Record Playback Musings

[MylesBAstor]

Many subscribe to the thought that the best way to play back an LP is the way it was originally mastered. In other words with a linear tracking arm.

But should it stop there? From the Brinkman Audio site:

"Cutting lathes usually have AC synchronous motors, and their speed is strictly dependent on the frequency of the incoming AC power’s alternating current. These motors run at a very low speed because they work with high numbers of poles, so they drive the platter directly. Some of them have a viscous coupling similar to the one that can be found in an automatic gear mechanism. The very strong motor – cutting of course demands a lot more power than tracking – and the high platter mass effectively rule out any speed variations or at least minimize them substantially. A cutting lathe usually has a very high-mass platter with a larger diameter than the LP has, so it relies on the flywheel effect for speed stability."

So should a turntable have a massive platter that emulates the cutting lathe too?

[user510]

So should a turntable have a massive platter that emulates the cutting lathe too?

I believe that mastering engineers routinely listen to freshly cut lacquers using the the same cutting lathe that cut the master. Therefore the proof would be to use a cutting lathe as a turntable to validate this proposition.

-Steve

[Rob]

there's a vid on youtube of an extreme 'phile in Japan that uses a Neumann cutting lathe for a turntable. cant see it now because of "multiple third-party notifications of copyright infringements"

[JCOConnell]

of course a turntable should have a massive platter. the more mass it has the less susceptible to outside forces changing its velocity. (greater inertia).

[Johnny Vinyl]

I guess I'm screwed then. My Oracle Paris is a featherweight.

[fcrowder]

I think that speed accuracy and consistency is what is at issue and that there may be various ways of achieving that. My Rockport uses a 50 pound platter and a multi pole custom built AC synchronious motor/ aramid fiber belt; however, the motor controller/ power supply for the motor impacts speed as does the addition of a flywheel on the motor shaft. Later Rockports used a highly complex direct drive motor. My point is that speed accuracy depends on more than platter mass.

[Rob]

Fred, is your Sirius a series III? I believe Jeff Rowland built the power supplies for those, they were housed in a ginormous chassis that looked like a power amp.

[fcrowder]

Rob, my Rockport is a much modified Sirius I. One of the mods was the Jeff Rowland power supply. Unfortunately, Jeff synthesized the 60 Hz. sine wave in the digital domain which severely impacted the sound. Fortunately for those of us who bought one, Damian Martin was able to replace the digital signal generator with one that worked in the analog domain which was sonically excellent which I still use today. Damian also designed the power supply for the Sirius 2. The D.C. Motor on the Sirius III came with its own supply from the manufacturer.

[mep]

Are we down to micro levels of speed deviation now or nano levels? It doesn't make sense to me technologically in late 2016 that we have to talk about speed deviations with expensive turntables, but here we are. Are we still perfecting what hasn't been perfected or are we gilding the lily like the distortion wars of the late 1970s and 1980s? And I say this somewhat tongue in cheek because really good speed controllers do make a difference, but why aren't they standard at a given price point? Why are people still making turntables that are either incapable of maintaining the correct speed or selling you one that is incapable of turning at the correct speed without an external controller that doesn't come standard? Why do some companies like Rega sell you turntables that run too fast on purpose (hint: to make music more 'exciting')?

[Joe Pittman]

Everything matters. Regardless if a platter is low mass or high mass, it is the execution of the design and the real performance that results. There are so many variables to performance that it would take a book to describe them in detail. And in the end, regarding the mechanical side of the equation, the phono stylus can't tell the difference between turntable based distortions and that of the signal etched in the groove. The goal of the turntable designer/manufacturer is to get all forms of distortion to zero, including speed variations. A daunting task.

[Alrainbow]

My comments are only based on knowledge of engineering only not sound. Hopefully this may help some here .
Asynchronous means it uses the incoming frequently be it 60 cycles here . The number of poles has two effects one more poles is better rpm stability meaning less slip . Yes there is an inherent slip of every motor . The second is the speed each added set of poles cuts the sync speed in half . In your cutting or playback operation I would think a hall effect or other type of feed back loop would monitor the exact speed and make adjustments as needed. Now if this effects sound as I said I don't know. The added poles in this case gets it to more closers needed speed or rpm . Is the device a direct drive ?
There is another type of syncourse type motor that is more stable in speed . A DC type this type is about true sync of speed almost no slip . It can use the same ac in outside but a DC rotor the part that turns this locks in at the more exact sync speed . I thought I read somewhere about records that use a varying speed motor to compensure from freq or diameter as it changed. While I love the sound of analog in both forms from my view vinyl is very old school and filled with flaws and loose in generations as its cUT, pressed and what ever else is done. How good theye do around us an among a wonderful to me lol . But even though I am of the digital kind . The best or most pressing I won is from tape or vinyl Rips.

[Rob]

My comments are only based on knowledge of engineering only not sound. Hopefully this may help some here .
Asynchronous means it uses the incoming frequently be it 60 cycles here . The number of poles has two effects one more poles is better rpm stability meaning less slip . Yes there is an inherent slip of every motor . The second is the speed each added set of poles cuts the sync speed in half . In your cutting or playback operation I would think a hall effect or other type of feed back loop would monitor the exact speed and make adjustments as needed. Now if this effects sound as I said I don't know. The added poles in this case gets it to more closers needed speed or rpm . Is the device a direct drive ?
There is another type of syncourse type motor that is more stable in speed . A DC type this type is about true sync of speed almost no slip . It can use the same ac in outside but a DC rotor the part that turns this locks in at the more exact sync speed . I thought I read somewhere about records that use a varying speed motor to compensure from freq or diameter as it changed. While I love the sound of analog in both forms from my view vinyl is very old school and filled with flaws and loose in generations as its cUT, pressed and what ever else is done. How good theye do around us an among a wonderful to me lol . But even though I am of the digital kind . The best or most pressing I won is from tape or vinyl Rips.

Al, with turntables some mfrs also use 3-phase AC motors which have many advantages over the ubiquitous singe phase motor found in the vast majority of tables and consumer appliances/devices. By contrast DC motors require a PS and speed controller which also monitors drift (common to DC motors). I had a few conversations with Bill Carlin of the recently defunct Phoenix Engineering, he was working on an innovative DC drive system with controller for the aftermarket, which now appears wont see the light of day. there are a few cos. that presently offer DC drive systems for the aftermarket but some are very rudimentary and not really an improvement over AC types. The latest DC drive by Linn for their tables is cutting edge.

a third and much less known motor system for belt drives are digitally controlled stepper motors that have speed variation measured in parts per million. AFAIK the only turntables that used this technology were from Versa Dynamics. This is the same technology used in the motion control industry, disc drives, CNC controlled machinery, 3D printers, etc. it goes without saying speed control is highly accurate and rock solid with step motors.

[Beaur]

Damn, didn't know Phoenix had bitten the dust! Was going to pull the trigger on a controller for my Empire.

[MylesBAstor]

Some dealers still have supplies.

[Alrainbow]

Wow 3 phase , how do they achieve this ? Do they go dc to AC convertion ? In my RC stuff they use this method and pretty good speed control by feed back considering the massive load changes in flight . What I don't get if a platter weighs many pounds and is belt driven how much can it vary with a tiny needle being dragged across it . While so many I know and trust lay claim to big sound changed in tables I just cannot get my head around it. The arm or cartridge yes , also what ever happened to optical I always thought it had to be best if left analog through out ?

[Rob]

If you're into RC you've heard of Steve Neu? he mfrs some of the very best brushless DC motors extant, Ive know him for > 20 yrs we were in the same club in a former hobby-life of mine. anyways, i was helping Bill Carlin connect the dots and introduce them so they could make beautiful music together (figuratively speaking).

[Alrainbow]

How cool is that of course I know of him he is legendary lol.
I have a fleet so many are used. Castle creations , kong , YG for my protos. And actually Italian helicopter lol.

[Steve Lefkowicz]

of course a turntable should have a massive platter. the more mass it has the less susceptible to outside forces changing its velocity. (greater inertia).

Yet, there are excellent tables out there that go the low mass route. Pink Triangle, Funk Firm, Rega, even Linn. High versus low mass are just different engineering choices.

[MylesBAstor]

Are we down to micro levels of speed deviation now or nano levels? It doesn't make sense to me technologically in late 2016 that we have to talk about speed deviations with expensive turntables, but here we are. Are we still perfecting what hasn't been perfected or are we gilding the lily like the distortion wars of the late 1970s and 1980s? And I say this somewhat tongue in cheek because really good speed controllers do make a difference, but why aren't they standard at a given price point? Why are people still making turntables that are either incapable of maintaining the correct speed or selling you one that is incapable of turning at the correct speed without an external controller that doesn't come standard? Why do some companies like Rega sell you turntables that run too fast on purpose (hint: to make music more 'exciting')?

Interestingly, high-end tables still vary widely in their speed stability based upon Mikey's reviews where he measures variations using the Feickert software.

[mep]

But doesn't that tell you something about the quality of the engineering?

[MylesBAstor]

These were some highly regarded tables.

[mep]

But still....or, does that mean their speed variations don't matter?

[MylesBAstor]

My comments are only based on knowledge of engineering only not sound. Hopefully this may help some here .
Asynchronous means it uses the incoming frequently be it 60 cycles here . The number of poles has two effects one more poles is better rpm stability meaning less slip . Yes there is an inherent slip of every motor . The second is the speed each added set of poles cuts the sync speed in half . In your cutting or playback operation I would think a hall effect or other type of feed back loop would monitor the exact speed and make adjustments as needed. Now if this effects sound as I said I don't know. The added poles in this case gets it to more closers needed speed or rpm . Is the device a direct drive ?
There is another type of syncourse type motor that is more stable in speed . A DC type this type is about true sync of speed almost no slip . It can use the same ac in outside but a DC rotor the part that turns this locks in at the more exact sync speed . I thought I read somewhere about records that use a varying speed motor to compensure from freq or diameter as it changed. While I love the sound of analog in both forms from my view vinyl is very old school and filled with flaws and loose in generations as its cUT, pressed and what ever else is done. How good theye do around us an among a wonderful to me lol . But even though I am of the digital kind . The best or most pressing I won is from tape or vinyl Rips.

Thanks for the comments Al!

I think the bolded is an important point and know a designer who was working on a motor design with enough poles to run "natively" at 33 rpm.

Thought this old interview with Harry Weisfeld from an old Positive-Feedback review of the VPI Classic Direct turntable might be pertinent too.

HW: I always thought the problem was the motor and the interface between motor and platter. We worked with an engineering company when designing the Classic Direct on the issue of getting the table to run at exact speed. After much testing and listening, we decided on using a three-phase, extremely high pole AC motor of great accuracy in design. Military grade if you will! The motor we chose uses so many poles in a printed circuit design that cogging becomes irrelevant. It isn't like the older direct-drive motors plagued by slight cogging effects. As an example the Technics uses a 16-pole motor, about one-tenth of what you need for truly continuous rotation.

The more poles an AC motor has, the slower it runs as its native speed. At 60Hz, a 12-pole motor runs at 600 rpm and a 24-pole motor runs at 300 rpm. See the difference? To run "natively" at 33.33 rpm you would need roughly 216 poles. That is where the feeding circuit works and sets the speed using a change in frequency and locking that frequency to set the speed. The speed is driven by the frequency, not a DC voltage and feedback loop.

Many of the early direct-drive turntables used brushless DC electric motors and Hall Effect sensors to determine the position of the rotor; that information was then fed to the motor controller. This proved an excellent choice for the sensor (or magnet) and typical life expectancy is quite long. The problem is the sensor is a device that tells you what has already happened as opposed to real time.

A great expression by a motor engineer is "A DC motor knows where it was; an AC motor knows where it is." By contrast, the speed control used with the Classic Direct samples the generator frequency feeding the AC motor plus that 20 pound Aluminum platter and the real time effect of using an AC motor makes up the difference. This plays a significant role in turntable's speed continuity through heavily modulated passages.

The big thing, however, is the number of poles. Most direct drive motors use a finite amount of poles and the power is transmitted to the rotor in a sinusoidal way, pole by pole. This is very simplified but it explains some of what we did not like about older direct drives. With the Classic Direct motor, we use a printed circuit made in a horizontal "V" shape so no pole is over less than three coils at a time. Doing that leads to no dead spots and continuous torque all around the platter rotation.

Another important factor in the design of the direct-drive motor system is the thin gap between the stator and rotor. In the Classic Direct, the platter functions as the rotor and explains why the platter and drive cannot be separated in the field; this gap, done on a CNC lathe is on the order of 0.005 inches. The end result is that it transfers energy very well.

The Classic Direct speed accuracy is way better than test record accuracy and is checked using a magnetic head to read the results. We normally get readings less than 0.01% wow and flutter and noise down near -100dB.

[Alrainbow]

While I know someone must have tried this already but if you lowered the freq down you could be exact has anyone gone this route ? Unkess it makes noise or transfers vibration ?

[MylesBAstor]

Now here's the speed stability of VPI's DD table vs. the Onedof table. I think as Joe pointed out, speed stability is just one part of--albeit a big part--of the overall turntable design. I think it's like looking at one's cholesterol levels and evaluating risk without looking and taking into account other markers. Note Mikey's comments on the Onedof vs Coliburn's sound.