Doug,
I am a VPI TNT III owner with a poorly designed & now broken PLC controller that VPI no longer supports. I've also observed that the TT sounds better on thread drive than the stock rubber belts. However, slippage of the thread on the small pulley on the old 600 RPM motor makes thread drive difficult to keep in tune. I have been evaluating purchase of a Verus motor in comparison to VPI's upgrade path of SDS and newer motor. The Verus looks like the better alternative. Now if Chris is half as charming as Harry W's wife on the phone (answer: yes, he must be, even though I have never spoken to him), then I'll be buying a Verus. |
Doug,
While waiting for Verus I am considering adapting tape drive to the VPI TNT by machining new pulleys for motor & flywheel. In order to prevent tape crawl, would cutting 1/2" channels into the pulleys be desireable? What is the best material for a pulley (e.g. hardwood, brass, delrin)? I suppose you'd want something smooth but not slippery.
Currently to get traction I'm using three threads between flywheel & platter, and the stock round rubber belt between outboard motor & flywheel. This probably offers most of benefits of an all thread-drive system. By using threads to tightly couple the inertial masses of the flywheel & platter, the system is more stable & the motor has less work to do in dealing with the drag of the stylus. A rubber belt between motor and flywheel may actually help smooth out AC cogging & the flywheel should act as barrier to the rubber belt's torquing effects. In any case, the result is a much livelier, focused sound than you'd expect from a TNT. The only thing I don't like about it is the occasional pinging of the thread knots as they circulate through the grooves of the pulley on the flywheel.
With rim drive applied, do you think the ideal platter should be light or heavy? If heavy, it would be an interesting experiment to retain the flywheel and relocate it outboard of the Verus motor. The flywheel could be driven by a long tape loop from the platter. This would have the added benefit of snugging up the platter against the Verus motor capstan & centering the platter bearing. Centering the bearing was the purpose of the old TNT three-pulley system, which I needed to remove to enable thread drive around the platter. |
Pauly,
Thankfully, market forces in this cottage industry are quite different from banking, and time-value-of-money calculations are mostly irrelevant. Perhaps the hedge fund crowd would do better to maximize utility & profit margins all down the supply chain by sticking to oenophilia, art auctions, and the outsourcing of decisions regarding statement audio systems to Sound by Singer. |
Doug,
Thanks for suggesting a fly fisherman's blood knot. Now the thread runs smooth & quiet. Using this type of knot it's pretty much impossible to make two threads of identical length in order to run multiple threads. But a single thread works well if pulled tight. |
Pauly,
I think it's unfortunate to critique business issues that are premature and distract from consideration of the Verus motor as an engineered product that arrives at a timely moment in TT design.
Recent evolution in TT design seems to have mostly divided between belt-driven models with heroically massive platters & high-torque motors vs. lightweight born-again idlers & direct-drive models both new and remanufactured vintage. I've heard enough people whose ears I trust get excited about those damned Lencos to pique my curiousity. But intuition tells me that direct-coupled motors, together with the more sophisticated bearings, platters, and plinths of a modern TT (maybe almost ANY good modern TT), may be the next big thing. The Verus is the only solution I'm aware of that lets one test this proposition by performing a user-friendly heart transplate on his own TT in the privacy of his living room. It's an appealing idea. It might just upset the received wisdom that any given manufacturer's TT design is to be viewed as painstakingly cut from one piece of cloth that can't be improved upon outside of arm, cartridge, and platform substitutions. Of course if enough people find that this motor can make any belt-drive TT sound better, then how long will it be before the direct-coupled paradigm replaces belt drive altogether? And if heavy platters and their robust bearing assemblies are unnecessary with a direct-coupled motor, then how long before lighter assemblies take over & drive down costs of top models? |
Jean,
I think I understand your comparison of idler drive to belt drive, but I'm lost in your comparison of idler to Verus rim drive.
I would think the comparison of rim drive to idler drive boils down to the relative compliance of the interface between motor and platter. With rim drive there will be speed instability if the rubber ring around the transmission wheel has excessive compliance. Is idler drive really much better in this regard?
There is also the matter of transmission of motor rumble. But as with your replinthed Lenco, noise problem can sometimes be engineered.
The torque necessary to meet the changing force of stylus drag is far less than what is necessary to lift an 80 lb. plinth. But it is nice to know that a Lenco motor could be used to drive an electric bicycle. |
Dan_ed,
Somewhere in this thread it's reported that in testing, Verus rim drive produced the greatest improvement in combination with the lightest Teres platter. It would seem that with rim drive (as with idler drive), high platter mass might actually impede speed stability (probably at the point where the motor has insufficient torque to meet the higher rotational force associated a high-mass platter.) But I suppose that high-mass platters are also better at resonance control. So there is likely a trade-off with how light one would want to go without resorting to fancy TT mats and other approaches to resonance control.
Since with rim drive as with idler-drive, speed stability is entirely determined by the motor, it would be interesting to know whether the 1800 RPM motor of the Lenco offers an inherent advantage. I assume that with the Verus, the drive pulley is pressed onto the spindle of a low speed motor. Perhaps the best rim-drive design would be a high-speed motor with multiple wheels and a step-down transmission. This might also improve isolation of motor noise.
Finally, issues of force and compliance surrounding stylus drag can't be too much different than issues regarding VTF. This is handled easily in a TT arm by counterweights & gravity.
|
"A given motor speed and torque in the rim drive system may have a range of platter weight that works best with that given motor. Then again, it could be testament to how well these heavier platters with mylar belts actually work."
I'd like to hear an opinion from Teres on whether the Verus with a light Teres platter surpasses their heaviest platter with mylar tape drive. |
Pauly,
The flywheel effect of the platter on that cutting lathe would be negligible compared to the 75kg/cm torque generated by the motor. From pictures on the net it's evident that a really decent cutting lathe like the Neumann has a much stronger drivetrain. A lathe strong enough to handle the fundamental drag on the cutting tool should be impervious to small modulations in drag. Still, somehow tools never quite seem to be as good as they should be. I have a metal lathe with a 10" chuck & a 2hp motor & I still manage to find jobs that are too big for it.
I did find a reference to pitch problems introduced by stylus drag on lathes used to cut 78rpm records in the 1920s. |
Lew, while browsing one of my father's old EE textbooks from the early 50s, I read that a block of iron placed on top of a transformer improves coupling between the magnetic fields. This is how how a VPI brick is constructed. I don't know about the Skakti stones. |
