Putting on weight

[docfoster]

I've been using a Decca Super Gold in a PL-71 for about a year now.
In my more idle moments I have been experimenting with adding and removing mass from the headshell. I've found that for my ears, additional mass causes more problems than it solves.
Obviously my ears are the ultimate arbiters of how to tweak my TT, but on a theoretical level, how does changing headshell mass affect the sound? Is it something to with inertia...?



All suggestions welcome!

Ben

[Nick]

Not sure of all the complexity, but increasing the mass at the end of the arm will lower the resonant frequency of the arm and cartridge. One of the tracks on most test disks allows you to find the resonant frequency. To high and its into the audio band, to low and it can be excited by warped records. Also increased mass will mean that the cartridge cantilever and suspension will have to exert more force as it rides over warped disks.

Force is proportional to mass * acceleration (acceleration is rate of change of velocity)



The natural frequency of a simple mechanical system

[docfoster]

Nick,
Thanks.
I should probably get myself a test disc.

The main issue with adding mass was that on audiophile/Dj pressings there was significant break up in passages of heavy bass. Could this have been a resonant frequency issue?

Ben

[Nick]

It could be, it could also be the extra mass "fixed" the cartridge in place more, forcing the cantilever to actually track the bass passages instead of moving with them. But thats just a guess.

[Diamond Geezer]

I've been using a Decca Super Gold in a PL-71 for about a year now.
In my more idle moments I have been experimenting with adding and removing mass from the headshell. I've found that for my ears, additional mass causes more problems than it solves.
Obviously my ears are the ultimate arbiters of how to tweak my TT, but on a theoretical level, how does changing headshell mass affect the sound? Is it something to with inertia...?



All suggestions welcome!

Ben

Hi Ben

Unless I am very much mistaken, the mass of a pickup arm is in the whole of the arm, from headshell to balance weight and includes the weight of the cartridge. i.e. The Sun has Mass, as does the Earth. By adding weight to the headshell, you are upsetting the mass of the arm. This is a mistake I made many years ago. You are right, it is an inertia problem.

Any weight you add to the headshell, loads weight onto the stylus and its cantilever, so it just digs deeper into the groove and will ultimately cause damage to both the groove and the stylus. It also upsets the Vertical Tracking Angle ( VTA), hence the sound gets worse. You need to add a small amount of weight to the whole arm-tube, not the headshell.

Not having seen one, I assume the arm is a small diameter alloy or brass tube, of about 6-8 mm. If you have ever seen the Rega RB250/300 arms, they are made of cast alloy and of tapered construction. These have higher mass than SME 3009 series arms, hence the reason they track better.

The best way to experiment with adding mass to your arm, is to try winding some masking tape around the full length of the tube. It will only add a few milligrams of weight/mass to the arm, but may give far better results than just adding a lump of Blutack to the headshell.

The other method - and possibly the better one, if the balance weight is moveable - is to add some Blutack to the weight and move it closer to the fulcrum. This allows the stylus to track the groove better.

If you remember your school physics lessons, to lift a heavy weight, you use a long lever and put your fulcrum close to the object you are trying to lift. You then need less effort to lift the weight. The reverse of this is the principle of how the arm and cartridge work.

I hope this is of use to you, in resolving your problem.

Regards

Russ

[Nick]

Any weight you add to the headshell, loads weight onto the stylus and its cantilever, so it just digs deeper into the groove and will ultimately cause damage to both the groove and the stylus. It also upsets the Vertical Tracking Angle ( VTA), hence the sound gets worse. You need to add a small amount of weight to the whole arm-tube, not the headshell.

I was assuming that any extra mass was balanced at the counter weight so there was no extra downward force on the cartridge. If you add the mass at the end of the arm tube you will affect the resonant behavior of the arm as a structure, but from the perspective of the cartridge you will need to add less mass to get the same effect the closer it is to the cartridge (the effect of a lever again or moment of inertia, whichever way you want to look at it).

[shane]

The other method - and possibly the better one, if the balance weight is moveable - is to add some Blutack to the weight and move it closer to the fulcrum. This allows the stylus to track the groove better.

Adding mass to the counterweight and moving it closer to the pivot actually reduces the effective mass as seen by the cartridge. "Effective mass" is badly named. It is nothing to do with the overall mass of the arm/cartridge. It is an expression of the rotational inertia of the whole arm/cartridge assembly around the pivot. Rotational inertia is proportional to mass, but inversely proportional to the square of the distance of that mass from the pivot, so if you double the mass of the counterweight, you will need to halve the distance from counterweight to pivot to balance everything out, which reduces the inertia by a fourth, so you have effectively halved the mass seen by the cartridge.

Clear as mud...

[docfoster]

Any weight you add to the headshell, loads weight onto the stylus and its cantilever, so it just digs deeper into the groove and will ultimately cause damage to both the groove and the stylus. It also upsets the Vertical Tracking Angle ( VTA), hence the sound gets worse. You need to add a small amount of weight to the whole arm-tube, not the headshell.

I was assuming that any extra mass was balanced at the counter weight so there was no extra downward force on the cartridge. If you add the mass at the end of the arm tube you will affect the resonant behavior of the arm as a structure, but from the perspective of the cartridge you will need to add less mass to get the same effect the closer it is to the cartridge (the effect of a lever again or moment of inertia, whichever way you want to look at it).

Yes. The tracking force was set after adding the headshell weights.
Thanks for the responses. I'm going to have to read these most recent posts tomorrow. Just got up after a day in bed with the flu...Brain is a bit fuzzy.

[Mike H]

Oo that's not good, extra vitamin C!


One possibility I can see for adding weight to a headshell is if the cartridge is too light for the arm


Just a thought



 

[Nick]

Yep, for example the Denon 103 needs some mass to work against, 80's ultra low mass arms bring out the worst in it, hence the bluetack'd coins on the headshell.