Cheap TT with speed control?

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Coffee Phil
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Re: Cheap TT with speed control?

Post by Coffee Phil » 25 May 2019 18:22

Speed stability and absolute speed accuracy are two separate issues. I believe that most folks would be bothered by unsteady pitch caused by poor speed stability but I don't think belt drives need to have unacceptable levels of this. My main machine is a direct drive but I have never been bothered by wow with my suspended chassis belt drive Beogram 3000.

Most folks do not have absolute pitch. I would not notice a 78 RPM played at 80 RPM or an Edison Diamond Disc played at 78.26 RPM without an AB comparison.

That said, if I know the speed is off it bothers me. I bought a NOS Admiral 78 only changer and it spins at 80 RPM. After I get it mounted, plans for an adjustable frequency power supply to get it on speed are in the works.

Phil
rewfew wrote:
25 May 2019 16:15
Having used belt turntables for years I'd been plagued with unsteady speed stability. Fast, slow, modulation with stylus drag, line voltage. During my modest income years I had a cheap Technics belt drive with strobe and servo speed pitch adjustment. Which allowed a capability to get back to stable speed, for awhile. Fast forward with more available green, I bought a Rega, which I though would upgrade to a higher level of quality. Other than an upgrade in tonearm quality. Playback was prone to speed variations with no ability to compensate for, and acoustic feedback, giving a false sense of dynamics, sometimes causing my amplifier to blow it's fuse.
Investing later into direct drive solved all these issues. If speed variation is as much a problem to record playback as was with me, and what the first post alludes to. Then how cheaply you can alleviate the problem are either searching for vintage direct drive or investing in current offerings. To me, it's worth it. No more piano or vocals changing tonal pitch. Heavily damped plinth, so no more feedback issues. Add in convenience with speed selection, VTA adjustment, headshell mounted cartridge change out with easy and accurate setup. What amount of money spent to get the accuracy of quartz locked frequency generator direct drive would be formidable with belt drive. It's not a problem to value the perception of pitch speed until it changes.

Bob Dillon
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Re: Cheap TT with speed control?

Post by Bob Dillon » 25 May 2019 19:04

cats squirrel wrote:
25 May 2019 12:24
why is it so important to have the record turning at exactly 33.33 rpm? I bet NO-ONE could tell it was 0.2rpm too fast, NO-ONE, just by listening, so what is the problem?

The instruments on a recording are not tuned to that accuracy and precision, and if they could be at the beginning of a tune/song, they wouldn't be at the end of it!
If the instruments drift out of tune, I'd like to hear it as it was, I don't need the turntable making them more so.

rewfew
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Re: Cheap TT with speed control?

Post by rewfew » 25 May 2019 20:44

Coffee Phil wrote:
25 May 2019 18:22
Speed stability and absolute speed accuracy are two separate issues.
Maybe by definition. But with turntable operation they're fairly intertwined. Absolute accuracy is all well and good, but as mentioned small pitch deviation can be tolerated if maintained. When heavily modulated music come's around and stylus drag enters into play more prominently the effect of maintaining accuracy of speed is enabled with greater imperceptibility with the instantaneous correction of the linear frequency generator feedback in direct drive. Being applied smoothly and constantly if inconsistency is detected. Belt drive with it's flexible linkage can't make such a seamless correction. This is apart from the flywheel effect that any turntable drive system inherently has. For me at least, the dynamic nature of music is marred when this occurs. It takes away from the audio illusion being created by the system and draws attention to the equipment.

Woodbrains
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Re: Cheap TT with speed control?

Post by Woodbrains » 25 May 2019 22:12

Bob Dillon wrote:
25 May 2019 19:04
cats squirrel wrote:
25 May 2019 12:24
why is it so important to have the record turning at exactly 33.33 rpm? I bet NO-ONE could tell it was 0.2rpm too fast, NO-ONE, just by listening, so what is the problem?

The instruments on a recording are not tuned to that accuracy and precision, and if they could be at the beginning of a tune/song, they wouldn't be at the end of it!
If the instruments drift out of tune, I'd like to hear it as it was, I don't need the turntable making them more so.
Hello,

You are missing the point here, you can't hear the instrumehts slightly out of tune, just as you can't here a table running ±0.5 % out of speed. There is no need to worry and fuss. Very few things in the world are within ±0.5% tolerance, if we worried about measurement that don't amount to anything we would all go nuts. In fact grand pianos are purposely tuned slightly flat, no one can hear it. I'm sure if it mattered, the musicians in the orchestra, who must have fabulous sense of pitch, would hear it.

Speed stability is another matter. Something pitched slightly lower or higher will not be noticed; slight changes in pitch is very noticeable. If the speed of the table is nuts on 33.5 then there is no problem. Fixating on the absolute numbers is futile, absolute 33.333 is not worth fretting over. If you could get it, it would be different that evening when the room temp drops and the belt stiffens and the bearing lube thickens and the bearing itself contracts and the sub platter's diameter shrinks......

Mike.

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Re: Cheap TT with speed control?

Post by Bob Dillon » 25 May 2019 22:35

Woodbrains wrote:
25 May 2019 22:12
Bob Dillon wrote:
25 May 2019 19:04
cats squirrel wrote:
25 May 2019 12:24
why is it so important to have the record turning at exactly 33.33 rpm? I bet NO-ONE could tell it was 0.2rpm too fast, NO-ONE, just by listening, so what is the problem?

The instruments on a recording are not tuned to that accuracy and precision, and if they could be at the beginning of a tune/song, they wouldn't be at the end of it!
If the instruments drift out of tune, I'd like to hear it as it was, I don't need the turntable making them more so.
Hello,

You are missing the point here, you can't hear the instrumehts slightly out of tune, just as you can't here a table running ±0.5 % out of speed.

There is no need to worry and fuss. absolute 33.333 is not worth fretting over. If you could get it, it would be different that evening when the room temp drops and the belt stiffens and the bearing lube thickens and the bearing itself contracts and the sub platter's diameter shrinks......

Mike.
Well now, you shan't suggest to me what I can hear, buckaroo. I do get the point you are trying to make. :harhar:

I'm not using a belt drive TT at this time, so this last part is moot for me. My DD TT runs at consistent speed all day every day.

Coffee Phil
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Re: Cheap TT with speed control?

Post by Coffee Phil » 25 May 2019 23:08

Hi renfew,

The bandwidth of the feedback loop in a direct drive is analogous to the flexability of the belt in a belt drive. Wide bandwidth is like a stiffer belt. Wide bandwidth means the frequency generator had better not have FM on its output when the platter is turning at constant angular speed. When I converted my KD 500 to four speed quartz lock I noticed that the shutter wheel in the frequency generator was not perfectly centered on the motor shaft and had FM on it’s output. I delebrately kept the bandwidth lower than what could be achieved to avoid wow. Since working on other KD500 motors I have developed the courage to attempt to align the shutter wheel. I may go back to my main machine, tweak the shutter wheel, then push the bandwidth out more.

The point is, whatever the design of the machine the performance will depend on how well it is executed.

Phil


rewfew wrote:
25 May 2019 20:44
Coffee Phil wrote:
25 May 2019 18:22
Speed stability and absolute speed accuracy are two separate issues.
Maybe by definition. But with turntable operation they're fairly intertwined. Absolute accuracy is all well and good, but as mentioned small pitch deviation can be tolerated if maintained. When heavily modulated music come's around and stylus drag enters into play more prominently the effect of maintaining accuracy of speed is enabled with greater imperceptibility with the instantaneous correction of the linear frequency generator feedback in direct drive. Being applied smoothly and constantly if inconsistency is detected. Belt drive with it's flexible linkage can't make such a seamless correction. This is apart from the flywheel effect that any turntable drive system inherently has. For me at least, the dynamic nature of music is marred when this occurs. It takes away from the audio illusion being created by the system and draws attention to the equipment.

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Re: Cheap TT with speed control?

Post by Woodbrains » 26 May 2019 00:24

Bob Dillon wrote:
25 May 2019 22:35



I'm not using a belt drive TT at this time, so this last part is moot for me. My DD TT runs at consistent speed all day every day.
Hello,

How do you know your table runs constant speed, day and night? If it runs (more or less) constant for the duration you are listening then great, I think my belt, direct and idler drives do, also. But I can't say they run exactly at 33.33 every time every day. How could I possibly know. One has a strobe provided by an electronically generated signal. Does that work to 0% tolerance; the components in the circuit are likely to have 5 % tolerance on values perhaps 20% on some resistors and capacitors and it is 30 years old. Cumulatively all those errors will add up to some degree of inaccuracy. Its a big ask to expect it to be within .5%. I have strobe discs that are set with a mains AC generated light, but even in Britain where great pains are taken to keep the phase consistently at 50Hz (so electric clocks still stay accurate) that is only averaged over a day, all bets are off as to how accurate the strobe is at the time it is observed. I have never tried a phone app tacho and never will, there is no hope at all for the accuracy of those to be better than 0.5%. and those hand held tachos from China available on Amazon etc. have stated tolerances of as much as 5%. It is impossible to tell if our tables are exactly any speed, only consistently (or not) approximately 33 ± some degree of error. It is consistent speed we need, absolute accuracy is chasing a rainbow.

Mike.

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Re: Cheap TT with speed control?

Post by Bob Dillon » 26 May 2019 01:26

Woodbrains wrote:
26 May 2019 00:24
Bob Dillon wrote:
25 May 2019 22:35



I'm not using a belt drive TT at this time, so this last part is moot for me. My DD TT runs at consistent speed all day every day.
It is consistent speed we need, absolute accuracy is chasing a rainbow.

Mike.
Well, I think we're onto something here. I'm not saying I could tell if the TT was running 0.005 percent off one day to the next either.

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Re: Cheap TT with speed control?

Post by cats squirrel » 26 May 2019 11:54

Bob Dillon wrote:
25 May 2019 19:04
cats squirrel wrote:
25 May 2019 12:24
why is it so important to have the record turning at exactly 33.33 rpm? I bet NO-ONE could tell it was 0.2rpm too fast, NO-ONE, just by listening, so what is the problem?

The instruments on a recording are not tuned to that accuracy and precision, and if they could be at the beginning of a tune/song, they wouldn't be at the end of it!
If the instruments drift out of tune, I'd like to hear it as it was, I don't need the turntable making them more so.
or less so! :?

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Re: Cheap TT with speed control?

Post by rewfew » 26 May 2019 16:09

Coffee Phil wrote:
25 May 2019 23:08
The point is, whatever the design of the machine the performance will depend on how well it is executed.
Phil I admire your intellectual investigation into DIY modification of your table. So, I wouldn't spar with you based on your acquired technical know how. I'll instead with your quote, apply that as a confirmation bearing out the superior specifications of low w/f exhibited by direct drive compared to belt drive. Of note also from the KAB myth's section is pointed out that the dynamic and static drag effect measurement for the Technics is still only 0.035 % peak w/f.. Probably a specification of pride what this design can accomplish. These days, specifications tend to regard weight alone for the turntable unit as a pertinent fact.

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Re: Cheap TT with speed control?

Post by rvb » 01 Jun 2019 00:22

I know the exact speed, thanks to the runout groove method.

33.316 rpm, 0.017 rpm lower than should be.

For the sound this is fine, but it is difficult in Audacity to compare, but Joe Z stated I can allign the soundbytes in Audacity, so my problem is solved.

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Re: Cheap TT with speed control?

Post by rvb » 01 Jun 2019 00:37

The runout groove method is very nice, it will give me the speed for every recording, I will file it.

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Re: Cheap TT with speed control?

Post by rvb » 01 Jun 2019 00:47

I'm thinking about turntable design in general and somehow I think it is peculiar that there is no read out of the speed at all the turntables I saw the last 2 months.