For what? Turntable? Car? CD transport?
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Dear Blueranger: Advantages?, through my AS experiences the only advantage is that for our friends is a better " looking " item.
I tested my TTs with additional motor comparing it the TT with one motor and I can't detected any kind of TT improvement in its quality performance level.
Of course you can try and decide by your self.
Btw, I like a lot the TT bearing design and motor controller, both first rate and better than other very very high price$$$$ TT out there.
Regards and enjoy the music,
If your tracking force is 2g, then the torque required to turn the record just by stylus drag at the outer edge of the record would be about 0.62N-mm or 0.0055 lbf-in. (That's assuming a coefficient of friction of 0.2) If you want to figure additional drag due to groove modulation (pushing the stylus back and forth) then figure a torque as high as 0.027 lbf-in. That would be a sideways groove which would pop the stylus out of the track. Additional torque is needed, of course for bearing friction and windage. Let's figure windage is negligible since the platter is spinning at just 0.56 rev/s. You can calculate the bearing friction torque if you have a way to measure speed change over time and know the moment of inertia of your platter or with a force gage.
My point is that the extra torque isn't needed; but I wonder if the added motor/belt provides additional sinking of vibrations away from the platter to improve the sound. If that is the case, then idler pulleys with extra belts might have the same advantages. Haven't I seen VPI TNT tables with extra belts and idlers? Maybe some one that has that type of set up can weigh in on if it helps or not with the sound.
One of the most ridiculous concepts put forth by some non-technical turntable experimenters (can't call most of these guys "designers") is the concept of multiple motors. Not necessary, and they introduce more noise, more instability, the reality of beating against each other (search "beating" of 2 frequencies), and other problems. When you see multiple motors you at least know quickly to search other brands.
We will see Monday when upgrades arrive UPS. My interest in 2 motors started last year when I heard a 30k Clearaudio turntable with 2 motors and it sounded spectactular. Buttery smooth with detail. That made an impression on me. He did not have a first rate system hooked to it and that made it all the more surreal. It also had the same tonearm and cartridge attached to it that I have! Benz L2 and Graham tonearm. I know his TT set up cost about 4 times as much as mine and cant compare apples to apples. One other reason I bought an extra motor with belts is uncertainty of AS being around in 5 years. On reason I went there was to buy a vintage Nak deck off his Craigslist ad. I had a chance to buy an extra arm for my Graham 2.2 but he wanted too much for it. Another reason was to see if my cartridge was the source of hum in my chain. He put my cartridge on spare wand and hooked it up to TT and it clearly was. Hum bothered me for over a year. After that I bought a cheap $39 shure and no hum. Then hum slowly set in again!!!!!!!! Found the culprit. Bedini clarifier was less than a foot away from cartridge. Live and learn. Actually the cheap cartridge sounded ok if you have a decent turntable. I did get the platter upgrade this summer with the 24 silencers and liked it. Tighter focusing with clarity.
With "hum", my general experience is that most times what you think cured it turns out not to have cured it. It finds its way back somehow. Balanced circuitry does away with the problem, completely and forever. Anyway, I hope that is not the case for you; I hope the hum is indeed gone. Also, what some of us call hum is not really hum, in strict terms. Hum is 60Hz or 120Hz pure tone. Is that what you heard? Most of the time, it's noise, a mixture of frequencies, e.g., a buzz.
The height difference of pullys is about 1/8" inch. I have a KAB strobe but havent checked it yet. What is there on market reasonably priced that would check speed stability? Test record? Piano decay? Motor noise is less than before and speed stability has improved hence the purer tonality Im experiencing. More motors more speed stability in my case with less noise. I will try one motor sometime and check results one day. I dont doubt your opinion Stringeen. Could you tell me which brands you observed the increased noise on and was the turntable on a rock solid base and how old was the motors? The new AS motors are very quiet.
There are plenty of theoretical reasons why extra motors is a bad idea, but, since you have an opportunity to hear the result, don't worry at all about them. I have no idea if that difference alone has a positive or negative result.
What I do know is that I heard great sound - very dynamic and incisive sound from a three motor machine: the big table from Audionote. It had three huge power supplies for the motors that made it impractical for my system so I passed on the opportunity to own one at a decent price.