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Actual Proof: SOME Direct Drive turntables do have cogging

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Actual Proof: SOME Direct Drive turntables do have cogging

Postby flavio81 » 28 Dec 2011 19:32

Hi,

The anti-Direct Drive topic has been discussed at length, but so far there wasn't any good evidence of "hunting and pecking" or "cogging" on the typical Direct Drive tables. Now i have found some very commendable forumers that do have the strong evidence in some DD motors. This in a GREAT thread in another forum (link below).

Let me first comment that not all DD motors are of the same design. But many of them follow the typical Technics design.

Here's the thread. It's 22 page long and you'll either have to read all the thread (if your technical level is good) or read my summary below:
http://www.pinkfishmedia.net/forum/show ... hp?t=70027

SUMMARY

Many turntables are compared by using a record with a 3KHz tone and then analysing this using a computer. The actual speed at the record at every angle of the rotation is then plotted in polar fashion. With the SL-1200MK2 and Pioneer PL-71, the polar graph clearly shows speed variations that are perfectly coincident with the 'impulse' given by the motor. Extreme example is the PL-71, a highly rated Pioneer turntable which i own [great construction, great tonearm], and which my ears suspected it suffered from cogging. Now i see that i was correct:

Pioneer PL-71 speed vs angle of rotation (several rotations)
Image

PL-71 motor design, similar in arrangement to most Technics designs
Image

The cogging showed as a flutter component at 6Hz. This could interact with the cartridge-tonearm resonance, intermodulating the signal and reducing sound quality in the same way that sound quality is reduced when using a cartridge of too high compliance for a certain tonearm.
Image

SL-1200MK2 (green trace)
Image

The SP10 (i assume MK2) also showed a faint trace of cogging, but significantly smaller than the PL-71. Platter of the PL-71 is 1.5Kg; platter of the SP10MK2 is 2.9Kg. Repeating the test increasing the PL-71 platter mass to 2.5Kg didn't show any improvement at all; it seems that a significantly higher mass would be needed and/or the control system of the SP10MK2 being much better. In my view this would mean the 10Kg-platter SP10MK3 would show no cogging effects at all, but then the motor of the SP10MK3 is much more powerful, which is not good for cogging.

SP10MK2
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For comparison, an EMT 930 idler drive, the non-plus ultra of Idler Drives, with an enourmous platter mass:
Image
Mechanism imperfections are visible in the plot but they won't manifest as a flutter component in the critical 4-10Hz range, unlike the PL-71 example. It would manifest on a lower frequency.

Linn LP12, the flutter components are of higher frequencies, where (IMHO) won't excite the cartridge+arm resonance.
Image

Lenco L75 flutter spectrum!! (Idler wheel, 4Kg platter.) Compare with PL-71 samples. I own both turntables...
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The graph don't show that the Lenco manifested a flutter component at 30Hz which is most probably rumble from the motor (1800RPM). This can be significantly reduced with mods.

CAVEAT
It is still not clear to me what is the scale of the above graphs. There is still a chance of the cogging effects shown to be too faint to be considered of importance. However, my personal experience is that i could hear "something wrong" with the rotational smoothness of my PL-71 and SL-1401 (same motor and platter mass than the SL-1200MK2), while my Lencos (L75/L78) and Thorens (TD125MK2) didn't show said effect. But this is just a personal opinion.

ULTRA SHORT SUMMARY
DD motors of Technics-like motor construction, with platter weights of 3Kg or less, will cog and show a flutter component in the (IMO) dangerous zone of 4-10Hz. Add a lot of mass to a DD motor and it might approach rotational perfection. This could open a new trend for the turntable DIY people -- add mass and/or reduce power!!
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby bogle111 » 28 Dec 2011 20:06

Oh dear flavio81, you really are sending out 2011 with a good one.

Seriously though, this will be interesting to read. As a non-techy sort of person, I'll be back about February to check up on the general consensus and the injury status/count!!

Happy New Year to you and everyone else that reads, 'cause I think there will be many.
Regards
Peter
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby JaS » 28 Dec 2011 20:29

Interesting. Have you any idea yet which SP10 was tested (mk1 servo/mk2 quartz/mk2P/mk2A) and whether it has been serviced in the last 30+ years, especially the many capacitors? Also which LP12? 1973 with basic phase shift supply, Valhalla, Lingo etc? Was the SL-1210 new or a 30 year old DJ deck? Were the graphs done with the same program/record and who made them? I saw a certain Linn dealer involved in the discussion which makes me the slightest bit suspicious :lol: but it's interesting stuff, if highly unscientific in it's current form - I would struggle to use the word 'proof' to describe the findings so far - more like useful pointers for further investigation?

FWIW The SP10s I've heard have had spectacularly good pitch stability and a clean, uncoloured sound which doesn't seem to fit with the shape of the graph you've shown :-k

Also has anyone done DBT listening tests to see if the measured phenomenon is audible? Would it be possible to create different levels of what you are referring to as 'cogging' in the same turntable and do listening tests? I'm happy to accept that belt/idler/direct drives have different performance in this area, but it's important to show evidence that the measured effect is audible.

Regards,
JaS

PS Can anyone do this at home? What equipment is needed? Can it be used to improve the sound of a deck eg will adding a record weight really improve the sound or increase cogging? Has anyone measured the effects of different power supplies for belt drives/idlers to see if the traces change? Questions, questions :)
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby flavio81 » 28 Dec 2011 20:45

Lots of questions, JaS...

JaS wrote:Interesting. Have you any idea yet which SP10 was tested (mk1 servo/mk2 quartz/mk2P/mk2A) and whether it has been serviced in the last 30+ years, especially the many capacitors? Also which LP12? 1973 with basic phase shift supply, Valhalla, Lingo etc? Was the SL-1210 new or a 30 year old DJ deck? Were the graphs done with the same program/record and who made them?


I have some of the same questions but don't want to open up a new forum account!!

As for your "highly unscientific" claim, let me just say that:

- all the graphs were computed by the same person,
- the test records were not always the same BUT record eccentricity manifests at 0.5Hz, not at the frequencies pointed out as "flutter". Furthermore it would be totally unreasonable to assume that the cogging 'star' pattern was embedded in the test record. Some of the tests were done with exactly the same test record (and different turntables), yet the cogging 'star pattern' appeared on one deck vs the other
- in one case, trying a different test record on the same turntable revealed similar results.

Remember, they are not measuring ABSOLUTE flutter and trying to compare it between TTs (which would require exactly the same test record and a very good one), but they are measuring the pattern of the flutter components.

JaS wrote:I would struggle to use the word 'proof' to describe the findings so far


JaS, i wrote "actual proof that SOME DD turntables do have cogging", see ;) ?

JaS wrote:Also has anyone done DBT listening tests to see if the measured phenomenon is audible?


That's a great idea.

If you want to replicate the test, you can do it at home by using a record with a 3KHz test tone. Or 1KHz, it will still be valid. Then send the file to the guys at that forum. A popular record used was the Decca "stereo demonstration test record", one that i also own and find very high in sound quality by the way. It contains the 3KHz flutter tone. The other one is the "Ultimate Analog test LP". Both of them are not centered enough for a good WOW analysis but good enough for this analyis, imo.
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby steve195527 » 28 Dec 2011 20:54

You haven't just posted this,especially relating to Technics with platters below 3Kg,to wind up a certain Australian member have you?Remember the Fremer thread!!
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby flavio81 » 28 Dec 2011 20:56

bogle111 wrote:Oh dear flavio81, you really are sending out 2011 with a good one.

Seriously though, this will be interesting to read. As a non-techy sort of person, I'll be back about February to check up on the general consensus and the injury status/count!!

Happy New Year to you and everyone else that reads, 'cause I think there will be many.
Regards
Peter


Thanks Peter!! I like reading the service manual for turntables and having always seen the technical descriptions of the motor on the Technics SL-1xxx line (and the one in the Pioneer PL-71), i always thought it HAD to cog in some way, the question was 'how much relatively to other turntables?'. Synchronous motors can cog too; the ones that are cogless are the shaded-pole induction motors typically found on (ahem) IDLER drive turntables.

If you read carefully you'll see that it's not in my agenda to go against DD decks and, quite the opposite, i find these findings favorable to DD turntables in the way that they point that smooth rotation IS POSSIBLE with Direct Drive turntables too; which is very different to the snobbish "ALL direct direct drive turntables suffer from cogging" or the technically innacurate "hunting and pecking".

Moreover the PL-71 was thought by some forumers to be free from the nasty effects typically associated to DD decks by virtue of it's control system, which is not quartz locked, nor phase-locked; it's simpler. Well, a phase-locked, quartz-locked SP10 performed better.

I think this may open new paths for the DIY people, since the findings on the above-linked thread suggest that high platter mass might make the DD a drive system as good as anyone. I look forward to see highly modified Technics SL-1XXX platters and motors (and other DD motors) turned into DIY giant killers, in the same way as Lencos are right now once their potential was discovered.
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby avole » 28 Dec 2011 20:59

Except, given the SL1200/SL1210 graphs don't show a major problem, it may be the cogging, if it is really a problem, isn't audible;

I seem to remember the criticism of the quartz locking was always that corretion never stopped and, in theory, could be audible.

Incidentally, were these measurements with quartz locking in place, or without? That might be an interesting avenue to explore.

Nice to see the LP12 figures in there, by the way. Goes to show a good belt drive is up there with the best.
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby flavio81 » 28 Dec 2011 21:01

steve195527 wrote:You haven't just posted this,especially relating to Technics with platters below 3Kg,to wind up a certain Australian member have you?Remember the Fremer thread!!


No... Which member are you talking about?

Also let me point out that i will never 'rubbish' the SL-1200MK2. Last week i dissasembled one again. The overall construction is very solid and very high quality (unlike budget Rega decks for example), the platter is damped on the underside from factory (unlike 90% of all turntables), the plinth has nice rubber damping (a great thing), and, unlike many people, i find the tonearm well designed and very well built. For the price, it's a TREMENDOUS value.

On the other hand, i still think it's an overrated turntable, though!!
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby JaS » 28 Dec 2011 21:03

flavio81 wrote:
JaS wrote:I would struggle to use the word 'proof' to describe the findings so far


JaS, i wrote "actual proof that SOME DD turntables do have cogging", see ;) ?

I'll settle on 'test results that show some turntables MAY show traces of cogging' :wink: To be honest I'm not surprised that the traces show something as the way the motors are driven is so different - the difficulty now is proving that it's (a) audible and (b) not down to the small sample size? It's a bit like hazy photos of ghosts at the moment :-k

flavio81 wrote:
JaS wrote:Also has anyone done DBT listening tests to see if the measured phenomenon is audible?


That's a great idea.

If you want to replicate the test, you can do it at home by using a record with a 3KHz test tone. Or 1KHz, it will still be valid.

Any idea what software was used to produce the graphs? It would be nice to have a play myself.

Regards,
JaS
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby JaS » 28 Dec 2011 21:09

flavio81 wrote:i always thought it HAD to cog in some way, the question was 'how much relatively to other turntables?'

I think a lot of reviewers back in the day thought the same, and this perception affected what they heard. Or maybe they heard what they perceived. Or maybe they perceived and heard nothing and just copied their reviews from the brochures...

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JaS
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby steve195527 » 28 Dec 2011 21:10

If any member reading this feels so disillusioned with DD that they are going to chuck their SP10mk2 in a skip,drop me a line,I'll take it off their hands and happily put up with its poor performance!
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby JaS » 28 Dec 2011 21:13

steve195527 wrote:If any member reading this feels so disillusioned with DD that they are going to chuck their SP10mk2 in a skip,drop me a line,I'll take it off their hands and happily put up with its poor performance!

LOL I'm so besotted with the sound from mine it could have a trace like a starfish and I still wouldn't hear it. I'd still like a snapshot of it's face though :lol:

Regards,
JaS
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby flavio81 » 28 Dec 2011 21:16

JaS wrote:Was the SL-1210 new or a 30 year old DJ deck?


That one is a good question. Also your point about the capacitors being in good shape. I think this is CRUCIAL.

JaS wrote: I saw a certain Linn dealer involved in the discussion which makes me the slightest bit suspicious :lol:


JaS, for the prices the Linn turntables are sold, the Linn fared poorly on that test!!

JaS wrote:Can it be used to improve the sound of a deck eg will adding a record weight really improve the sound or increase cogging?


Quoting the PL-71 experiment, a record weight (circa 500gr) wouldn't make any improvement regarding cogging. But i would say it would change the resonance signature of the record, since the record would be tightly coupled to the mat.
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby flavio81 » 28 Dec 2011 21:17

steve195527 wrote:If any member reading this feels so disillusioned with DD that they are going to chuck their SP10mk2 in a skip,drop me a line,I'll take it off their hands and happily put up with its poor performance!


Me too, and I think you have discovered my evil plan...
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Re: Actual Proof: SOME Direct Drive turntables do have coggi

Postby steve195527 » 28 Dec 2011 21:20

JaS wrote:
flavio81 wrote:i always thought it HAD to cog in some way, the question was 'how much relatively to other turntables?'

I think a lot of reviewers back in the day thought the same, and this perception affected what they heard. Or maybe they heard what they perceived. Or maybe they perceived and heard nothing and just copied their reviews from the brochures...

Regards,
JaS


You're not insinuating that some reviewers wrote a load of bo**cks are you?never they all knew/know what they are talking about!
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