Mu metal and the 1210 PCB

[Wakefield Turntables]

I'm in the process of yet more mods to the 1210, yep its that time of year again. This time I got round to thinking about the magnetic assembly on the platter. I have a MN copper bound platter with the magnetic assembly housed as it should be directly under the platter. BUT! Will this produce a magnetic field directly over the PCB and thus introduce some element of EMI into the PCB??? Would it not be better to cover the whole PCB in Mu Metal or something similar?????????? :scratch: Forgive me if this sounds like a stupid idea but I suppose things cant move forward unless silly/crazy ideas like this don't get mentioned!

[Stratmangler]

BUT! Will this produce a magnetic field directly over the PCB and thus introduce some element of EMI into the PCB??? Would it not be better to cover the whole PCB in Mu Metal or something similar??????????

I prefer to listen to music instead of worrying over such trivialities.
I've even managed to spend half an hour or so playing guitar, which was good, because I've spent the last three days working South of Watford, and as such I have been abroad (well, far away from the North Country, where men are men and sheep are perpetually worried) :eyebrows:

[sq225917]

You'd be better off making the pcb remote than trying to shield it. Far easier to eliminate any potential issue completely rather than applying a band aid. This of course assumes that the proximity of the pcb and the motor cause any issues.


To be honest I'd assume proximity of motor to stylus is a greater issue than motor/pcb given that the cart is effectively a very sensitive magnetic field sniffer. Certainly removing a Valhalla from my old lp12 improved the noise measured from the cart output. Placing the Valhalla directly under the motor had no adverse noise effect. Seemed like a worthwhile thing to check at the time.

[chris@panteg]

I prefer to listen to music instead of worrying over such trivialities.
I've even managed to spend half an hour or so playing guitar, which was good, because I've spent the last three days working South of Watford, and as such I have been abroad (well, far away from the North Country, where men are men and sheep are perpetually worried) :eyebrows:


:lol::lol:

I'm always weary when i go up north Chris , worth it for the beer though :)

[Wakefield Turntables]

I prefer to listen to music instead of worrying over such trivialities.


Attention to detail provides better sonics. And I enjoy "worrying" as I'm a tweek geek at heart


You'd be better off making the pcb remote than trying to shield it. Far easier to eliminate any potential issue completely rather than applying a band aid. This of course assumes that the proximity of the pcb and the motor cause any issues.


To be honest I'd assume proximity of motor to stylus is a greater issue than motor/pcb given that the cart is effectively a very sensitive magnetic field sniffer. Certainly removing a Valhalla from my old lp12 improved the noise measured from the cart output. Placing the Valhalla directly under the motor had no adverse noise effect. Seemed like a worthwhile thing to check at the time.

You cant isolate the PCB how's the platter going to spin :scratch:, hence covering the PCB with Mu Metal (which would isolate the PCB). I have a copper bonded platter so that takes care of magnetic fields travelling up through the platter to the cart.

[sq225917]

Can't you pull like 90% of the pcb out leaving only the motor and stator parts, and just have em on longer wires, or is it all one pcb for everything?

[Reid Malenfant]

Motor drive & control as well as everything else is on a single PCB that surrounds the open frame motor on a 1210, apart from the standard regulator, transformer & other odds & sods.

If you had the chance to look inside of an Aiwa AP2600 you'd find that the control PCB is totally seperate from the motor drive PCB which happens to be buried inside of a steel enclosure to screen it.

There is some logic to what you are attempting to do, but screening the whole lot might not be the way to go. If you can screen the motor drive circuitry from control circuitry then it might benefit the overall sound :scratch:

[Wakefield Turntables]

Can't you pull like 90% of the pcb out leaving only the motor and stator parts, and just have em on longer wires, or is it all one pcb for everything?

NO! Besides how would you screen anything?


Motor drive & control as well as everything else is on a single PCB that surrounds the open frame motor on a 1210, apart from the standard regulator, transformer & other odds & sods.

If you had the chance to look inside of an Aiwa AP2600 you'd find that the control PCB is totally seperate from the motor drive PCB which happens to be buried inside of a steel enclosure to screen it.

There is some logic to what you are attempting to do, but screening the whole lot might not be the way to go. If you can screen the motor drive circuitry from control circuitry then it might benefit the overall sound :scratch:

Thanks, a sensible reply at last:D Mark, can I asked how you came to this decision?? I'm intrigued why you think screening the motor-drive circuitry might be beneficial. Surely all components would benefit from EMI protection:scratch:

[Reid Malenfant]

Well the motor drive circuitry is feeding square waves to the motor coils. These act like transmitters the same as any coil will if fed with a steeply or should I say quickly rising voltage. It's the same as clipping an amplifier - you get harmonics!

I should have mentioned that the AP2600 motor is a single unit as well, built into a steel case, so that is also screened :)

[Wakefield Turntables]

Well the motor drive circuitry is feeding square waves to the motor coils. These act like transmitters the same as any coil will if fed with a steeply or should I say quickly rising voltage. It's the same as clipping an amplifier - you get harmonics!

I should have mentioned that the AP2600 motor is a single unit as well, built into a steel case, so that is also screened :)


Thanks for that! Looks like the 1210 guys had an eye on screening at every turn.

[Mike_New]

I do not think that any interference of, or from the motor assembly is going to be of any practical concern. When you look at the coil assembly on the PCB you will see that it is surounded by a metal shield (this may be Mu metal). Also the magnet fits in between this sheild and the coils thus forming a reasonably tight magnetic circuit. The magnet is radially magnetised so most of the stray field will be radially biased. I have however checked the field produced by the magnet and it can be detected in the vertical direction, ie axially.

[sq225917]

Anyone got a shot of the guts?

edit: ah found it. Is there no way to remove everything but the motor unit?

[Mike_New]

The coil assembly, position sensors and drive electronics are all one integrated package connected to the PCB and cannot be easily separated. The SL1500 however did have a more defined separation between the coils and the PCB board.

[sq225917]

That's a shame, there would likely be some mileage in removing them. Certainly making a Valhalla remote from the underside of an LP12 provides a measurable reduction in signal noise and 'very' slightly improves speed stability.

[The Grand Wazoo]

....and 'very' slightly improves speed stability.

Aren't you moving into the realm of the magic bean here Simon? How would your much touted laws of physics explain that then?

[chris@panteg]

That's a shame, there would likely be some mileage in removing them. Certainly making a Valhalla remote from the underside of an LP12 provides a measurable reduction in signal noise and 'very' slightly improves speed stability.

Simon , with respect the SL1200 series has no issues with speed stability even with the much maligned OEM psu , I really don't think this is an issue myself :scratch:

[Wakefield Turntables]

That's a shame, there would likely be some mileage in removing them. Certainly making a Valhalla remote from the underside of an LP12 provides a measurable reduction in signal noise and 'very' slightly improves speed stability.

This isn't about the LP12 so its relevancy is lost on me.


Aren't you moving into the realm of the magic bean here Simon? How would your much touted laws of physics explain that then?

More common sense, thanks!


Simon , with respect the SL1200 series has no issues with speed stability even with the much maligned OEM psu , I really don't think this is an issue myself :scratch:

+1 with your comments here Chris. Simon you need to look at the spec of the 1210 before making any further comments. The 1210 is Quartz locked, its famed for its stability unlike your LP12 (which I have incidently) that relies on IMHO a naff belt design.



Mike, thanks as always for your comments. So it just goes to show that there is SOME stray magnetic field. If this has an impact on the PCB I guess I'll never know 8-(