Motor for turntable.

[GaryB]

Originally posted by krishu
i tried several motors on my diy tt and can tell you a few things:

i built one just using a LM317 voltage regulator and this did not work well. When the needle tip dives into the groove of the record, speed decreases dramatically. Which means, the speed not only depends on the voltage, it also depends on the mechanical load. This varies across the radius of a record an from music to music.

[/B]

I built one of the early Teres turntable kits using the Maxon motors and found the strobe disk / motor controller difficult to get working. As an interim way of listening to music, I hauled out a nicely regulated lab DC supply and it seemed to work fine with speed reasonably stable. So it seems that the high mass of the Teres platter along with the stronger maxon motor makes a non-feedback DC supply acceptable if not the ultimate.

The long departed (and lamented) dice45 recommended use of a L200 chip as a simple motor controller. The datasheet / app note ( http://www.us.st.com/stonline/books/pdf/docs/1678.pdf ) shows a simple circuit for use as a motor controller. The current from the motor is included in the feedback circuitry which allow better control for varying loads on the motor. Take a look at page 11 and Fig 25.

Alternatively, the following application note for OPA548 motor controller looks pretty interesting and has a good explanation of how one can use the motor current to monitor motor load and maintain good speed regulation without a strobe disk for feedback.
http://focus.ti.com/lit/an/sboa043/sboa043.pdf

I've been meaning to build a motor controller along these lines but haven't gotten around to it.

---Gary

[jackinnj]

Originally posted by GaryB


Alternatively, the following application note for OPA548 motor controller looks pretty interesting and has a good explanation of how one can use the motor current to monitor motor load and maintain good speed regulation without a strobe disk for feedback.
http://focus.ti.com/lit/an/sboa043/sboa043.pdf

I've been meaning to build a motor controller along these lines but haven't gotten around to it.

---Gary

In the application notes for the LMD18200 and LMD18201 there are "tach-less" motor control notes. I use these beefy PWM controllers in photo-processors.

[analog_sa]

No, Linn has (had) a whole range of power supplies for the LP-12 -- here's an article on the Linn Lingo: http://www.stereotimes.com/acc030903.shtm

Same thing - cleanish AC oscillator as all other supplies. You're not really designing one with 317s, are you?

[jackinnj]

no, I would take a 32.72kHz crstal, divide down to 60Hz, filter it to get a nice sine wave and just use a voltage amplifier to drive the motor.

there are DC motor replacements for the LP12.

[analog_sa]

The dc motors are not from linn. And the method above is very close to what Linn do in all their PSs. Amazingly the Valhalla does not show any attempt to stop the digital hash getting back into the mains. No idea bout the Lingo, but everyone seems to think it really screws up the sound of other components on the same spur.
Anyway, my claim was only that Linn's PSs are not really 'controllers'.

[fdegrove]

Hi,

At first the motors in the LP12 were sourced from MBLE (Philips Belgium).

Later they were bought in from Airpax, another Philips subsidiary, I think.

Cheers,

[Padel]

Hi all,

Well the guys at TL Acoustics in Greece, sell a motor-controller combination, both from Maxon. The motor is from the A-Max range (cannot see part number!!!) and the controller is a dedicated one for that range of motors which in my case works as current sence with great speed stability. They also have an add-on digital encoder for voltage feedback for ultimate stability that i will try very soon. The controller is battery powered and the motor rod is over 12Kg of solid stainless steel.



Cheers


Analogue still sounds ............. better

[Vinyl-Addict]

Originally posted by fdegrove
Hi,

Brett,

I don't know of any Nottigham Analogue design that needs a hand start and I all know them inside out.
I'm very familiar with Tom who's as helpful as I can possibly imagine.
Could it be the belt needs replacing?

Cheers,

Nottingham does indeed need a hand start to get the platter going. That is their design, the motor is always on and is very low torque, hence the handstart to get it going.

[fdegrove]

Hi,

That is their design, the motor is always on and is very low torque, hence the handstart to get it going.

What model exactly?

I can only think of the Omega Point model that didn't even have an on/off switch.
It took maybe 15 seconds to get it up to speed (without user interference) and you just left it spinning while changing records.
That's just a midweight design....
This applies to all the 240 VAC models, it could very well be that the 115/110 VAC models have less torque.

The 80 lbs platter Mentor and Mentor Reference start up fast and are up to speed within 10 secs. It will take a firm hand to stop the platter from spinning due to its very high inertia, about 120 tons in fact.

If a TT needs a hand to get up to speed than there's something you can do; either something is wrong with the bearing, its oil or its belt, or you could try applying a small amount of PTFE charged oil.

The latter can make a huge difference on any TT model, from a humble Thorens to a top flight NA design.

Always make sure platter, belt and pulley are squeaky clean; no greasy deposit whatsoever should be present.

BTW, the bearing assembly and concept of the Mentor and its derivatives were designed and developped in the early Eighties already with the help of...yours truly.
A concept that seems to have have stood the test of time...

And in case you really want to splash big cash...yes it does beat the 20.000$ TTs hands down....just dn't take my word for it, always listen for yourself first.

Cheers,

[Kees]

World class record player motors come from Premotec in the Holland.
You have to use a synchronous motor from the SY31 series.
The best solution for a belt driven system.
There are special turntable version available.

You can buy them at Mclennan Servo Supplies in the UK.