Saturday, January 25, 2014

Turntable Drive Systems

Here's one on which currently my friend Tim disagrees.  He likes a short Rega belt drive system as being optimal.  He claims the platter mass is the best defense against wow and flutter.

I'm not so sure.  I remember reading about grove drag speed modulation in Peter Moncrief's International Audio Review (IAR) in the early 1980's.  The Japanese had realized the importance of that issue in the mid 1970's, if not before, and designs like the Sony TTS 8000, Technics SP 10 Mk II, and Denon DP 6000 were taking it very much into account with massive torque finely delivered, and proclaimed in specs.  For example one turntable claimed 0% deviation in speed with up to 150g of resistance.

Peter was worried about belt drive, IIRC.

(Update: Peter wrote again (?) on this very same topic in his latest online IAR.  Unfortunately this review hasn't been completed in a long time.)

I think looking just at platter mass is the wrong thing.  One has to see the drive system first as a complete system.  In that system, the platter mass serves as part of a low pass filter, as a parallel capacitor.  A belt or idler serves as a combination of resistance and inductance.  But the belt or idler has dynamic properties which may further help or hinder.

Now belts and idlers have different properties.  I believe it is probably easier to get better motor noise reduction with a belt.  That's because it's easy to get arbitrary amounts of "inductance" (stretchiness).  And one can use a weak motor (high resistance).

But I believe there is also more lag with regards to motor correction stability.  Any errors take some time to work themselves completely in a belt drive system.  An idler wheel doesn't vary as much.  There isn't much stretchiness, and the motor is high torque.  Also the idler rubber recovers instantaneously, it doesn't have to work itself out, re-stabilizing the entire length of the belt.

Belt drives where the motor isn't fixed to same plane as the platter also introduce the possibility that timing may be slightly thrown off by suspension movements.  Idler drive motors can move, but the range of motion is very limited, usually restricted to vertical only, and this has little effect on timing.

So why did people hear better timing with belt drives?  I argue they didn't.  As Arthur Salvatore says, the Linn simplifies the music.  In less complex music, the rhythm and timing becomes a more significant, ultimately the only remaining part.

Small degree of flutter caused by belt drive is exactly this…a simplifying effect.  Small timing errors are another way of raising the sound floor, of covering up micro details.

Update: I've now won a Lenco L75.  I will shortly have two working late generation direct drive tables (Mitsubishi LT-30) and one non-working one I hope to get repaired (Sony PS-X800).  I still look at listings for the top direct drive models from Technics, Denon, and Sony.  I got myself the two Mitsubishi's (one for backup) and the Lenco for my birthday instead of getting the Rega RP6 or Michell Gyrodec.  I have placed a bid on a high end tonearm for the Lenco.  After I win a tonearm, I'll order an appropriate plinth for the Lenco.  My initial hesitation in getting the Rega had mostly to do with their anti-record-clamping philosophy and lack of VTA adjustability (which I see as a conspiracy to deprive us of the right to use other phono cartridges than theirs).  My hesitation, if you can call it that, in getting the Gyrodec had mostly to do with the total cost of a loaded and new Gyrodec system, $6000 or more as I had envisioned it, including upgrades and SME 312 arm.  But as a result of my new distrust of belt drive systems, as described above, which only a few weeks ago I was making fun of  ("Idler drives rumbling into the future"), I'm not particularly interested in getting a belt drive now.  I only have some regrets in not getting a new and likely perfect for 10 years table as I think the Rega would have been.  Even the one Mitsubishi I have received so far has a minor but worrisome issue--the moving base of the arm makes a slight bumping sound when the servo moves it for linear tracking.  This likely is not audible.  If you're not into belt drive any more, there aren't as many new choices as there were in 1980, at the height of the Japanese direct drive table phenomenon.  The Rockport which Peter Moncrieff started to review is a custom built direct drive for $100,000.

No comments:

Post a Comment