Linn LP12 Motor wobble - can this be saved?

[hirscwi]

I suspect that's the case - only difference is pulley size - based on what I've read in several places and drawing some conclusions. Based on the datasheets, it appears that the motor runs at 250 rpm on 50Hz and 300 rpm on 60Hz - which makes perfect sense for a synchronous AC motor (speed determined by frequency, not voltage). Linn adjusted for speed variation with a different diameter pulley (as near as I can discern). This is a clever approach.

So I think I'm going to give it a try - I like experimentation. It will give me an excuse to try one of the inexpensive RPM meters. I suspect it will be a bit tricky to remove the pulley from my existing motor.

My one worry is that the Valhalla p/s drives the motor at 250 rpm and the pulley I have is for a 300 rpm motor. I'll keep researching the Valhalla p/s to see if I can learn the output frequency. It is outputs 50Hz, then I have a problem using my current pulley. Perhaps the Valhalla p/s has a variable/adjustable output frequency? Or perhaps I can find a different pulley if needed. If there's interest, I'll keep this information posted as I go along.

 

[muovimies]

It seems a course of action is already decided, but just out of curiosity, did you actually hear the wobble in the sound your turntable produces?

The most important factor is the ratio of pulley size vs. the inner platter diameter, which determines the speed the platter spins. Variation is pulley - inner platter distance doesn't seem to have an effect on the speed (in my experience), provided that enough but not too much tension for the belt exist at all times.

I have one turntable with a bent motor shaft, the wobble is quite noticeable by eye, but not by ear - I just can't hear any wow or flutter. Given the chance, of course I would replace the motor, but at the moment I'm not inclined to invest any cash in doing so, because I can't notice a lack in performance.

 

[hirscwi]

Great question. I can detect the wobble only with a test record, single tone. So it's probably a waste of money to make the switch, but I like to tinker. I've been wanting to upgrade to the Valhalla power supply and this is the time to change out the motor.

It seems a course of action is already decided, but just out of curiosity, did you actually hear the wobble in the sound your turntable produces?

The most important factor is the ratio of pulley size vs. the inner platter diameter, which determines the speed the platter spins. Variation is pulley - inner platter distance doesn't seem to have an effect on the speed (in my experience), provided that enough but not too much tension for the belt exist at all times.

I have one turntable with a bent motor shaft, the wobble is quite noticeable by eye, but not by ear - I just can't hear any wow or flutter. Given the chance, of course I would replace the motor, but at the moment I'm not inclined to invest any cash in doing so, because I can't notice a lack in performance.

 

[muovimies]

Great question. I can detect the wobble only with a test record, single tone. So it's probably a waste of money to make the switch, but I like to tinker. I've been wanting to upgrade to the Valhalla power supply and this is the time to change out the motor.

I wouldn't say it's a waste of money, after all you *can* hear it, even if only with a test record. And even if you couldn't, replacing the motor gives you the feeling of having your turntable performing flawlessly, while with the old motor you'd always *know* it wobbles there underneath the outer platter, even if you can't hear it doing so. If you are the type of person things like these matter to, then it'll probably be money well spent, or at least spent

 

[hirscwi]

Correct on all counts! Plus, I think I'll try the 31813 replacement - another bit of experimentation. I am going to rebuild the Valhalla p/s I just purchased (new caps, diodes, possibly surge resistor) and will give it a try with the old motor before I buy a new one since they seem to be readily available.

I wouldn't say it's a waste of money, after all you *can* hear it, even if only with a test record. And even if you couldn't, replacing the motor gives you the feeling of having your turntable performing flawlessly, while with the old motor you'd always *know* it wobbles there underneath the outer platter, even if you can't hear it doing so. If you are the type of person things like these matter to, then it'll probably be money well spent, or at least spent

 

[grottyash]

Out of curiosity what motor does your RP6 have? I have a feeling it is a Premotec and very similar to the 31813.

 

[hirscwi]

I can't really tell for sure - it's covered. The next opportunity I have, I'll pull the cover and check it out. I have seen the 31813 listed as a replacement for Rega and I'm fairly sure they use the same motor in most of their tables (based only on what I've read - I'm no Rega expert). I have the TTPSU with the Rega (I think it came with the RP6) so I might hook it to my scope to see the voltage and frequency of the output.

As an aside, I can't believe these specialized turntable power supplies are so expensive. It is relatively simple to convert to DC then drive a clock/oscillator which powers the motor. That's all the Valhalla does (and the TD125) from what I can tell. I may scour the DIY forums to see if anyone has built such a p/s. I suspect it can't be terribly expensive since I see a p/s on eBay that works the Linn motor - for only $199 (from China of course).

Out of curiosity what motor does your RP6 have? I have a feeling it is a Premotec and very similar to the 31813.