Turntable speed accuracy

Hi Lewm. Papst made a huge variety of motors. I think the company still exists and now makes industrial fans. I haven't seen the external rotor type being implemented for dd nor do I think it would be a good idea to try. They did make a number of dedicated dd motors though . The SOTA turntables (as well as many other brands in the 80's & 90's) used a papst dc 'pancake' motor up to series iii . I did have a star iii as well and now now use the platter, bearing and vacuum pump in a DIY tt but with a different motor.

I owned a Sota Star Sapphire III with vacuum for many years. It was eclipsed handily by my Nottingham Hyperspace, which revealed to me that piano music does not have to have the wavering pitch that I always heard with the Sota. In fairness, the later Sota products are said to be much better in this regard. But then in turn the Notts was eclipsed by the Lenco and direct-drive, IMO and in my system. Actually the contrast between the SSS III and the Hyperspace may have been greater sound quality-wise than was the contrast between the Hyperspace and Lenco. I think the pitch instability of the SSS was caused by belt stretching as the platter bounced on the spring suspension whilst the motor stayed still because not suspended.

Lespier, Thanks for the information. When I wrote what I wrote, I was thinking of the seminal Papst motor, as used in the Empire tt's. I actually thought that the term "Papst" (Pabst?) refers to a particular motor configuration, patented or invented by someone named Papst, not to a company that makes a wide variety of different kinds of motor. But maybe you are inferring that the Papst type motor can indeed be adapted to direct-drive. Good idea with the Dual motor.

Lewm asked, 'What Turntable', I'm thinking that he was asking what Magnepan was using at the CES.
Memory of 30 years ago tells me it was a Linn Sondek, but that seems wrong...
Funny, Linn ruled for a while, when SOTA entered. Sota which was more neutral, maybe less 'musical', but they did some things that were 'better' from a design standpoint. The center of gravity, with weight sprung beneath the platter...for better stability and less 'skip' with 'footfall' issues in homes.
That, and an 11 pound platter, for greater 'speed stability'...the inertial effect of the 'drag' of the cart, having less effect as the inertial effect of that weight made for fewer speed issues in the short term/time interval.
I still have a Linn, that's not been used much AT ALL...perfect condition...I may sell it...my vinyl has dissipated over the years.

Great discussion and a great memory lane moment for me.

Larry

I meant to say that Thorens offered an external rotor papst 3 phase motor as a replacement after they stopped making the original induction motor for the TD124. The jury's out on whether or not it constitutes an upgrade.....consensus on an audioasylum thread was that the original motor was preferred. I suspect it's because the papst 3 phase doesn't like being slowed down by the eddy current brake. With a proper 3 phase variable frequency power supply and setting the eddy brake to minimum I think the situation could well be quite different.
Lewm, your (and other's) journey of discovery with respect to direct drives & lencos is inspiring me to take the plunge and go down that path.
I'm planning a diy using the dual eds 1000 motor and I also have a Lenco GL78 I want to play with.
I'd also love to get my hands on a Denon DP80 or 75 .

"You would not use a Pabst motor in a direct-drive turntable"

Lewm
Pabst is a company that made many motors. The external rotor one used in the Empire(Atmaspere)turntables is merely one of their products.
They made dd motors for Revox and Goldmund and I I believe they also had something to do with the Dual eds motors.
The external rotor one was used as an upgrade for the TD 124 and the also made a dc motor for belt drive that was used in the early SOTAs.

There are also crappy bearings in turntables both old and new.
As a lover of vintage turntables for perhaps irrational reasons, I want to agree with you, Thuchan, but a modern machinist would probably tell us that with the digitally controlled cutting equipment (CAD) and laser technologies available now, it is possible to create bearings that are at least the equal to anything ever made in the mid-20th century and for much less cost (because less human labor is needed). But whether this leads to BETTER bearings in modern top of the line turntables, I do not know. Anyway, we are talking about the creme de la creme of modern turntables, not those middle of the road products that "only" cost $5000. Your Continuum is said to have a spectacular bearing; have you examined it closely?

Ketchup,
TT bearings of the 50is are bigger, more stable and usually in good TTs of a much superior built quality than those of most modern concepts.

best and fun only

How do TT bearings in motors from the 50s differ from those used now?

I think you have it a bit backwards. Generally the motor chosen is related to the intended drive system. Plus there is a time-related effect. With regard to my first point, direct-drive motors pretty much must use some speed corrective mechanism, e.g., the well known quartz-linked servo. There are many ways of implementing this kind of circuit, and I am certainly no expert. The science of motors per se is amazingly arcane. However, just about all DD motors are either 3-phase AC synchronous types or DC types. Even within those two categories, there are many different ways to build each, which also will affect how the tt "sounds". Modern belt and direct drive turntables are still using the same technology, only with perhaps faster electronics. As regards my second point, 1960s and earlier turntables tended to use cruder single-phase or two-phase motors, e.g., Thorens, Garrard, and Lenco. But these were idler-drive and the motor is suited to that application. I just mean to say that you have broached a very complex subject and that in general it is not accurate to generalize on what type of motor per se is "best". You would not use a Pabst motor in a direct-drive turntable, for one example. There is more that I don't know about motors than what I do know. That much I am sure of. There are websites like this one where eggheads chat about motors 24/7, for example. Their jargon is at least as obscure as the one I work with all day long as a molecular biologist.

This is an interesting discussion! Thanks all who have participated. I'm particularly interested in the role of the type of motor as it relates to speed stability. It seems that DC motors require a lot of fancy/expensive control mechanisms to achieve speed stability, many with a feedback loop of some sort for control. And as with any feedback loop, there is an opportunity for oscillation, which is certainly a problem.

On the AC motor front, you have synchronous motors, but perhaps the best performance came from the 3-phase motors, like the old Papst pancake motors that a number of high-end turntable makers used to use. I think technically they are eddy-current motors, and hugely inefficient. But their design with the spinning outer rotor and inner coils gave the motor a bit of flywheel effect regardless of the type of platter being used. It seems to me that the Papst motor is what is in the turntable that Atmasphere was raving about earlier.

Are there other 3-phase eddy-current turntable motors still in use today? I know that Papst ceased production of theirs, and it was problematic in several areas (the vanes make a whirring sound, for instance, and the bearing technology is 1950's era).

What other types of motors are best for speed stability?

The argument between measured performance and audible performance must be as old as our hobby. Both sides of that coin are being described here regarding speed.

I don't have any musical training and I expect my perception of timing (tempo) is better than my sense of pitch, which is certainly not absolute. A few years ago when I bought my SP-10 Mk 2A I had a tech friend go through all the calibrations described in the Service Manual. The strobe showed steady speed but when I listened to any recording with a sustained piano cord I could clearly hear a wavering. My friend could not find a correction for that so I took it to a professional tech. With the aid of one of my observed recordings he was able to find another adjustment that eliminated the wavering. After that there was not observable difference in the strobe but there certainly was an audible difference.

Thus I don't feel any need to investigate this Timeline device.

What turntable?

No doubt repeating a point someone else has made.
If the speed is off, the pitch is off, a cardinal sin for me.

Interesting story which I shared years ago.
I was in Chicago at the CES...circa 1984. I had lobbied Magnepan for their line a lot. A LOT, LOT, LOT. To their credit THIEL beseeched me to carry Maggies.
At the CES in Chicago that year, I went in to the Magnepan booth...they were, as I recall playing the MG III's.
Jim Winey asked me to 'have a seat, listen and tell me what you think.'
I had told him on entering that I'd been trying to get his line to no avail...like a Zen Master, he listened and nodded patiently...'Sit, Listen'.

After I listened to a cut I knew, from 'Jazz at the Pawnshop', I stood.
Mr. Winey said, 'What do you think?'
I said, 'It sounds great, just one small issue.'
'Yes?'
'Your turntable is turning too fast, the pitch is sharp.'
He only nodded.
A week later, I got a phone call from their then Director of Sales Dave Carambula (memory)...
'If you still want the line, we'll ship tomorrow.'
They did.
When Dave showed up, I introduced my Wife...he said, I don't remember her, but we remembered you...especially Mr. Winey remembered.'
'Oh?'
'Yes...he told me, give that man our line, anybody who notices the pitch differential deserves to have us in his store.'
He turned to my wife, 'Yes, your husband's the one who told us that our turntable was set up wrong.'
That is how I ended up with the Magnepan line.

Funny how the best stories are always the true stories.

Larry

"A turntable needs the right speed, knowledge to make the area of the needle silent and a solution to remove the energy from the tracking." Amen. Very Zen.

....It's a complex and zen system at the same time.

For a lot of Audiophiles everything is more or less a fascinating wonder when a light stars to shine and something is beginning to move. A turntable needs the right speed, knowledge to make the area of the needle silent and a solution to remove the energy from the tracking. All together in the best possible way (Engineering).
The Story is simple. But not for everyone :-)

Lewm: " As you know also, the next mod was to remove the rubber bushing at the anchor point of the idler arm, so as to disallow even that small amount of play at its pivot. I have not done that, in the belief that there is some benefit to dissipating vibrational energy in the idler arm itself, by letting the arm "rattle" a little bit, so energy is not reflected back into the idler and thence into the platter. It's all a head game, because I have no data either way."

It is, indeed, a head game. Sometimes I wonder if we make rigid on all the linkages such as the idler arm, rubber bushing, to not allow any flexing, will the speed be even more stable and what will happen to the sound. The brilliance of the Lenco is in the use of tension: the idler arm pressing on the motor, the spring pulling the wheel towards to motor shaft, and 3 point suspension pushing up the motor towards wheel and then the platter. It's in this chain of tension of push and pull that makes the whole system work in unison. It's a complex and zen system at the same time. I wonder if making any one or all part(s) rigid will ruin this system of tension and its sound. Or it might improve it. I do not know... but it's a fun head game. :-)

To me the idea of direct drive having only one single moving part is even more zen.... and that one moving part rotates at 33.33rpm is super cool... at least it runs circle around Art Dudley's head. ;-)

______

Dover, Cannot fairly answer any of those questions yet. I love them all in different ways, at this moment. With the Lenco, you want to root for it, because it is relatively inexpensive. If I thought I could live with only the Lenco, I could sell the others and put several thousand bucks in the bank (or elsewhere in my audio system). As Raul is fond of noting (and i agree), you cannot compare turntables when the tonearm(s) and cartridges are all different. But it would surprise me if the Lenco was the best of these three (or these four, if you include the DP80).

Lewm,
Which of the 3 tt's the Lenco L75, Technics SP10mk3, Kenwood L07D do you find the most musically satisfying. Have you ended up with same or different sounding decks, or through choice of arm/cartridge deliberately tried to dial in different strengths ? Which one assuming all are speed accurate do you feel gets the most off the record.

Hiho, FWIW, I use a 2nd generation PTP. As you know, it has provision for sliding the idler wheel without removing the platter; one is supposed to leave the two bolts under the platter slightly loose and tighten down only the one that is visible and accessible with the platter in place. That way, you can slide the idler by loosening only the one accessible bolt. However, I am not following that directive. I thought I was better off to get the speed as close to perfect as possible, with all bolts loose, and then to tighten down all 3 of them very firmly. From then on, I make fine adjustments to speed via the Walker Motor Controller. As you know also, the next mod was to remove the rubber bushing at the anchor point of the idler arm, so as to disallow even that small amount of play at its pivot. I have not done that, in the belief that there is some benefit to dissipating vibrational energy in the idler arm itself, by letting the arm "rattle" a little bit, so energy is not reflected back into the idler and thence into the platter. It's all a head game, because I have no data either way. I do like what I've got, however.

Dev, I hope I did not discourage you to pursue the Lenco. It's a great sounding turntable although I never had the time nor effort to set it up properly but I have friends who got good results from adding a little elbow grease.

For an idler design, it is very quiet, thanks to the brilliant simplicity, its quality core components: motor, bearing, and platter. Its idler wheel is also the thinnest and lightest among idler-drive designs and that might partly contribute to its silent running. The idler wheel is also quite stiff and low compliant compare to Garrard, Thorens, Rek-o-kut, etc... and consequently, I believe, less "meaty" sounding, which can be a plus to some people. Admittedly, I quite like that beefy tone on idler tables with thick fat wheels but they are also harder to tame the noise, especially if they use a huge fast running motor, eg, that monstrous Ashland motor in the ROK or McCurdy or Russco. To me the Garrard definitely has a juicier tone than the Lenco but it's not as quiet. Lenco is also, I believe, easier to obtain correct stable speed. My experience is that the thickness, compliance, and among of rubber of the wheel correlate with the tone and tonal balance. (Let's not get into the audio political correctness of neutral game, "my table is more Neutral than your table" pissing contest. I cringed whenever audio reviewer using that term. I equate "neutral" with neutered.) I still marvel at the enormous bass dynamic and heft of a McCurdy idler table with a huge motor...but, alas, it was really noisy--good luck taming that beast!

Anyway, if the noise issue is taken care of, idler tables are great musical machines and can get quite addictive with its ballsy tone... other tables (like some Scottish sacred cow) might sound wimpy as the musicians are playing with one testicle missing. If the table pass the Timeline test, would that be balls to wall? :-)

Sigh, so many toys so little time...

_____

Hiho, thats crazy and thanks for sharing. That's exactly what I enjoy about these forumns sharing such, I'm always open minded, learning something new and find tables alone there is allot to learn.

Lewm: " I believed that firmly and permanently anchoring the distal end of the idler arm was preferable to using the external adjustment mechanism, wherein the pivot of the idler arm rides on a rail across the motor drive shaft, as you select speed."

I agree. All Lenco tables in stock form have speed issue. Not the fault of the motor, idler wheeel, nor the design. It is in the sliding mechanism that holds the idler arm that is always loose. You can hold it and feel it with your fingers and it's loose and it is this looseness in holding down the idler arm that's preventing the speed to be spot on. You can lock it down of course but then you lose the speed adjustability, hence the PTP approach but adjusting speed would be, indeed, a pain in the arse. Only by keep the opposite end of the idler wheel solidly in place will the speed be stable. It's a very mechanical turntable and if the idler wheel is allowed to move even microscopically on the tapered pulley the speed will change. I have several stock Lencos and they all have the same issue. It's no wonder some diyers made a micrometer to slide the idler arm in keeping in position and having the adjustment ability.

Part number 14 is the culprit.

_______

One more thing. I realized whilst taking my evening stroll that I had misrepresented the Lenco. I alone have set up mine so that the speed adjustment is so tedious. On a stock Lenco, there is an external lever that allows you to select 16, 33, 45m or 78 rpm without ever removing the platter, once you have manually set the idler wheel in relation to the motor shaft. So, possibly the guy who told you that the speed was not spot on was using a stock Lenco L75 and was not hip to the fact that a small speed error can be easily corrected with a little DIY effort. I believed that firmly and permanently anchoring the distal end of the idler arm was preferable to using the external adjustment mechanism, wherein the pivot of the idler arm rides on a rail across the motor drive shaft, as you select speed.

Lewm, thx that's great info.

Dev, As I wrote, I used the Walker because (1) the exact final speed adjustment using only the Lenco idler wheel requires a bit of fiddling. (For example, you have to remove the platter to loosen the adjustment screws, the way I have rebuilt mine, then replace the platter to set the speed, then remove the platter to tighten down the adjustment screws, then replace the platter again, etc.) And, (2) there are some unrelated benefits of using a motor controller; namely it isolates the tt motor from the AC line. Thus any EMI emanating from the motor cannot get back to contaminate AC feeding my phono stage, etc. Is that clear enough? Nothing mysterious.

Also, I already own the Walker, so why not use it? The Walker is useless with any of my other tt's, which are all direct-drive.

Hi Lewm,

thanks for the reply back and clarification. I have nothing against Lenco tables and was actually looking at buying one as mentioned prior, really just conversation and learning.

That being said at the same time I was shocked when I had asked this seller what I felt was a pretty basic question and the reply back was they are not spot on.

Your reply in general has left me wondering, if you can set-up the speed as you suggest then why in the heck would you be using what you are? there must be a reason.

Here is a link: Go back up the thread two or three posts of mine, and you will find it. Anyway, there is no need, because I just summed up the story. The oddity is that he claims to be unable to sing a single note but to have a perfect sense of pitch. OTOH, I sing jazz informally and sometimes formally but sensed the tempo error, not the pitch error.

A lot of good jazz singers sing on the low edge of the note, if you know what I mean. (I refer here to real professionals, not me. If I do it, it is a mistake.) It imparts a blue-sy feel. (Examples might be Betty Carter, Chris Connor, Kurt Elling.) Perhaps that is why I was not hearing the pitch error. Kind of like tuning an orchestra to 438Hz instead of 440Hz.

Lew,
You both 'heard' it :^)
I think our descriptive language pertaining to audio......is subjective and ill-defined by convention?
I also have doubts that others here......really understand what people mean when they attempt to describe their impressions? :^)
Sorry......I missed your Lenco story. Is there a link?

Ummm..., Dev, I think you took what I wrote and ran away with it. You can't have it both ways; either a turntable is given to you with the possibility to adjust its speed and therefore correct for any inaccuracy, or not. In the latter case, the turntable had darn well be speed-stable under all conditions, because there is nothing you can do about it. I take it as a virtue that the Lenco mechanism provides an easy way to adjust speed over a very wide range.

By the way, I meant to convey that I was too lazy to do a fine adjustment of the idler wheel, to get my Lenco back to exact speed, so I did it with the Walker motor controller. Since the needed correction was tiny, it was not an issue to do it with the Walker, and I had been meaning to re-insert it in the system in any case, to isolate the Lenco motor so as to block EMI from getting into the AC feeding my preamp.

Then, too, there are two different issues: speed adjustability and stability with no load vs speed stability under the actual condition of playing an LP. That latter property has more to do with torque, compliance in the drive system, platter mass, presence of a servo feedback loop (really only a property of DD turntables), etc. I've been saying this over and over. I guess if you don't like the Lenco, that's cool, but I think you are criticizing it for the wrong reasons. Have you ever heard an LP being played on one? They impart great clarity and drive for a fraction of the cost of other tt's that sound as good (unless you buy a dolled-up version). Isn't that why we are here? I recommend that you listen to a "street version", if possible, before you dismiss the idea.

Henry, You wrote, "well trained ears are our best tools". Did you read my story about listening to my Lenco when it was going too slow, where I heard it as a slowing of tempo and my friend heard it as a flattening of pitch. Two pairs of "well-trained" ears that heard the same music in different ways.

Dear Raul,
It's good to get your feedback.
It appears that your Acoustic Signature keeps consistent speed (without any stylus drag).......so I agree with you wholeheartedly that absolutely correct speed as in 33.3333rpm is not essential.
And if you read some previous posts.....you will see that is discussed at some length?
It's interesting to read that your Denon is 'spot-on'......as so far.......it seems from anecdotal evidence on this thread.......direct drives are the only ones which consistently can make this claim?

I also agree with you...that well trained ears are our best tools :^)
Cheers
Henry

Dear Halcro: A friend of mine brought his Timeline with him at my place two-trhee days ago and we made some tests in my Denon DP75 and both Acoustic Signature's.

We found out that DP-75 was and is right on target but the AS were off even that through a strobe showed were fine. So I dialed through the Timeline, something that's very simple task on the AS motor controler through trimpots. We tested with and with out cartridge playback and things were the same: non detected speed fluctuation because stylus drag ( two on the Denon. )

Before the test I was a little " worried " about the Denon becuase has no external pitch control as the DP-80, fortunately runs splendid.

Now, through the AS and before we aligned with the Timeline we heard three specific tracks : before and after correction and we were unaware to hear differences even that we " want " it and looking for.

Seems to me that depend how wide the speed is off we can or we can't hear differences and obviously depend on our skills/knowledge and system.

Btw, as Lewm posted every TT has a speed controler by design because is the way the TT speed was set up from factory. The DP-75 certainly has it internally as the Technics ones and every other TT.

Yes, I agree with some of you that posted that the primary target on a TT design is speed accuracy and speed stability, with out these there is no TT.

No, I don't think, for that price, that the Timeline is a must to have especially because with the AS we can't detect any differences but as you in other TT set ups things could be different and the Timeline is a necessary tool. Good trained ears and high knowledge audio/music level can tell you the whole " history " maybe better than the Timeline.

Anyway, worth those experiences I had.

Regards and enjoy the music,
R.

Hi Lewm,

Thanks for the reply but if I'm paying top dollar for one I don't feel that I should be the one worrying about this as it should be provided being spot on from the get go.

So really what you are saying is using a generic motor controller such as the Walker or SDS motor controller is to correct the actual speed incurracy.

So this makes sense to me that this well known seller is just being honest and saying they do not offer spot on speed accuracy and your info. above confirms such.

Dear Dev, Your question was: "don't you think it's strange that a well known source who is selling these replied by saying they are close and not as you did saying it can be set to be spot on?" To that, my answer has to be "yes, I think it is strange". Perhaps the responder did not wish to guarantee that his Lenco would be "spot on" in the presence of stylus drag, but there is no doubt that the speed can be adjusted finely via setting the idler wheel position in relation to the length of the tapered drive shaft. If you take a look at photos of the drive system probably available on Lenco Heaven, you will see in a moment what I am talking about. It might be a pain in the arse but it can be done. Moreover, a generic motor controller like the Walker or the SDS could be used to make up for any slight error above or below exact speed. So, I am with you on that.

Hi Ct0517,

I really did not pay attention, the owner said it showed dead on and that's what I was going by and when the TimeLine was placed on showed ii was off. The spindle of his table is approx 20 from the wall.

Hi Lewm,

thanks for that info. in relation to the Lenco, don't you think it's strange that a well known source who is selling these replied by saying they are close and not as you did saying it can be set to be spot on? Personally I thought this to be odd, I was inquiring about purchasing from them to have another table and one of my questions. I asked are you familiar with the Sutherland TimeLine and if I were to use mine on your table would it show to be spot on for accuracy playing a record at both speaads?

Dear Mab, L07D is not in service at this time. I am re-wiring the tonearm.

Hi Dev - just curious regarding the sp10 mkII that you tested. You said

"I tried it on a "DD" SP10 MK2 and it was off"

What was the strobe doing while you tested it? I have a seen a strobe on a SP10MkII one time "waver" back and forth - it could also be heard in the music. It needed adjustment. How steady was the strobe light in this case.

Cheers

What harm do you think there is if the two threads touch?

Increased friction and additional vibration/noise, especially when the knot of one rubs past the other thread.

Which Empire TT are you referring to? AC or DC drive ,belt type?

The Empire is of course AC synchronous drive. But most of my experience with it is actually with our variant of the machine, which we have been doing since the mid-90s:

http://www.atma-sphere.com/Products/#Atma-208

Dover,
I kind of like the idea of not placing lateral loads on the platter bearing....and this arrangement is working so well I don't know what there is to gain with the one motor?
What harm do you think there is if the two threads touch?

Empire TT's based on AC motors using belts.

Halcro - looks like the 2 threads are touching. If so you might want to put a shim under one of the motors to lift it slightly and separate the threads. Would be interesting to try 1 motor/thread. Cheers.

I decided to try another method for the thread drive.
I connected a thread to the platter and one motor (green French silk).....whilst another thread altogether connecting the other motor to the platter (black French silk).
2 THREADS
Re-calibrated the motor-controller using the Timeline (needed to increase the speed due to stylus drag) and listened to the previously warbling flute on the Massenet Le Cid.
No warbling now :-)......and the Timeline is slightly more constant than with the rubber belt.
GREEN BELT
BLACK BELT

Lew, how about the L-07D? Sorry if i missed it...

Henry, I've done it both ways with the Lenco and Mk3. The DP80 has no cartridge mounted at the moment, so could not do it with "stylus drag" factor. Likewise, I don't have 3 tonearms on any one tt, so could not repeat that show either.

If the tt is not slowing due to stylus, based on Timeline, then one would also not expect to see it with the KAB, so I am in no position to argue your point that only the Timeline can reveal it. Nor do I doubt you, absent any experience of my own.

And finally, all this chat is still overlooking what I thought was the real issue: speed variation due to stylus drag. None of the above mentioned observations really tell us anything about that. Unless sensitivity to stylus drag is gross, the Timeline may not reveal it.

Lew.......have you not tested the Timeline with and without 'stylus drag' yourself?
I assume all the comments on the Timeline tests are 'with' the stylus playing as demonstrated with 1,2,&3 styli engaged on my YouTube video?
I can assure you that the Timeline is the ONLY device currently available......capable of graphically demonstrating the most marginal of drifts due to stylus drag.

Hiho, The motor was grounded. I am not the only one with a hum problem on their Classic. There is a thread about it on this forum.

(quote)Sarcher, What is the evidence that the hum is (or was) due to the motor/cartridge interaction? (/quote)

The hum occured when the tonearm was swung over the platter in both cases. With the motor off on the Classic there was no hum with the tonearm over the table. The LP12 was likely the power supply because I had to unplug it to make the hum go away with the arm over the platter. I have solved the hum issue on the Classic by using an outboard Teres motor.

Halcro,

In my statement about AC belt driven TT's vs DC motor driven TT, I was meaning belt driven DC TT's, not a DC driven DD.

I have no experience with DD's yet. If I get a timeline will try to post some results.

Atmasphere,

Which Empire TT are you referring to? AC or DC drive ,belt type?

Halcro, I'm not sure I agree with Peter on this one. Our model 208 has the motor quite close to the platter (opposite the tone arm; there are no hum problems even with Grados). However the 208 uses a motor that would easily qualify as a flywheel in its own right. Keep in mind that in a belt drive, cogging is almost a non-issue due to the rotational speed of the motor, and then really only applies to DC motors for the most part.

AC motors are not particularly prone to cogging effects. The best tape drives all have direct-drive capstan motors, usually AC, and they often have rock-solid speed stability that turntables struggle to match.

The Empire that our machine is based on was one of the most speed stable made for quite a long time. Julian Hirsch complained in one of his reviews of it that the speed variation was "buried in the noise" of his instruments, making an exact number difficult to gauge (although Empire did publish specs at the time). Sounds to me like he could have used a Timeline...

I've played with a variety of belts on the machine. Interestingly, even mylar variants sound exactly the same. Its my opinion that if the belt alters the sound then there is a problem in the drive system somewhere.

So I don't buy the idea that drag in the bearing results in speed stability at all although it would not surprise me to find that some designers may have created this story for reasons of their own (obviously the 208 flies right in the face of Peter's comments). OTOH I don't doubt that the belt-drive Thorens had some problems! I think that is why the earlier Thorens are the ones people are looking for.

Sarcher, What is the evidence that the hum is (or was) due to the motor/cartridge interaction?

Banquo, I have some knowledge but not much skill when it comes to the electronics of either a motor controller (for BD) or a drive system for a DD tt. If I have a problem, I rely upon Bill Thalmann to deal with it, at my expense. But I do have the good fortune to live within 30 min of Bill's shop.