protractor question

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vjvarta
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protractor question

Post by vjvarta » 25 Aug 2019 14:07

Hello all. I have a Telefunken CS 10 and i was wondering what is the optimum protractor to use for cartridge alignment.

effective tonearm length 216.8 mm
tonearm offset angle 24.75 mm
headshell overhang 17.8 mm

lini
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Re: protractor question

Post by lini » 26 Aug 2019 14:48

As you've got the complete set of data, why don't you simply enter that in JaS' alignment calculator, which you can find in the "Tools" section of VE. That way you can determine the original alignment.

Did that for you: https://www.vinylengine.com/tonearm_ali ... =calculate

As you can see, Telefunken apparently chose an alignment very close to Baerwald/Loefgren A calclated for an LP playback area according to DIN. So a Baerwald/Loefgren A protractor calculated for DIN radii would get you very close to the original alignment - or you could make yourself a custom two-point protractor with null points at 61.8 and 119.7 mm, if you'd like to exactly replicate the original alignment.

Greetings from Munich!

Manfred / lini

vjvarta
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Re: protractor question

Post by vjvarta » 28 Aug 2019 10:41

very appreciated.

JeanPP
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Re: protractor question

Post by JeanPP » 28 Aug 2019 16:12

There is something I don't understand :

the tonearm is :
effective length 216.8 mm
offset angle 24.75 mm
headshell overhang 17.8 mm

If Lofgren A choosen, tonearm should be :
effective length 216.8 mm
offset angle 24.88 mm
headshell overhang 18.124 mm

How is it possible to increase headshell overhang without increasing effective length ?

Japi Roelofs
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Re: protractor question

Post by Japi Roelofs » 28 Aug 2019 21:27

JeanPP wrote:
28 Aug 2019 16:12
How is it possible to increase headshell overhang without increasing effective length ?
It isn't possible. But if you play with the numbers of the inner and outer groove dimensions, you will be able to make the Lofgren A specifications to be exactly the same as the ones of your tonearm.

https://www.vinylengine.com/tonearm_ali ... =calculate

So if you'd want to use the Conrad Hoffman protractor program, these are the numbers you can use:
Telefunken CS 10 data.JPG
(29.02 KiB) Downloaded 80 times

JeanPP
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Re: protractor question

Post by JeanPP » 28 Aug 2019 21:38

OK, thanks

I have to get used with theses tools.

Thanks again,

Jean

lini
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Re: protractor question

Post by lini » 29 Aug 2019 00:33

Jean: The calculation above just served the purpose to show, that the original alignment of that Telefunken is very similar to Baerwald/Loefgren A.

For an alignment comparison for that model one would of course need to calculate with the mounting (aka pivot to spindle) distance instead - like this: https://www.vinylengine.com/tonearm_ali ... =calculate As you can see, then the effective lengths would differ accordingly, just as expected.

Greetings from Munich!

Manfred / lini

jdjohn
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Re: protractor question

Post by jdjohn » 29 Aug 2019 16:58

The offset angle changed. Since the effective length side of the triangle is still the same, the length of the other sides would change due to that small offset angle change.

JeanPP
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Re: protractor question

Post by JeanPP » 29 Aug 2019 17:39

jdjohn wrote:
29 Aug 2019 16:58
The offset angle changed. Since the effective length side of the triangle is still the same, the length of the other sides would change due to that small offset angle change.
If effective length is still the same, physically you can't change the others sides : the length of the tonearm can't change, no matter it is J or S shape, unless to break it. And consequently, overhang doesn't change.

If ovehang changed, automatically effective length is changed, this is pure geometry.

And if you change overhang, effective length changes as a geometrical result and also the offset angle changes.

jdjohn
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Re: protractor question

Post by jdjohn » 29 Aug 2019 18:35

Forgetting about modifying/breaking tonearms, and just focusing on geometry, look at this:
Triangles.jpg
(6.79 KiB) Downloaded 48 times
In the diagram, A (effective length) is the same in both. When the offset angle (arrow) changes, the length of B & C change. Consider C as overhang, and you can see how it can change when the offset angle changes, but effective length does not.

JeanPP
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Re: protractor question

Post by JeanPP » 29 Aug 2019 19:43

There is something I don't understand.

The angle you point with the arrow is not the offset angle and its value is greater than 90°

The angle you point can't change by construction of the tonearm.

Offset angle is between the small side (C) and the effective length (A).

Am I wrong ?

jdjohn
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Re: protractor question

Post by jdjohn » 29 Aug 2019 20:26

You are correct about my arrow pointing to the wrong angle - angle A/C is the offset angle #-o

Let's go back to what you said here:
JeanPP wrote:
28 Aug 2019 16:12
There is something I don't understand :

the tonearm is :
effective length 216.8 mm
offset angle 24.75 mm
headshell overhang 17.8 mm

If Lofgren A choosen, tonearm should be :
effective length 216.8 mm
offset angle 24.88 mm
headshell overhang 18.124 mm

How is it possible to increase headshell overhang without increasing effective length ?
In this case, the assumption is that those are two different tonearms, with two different offset angles, but with the same effective length. They would have different construction due to the different offset angles, so different overhang is not a surprise.

JeanPP
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Re: protractor question

Post by JeanPP » 29 Aug 2019 21:33

OK, thank you

Now I think my understanding is correct.

In your figure above, B is constant and angle between B and C is also constant.

So if overhang increased ( C side increased) offset angle should decrease. Only C can change by changing overhang inducing a change in the offset angle.

With the tonearm given above it is not possible to chose a Lofgren A protactor because overhang and offset angle increase at the same time.

Jean

Jim Leach
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Re: protractor question

Post by Jim Leach » 29 Aug 2019 21:43

Not to muddy the waters here, but...

The cartridge (unless a direct plug-in mount) has some "wiggle" in the head shell, to tweak offset angle as well as length, by sliding in and out in the slots.

My Rega is set up with a Baerwald, which is slightly different from the "rega" set up (but more accurate/correct) so my cartridge is slightly "twisted" in the headshell, and out as far as it can go in the slots if I remember correctly. Point is: don't sweat a degree or less and a mm or two length difference. Just print your template accurately and align the cartridge to it accurately and enjoy the music!

JeanPP
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Re: protractor question

Post by JeanPP » 29 Aug 2019 21:51

Yes, I agree

This is exactly what I did with my Technics SL1500C. I twist a little bit the cart in the headshell (2°), increasing offset angle, to be closer to a Baerwald than a Stevenson A.

But I was not sure I was right to do that.

Now, thank to you guys, I am sure it is OK.

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