Cartridge Overhang?

the thin end of the wedge
MikeTT
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Cartridge Overhang?

Post by MikeTT » 14 Dec 2010 23:49

Ok, i just don't understand overhang as with a protractor there is no specific overhang measurement in mm.
This is what i have in the manufacture's manual: Effective Length 213mm, overhang 14mm.
Ok, so i have a cartridge mounted on a slotted headshell which i can move in and out.
I have a DBP-10 protractor.
I am confised as it does not seem to matter where i have the cartridge mounted in the headshell, all the way forward, all the way back, or in the middle.
I can set up to both null points slightly twisting the cartridge in the headshell and get it bang on regardless if the cartridge is full forward, in the middle or all the way back in the slotted headshell!


So my question, how do i know where the cartridge should be in the headshell to get exactly 14mm of overhang?

pogo
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Re: Cartridge Overhang?

Post by pogo » 15 Dec 2010 00:06

MikeTT wrote:Ok, i just don't understand overhang as with a protractor there is no specific overhang measurement in mm.
This is what i have in the manufacture's manual: Effective Length 213mm, overhang 14mm.
Ok, so i have a cartridge mounted on a slotted headshell which i can move in and out.
I have a DBP-10 protractor.
I am confised as it does not seem to matter where i have the cartridge mounted in the headshell, all the way forward, all the way back, or in the middle.
I can set up to both null points slightly twisting the cartridge in the headshell and get it bang on regardless if the cartridge is full forward, in the middle or all the way back in the slotted headshell!


So my question, how do i know where the cartridge should be in the headshell to get exactly 14mm of overhang?
"Bang on" with the protractor is what you're after.
Overhang, effective length, and offset angle are what determines the two null points and the tracking error. (twisting the cartridge in the headshell was simply adjusting offset angle.) If you measure the distance from the tonearm pivot (or know it otherwise) to the center of the platter and subtract it from the distance from the tonearm pivot to the stylus (effective length) the result is the overhang. Realize that the measured effective length may or may not be what the manufacturer specs, and 14mm is a common mfr spec for overhang, but is rarely (never?) optimum. What protractor are you using?

MikeTT
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Post by MikeTT » 15 Dec 2010 00:20

I just don't understand how i would know where to properly install the cartridge on the headshell to get the proper overhang.
Aligning the cartridge at the two null points is not a problem, what is confusing is knowing where the cartridge should be (fore and aft) in the headshell which is my overhang if i am understanding this correctly.

nat
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Post by nat » 15 Dec 2010 00:26

There is a fixed relationship between overhang and arm length if the offset angle is specified (which is what the manufacturer intended -- it's hard to convince the public that a turntable is well designed if the cartridge is cocked relative to the headshell). but if you are willing the change the angle, then you have all sorts of possible correct alignments.
This is clearly evident by the different null points for the 3 main alignments (Baerwald, Stevenson, and Lofgren (or whatever their names actually are)). There are actual reasons for choosing one or the other, but for sanity's sake, just choose one and get the cartridge parallel to the headshell when aligned.
If you have a Technics table, you may find that its impossible to do unless you use a Stevenson (I think that's the one) protractor.

pogo
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Post by pogo » 15 Dec 2010 02:26

MikeTT wrote:I just don't understand how i would know where to properly install the cartridge on the headshell to get the proper overhang.
Aligning the cartridge at the two null points is not a problem, what is confusing is knowing where the cartridge should be (fore and aft) in the headshell which is my overhang if i am understanding this correctly.
15862

hesson12
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Post by hesson12 » 15 Dec 2010 05:00

Do you have the instructions to the DBP-10? They tell you how to achieve overhang pretty clearly, but you have to study them a bit. I think if you take your time and read them carefully, you'll figure it out. I couldn't explain it any better than the instructions. Best of luck.
-Bob

pogo
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Post by pogo » 15 Dec 2010 05:39

MikeTT wrote:I just don't understand how i would know where to properly install the cartridge on the headshell to get the proper overhang.
Aligning the cartridge at the two null points is not a problem, what is confusing is knowing where the cartridge should be (fore and aft) in the headshell which is my overhang if i am understanding this correctly.
Have you looked at this or this? The first tool wiill let you calculate the optimum based upon the protractor you're using, the second will compare the result to the mfrs speced conditions. They both include another illustration, and definitions for the three most popular two point protractors. A quick look will tell you that 14mm is probably not what you want. If you still want to know how to measure overhang look at the diagram I posted or the one at these two links. If you want to know what the optimum is, use the tool and then set that. You didn't mention what protractor your using. Most likely it's Baerwald. You can confirm this by measuring the distance from the spindle center to each null point and comparing them to those in the tool

MikeTT
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Post by MikeTT » 15 Dec 2010 11:26

hesson12 wrote:Do you have the instructions to the DBP-10? They tell you how to achieve overhang pretty clearly, but you have to study them a bit. I think if you take your time and read them carefully, you'll figure it out. I couldn't explain it any better than the instructions. Best of luck.
-Bob
Yes, i have the instructions and set it up by the instructions on many tt's but where does it tell me how many mm my overhang is?
As i said before i can locate the cartridge on the headshell anywhere fore and aft and get the two null points on.
How do i know where 14mm of overhang is?

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Post by kelvinMunson » 15 Dec 2010 11:51

Mike, from your posting it seems you are twisting the cartridge at both null points to achieve alignment ?

You should aling the cartridge square in the headshell and achive alignment at the inner null point by moving the cartridge back and forth only...... not twisting, There should only be one position in the headshell at which you achieve alignment.

You then move to the outer null point and correct for alignment at that point by twisting the cartridge, as necessary.

You may need to repeat the process to achieve the best compromise.

Alec124c41
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Post by Alec124c41 » 15 Dec 2010 19:54

If you get the cartridge perfectly aligned with the grid at the inner null point, then move to the outer grid:
1 - it aligns perfectly. Play music.
2 - it is angled to the outside. Move the cartridge forward.
3 - it is angled toward the inside. Move the cartridge back a bit.
Get that right, and the overhang will be right. Note that the overhang specified in the owner's manual will only be the same if you use the same alignment specs. If the manufacturer has used Stevenson and you are using Baerwald (recommended) the overhang will be different.

Cheers,
Alec

pogo
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Post by pogo » 15 Dec 2010 20:04

MikeTT wrote:Yes, i have the instructions and set it up by the instructions on many tt's but where does it tell me how many mm my overhang is?
As i said before i can locate the cartridge on the headshell anywhere fore and aft and get the two null points on.
How do i know where 14mm of overhang is?
First let me apologize for badgering you about what protractor you are using. Some how when I read your original post I failed to realize that DBP10 was the model number of a commercial protractor -- Don't know why.

I'm not familiar with the protractor, but a quick look it seems to be a universal model that will let you pick your own null points. When I ask "what protractor" I guess I really meant what null points are you trying to hit?

But I may be overthinking your question. If all you really want to know is how to set an over hang of 14mm, that's easy.

Get a ruler with a millimeter scale.
Butt the end up to the spindle on the side away from the tonearm.
Turn the table till you can sight directly down the ruler to the tonearm pivot.
Now move the tonearm over till it's over your ruler.
Note the measurement from the spindle to the stylus.
Subtract 3.5 mm (approximately the radius of the spindle) from the measuerment.
The result is the overhang.
Move the cartridge till you get 14mm.

Good luck. This should let you set the overhang. Don't bother with the protractor. You didn't mention the offset angle spec, but for a 213mm Effective length and 14mm overhang, I had to back the offset angle down to 21 degrees to produce two null points that are on the record. That produces nulls at 60 and 100 mm, and really high tracking error at the outside edge. If the Mfg says 14mm then it probalby only produces one nulll and a max tracking error that they consider acceptable across the record. An offset angle of 22 degrees (a number mfrs seem to like) would produce tracking distortion less than 1% over most of the record (but not all). You probalby can't improve this unless your able to set an overhang in the range of 19.5 mm and an offset of 26 degrees. This may or may not be physically possible on your turntable.

MikeTT
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Post by MikeTT » 15 Dec 2010 21:56

Thanks for the responces guys, what Alec/Kelvin said pretty much sums it up! :wink:
I was also playing a couple test records (Shure/Sound Canada) and i have the cartridge set pretty good but not a perfect 5 yet(mistracks a bit in test 4+5).......
Going to reset the cartridge and see if perfection is possible,lol.

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Post by Conrad Hoffman » 18 Dec 2010 19:24

Get an opaque black marker. Anyplace in arm or turntable literature that overhang is mentioned, cross it out. Overhang is not a parameter that they have close control over. Next, look in the cartridge literature. Anyplace you see overhang mentioned, cross it out. They have no idea what geometry will apply, and thus can say nothing about overhang. Now search the rest of your literature (plus the internet) and cross out any references to overhang. Finally, you're ready to think about alignment. Choose a template (mine is nice, so are others), choose an alignment strategy (they're all surprisingly similar) and have at it. When you're done, the cartridge will have an overhang. It's of no concern what it is, as the alignment templates have taken care of it.

Best,
Conrad

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Post by Whitneyville » 19 Dec 2010 01:25

Excellent point Conrad. I moved my cartridge 1.5mm forward from "spec" on my Grace 707 MkII arm, beacuse it sounds better. I effectively "lengthened" my arm 1.5mm so it "fits" the Heybrook TT II protractor null points a little better (extreamely broad). I measured it with a digital venier caliper, and "tweaked" from there. Used a friend's DeWalt laser construction level to set "level" and offset angles to +/- .01 degree. Then I generated a "customised" protractor for moving the cartridge forward. I consider the "specs" as very good starting points, that I will adjust until it sounds the best. Isn't that what this whole excercise is about? (and reducing record wear)

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Post by avole » 19 Dec 2010 04:24

I use the gauge that came with the SL1200MK5. It sets the overhang precisely, and works well.

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