Need help trouble shooting 3D arm

Need help trouble shooting 3D arm

Postby Bill Stevenson » Sun Dec 16, 2018 5:44 pm

I have a Prime with two arms, one 3D and one metal both fitted with dual pivots. The 3D arm is fitted with a Counter Intuitive. The 3D has a 2M Black and the metal has a 2M Mono SE (i.e. the 2M Black modded for mono). The metal arm works fine. The 3D has distortion starting at about mid play and getting worse toward the spindle. VTF has been checked and re-checked. I have checked visually and cannot see any interference. The arm is sitting properly on the unipivot, the arm is parallel to the record surface or nearly so. Everything looks OK. I removed the arm and inspected for damage and everything looks OK. I inspected the stylus under my Wild Heerbrugg microscope and everything looks OK. I've tried several records with the same result. I've played some with the periphery ring and some without, and it does not seem to affect this problem. Although I don't normally use the anti-skating device, I tried it and found that it makes the problem worse. I am out of ideas. Any suggestions short of throwing the Prime over the transom would be appreciated.
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Re: Need help trouble shooting 3D arm

Postby jonathanb » Sun Dec 16, 2018 5:48 pm

Have you realigned the cartridge yet?
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Re: Need help trouble shooting 3D arm

Postby teenage diplomat » Mon Dec 17, 2018 12:23 am

There could be several issues at play, including most importantly IMHO, tracking force and the amount of antiskating actually being created by the 3d’s wire loop. On the former, make sure that you are measuring tracking force at the level of the record, not by putting a conventional gauge on the platter. HW long ago did tests that showed doing it with the gauge on the platter overstates actual tracking force - you actually are tracking at a lower force than what the gauge says by about .2 g. The only exception would be a digital stylus force gauge that uses an outboard platform at record level on which you place the stylus. On the question of antiskate, it has been my experience that as it comes from VPI, the degree of twist in the wire is too tight; it exerts too much antiskating force, and sibilance in the right channel occurs. Try an experiment: blutac a small weight to your counterweight, one with just enough mass to allow the arm to float just above record level. Move the arm in towards the center. Let it float. If it moves away from the spindle quickly, you have too much AS force. Untwist the wire a full turn of the lemo and retest. Continue untwisting until you have only slow outward drift on the floating arm. Take the blu tac’ed weight off and listen. If AS was the cause, and the distortion was mostly in the right channel, it should be better. Oh, you also might want to take the bit of tonearm wire an inch or so above where it exits the arm and bend it towards the lemo, forming a (more or less) right angle turn. Hope these ideas help.
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Re: Need help trouble shooting 3D arm

Postby Brf » Mon Dec 17, 2018 11:20 am

Switch the cartridges between the two arms. If the problem follows the switch, you will know that it is a cartridge problems and not a arm/cartridge issue.
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Re: Need help trouble shooting 3D arm

Postby teenage diplomat » Mon Dec 17, 2018 4:20 pm

Just a small correction to my previous post: excessive sibilance occurred in the left channel, and disappeared after I untwisted the wire, lowering the amount of antiskate.
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Re: Need help trouble shooting 3D arm

Postby Stringreen » Tue Dec 18, 2018 6:56 pm

If the left channel is mistracking you need to increase the antiskate and/or increase vtf. Your assessment sounds odd.
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Re: Need help trouble shooting 3D arm

Postby teenage diplomat » Tue Dec 18, 2018 10:51 pm

Stringreen, I know that is the textbook answer. All I can tell you is that with my arm, there was so much antiskating force being applied that sibilant portions of LPs spread hot “s” sounds from the center to the left of the soundstage. Reducing the antiskate force in the manner I described resolved the issue. Theory: misstracking left channel due to too much antiskate. Simple to test my theory if that is what the OP is hearing. That may not be his problem.
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Re: Need help trouble shooting 3D arm

Postby Golear » Wed Dec 19, 2018 4:01 pm

Perhaps once a cartridge misbehaves too much, all bets are off.

I also suppose there's nothing wrong with setting the anti-skate via twisting the wire. The big question is: how much force does the twist generate? If there was a way to measure this and adjust it, then it should work as well as any other method. There are many kinds of wire, and they're no doubt mounted in the arm in different ways, so there'd be a lot of variations. The Soundsimith's method of setting the anti-skate may still be relevant for arms where the anti-skate is set by twisted wires.
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Re: Need help trouble shooting 3D arm

Postby Mr_Putty » Wed Dec 19, 2018 10:25 pm

Golear,
What you mention about the wire is what I confirmed today. I removed more twist in my Prime arm wire as there was too much antiskate. It is now much better and I do not need the weighted-mechanical arm for skate, so far. I use a second pivot and it’s required downward force is also more consistent across the record path. To be clear about the antiskate, after the wire was relaxed, there is no apparent force on the arm at the beginning of a record (or very little).
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Re: Need help trouble shooting 3D arm

Postby JimmyL » Thu Dec 20, 2018 4:58 pm

I am not the most experienced in this (more of a newb) but have just gone through a very extensive setup regimen so have a few things working my way now. From the picture you sent, your Lemo wire has an aggressive twist that's easily seen. Not sure who had suggested it but removing the arm and allowing the wire to dangle free while mildly untwisting (I even used a hair dyer to add a slight bit of heat), relieved a lot of the tension. After doing so, I found that the amount of skate was predictable and reasonably constant across the record surface and I could dial in the correct AS. Not sure it will solve your issue but I would start with that as I'm very pleased with the results I achieved.
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