Hot Rod Jelco – Part-1

We've been on a bit of a roll with tonearms as of late - first, with the Hybrid Kuzma (click here), and now with the Jelco SA-250. The Jelco architecture always teased us with its  untapped potential.  While it's no longer in production, the fact that we still have inventory gave us reason to explore this. (March 20 2022 - this modification is now in production and the story can be found here). The obvious low hanging fruit is the Jelco's counterweight architecture, but as we explored the tonearm further, we found this to be the proverbial tip of the iceberg.

Background

A few months ago, I disassembled the arm to study it.   The first thing I noticed was the beauty of its simple bearing architecture - two pairs of needle bearings control vertical and horizontal movement.

With Jelco's parent company being Ishikawa Jewel Co., it should come as no surprise that the contact cups employ jewels.  The astute reader might notice that a recent major upgrade to the Kuzma 4Point tonearms involved replacing the polished steel bearing cups with jewels.

The lossy counterweight connection was the starting point for our modification, but upon disassembly, I found another more significant weakness - the arm stub architecture.

The above photo is a proof of concept prototype, and is nothing pretty to look at.  Continuing fallout from COVID is resulting in extraordinarily long machine shop turnaround times, which has had a big impact on our prototyping and other "one-off" machining jobs.

Off to the home shop with primitive tools, and this is the result.  Functional, but not elegant.

Auditioning

I fabricated the prototype weight to the same mass as the production counterweight.  We've demonstrated countless times, that subtle adjustments to counterweight mass can alter the interaction between a cartridge and a tonearm.  When we set up a Kuzma 4Point (or any tonearm with multiple counterweights), a key final tuning step involves experimentation with various counterweight combinations.  Tuning matters.

Intelligible (adjective):  capable of being understood or comprehended.

If you know me, you know that a key element of any design I sign my name to is musical intelligibility.  What are the performers trying to say?  At the end of the day, what could be more important in a musical playback system than comprehending the musical intent of the piece as well as the performers' interpretation?

This new assembly is manifesting a more stable and physical presence in the music, along with more intelligible musical lines.  Noise floor is a bit lower, but not dramatically so.  The bass is beginning to take on the characteristics of the Kuzma 4Point.

Is it worth the effort?

Let's get this out of the way.  This hot rod Jelco is no Kuzma or Schröder.  You really didn't expect that, did you?

People continually ask me about the next step up from the Jelco and Rega class of tonearm - a midpoint on the continuum between these arms and the Kuzmas and Schröders of the world.  I advise them to hold pat until they can make the big leap, as the money invested in these intermediate solutions isn't justified in light of the sonic return.

The short of it is, that I expect this modification to present an excellent value proposition to the limited number of people who are fortunate enough to acquire one of these arms.

Moving forward  ...

I'm completing drawings for our machinist.

The design will consist of a multiple counterweight set - a main weight, along one or two ancillary weights (to be determined in pre-production testing) to facilitate mass tuning and cartridge matching.

March 20, 2022 update:  the counterweights are in production.  Click here for part - II.