Jelco Arm Stub and Counterweight Set
$249 for the kit and $279 if we install it
This is a complete re-thinking of the energy mitigation strategy for the Jelco tonearm's rear section.
The lossy arm stub is replaced with threaded, 316-stainless steel rod, and a set of 303-stainless counterweights is provided (two are shown here) for compatibility with a wide range of cartridges and tonearm lengths. A fourth, fine-tuning weight is also included.
Also provided is a non-marring (brass-tipped) set screw for the VTA lock, to prevent further divots from wearing into the arm stub.
Read this blog post for background.
We developed this system around the tonearm we collaborated on with Artisan Audio - an OEM Jelco SA-250.
- The new arm stub length is 2" (51mm)
- The diameter of the counterweights is 1.25" (32mm).
- The SA-250's original arm stub is 1.75" long (approx. 44.5mm)
- The stock counterweight diameter is about 1.4" (approx. 36.5mm)
We can't speak to clearance with turntables having dust covers, but our take is that if your turntable has a dust cover, its resonant drone will negate many of this modification's benefits.
- Ensure compatibility with a wide range of cartridges
- Allow for mass tuning by using different weight combinations
- Have enough range to balance heavy cartridges on 12" arms
Shown above is one weight combination we used with the 7.3g Lyra Delos (tracking at 1.72g).
The 5.0g Hana SL can employ the same weight combination, but shown here is an alternate approach, employing the small tuning weight.
This provides an opportunity to experiment with mass tuning.
At the heavy end of the spectrum, the 17.5 gram, Kuzma CAR 40 easily balances with this (large/small) weight combination.
Other Jelco Models
To date, we've modified the following models:
Given the span of years between development of the SA-250 and the most recent arms (the 850 and 950 series), we suspect all arms manufactured by Jelco employ the same arm stub and counterweight strategy.
We can't guarantee this however, and as more arms pass through our shop, we'll update this compatibility list.
We offer an installation service, and we can inspect your arm for compatibility as well as perform the installation.
If the arm is incompatible, we'll pay the return shipping. Otherwise, we'll install the kit for you and pay return shipping (to the Continental US) for an additional $30 (total delivered price: $279).
To date, every cartridge we've experimented with has employed either:
- The main, large weight with the smaller of the two round weights (shown in the Lyra Delos example, above)
- The main, large weight with the knurled tuning weight (shown in the Hana example, above)
- The main, large weight with both the smaller round weight and the knurled tuning weight
At least two weight combinations are possible for any given cartridge.
The medium of the three round weights is a bit of an outlier - intended to anticipate the the surprise cartridge or headshell combination.
These weights are only sold in complete sets as shown in the photo above.
Also Included is a replacement grub screw to lock your VTA/SRA pillar in place.
This non-marring screw prevents further "divots" from wearing into the arm stub, so the arm height can be adjusted without the new setting "hunting" for a divot.
To repair previous damage, sand the area with 500 or 600 grit sand paper. You will remove the anodizing, but this is inconsequential.
If the following procedure makes you uncomfortable, we'll install the kit for you for an additional $30 ($279 plus shipping).
Step-1: Remove arm stub set screw
- The arm stub is removed in step-2.
- Leave the arm stub in place when performing this operation.
- We removed the arm stub for this photo so you can better see how the set screw engages the screw and bushing assembly.
This step takes a bit of finesse. We'll be loosening a set screw which locks the arm stub bushing screw in place.
You'll be hunting for the hole shown in the photo (click for an expanded view).
You may have to rotate the arm wand in order to gain enough clearance to insert the hex key.
When you've engaged the key in the set screw's socket, the key will be nearly "bottomed out". The set screw is inserted fairly deeply into the hole.
Insert the hex key as described above and loosen it by approximately 1/2 turn.
Remove the key to re-position it, and loosen the screw another 1/2 turn (one full turn in total).
Click the photo to enlarge.
Step-2: remove the old arm stub
The key takeaway in this step is to avoid unnecessary stress on the bearing.
Hold the tonearm by the wand and the arm stub. The first photo in the sequence below attempts to show this. Take a moment to get a feel for gripping it in this manner.
Once you're comfortable in gripping the arm, the process involves progressively "wiggling" the stub back and forth. The following six sequence photos show this.
You'll begin to see a rubber bushing. Keep wiggling the stub back and forth until the arm stub is free of the rubber bushing.
Click the gallery below to scroll through an expanded view:
Arm Stub Removed
Your Jelco should look like this photo (click to enlarge).
Take note of the shortened hex key we provide you.
You'll be using it in the next step.
Step - 3: Remove the Screw and Bushing
This is the step where you might experience some resistance to turning the screw.
If you do so, contact us before proceeding.
Click the photo to expand it.
For your parts "archive":
- Arm stub
- Bushing assembly
Step - 4: Install the New Arm Stub
Photos to follow ...
- Thread the new arm stub into the hole where the bushing assembly was affixed.
- Tighten the set screw - the screw you loosened in step-1.