BIC 960 tonearm eff.mass - diyAudio
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Old 4th August 2006, 01:52 PM   #1
percy is offline percy  United States
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Default BIC 960 tonearm eff.mass

Does anyone know the eff mass of the stock tonearm on the BIC 960 turntable ? Or atleast a rough estimate whether it is a high, medium or low mass arm ?
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Old 6th August 2006, 10:41 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

I'd say medium / high effective mass. The headshell arrangement
looks extremely cumbersome. IMO with a DIY fixed headshell then
it would then probably be medium mass and sound far better.

/sreten.
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Old 6th August 2006, 01:31 PM   #3
percy is offline percy  United States
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This is how it looks like under. I just pulled it out and let it rest on its back. I am going to change the tonearm wires for sure and in the process I will be removing the "plug-socket" arrangement (and the 50 mile cartridge wires) as shown in the pic and go straight to the cartridge pins/clips.
A diy headshell..hmm...will search and see whats involved in that.

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Old 7th August 2006, 01:21 PM   #4
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Hi, a brief look at the arm suggests a couple of things to me that might improve it. Here's some thoughts:

First, it looks as if all the mass is in the wrong place! Far too much weight in the headshell, not enough in the counterweight.

If you were to re-wire with an inexpensive but decent wire, like maybe:

http://cgi.ebay.co.uk/RE-WIRE-TONE-A...QQcmdZViewItem

You'd save the weight of those connectors and stuff. At the headshell end, every gram counts. I guess you could also lighten the headshell by drilling and filing without losing rigidity.

The basic geometry looks good - the bearing/mass/stylus centreline is in a straight line. I think the counterweight is *much* too far back, giving a high Polar moment and raising the effective mass. Try to get the weight as close as possible to the pivots, preferably by lightening the headshell end. On a 2-gimbal arm like that with the yaw bearings way below the centreline, I'd make a weight with a low cg, providing it was heavy enough to be near the pivots. it should help bearing chatter.

A guess says that the arm tube looks rather resonant, especially as it's one piece through to the counterweight, so maybe try fitting a couple of "o" rings or small strips of heatshrink tube to it.

I do have calculations for effective mass, resonant frequencies and stuff, but it means having weighed each arm component first.
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Old 7th August 2006, 04:23 PM   #5
percy is offline percy  United States
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Well it seems like itís a low-mass tonearm. One of the articles I found while searching was this - http://www.epinions.com/content_4444954756 (yeah on Epinions of all the places!)

So I guess reducing mass in the headshell will certainly work towards that objective (a low mass tonearm). I guess using a lower mass/weight cartridge would help too ? They vary from 4.2g(goldring elektra) to 6.6g (shure m97)!

Btw itís a plastic headshell and the cartridge mounts on a sliding aluminium or alloy fastener plate kinda thing. I wonder where the rigidity is ? I am getting more and more attracted to the idea of a diy headshell.

If your method of determining the eff.mass of the tonearm requires dissassembling the tonearm then I am not confident enough to go that far but I'd certainly be interested in knowing about it. I have found Mark Kelly's torsion pendulum method which seems doable, but for now knowing that itís a low mass arm helps.
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Old 7th August 2006, 04:45 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

Getting hung up on effective mass is fairly pointless, most modern
cartridges are designed for medium mass arms so simply don't
worry about it.

Rigidity and resonance is worth worrying about. The mechanical
integrity of the headshell connection seems to me to be very poor.

If possible put heatshrink tubing (non-adhesive) on the armtube.

It appears converting to fixed headshell by glueing on another
section does not look difficult, unless cartridge hieght is an issue.

/sreten.
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Old 7th August 2006, 05:10 PM   #7
percy is offline percy  United States
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I hope they make heat shrink tubing in aluminium or metallic color I don't want a bright orange tonearm certainly will fail the waf test.

did you mean glue the same headshell or make another out of other material and glue that one ?
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Old 7th August 2006, 06:38 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

I thinking of reusing the existing fixed section, but if you can
replace all of the headshell parts with one piece would be better.

/sreten.
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Old 8th August 2006, 11:12 PM   #9
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Quote:
Originally posted by sreten
Hi,

Getting hung up on effective mass is fairly pointless, most modern
cartridges are designed for medium mass arms so simply don't
worry about it.

Rigidity and resonance is worth worrying about. The mechanical
integrity of the headshell connection seems to me to be very poor.

If possible put heatshrink tubing (non-adhesive) on the armtube.

It appears converting to fixed headshell by glueing on another
section does not look difficult, unless cartridge hieght is an issue.

/sreten.
yip ...medium mass will play safe

could be that light "TYPE" alloy tube and plastic in the arm...

main thing if you want to know effective mass OF TONE ARM with a known cartridge...is to use a HIFI NEWS test record...this will let you know if u work backwards and use this chart:
http://www.vandenhul.com/artpap/phono_faq.htm#a2

i would worry more about the arms ability to track Parallel to the record...if there is no height adjustment??


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