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Old 13th February 2014, 05:58 PM   #1481
bgruhn is offline bgruhn  United States
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Location: Medfield, MA, USA
Quote:
Originally Posted by spinning wheel View Post
Look what happens with DVM readings as soon as the battery collaps , weird values , same story with a scale I guess .
Put new batteries in and reset the cal. Penny weighs 2.5 grams now. All better now.

Thanx
BillG
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Old 13th February 2014, 07:00 PM   #1482
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mine has a reference weight and I just check it once in a while .
it never let me down so far

another question keeping me busy here , does anyone know about a real good methode to check the azimuth , other than by the eye ?? I have a dual channel scope here , a decent RMS Millivolt meter , test record . but what is the very best methode ?? hope someone can teach me the right trick

THX
Paul
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Old 13th February 2014, 07:18 PM   #1483
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Just use your eyes on this. I usualyt lower the cartridge onto a mirror. If the reflections are parallel, then that's more than good enough.
Chris
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Old 13th February 2014, 09:11 PM   #1484
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spinning wheel;

Your ears will be the ultimate judge. Cartridge stylus are not always made/aligned perfect either.
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Old 13th February 2014, 09:32 PM   #1485
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For those interested here is the carriage design and setup. So simple it's ridiculous .
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Old 13th February 2014, 10:32 PM   #1486
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Quote:
Originally Posted by vynuhl.addict View Post
For those interested here is the carriage design and setup. So simple it's ridiculous .
Here's another one , with an additional adjustment this time
Looks great , Colin !

THX
Paul
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Old 14th February 2014, 08:08 AM   #1487
niffy is offline niffy  England
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Default centre of mass/gravity

The cog HAS to be just in front of the pivot. If the cog is directly underneath the pivot the carriage would balance perfectly and there would be no down force at the cartridge. If I remember correctly Colins carriage weighs 30g Inc cartridge and has a 75mm effective length. To achieve a 1.4g tracking force, as recommended for the at120e, the cog needs to be 3.5mm in front of the pivot.
With this design almost the entire mass sits below the cog. This will cause the tracking force to increase as the cartridge passes over a record warp. (if the cog was above the pivot the tracking force would decrease) A slight increase in tracking force when negotiating a warp is probably a good thing.
Looking at Colins latest photo of the carriage (nice work Colin) I would estimate the cog, with the cartridge and counterweight in place, to be about 20mm below the plain of the pivot. A quick calculation would show that when negotiating an average warp at the outside of a record, a warp of about 0.3mm, the tracking force would increase to about 1.43g, an increase of 2.3%. Definitely not enough to misalign the cartridge generator significantly but probably helpful for tracking.
Warp wow with such a short arm and high pivot still worries me a bit but as Colin and Bill have not found this to be a problem I'm probably worrying unduly. A good record clamp will help reduce this problem anyway. In my book it's much better to move the problem of warps to be dealt with by the deck rather than the arm anyway.

Colin

It looks like your homing in on a final design. Are you planning on rebuilding for cosmetic reasons or are you happy with the looks? This is undoubtedly the best thread on diyaudio. Great work

Niffy
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Old 14th February 2014, 06:04 PM   #1488
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Quote:
Originally Posted by niffy View Post
The cog HAS to be just in front of the pivot. If the cog is directly underneath the pivot the carriage would balance perfectly and there would be no down force at the cartridge. If I remember correctly Colins carriage weighs 30g Inc cartridge and has a 75mm effective length. To achieve a 1.4g tracking force, as recommended for the at120e, the cog needs to be 3.5mm in front of the pivot.
With this design almost the entire mass sits below the cog. This will cause the tracking force to increase as the cartridge passes over a record warp. (if the cog was above the pivot the tracking force would decrease) A slight increase in tracking force when negotiating a warp is probably a good thing.
Looking at Colins latest photo of the carriage (nice work Colin) I would estimate the cog, with the cartridge and counterweight in place, to be about 20mm below the plain of the pivot. A quick calculation would show that when negotiating an average warp at the outside of a record, a warp of about 0.3mm, the tracking force would increase to about 1.43g, an increase of 2.3%. Definitely not enough to misalign the cartridge generator significantly but probably helpful for tracking.
Warp wow with such a short arm and high pivot still worries me a bit but as Colin and Bill have not found this to be a problem I'm probably worrying unduly. A good record clamp will help reduce this problem anyway. In my book it's much better to move the problem of warps to be dealt with by the deck rather than the arm anyway.

Colin

It looks like your homing in on a final design. Are you planning on rebuilding for cosmetic reasons or are you happy with the looks? This is undoubtedly the best thread on diyaudio. Great work

Niffy
Niffy , when we staticly balance the arm w/o the cart + CW attached , the COG is exactly under the pivot ! nowhere else . Of course if we than install the cartridge alone , there's downforce on the stylus as much as the weight of the cart , and the COG moves upfront .
The CW will bring this back into the ballpark depending on it's weight and location . no math applied here at all .

THX
Paul

Last edited by spinning wheel; 14th February 2014 at 06:10 PM.
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Old 14th February 2014, 07:03 PM   #1489
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Because air ultimately can be compressed as in air bearing tone arms?
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Old 14th February 2014, 07:03 PM   #1490
niffy is offline niffy  England
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Quote:
Originally Posted by spinning wheel View Post
Niffy , when we staticly balance the arm w/o the cart + CW attached , the COG is exactly under the pivot ! nowhere else . Of course if we than install the cartridge alone , there's downforce on the stylus as much as the weight of the cart , and the COG moves upfront .
The CW will bring this back into the ballpark depending on it's weight and location . no math applied here at all .

THX
Paul
Paul

Sorry misread you post on the previous page concerning cog. You were balancing without cartridge or weight, missed that.

I like to find something that works (like this arm), do the math to find out why it works, then see if it can be improved. Maybe I'm weird but enjoy the math part of design.

My point on the vertical location of the cog was that Colins current arm and the math happily agree with each other.

Niffy
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