Speed control chip for DC motor in turntable? - diyAudio
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Old 4th December 2011, 09:54 PM   #1
ljames is offline ljames  Canada
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Join Date: Oct 2011
Default Speed control chip for DC motor in turntable?

My turntable using a DC motor, the voltage is about 8-9V, and the power supply after I open the box, to my surprise is only a LM317, no wonder it sounded very unstable.
I think I will use old day's speed controller in tape recorder or something, I hope it's single chip easy solution, just a better improvement over LM317 is sufficient.

I found NTE1844 may be suitable (however, no way to find schematics for it). Also AN8850 or AN6652, but seems nobody selling it, also not sure the output AMPs is good enough.

anyway, anne know any simple/single chip can solve the problem? Thnaks a lot!
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Old 4th December 2011, 10:29 PM   #2
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Hi,

If its simple DC, as opposed to a DC servo arrangement, then you need a
DC supply with a negative output impedance equal to the motors resistance.

I'm sure it can be done with regulators, but I only know how to do it with
amplifiers, and thats fairly obscure. But nevertheless you need to arrange
some positive feedback on the regulator to cancel motor winding resistance.

If you can do this, then motor speed is directly related to drive voltage.

rgds, sreten.
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Last edited by sreten; 4th December 2011 at 10:34 PM.
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