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Tecnodec w/HR PSU - Speed Problems - Help?

I own a Michell Tecnodec w/HR Power Supply. To set/check the speed I used a KAB Stobe disc.

I set the speed perfectly using the HR PSU. Then, I turn off the motor and re-check and the TT is running slower. Actually, everytime I turn off the motor and switch it on again the speed is different. If I leave it alone for 30 minitues the speed goes back to the original (where it was set the first time). It's not major maybe 0.5% variations.

This concerns me a little because this means when I listen to a second, third record the speed will be different than that of the first due to shutting down the motor to change an LP.

This also happened with the original cheaper PSU.

Is this a normal occurance with DC motors?

Thanks guys for any help,
Balance
dr_balance
9 responses Add your response
restock
831 posts
 
Balance, thanks for your post. I never tried a strobe disc, but I might try to get one now that you mention a speed instability with the Tecno. By the way: Did you feel the HR was an improvement otherwise over the basic ps?
twl
3,251 posts
 
With a DC motor, the speed is set by voltage level. Small changes in voltage can affect the speed.

It is possible that maybe in the switch(or something) that very small variations in the voltage passed to the motor are happening as you turn the PSU off and on. This could cause a very minor speed change, and account for what is happening.

This is just a guess, because I can't be there to actually test and diagnose, but it could be that.

This is why some DC motor TT systems(like Teres) use a strobe on the platter and an automatic motor controller. Additionally, a non-controlled DC motor can slightly slow down during the course of playing one side of a record, due to stylus drag.
dr_balance OP
16 posts
 
Twl, not to correct you but I thought un-contolled DC decks slowd down due to heat. The stylus will actually produce more drag on the outer edge of a record.

I know nothing about this stuff, I just read this on KAB's website. So correct me if i'm wrong

-Balance
dr_balance OP
16 posts
 
I think my problem is "Bearing friction". I say this because I noticed the speed only changes when I move the platter slightly before turning it on again. When I simply don't touch the platter and just turn it on and off the speed remains the same. Example, reclamping a record will cause me to move the platter slightly, mabe a little pressure on the bearing. Only during this does the speed chage for the next "run".

Restock, when you get a stobe, try this and let me know?

It seems normal to me though because I hear no noise from the bearing and it turns very smoothly, also it is like a month old.
twl
3,251 posts
 
Speed change from stylus drag is cumulative over the course of the entire LP side. Also, any bearing drag or any other things could enter into this equation. Basically, after you set the speed at the beginning of play, anything that drags it or holds it back at all, can slow it down during the play of the LP. This may differ in severity depending upon the TT in question. Some TT's may not exhibit this characteristic at all, if certain conditions are present.

I'm not sure why your speed changes only when you touch the platter or bearing structure. That's a new one on me. Maybe you are low on oil.
dr_balance OP
16 posts
 
TWL, oil is okay, I was actually concerned that I put too much in the beginning.
dr_balance OP
16 posts
 
Seems to be much more stable now. Is it possible the PSU needed to warm-up to stabalize? I just got it, and posted within 3 hours of using it. Anyone, TWL?
twl
3,251 posts
 
Dr. Balance, you have got me stumped on this one.
psychicanimal
1,738 posts
 
¿Quartz-lock, anyone?
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