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LP12 motor. Lack of torque.

Cheers SQ. I've had two motors on the Valhalla with the same results. The deck is built up now and running ok with 83 volts on the blue wire phase and 93 volts on the red wire phase. If I run equal voltages or near enough the motor will turn but a finger resting on the pulley will stop it. It was said in another thread that the voltages were 75 and 85 respectively and as I can't alter the voltage on the blue phase I've set the red phase ten volts over and it all seems fine.
 
The blue wire phase is derived from the red wire phase via just a capacitor so in theory increasing the red voltage should also increase the blue voltage. There will be a voltage difference between them because the 0.22u capacitor has significant impedance at 50Hz, but the ratio of voltages, in theory, should remain constant for a fixed frequency.

I suspect that the Zeners across the blue phase of the motor are limiting the voltage on that phase, which is why, in practice, it appears that the blue phase voltage is not increasing. If that is the case the blue phase waveform is probably being distorted, which could explain why increasing the voltage on a Valhala'd LP12 is associated with a sound quality degradation compared to others that report no issue with increased voltage on other decks.

My assumption is that the zeners are there to clamp back-emf from the motor on the blue phase due to the high impedance of the 0.22u cap. It looks like the clamping will kick in around 68.5V for a signal which should peak at ~120V. Is there something else going on here?

Andy
 
The blue wire phase is derived from the red wire phase via just a capacitor so in theory increasing the red voltage should also increase the blue voltage. There will be a voltage difference between them because the 0.22u capacitor has significant impedance at 50Hz, but the ratio of voltages, in theory, should remain constant for a fixed frequency.

Andy


So most of the stuff on the Valhalla board is just to produce a perfect 50 Hz sine wave at the correct voltage and the other handful of components works more or less like the basic supply?
 
Yes, it's an AC regenerator tacked onto your basic dogshit phase shift capacitor arrangement. It's a nice Ac regenerator though, good clean sine wave.

So much better to have a biphase adjustable controller and run identical voltage to both phase.
 
That's what I thought after reading AKPs post. I'm wondering how hard it would be to take two Valhallas, remove the basic power supply stuff and use one for each phase of the motor. The trick I suppose is how to lock them with one out of phase to the other. I'm wondering if one of the ICs has an equal but out of phase output that can be used to drive the rest of the circuitry on the second board perhaps. I'm no electronics engineer so I hope some of you can understand the what I'm getting at.
 
There was a guy selling a double Valhalla on Audiogon not that long ago:

https://app.audiogon.com/listings/t...n-outputs-2014-11-17-analog-18938-new-hope-pa

The easy bit is generating the phase shifted signal, you would take the Qbar output (pin 2) of U5A on one board and feed it to the CLK input of U5B (Pin 11) on the other board (instead of taking the signal from the output of Q on U5A (Pin 1) for that board).

The tricky part is to ensure that all the control lines are correctly connected, in particular the reset line to U5B needs to be the same for both boards to ensure that the phase shift is in the same direction each time. The Q and Qbar outputs of U4A are also used to shutdown the amplifier so they would need to be connected from one board to the other.

One area that may have some impact is the matching of the filters between the two boards that may cause some phase mismatch. I am in the process of off-boarding my Valhalla board and I have a spare board lying around so maybe I will try it out at some time.

Andy
 
Good stuff Andy, I thought I might have been talking rubbish. I don't have the ability to work it out for myself but I can follow ok. If you decide to give it a go let us know how you go on.
 
A double Valhalla is a good idea but in practice I suspect a DIY Geddon is an easier and better solution. It is very simple, a 110V trafo hooked up to one of Si's "basic dogshit phase shift" networks, otherwise known as "a capacitor".
 
You're probably right Steve. I think the Geddon would be more acceptable to the average Sondek owner. Using two Valhallas was just a thought and then I find out it wasn't such a daft suggestion and someone has already done it. That made me happy anyway and besides for a diyer it could be an interesting project.
 
I think the bearing liner issue is only true of very old LP12 bearings - ones significantly earlier than the Cirkus bearing. However, I should add that I don't use oil at all as such, I use silicone and this is very much thicker than even quite thick oil. In addition, there is no vertical contact in my bearing and the lateral frequency of the suspension is different to that of an LP12 - so plenty to consider (sq's deck does have bearing point contact but it doesn't have a suspension in the way an LP12 does).
 
Slideway lubricant is much better than oil. It has an inverse drag coefficient compared to oil or grease.


JC
 
Would silicone lubricate the point contact ok for those that don't use mag lev?

I would argue that there isn't actually any lubrication at the actual point of contact in most turntable bearings. The point load is very high and the bearing isn't pressurised so the oil is simply pushed out of the way of the contact point. Yes there is oil just to the side of the contact point but that is rather irrelevant as that isn't where the load is carried :). What the oil does do is stabilise the lateral load on the bearing and the greater the viscosity the more profound this coupling is. I would argue that the advantage of adding moly-slip (etc) to TT oils has little to do with lowering friction or pressure issues and more to do with the fact that it significantly raises the viscosity of the oil. If one really wants to lubricate all the load bearing surfaces then the bearing must be pressurised (in some way).

The very problem with the motor drive is that whilst the motor has high potential torque it is directly proportional to load. As load approaches zero then so does torque. Whilst there is load at startup (platter inertia to overcome) there is very little once running speed is reached - this is even more true with dynamically balanced platters and super low friction bearings. Whilst a low friction bearing is good in terms of low noise, it is actually less good in terms of maintaining drive stability.
 
I do run a Teflon thrust pad in mine so it has different vertical termination to a boggo Lp12 bearing.

Can't say enough good about added drag and fully adjustable speed. The speed stability is good its not even funny.
 
Sí, sorry to be a pain but could you post an ebay link to the super viscous silicone fluid again.

Thanks

Dan
 
Sorry, I haven't got a specific link but heavy weight silicone fluids are sold for the transmissions in model racing cars.
 


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