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Old 15th June 2007, 07:24 PM   #1
roger-k is offline roger-k  Norway
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Default Motor question?

I'm looking for a good motor for a DIY turntable.

Is this good?
It is a brushless DC-motor with internal speedcontroller.

LINK:

http://www.rsonline.no/cgi-bin/bv/rs...0&cacheID=noie
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Old 15th June 2007, 07:45 PM   #2
roger-k is offline roger-k  Norway
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Datasheet:

http://www.mclennan.co.uk/datasheets...ght=bldc58-35l
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Old 15th June 2007, 08:12 PM   #3
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Looks like a good prospect. Many of the DC turntables used cheap slot-car motors.

Two points that I would watch out for:
(1) The feedback controls are often not what they should be. Servo control is sloppy unless very well designed. Example, an old style cassette deck with a large heavy flywheel often has better speed control than a servo controlled motor. Sloppy control is like a DVM that keeps updating and never gives a steady reading.

(2) Make sure that the hub is machined round and be suspicious of an inexpensive rubber belt. It may not have the same tension at all points. Don’t drive a one-piece platter, use an inner hub. Nylon seems to be better than metal in the sense that it doesn’t warp with age, if you are going to strip hardware out of another turntable. A very slight vertical warp can cause a significant speed error. A huge heavy platter is a cure for most everything if the bearing is right.
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Old 15th June 2007, 09:42 PM   #4
roger-k is offline roger-k  Norway
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No, I'm not going to strip hardware out of another turntable.
I will cut the hub in a turning lathe and use ball-bearings to get best stability. Inside the hub the wil be an axle. In the end of the axle I will turnery a pipe flange, with a track for the rubber belt. In the pipe flange there will be mounting holes to install the TT with bolts.

Is MDF a suitable material for the turn-plate?
(I know Rega use MDF)
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Old 15th June 2007, 11:22 PM   #5
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http://audioenz.co.nz/2007/vinyl_rega-rhapsody.shtml

This link has some MDF commentary in it. Doesn't seem to be a high end material.

There is a conversation in DIY about how pleased YNWOAN is with a magnetic modification to his turntable. It is a good read. It is near the top of the analogue list.

The ball bearing sounds noisey. I'm still learning about turntables and it is amazing how sensitive the platter is to the transmission of seemingly negligible noises.
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Old 17th June 2007, 03:25 AM   #6
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Default Re: Motor question?

Quote:
Originally posted by roger-k
I'm looking for a good motor for a DIY turntable.

Is this good?
It is a brushless DC-motor with internal speedcontroller.


No, it's a poor choice for a TT.

A BLDC motor is DC in name only, it's actually a permanent magnet 3 phase EC motor with a set of drive electronics which uses feedback from the motor to approximate the voltage vs speed and speed vs torque curves of a DC motor.

The drive electronics will be based on trapezoidal commutation which gives quite high torque cogging.

The electronics will give you a speed vs torque characteristic which must be compensated but will also make the compensation difficult to optimise.

The motor is designed for very high speeds so it uses ball bearings (which are noisy) and it will become increasingly difficult to drive at lower speeds, increasing the percentage of torque cogging.
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Old 17th June 2007, 09:06 PM   #7
roger-k is offline roger-k  Norway
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Join Date: Mar 2004
Location: Karmøy in Norway
OK, thanks for the answers.

What I need is a quiet DC-motor.
Can any recommend a good motor and/or motor supplier?
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