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Tonearm mounting rigidity and considerations?

I posted this on AK and it has brought up some interesting discussion. I decided to post my initial post verbatim over here because I know there are some very knowledgeable folks on here and I would like your input. If you follow the links you can see some of my build thread on the custom aluminum sub armboards that will hold the interchangeable armboards that I’m machining. This subject seems to have a lot of differing opinions, I’d like to hear from the folks on here so I can learn.Thank you BillWojo---------------------------------------------------------------------------------------------- "Something I’ve been thinking a lot about over the past several weeks as I design and build new arm boards for a two arm Victor (JVC) constrained layer plinth. You can see the thread on my build progress on page 11 of this post. https://audiokarma.org/forums/index.php?threads/jvc-ql-owners-thread.909550/
There was this thread that made it clear as to how important it really is. https://audiokarma.org/forums/index.php?threads/jelco-easy-vta.916431/
Here is a quote from that:
"I use one and couldn’t be happier.
For me, the improvement in the arms sound quality alone was worth the price of admission.
Being able to adjust VTA "on the fly" is just an added bonus."
Seems the Jelco VTA attachment really helped with the rigidity of the mounting.
When I was searching for post on armboard material I found all kinds of opinions as to what sounds better as well. That’s what really made me think about what was happening.
The tonearm has to move very freely in two axis of motion all the while being fed a steady stream of vibrations. Any looseness in the tonearm bearings or the mounting will degrade the sound. Thin armboards are vibrating with the tonearm and are "coloring" the sound. Even if the bearings are adjusted properly the tonearm may be vibrating in the support collar, especially if it’s the type that is only locked into place with a single screw of some type.
My thinking is that the tonearm should have good bearings, properly adjusted and the tonearm post should be held very rigidly to the plinth. The tonearm tube should have either internal or external damping as well to quell the vibrations.
Has anyone here experimented with this idea? I need to make an armboard insert for the back position of my Victor and I think I will do away with the stock mounting collar. Instead I will make a clamp that will support the tonearm post and it will be rigidly secured to the armboard. It will fill the entire area of the armboard cutout and be secured by 3 or 4 screws per side for maximum rigidity. Material will be aluminum. The tonearm will be a Audio Technica ATP-12T using a Denon DL-103 cart. That cart should feed a lot of energy into the tonearm.
I appreciate any and all thoughts on this.
Thank you"
billwojo

Showing 2 responses by millercarbon

millercarbon's avatar
millercarbon
12,531 posts
 
Could be. Point is, hard to be sure. Could just as easily be the majority of arms are screwed down simply because that's what everyone does and what everyone expects to see. Its also easiest. None of which means its the best.

My arm before the Conqueror was the Graham 2.2. The Graham uni-pivot, the Conqueror uses two pivots. Same idea, eliminate all bearing play, but using two for greater stability. Anyway point is the Graham screwed down but did not have to be screwed down. It balanced and was stable just sitting there.

All arms if you think about it are stable like this. They all use a counterweight and pivot on the center of mass. So of course they will all be stable. Duh! So this is yet another case where we can easily just try it and see.
millercarbon's avatar
millercarbon
12,531 posts
 
Your reasoning sounds really good on paper. Now here's the reality. My Origin Live Conqueror arm slip fits into the table. Its held in place by gravity. There's not much play, but neither is it a snug fit. Directions for cutting the hole had something like a 1/8" tolerance. Not fussy at all. Sounds great. 

Would it sound better to be more tightly anchored? I don't think so. Not just because of the manufacturer either. The one mod I did was to replace the OL collar with one machined by a modder who added a teflon layer to the top. So with this its even less tightly held in place. It sounds even better!

The moral of the story is not that the arm needs to be free to move around. Nor is it that the arm needs to be rigidly mounted. We don't know that either. All we know is we just don't know. 

My advice is do your proof of concept. Build one each way. Try em and see. Only way to know for sure. Too many guys waste mass time and effort trying to make everything perfect the first time. Remember, anything worth doing is worth doing poorly. 
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