PTP4/Slate Plinth ground hum

[stevieg69]

Hello,I posted something similar before but this is unusual.i notice that most of my cartridges have hum issues the closer to the spindle it gets.I changed out the motor to a 50/60 HZ motor.Got the same issue.Then I changed out that motor with a strictly 60HZ motor.
I'm in U.S.,that helped somewhat but still there.Also i had to run a ground wire from top plate to the same phono ground on my
phono preamp(phenomena II).That fixed some of the ground issues.
What am I doing wrong?This rig was bought from a dealer in NYC.
Its featured by a member on this forum.But he might have passed away.When he had it there were two platters and he used a Graham Phantom B44.
I do not want to use stacked platters.Today i bought a piece of MU METAL on ebay.
MY biggest question is this,ad I apologize to Peter up front,IS THIS NORMAL FOR PTP4 builds?
I have a table next to this one a L70 with a Jelco 750 arm.On this rig I have ZERO hum and feedback issues.
On the Slate one i am using a ortofon AS-212.
Could this also be a tonearm wire/cable issue?
I'm kinda stumped on this.The tonearm was bought from audio-salon,he sells on the bay.Hes got one for sale right now.
i think i'll make another armboard and try out another arm.the Ortofon is hard wired so i cant do anything there.
Any suggestions?
heres a Lencoheaven link for the table:http://www.lencoheaven.net/forum/index.php?topic=14271.0

[ian]

Hi Stevie,
I don't know what the source of your hum is but I can absolutely confirm that it is not an inherent problem with  PTPs and slate.  I have built more than one of these with no hum problems and no earthing of the plate either.  Is your motor earthed?  Sometimes too many earths can in itself be a hum problem - might be worth trying with just the arm and motor earthed.

Cheers, Ian

[OsteSpiser]

Hum increasing towards the spindle does suggest the source is the motor coils.
I agree with Ian that you should explore the top plate/arm grounding arrangement.

The L70 benefits from Lenco engineers sorting out any hum issues 

-kristian

[stevieg69]

Yes,
tried researching but most everything is European stuff,220 Volt.
Houses with 50 year old wiring,grounding to water mains and other nonsense.
in disgust i finally solved the hum issue,turned on my CD player and put a disc in.
No issues and good sound.Just kidding but seriously folks i get so fed up with all this.
Most likely i will set this rig aside and probably sell if this mu metal thing doesn't help.
The irony of it is my crappiest Lenco build is the best sounding.i just expected great things from this PTP4 slate plinth
gimmick and things didn't pan out.
Did switch over to a Stanton 881 and the issues are mitigated

[stevieg69]

BTW,
i saw one post abot running a wire from a screw on the motor to the top plate.
Doesn't hanging a motor with metal springs do about the same thing,isn't that a physical link to the top plate?

[ian]

I have a table next to this one a L70 with a Jelco 750 arm.On this rig I have ZERO hum and feedback issues.

Given the above the problem is obviously in the new deck - it's a matter of finding out why so don't give up just yet .  Have a look at your L70 and see how this is earthed then repeat pattern on your PTP.  Maybe switch arm and cartridge over and see if that makes a difference.  These things are always frustrating but usually solvable.

Chin up.

[stevieg69]

i have extra caps i bought awhile back.If I add one to the motor or replace existing one,will it help.
I don't get the turn on thump now so probably don't need to change out,right?

[fetteler]

Given the above the problem is obviously in the new deck - it's a matter of finding out why so don't give up just yet .  Have a look at your L70 and see how this is earthed then repeat pattern on your PTP.  Maybe switch arm and cartridge over and see if that makes a difference.  These things are always frustrating but usually solvable.

Chin up.

Absolutely, with one addition... always solvable



Have you read the LH howto on earthing?

Steve.

[niclaspa]

Hi Stevie!

I read about your ptp4 in the link that you provided.  It looks like a nice build.  The previous owner seems to have found it performing on a similar level to some other really expensive turntables.  When you write that it does not sound so good, I am thinking that there is something that is not right with it now, apart from the hum.  There are loads of things that could go wrong, but it looks like the turntable has potential so it might be worth your while to continue tinkering with it.

Grounding issues can be really frustrating and hard to get your head around.  If you have a multi-meter, it can be very useful here.  If you don't have one, it is a good investment!  Disconnect all cables from the turntable, including the mains.  Make sure that the tonearm tube has electrical contact with the ground wire coming out of it and make sure that it has no contact with the motor when all the cables are unplugged.

If you are still using the speed controller, plug the turntable into the speed controller, but do not plug the speed controller into the mains.  With the multi-meter, verify that the motor has electrical contact with the ground pin on the mains cable coming out of the speed controller.

[OsteSpiser]

  Have a look at your L70 and see how this is earthed then repeat pattern on your PTP.

If it's a stock L70 the arm is bolted firmly to the (metal) top plate - the PTP has no provision
for this. Then again, TD124s and GL88s (amongst others) are similar, and tend to do
just fine. 

-kristian

[stevieg69]

Not using speed controller.Also the arm is a Ortofon As-212.
About a midrange arm.I have a meter but my electrical knowledge is small.
Should I check for resistance or what were you referring to?
i researched the other stuff and without pictures its Greek to me.
Could the motor be wired up wrong?i went with the same arrangement as it came with.

[stevieg69]

also as far as i know theres no neutral or positive on US AC voltage.
i had to change out a panel and the manual said the power ins did not matter since theres no polarity

[pde2000]

according to this website;  http://hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld.html  the usual arrangement is to have a ring mains that gives live and neutral 120v, and spurs for furnaces etc that can supply 240v by using two lives (hot).

With a regular digital multi meter you can measure the ac voltage between the earth and each supply which will indicate which is neutral and which is live (neutral is at zero volts with reference to earth).

[niclaspa]

Use the multi-meter to check for resistance.  Unplug everything and verify that there is no contact between the tonearm and the motor. 

[reinderspeter]

What cartridge are you using?