Roger Thorpe wrote:

William Sommerwerck wrote:
Many turntables have a line resistor. It "does something"
(that I don't
understand) to improve speed stability. Or torque. Or
something. It's not to
reduce the line voltage.


It's a while since I looked, and I could be wrong but:
The Rega planar motor is a pair of multi pole two phase
synchronous pancake motors sandwiched together with the
poles interleaved.
The resistor and capacitor are there to change the phase
(lag or lead?) of one motor so that the assemlby turns in
the right direction when it is started.
Incidentally mine is a Rega 2 and the resistor burnt out
too. A day after a short friendly 'phone conversation with
the company the postman handed me an envelope containing a
new resistor (with a higher power rating).
--

I read it that the resistor is in series with the whole
motor. How could that introduce a relative phase shift
between the two halves?

I looked at the site someone linked to, at the circuit for a
simple synchronous motor. When a resistor is used to drop
the supply voltage, the value of the recommended cap remains
the same. I didn't mention phase, therefore, not because I
know it's not significant, but that I have no evidence to
suggest that a resistor in series makes any difference.

Motors are something of a black art, AFAIK. Two motors in
parallel sharing a cap and resistor is about as black as art
can get. How can a symmetrical circuit favour one direction?
In what way is the circuit not symmetrical? Are you sure
that direction isn't determined by geometry?

Actually, this isn't a good place to explain such a thing.
If you have a name for the type of motor arrangement, maybe
I could look it up?

Ian