapest digital clock oscillator chip these days is accurate to five or six decimal places, so that part of the system should be a gimme. This means that any direct-drive system that "locks" the platter speed to a clock should be perfect to at least four decimal places. And if you see the speed change, like the strobe on some old turntables seemed to lurch a bit as they rotated, then something is slightly out of round and the speed actually is varying a tiny bit. (A system that is servo-locked shouldn't slow down due to needle drag, or to bearing friction, because it's supposed to look at the platter speed and adjust it so it matches the reference.) However, if your turntable has a speed adjustment, then that adjustment mechanism itself is a possible source of error. Many older turntables used "hysteresis synchronous" motors, which were locked to the line frequency itself, which is actually controlled to be pretty darned accurate by most power companies.
If your turntable uses belt drive, then you have the possibility of the belt slipping, and the size of the pulley becomes critical. And, if yours has one of those pulleys that's fatter at the center than at the edges, then, since the pulley has a sort of "variable size" in one sense, how tight the belt is and how stiff the rubber is will cause some slight variation. (The speed ratio is determined by the ratio of the diameter of the platter to the diameter of the pulley; if the pulley has slightly different diameters at the center and the edges, then which of those diameters "is the one that counts" will depend on things like how soft the belt is and how tight it is.) Many belt drive systems have a motor that has a very accurate speed - at the motor - but then connect the motor to the platter with a pulley - which can potentially slip or not be accurately sized.
The reality is that, by modern standards, record cutters from the old days weren't always perfect. (You also need to understand that, even if the record cutter and your turntable were perfect, if the speed of the master tape recorder or player was less than perfect, then the music on your record will be playing "at the wrong speed" even though the record is spinning at the exact correct speed.) This is why many modern turntables have the ability to adjust their speed (even though, with modern electronics, they should be capable of delivering the perfect correct speed). Of course, you also have to wonder how accurately the instruments themselves were tuned years ago - back when there were no inexpensive crystal oscillators, and everybody used a tuning fork (I wonder how much the frequency of a brass tuning fork changes when it gets warm).
My guess is that anything under a few tenths of a percent would be inaudible to most folks - including myself.
I would be much more concerned with speed VARIATIONS - which are much more audible than errors anyway.
Back in the old days, THE two most important specs for a turntable were "wow and flutter" and "rumble".....
Wow is slow variations in speed (like you might get with a platter that was off-center - or a record pressed that way).
Flutter is more rapid speed variations (like you might get from a pulley that wasn't smooth, or an irregular belt, or the individual drive pulses in a direct drive motor affecting the speed the platter is spinning at).
And rumble is the collective very low frequency noise from mechanical things like the platter bearing (usually a fraction of a Hz to a few Hz).
Since these were widely accepted to be the most audible flaws likely to occur with a turntable, and they aren't especially difficult to measure, it seems very odd to me that the manufacturers of many modern turntables omit to mention them. (And it leads me to wonder if a lot of those modern "premium" $5k turntables actually do perform better than the AR-Xb I bought forty years ago for $150 - and which had excellent wow and flutter and rumble specs.)
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Post by novisnick on Oct 8, 2015 13:18:21 GMT -5
No belt on this one. '68 Duel  |
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Post by AudioHTIT on Oct 8, 2015 14:26:43 GMT -5
Many older turntables did have 'pitch' adjustment for getting the speed dead on. It didn't only help if you had perfect pitch, but also if you wanted to play an instrument along with a record you could 'tune' the record to the instrument, useful when the artist didn't tune to A440 (with some instruments this was a lot easier than the alternative). They often also had strobes for getting them back to 33 1/3 when you were done, but many (most?) have dropped both features.
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