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Tips for grounding a carbon fiber tonearm?
Tips for grounding a carbon fiber tonearm?
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Old 1st March 2019, 04:24 PM   #11
russc is offline russc  England
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Drill a small hole and insert a screw.
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Old 2nd March 2019, 03:51 PM   #12
audiof001 is offline audiof001  United States
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My ccarbon fiber tubes are not conductive. I hadn't thought of coating the inside wth conductive copper paint... I may go for the 1/4" Tinned Copper Metal Braided Sheeving which, according to the description, comes out as .16 d. which may give me room for a small piece of silk.
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Old 2nd March 2019, 04:08 PM   #13
audiof001 is offline audiof001  United States
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Quote:
Originally Posted by russc View Post
Drill a small hole and insert a screw.
Yes, I've thought about that. I see the install going something like this:
Feed the ground wire thru the pivot hole and out the back (may need a monofilament lead to pull it with), where I'll solder it to the sleeve, which has two oval holes cut out of it for entry of the wires in at the pivot and out behind the headshell. Run monofilament thru the front to the pivot hole and another thru the front and out of the front exit hole. Then I'll tie these monofilaments together and to the arm wires. I'll pull the sleeving thru from the back to the front and wrap it over the front end and twist tie it in place - after the wires are installed, I'll pull it forward and cut it off.

Arm wires will be twisted pairs red/green and white/blue, a twist about every 1/4 inch. These will be wrapped more loosely around a thin piece of silk and, hopefully will enter the sleeving from the pivot hole and pull thru the front side hole. If successful, I'll check continuity, add a piece of a 5mm diameter O-ring stopper to the front and smaller pieces to close off the two small entry exit holes, then fill the arm with hermit crab sand. The sand is extremely fine and has damped other arms very well. I'll add another O-ring stopper to the end.

Sound right?
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Old 2nd March 2019, 05:50 PM   #14
audiof001 is offline audiof001  United States
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I will use the 1/8"d instead...
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Old 2nd March 2019, 08:03 PM   #15
jplesset is offline jplesset  United States
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Hm. Just a thought. Treat the cart like a balanced source. Remove the ground strap from the leg of the cart, and run that separate. Feed to a balanced-input pre-amp. Hum gone.
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Old 5th March 2019, 05:56 PM   #16
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by jplesset View Post
Hm. Just a thought. Treat the cart like a balanced source. Remove the ground strap from the leg of the cart, and run that separate. Feed to a balanced-input pre-amp. Hum gone.
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Old 8th March 2019, 01:02 PM   #17
Bonsai is offline Bonsai  Europe
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Have you got the hum when the stylus if lifted just off the record surface? Does the hum change when you move the arm across the record surface (but not touching it)? This will help you identify if its coming from the motor or some other source in the vicinity. One of the reasons high-end T/T's often mount the motor away from the platter is for electrical noise reasons and not just mechanical noise.

I had a Project turntable ('Carbon' IIRC) that was OK'ish with the needle off the record surface but terrible when playing the record - the cause was motor noise and I had to buy a special kit (25) from Henley (Project importers in the UK) to quiet it down. Why not just supply a turntable without this problem you may be asking which is the same question I had.

Anyway, assuming its not motor noise, you would need to determine the coupling mechanism - if it is electro-magnetic i.e. from the motor windings or a nearby transformer - shielding won't really help. For that problem, you need to rely on twisting the wires from the cart to the connectors at the base of the arm. If its capacitive coupling then screening the wires would help.

If you short out the wires at the cartridge end in the head shell do you still get the problem?

One other question, are you keeping your signal ground separate from the T/T ground, assuming it has one?

Last edited by Bonsai; 8th March 2019 at 01:06 PM.
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Old 15th May 2019, 06:03 PM   #18
audiof001 is offline audiof001  United States
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Finished my two arms - here's the 9" at it's highest adjustable height and installed on the table. I used a tinned copper shielding inside and hermit crab sand to damp the arm tube. It's on my 1962 Braun PCS5 for now. Original headshell of the Braun was upgraded last year. My 3D printed subplatter ring (not shown) reduces the 33-1/3rpm position speed to 33.7rpm by enlarging the subplatter's diameter. This was due to the motor being 50Hz and running fast under 60Hz US power. Using a thread belt also helped reduce speed. Sounds fantastic. Mono cartridge in the original arm.
Attached Images
File Type: jpg voth-arm01.jpg (641.1 KB, 42 views)
File Type: jpg voth-arm02.jpg (562.3 KB, 44 views)
File Type: jpg Braun PCS5.jpg (557.7 KB, 45 views)

Last edited by audiof001; 15th May 2019 at 06:08 PM.
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Old 15th May 2019, 06:09 PM   #19
audiof001 is offline audiof001  United States
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Finished my two arms - here's the 9" at it's highest adjustable height and installed on the table. I used a tinned copper shielding inside and hermit crab sand to damp the arm tube. Mounted it on my 1962 Braun PCS5 for now. Original headshell of the Braun was upgraded last year. My 3D printed subplatter ring reduces the 33-1/3rpm position speed to 33.7rpm by enlarging the subplatter's diameter. Using a thread belt also helped reduce speed. Sounds fantastic. Mono cartridge in the original arm.
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