Cartridge Potting


Id read quite a bit regarding potting cart bodies and after a little coercion from Grado aficionado eventually took the plunge.
A few lessons were learnt along the way which are worth sharing.

So What is Potting and Why Bother?

Potting of cart bodies involves applying an electrically inert compound to the cart internals to minimize unwanted resonances of the internal components.
I personally believe that locking down the fine internal coil to pin wires which are loose and free to vibrate is a key benefit.

After potting a Grado Z+ body using a nude stylus I got;
- Slight tightening up of the bass, adding more punch and control
- A cleaner all round definition individual instruments became more discernable, top end slightly crisper

Not a quantum leap, but noticeable and definitely worthwhile for the cost of a couple of our British Penny's

How to do it?

OK first up you need to consider what is moving before even contemplating this.
Moving Coil cartridges rely in the coils to move freely relative to the fixed magnet, any incremental damping of this relative movement will have a significant effect upon the response.
Personally I'd prefer not to risk any form of damage to MC carts - I know many have experimented but for me there's just too much at stake.
This is something that Id personally only recommend for Moving Magnet and Moving Iron Carts.

Grado cartridges, with removable styli lend themselves to DIY potting, as with the stylus removed, the coils and cavity are exposed for easy access without any need to split the housing.

They do, however, present an incremental challenge that is worth covering before we get started.
A small amount of black compound is applied to these carts to ensure the stylus assembly is held firmly in place when inserted.
On removing the stylus it is likely that some of this compound will remain in the stlyus pocket and there is a risk that it could impede correct alignment when re-inserting the stylus after the potting process has been completed.
Prior to commencing the potting process I chose to remove the excess compound from the pocket, but here care is required.

I've successfully done it on two bodies, but trashed another.
With time that soft compound hardens with age.
If it's relatively new and soft then there shouldn't be too much of an issue, carefully scraping out the stylus pocket.

If it's become hardened then this is where the risks come in.
It tends to harden into lumps, if those lumps form around the front of the coils then they are very likely to have wrapped around a loose flying coil wire.
In this case there is a significant risk that you will break a wire while excavating.
This is exactly what I did with a GF3.

I thought I'd been very careful in cleaning out the stylus pocket, only to find it had gone open circuit after mounting up. Grrrrr!
The culprit was a lump of hardened black goo wrapped around the now dangling coil wire which is just about visible in this picture

Grado GF3

So my advice would be to tread very carefully and if you witness hardened black goo keep well away from the front of the coils.

OK so youve got a nice clean pocket and body all ready for potting.

Grado Z+

So what to use to do the potting?

Well theres a whole host of potential materials, Bees Wax is quite popular and Ive even heard of Epoxy Resin being used.
My choice was very much linked to the knowledge of how easy it is to break a coil wire, I wanted to use an approach that minimized the risk of damage.

In the end I elected to use a paraffin based Lipbalm product.

Potting Compound

The reason for this selection is that, not only is it electrically inert and solid at room temperature, it also melts readily when heat is applied.
In a softened, almost liquid state it is much easier to apply into the coil cavity while applying minimal force.

I warmed it up over a household heater (a hair dryer would do the same job) and very carefully applied it, virtually dripping it in to the body cavity, ultimately dabbing it down on the surface as the cavity filled up.
As pictured I carved a flat on the end of a match stick and used this as my dabbing tool.
In the picture above, you can see the existing black seating compound left on the front/top of the coil assemblies. The softened potting balm was dabbed into the gaps that remained

This was the end result

Potted Grado Z+


After letting it cool down and set, I carefully wiped and cleaned the tops of the poles prior to re-fitting the stylus.
This I did with a cotton bud, one side lighlty damped with a mild IPA solution then used the dry end to finish off

Ultimately a MCZ stylus was then re-fitted to the body - semi-rigidly fixed with small blobs of blutac (replicating the black seating compund's function) ensuring a firm hold.

Grado MCZ 100x

Grado Z+ & MCZ

I've already stated the benefits of potting and when equipped with the nude MCZ stylus this really is a very nice cart.
I did some specific back to backs against a Grado Reference Sonata 1 and was amazed at how close it pushed it.

This little potted assembly gets regular visits to the turntables, in fact Im currently giving the DL-S1 a little break and this was my turn to replacement disgraced it is not.

Created by Mail To: davey_w@hotmail.co.uk: July 2012 - Last Updated March 2016