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Re: RE:better vibration control of the AC motor. (long)

I have experimented with mechnically isolating AC syncronous motors and not had favorable results. There must be more science to it than I give credit. However, I have had great results with a different AC power supply design.

The cap/resistor in the link below work really well on a Linn AC motor (or similar i.e. late model AR or Rega) and quite a bit better than the Basik supply - dare I say even Lingo like in performance. The isolation transformer is also a notable improvement and I am just using a cheap old RCA Isotap.

I tired the OL DC motor and while I will admit that it had definante merrits, overall I still prefer this approach with the AC motor. I also tried a Valhalla and found it not quite as good. I think there's a lot to be said about the authority you get from good old fashion torque once you remove the problems.

Also here's another couple power supply ideas stolen from the Linn FAQ text. The first one is almost like the one in the provided link, the second one is almost like the Linn Basik supply. I haven't had a chance to try either yet. I'm pretty darn happy with what I've got so far.

DIY "Gedon" (note cap values in nF)
-----------
"The transformer in the Naim Armagedon is a 340VA to 110V type. Then
comes the little phase shifter after which the output is 79V. The phase shifter
consists of a serial resistor to drop the voltage to 79V and two parallel caps
in one leg.
31V
---/\/\/\-----+------------- motor 1
|
| | +---| |---+--- motor 2
110V 79V | |
| | +---| |---+
---------------------------- motor common
The resistor is orange, orange, ? i.e. 33x? Ohm. I measured the current of my
Mantra motor (same as in LP12) that was 10mA. So I'd guess the dark third ring
is red. => 3.3KOhm (31V / 3.3k = 10mA).

The caps are Siemens types MKT. (Siemens MKH) These rectangular green types,
where the connecting legs are soldered onto the outside case. Dimensions are
7.5mm leg distance and about 4 mm thick.

So lets guess a little bit. My Mantra had a similar circuit (130V to 75V through
serial resistor) and then a 220nF cap in series to one motor leg. There are
several capacitors that would match from the dimensions side. There is a 220nF
100V type cap with just the right dimensions, But in the Armageddon has two in
parallel. There is also a 100nF 250V type which is the same size so that could
be the solution."


Do It Yourself Power Supply (note cap values in uF)
---------------------------
There has been some discussion on the list about power supplys for turntables.
Most turntables have an synchronous motor which has two windings (4 wires). An
alternating current supply is applied to the windings which forms a rotating
magnetic field. The motor's rotor follows the field produced by the stator at
the frequency of the supply i.e. the rotor turns at a speed synchronous with the
alternating current supply. Most motors require a supply with a voltage less
than the voltage available from the mains. The windings also must have supplys
of different phase ideally with a 90 degree phase shift. The most basic supply
uses combinations of resistors to drop the voltage to acceptable levels and a
capacitor to achieve the phase shift.

"Suggested values are (given a motor resistance of 8k8 ohms and inductance of
10H).
For 240V, 50Hz
C1
--------+----||---------------- Blue
| R1
+--/\/\/\---+---------- Red
240VAC |
= C2
|
--------------------+--+------- Grey
|
+------- Grey
R1 = 20k ohms C1 = 0.1uF, C2= 0.1uF, Vout is about 75V

For 120V, 60Hz
C1
--------+----||---------------- Blue
| R1
+--/\/\/\---+---------- Red
120VAC |
= C2
|
--------------------+--+------- Grey
|
+------- Grey
R1=3k3 ohms, C1=0.2uF, C2=.47uF, Vout is about 85V"




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