Copper Weights for Headshells, by Joe Hakim

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If you are into vinyl playback, it’s likely you will eventually run into the need for a headshell weight to improve the low frequency resonance point of your tonearm/cartridge combination. For those of you not familiar with this mechanism, a brief primer is presented below.

In vinyl playback systems (TTs), the tonearm + cartridge acts as a sprung mechanical system with a given natural resonant frequency. The “springiness” of the system and resultant resonant frequency depends on the effective mass of the tonearm, weight of the cartridge (+ mounting hardware), and the compliance of the cartridge.

The compliance of a cartridge is defined as the amount of deflection in the stylus.  The compliance of a cartridge is defined as the amount of deflection in the stylus when a given force is applied – in other words, how springy is the stylus if you push down on it. The cartridge compliance, weight, and the tonearm effective mass will determine the resonant frequency of any tonearm/cartridge combination.

The goal for any TT setup is to keep this resonant frequency between 8-11Hz otherwise you will impact the bass performance of your playback system.  Vinylengine has a nice little resonance calculator you can find here – Vinylengine Tonearm Resonance Calculator.  Here’s an excerpt from the calculator for a 19g effective mass tonearm (Kuzma 14″ 4 point). Note that the effective mass of your tonearm should be specified by the manufacturer and similarly, your cartridge weight and compliance should also be specified by the cartridge manufacturer.

The tool works as follows: enter the effective mass of the tonearm in the window and press the submit button. The tool will return a view similar to the one shown below. Once you have this plot, go along the vertical scale on the left hand side to find the compliance value for your cartridge (e.g. 10 x 10^-6 cm/dyne). Then move along that row to the right until you find the column with your cartridge + mounting hardware weight (in grams) to find the resonance frequency.

 

So you can guess now why a headshell weight might be necessary! As an example, my Kuzma tonearm with 19g effective mass and a Koetsu cartridge with a weight of 12g (including hw) and 5 x 10^-6 cm/dyne compliance. If you follow the table, this gives a resonant frequency of 13Hz which is not good (orange zone).  Now if I added a 4g headshell weight to my cartridge mount, you can see that would push me out of the orange zone to something around a 12Hz resonant frequency (there is no 16g column in the table but should still be in the 12Hz area).

Clearly this is not ideal but gets us closer to the green zone. Probably 6g of weights would get us to 11Hz or less, which is where we want to be.  Given my preference for Koetsu cartridges and the fact they have very low compliance, I have often been left struggling to get my TT setup in the proper range of 8-11Hz. I could never find anyone making headshell weights for this purpose – other than some made for Technics style removable head shells – here is an example from eBay – Headshell Weight.  removable head shells – here is an example from eBay – Headshell Weight.

The problem with these weights is that they are made of magnetic steel – not a good option for magnetic cartridges! They are also not machined so the mating surfaces are rough and do not provide a consistent mechanical interface between the headshell and the cartridge (though they’re designed to go on top of the headshell in their intended application, I could not use them this way with
my particular tonearms).

You can also get a set of calibrated cartridge mounting screws from Soundsmith but these won’t work on all headshell designs (e.g. they don’t work on the Kuzma) and they do nothing to help the cartridge/headshell interface.  My frustration with the lack of high quality headshell weights finally lead me to engage with an old college buddy of mine who is an industrial designer and commissioned him to design some custom weights for me.

My design criteria for these weights were as follows:
* develop 2g, 3g, and 4g weights
* three materials should be designed for – Stainless Steel (SS), Copper (Cu), and Titanium (Ti)
* thickness across all weights and materials should remain constant so that the user does not need to readjust VTA when changing weights
* center of mass should be the same across all the weights so that there is no change in the moment presented to the tonearm

My first prototypes were made from copper in the 3g and 4g weights so that is what I tested in my setup which included a Kuzma 14″ 4 point tonearm with Koetsu Blue Lace Platinum cartridge. Here’s a photo of one of these copper prototypes – the 3g weight is on the left and the 4g weight is on the right:

What I immediately noticed on my setup is the weight, articulation, and definition of the bass improved compared to no weights (adjusting VTA to similar value). Also the solidity of the imaging and the space around instruments improved.

Here is a photo of one weight on the Kuzma tonearm with the Koetsu cartridge:


In order to get other opinions and test these weights on different setups, I gave some prototype samples to fellow member Kevin Olson. Here’s what he had to say about the copper weights (compared to the carbon fiber spacers he was using on his headshell for VTA):
Just A/B’d with my Zu 103 on carbon fiber headshell.
Listened to Bill Evans Trio – Portrait in Jazz.
With one CF shim only for reference. Sounded pleasant. Nice tone. Staging a bit flat.
Added 4 gram copper shim.
Staging improved. Enhanced sense of recording space. Even better tone.
I think both the added mass on the low compliance Zu 103 and the vibration absorbing copper have been a net positive. More relaxed sound too. I forget to ‘listen’ and just groove to Bill and Trio.
I also benefit from the height of the shim.
This is mounted on a Technics SL 1200 G. The tonearm is magnesium and of medium mass. Not perfect for the low compliance Zu, but not bad. The copper weight is a nice tool to have.

And in response to my query about any improvement in the bass:
Yes. Definitely improved the sound of the string bass. Back further in the stage, but each note clearer and more fully formed. Better overtones and more sense of the wood
body.

I think the results will vary on different setups but I believe these weights could provide a
sonic improvement on many vinyl setups. Also, it will be interesting to see how the different
metals impact the sound on a given setup – will report on this once I get the additional prototypes
being manufactured for me.

 

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San Francisco Audiophile Society

San Francisco Audiophile Society