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Old 20th July 2015, 11:17 AM   #1
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Default Headshell screening

I have been fiddling with my Technics 1210 and my self built phono pre-amp during this weekend and noticed that the cartridge picks up a lot of RF noise when my arm comes close to it.
The turntable is stock (except for the RCA plugs) and i use the stock headshell with an Audio Technica cartridge. The wires in the headshell are twisted.
The phono amp is dead silent with the headshell removed from the turntable arm and the volume turned way up.
As soon as i connect the headshell with the cartridge, it picks up RF as soon as i close my arm (from about 20cm and closer) to the headshell. This leads me to conclude that the noise is picked up by the wires in the headshell.
The cartridge itself is plastic and some shielding metal that is connected to the ground of one of the two channels.
Has anyone changed the stock wires in the headshell?
Im thinking about using thin twisted coated copper wire instead of the stock wires and also shield the wires afterwards.
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Old 20th July 2015, 11:21 AM   #2
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Quote:
Originally Posted by rrrremus View Post
I have been fiddling with my Technics 1210 and my self built phono pre-amp during this weekend and noticed that the cartridge picks up a lot of RF noise when my arm comes close to it.
The turntable is stock (except for the RCA plugs) and i use the stock headshell with an Audio Technica cartridge. The wires in the headshell are twisted.
The phono amp is dead silent with the headshell removed from the turntable arm and the volume turned way up.
As soon as i connect the headshell with the cartridge, it picks up RF as soon as i close my arm (from about 20cm and closer) to the headshell. This leads me to conclude that the noise is picked up by the wires in the headshell.
The cartridge itself is plastic and some shielding metal that is connected to the ground of one of the two channels.
Has anyone changed the stock wires in the headshell?
Im thinking about using thin twisted coated copper wire instead of the stock wires and also shield the wires afterwards.
Since the cartridge generator itself is a pair of coils more probably THAT picks up RF. How does the RF manifests itself?
Did you ground the metal parts of the turntable - usually there's a wire coming out of it for that purpose.

Jan
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Old 20th July 2015, 11:32 AM   #3
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Originally Posted by jan.didden View Post
Since the cartridge generator itself is a pair of coils more probably THAT picks up RF. How does the RF manifests itself?
Did you ground the metal parts of the turntable - usually there's a wire coming out of it for that purpose.

Jan
Hello Jan.
Yes, the grounding is properly implemented.
RF manifests in the upper audio spectrum, just as if you were to connect an interconenct cable to the input of the phono amp and close your finder to the wire on the other side of it.
I should try to shield the whole cartridge then and see how that turns out.
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Old 20th July 2015, 11:52 AM   #4
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Originally Posted by rrrremus View Post
Hello Jan.
Yes, the grounding is properly implemented.
RF manifests in the upper audio spectrum, just as if you were to connect an interconenct cable to the input of the phono amp and close your finder to the wire on the other side of it.
I should try to shield the whole cartridge then and see how that turns out.
Have you tried another phono preamp? Did this start when you connected your new phono preamp?

Your problem is quite unusual and you should first delete all other possibilities. A not optimal ground system in the preamp could also do it.



Jan
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Old 20th July 2015, 12:09 PM   #5
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Well the pre-amp could do it because it is actually the HPS 5.1 and it is DC coupled and has no filter to cut the HF spectrum above audible.
I have also tried with the built-in preamp in the Technics amp and there the phenomenon is present but not nearly as noticeable.
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Old 20th July 2015, 12:11 PM   #6
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I still don't understand it well. RF is far, far above audio. How can you hear that? Or is it power supply rattle?

Jan
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Old 20th July 2015, 05:30 PM   #7
lexx21 is offline lexx21  United States
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If you are hearing it when you move your body close to the arm and it goes away when you move away from it, then it's picking up the electric field that your body produces.

Check the following:

1) Are the connectors clean on the head shell? I mean the ones on the connecting wires.

2) You said that the rca connectors are not stock. Check the wiring as one may have broken.

3) With the power off, check with an ohm meter that you actually have a ground from your ground wire to the arm itself.

4) With the cart removed, use an ohm meter to check the wiring between the connectors on the head shell wires and the rca jacks.

5) Determine which wires on the head shell are actually ground wires and ensure that those are connected to the ground pins on the cartridge. Look at the install manual for your cart for that info. Don't assume that they will match up.

RF is just a modulated wave. It can be 1hz all the way into the high Ghz range (and beyond). What you are hearing is most likely something akin to 60hz which is close to what your body generates.

If you don't have an ohm meter, you can get one at an auto parts store for very little money. All you are doing with it is checking continuity. Make sure it is unplugged when you do this and not plugged into the phono preamp.
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Old 26th July 2015, 01:00 PM   #8
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Well i changed the stock wires in the headshell with a proper twisted pair and although the problem hasn't been completely cured, the noise pickup is now greatly reduced. I'm guessing the exposed pins are picking up the rest of the noise. I will try to shield the whole assembly with copper foil to see if that helps
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Last edited by rrrremus; 26th July 2015 at 01:22 PM.
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Old 26th July 2015, 01:08 PM   #9
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Quote:
Originally Posted by lexx21 View Post
If you are hearing it when you move your body close to the arm and it goes away when you move away from it, then it's picking up the electric field that your body produces.

Check the following:

1) Are the connectors clean on the head shell? I mean the ones on the connecting wires.

2) You said that the rca connectors are not stock. Check the wiring as one may have broken.

3) With the power off, check with an ohm meter that you actually have a ground from your ground wire to the arm itself.

4) With the cart removed, use an ohm meter to check the wiring between the connectors on the head shell wires and the rca jacks.

5) Determine which wires on the head shell are actually ground wires and ensure that those are connected to the ground pins on the cartridge. Look at the install manual for your cart for that info. Don't assume that they will match up.

RF is just a modulated wave. It can be 1hz all the way into the high Ghz range (and beyond). What you are hearing is most likely something akin to 60hz which is close to what your body generates.

If you don't have an ohm meter, you can get one at an auto parts store for very little money. All you are doing with it is checking continuity. Make sure it is unplugged when you do this and not plugged into the phono preamp.
All checked and looks Ok. No grounding problems.
I have a good scope and also an Agilent spectrum analyzer, i will do proper investigations when time permits, i have posted here hoping that someone experienced this problem before and can provide a quick fix.
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Old 26th July 2015, 03:28 PM   #10
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Quote:
Originally Posted by rrrremus View Post
Well i changed the stock wires in the headshell with a proper twisted pair and although the problem hasn't been completely cured, the noise pickup is now greatly reduced. I'm guessing the exposed pins are picking up the rest of the noise. I will try to shield the whole assembly with copper foil to see if that helps
If you realize that millions of players work fine with exposed shells and wires, the inescapable conclusion is that THAT is not your problem.

How is your connection to your preamp, RCA? How is the grounding routed/connected?

Jan
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