Methods for Reducing Turntable Motor Vibration

[moray james]

Originally Posted by sq225917

Adjusting the phase offset gives you a real and meaningful improvement in vibration. Fiddling with motor drive voltage largely just reduces torque and is a crutch for incorrect phase offset.

so how does on go about measuring a motor? what do you need to do to adjust the phase offset? Do the individual windings need to be measured and what equipment is necessary to do this? I have an AC motor which vibrates too much to use perhaps this is all that is wrong? Thanks for any assistance or direction. Best regards Moray James.

[sq225917]

Which motor is it? Manufacturers specs should lead you to roughly the correct value +/-10% or thereabouts. You can measure the coil resistance and inductance and calculate it from there, or start with the recommended capacitance and add a 10% trimmer cap into the mix.

[moray james]

it's a french motor a Cruzen I think. I have the manufacturers suggested capacitor value. What would I expect to see for winding resistance values? Is going to be something I can measure with a multi meter? I do have access to an inductance meter as well. Should I be starting with a smaller cap and add the trimmer cap on? What is the process? Do I simply adjust the value till running operation seems smoothest or is there something specific to measure for? Thanks. Best regards Moray James.

[sq225917]

If you have the manufacturers value then there's little point bothering to calculate it based on measuring the motor, so skip that step.

I would start with 10% less than manufacturer recommended capacitance and work through increasing it to 10%+, via a trimmer or maybe substituting smaller cap vales to home in on a rough value.

If you hold the motor in one hand while it is turning you will feel the vibration increase and decrease as you adjust capacitance. I found the best value for mine was just under 0.2uf, the manufacturer recommended valuer is 0.22uf, the difference was significant both in vibration felt through the hand and also from a full speed demodulation produced from a 3k test tone when it was re-fitted to my deck. There's a great thread on Pinkfishmedia in the diy section called 'turntable sped analysis', there's a lot of good info in that thread.

http://www.pinkfishmedia.net/forum/s...ad.php?t=70027

[tabarddn]

I may be a little obvious, but one very effective way to reduce vibration is to dump the AC motor and go for a stand alone DC motor. Massive reduction in vibration because the unit is totally isolated (apart from the Belt contact). From what I can see there are two very cost effective options out there.

1) timaudio, 12 volt stand alone DC motor (I have one) very good value money at around US$100, until it goes wrong. Then they are a pain to deal with and they eventually sent a replacement motor. Trouble is it was a 9 volt not 12!!, works OK but I bought the 12 in the first place.

temaadaudio. Again a 12 DC volt motor, (have not tried it) but it is battery driven and costs US$85 and apparently you get over 6 hours use from one charge.

Both sell on Ebay

[moray james]

Thank you sq225917. I will start reading the attached thread. Best regards Moray James.

[YNWOAN]

Originally Posted by Mark Kelly

The second is a resonance between the moment of inertia of the rotor and the electromagnetic torque "spring" caused by the drive current being greater than the stall value at the output torque, which causes the angle between rotor and stator field to reduce. Since this is related to the difference between drive voltage and "generator voltage", the higher the drive voltage the worse this effect. It isn't as easily solved as the above effects and my first attempts were either abject failures or impossibly complex to implement. I'm still searching for a good simple solution to this one.

This is very interesting and is an area that I have investigated (and had some considerable success - sq225917 has taken part in my investigations).

[sq225917]

Yes you haven't looked back since first using the silicon fluid from my old Kuzma deck in your LP12 bearing.

[YNWOAN]

Originally Posted by YNWOAN

This is very interesting and is an area that I have investigated (and had some considerable success - sq225917 has taken part in my investigations).

Unfortunately, the above post has been misunderstood (my fault - too succinct); what I meant was that sq225917 and I have shared ideas and experience - he has also done a great deal of investigation with regard to power supplies (which I have been lucky enough to participate in - though have had no input).

[sq225917]

Thanks for the clarification Mark, I've always found that better outcomes are arrived at when working on a problem with someone else, especially so when working on a problem with you.