Tuesday, April 27, 2021

Turntable Headshell Connector

One of the biggest challenges in this turntable build was attempting to recreate the headshell connector.  This part allows for quick and easy interchangeability of needle cartridges between turntables.  Otherwise, I would have to unscrew and disconnect the cartridge cables every time I wanted to remove it.  Wanting this turntable to be compatible with my other ones, which accept standard headshells, I figured I had no choice but to make this connector.

The challenge here was the amount of small and complex parts needing to be made; a threaded locking mechanism, a slotted body, and insulated piece to house four spring-loaded brass contact pins, and the pins themselves.  Then on top of this, figuring out how it will connect to the tonearm and wiring it.

My version did a fair job replicating it, but it took a lot of hard work, several failed attempts and a few design flaws.  Part of the reason for my shortcomings was the fact that I didn't want to disassemble my Technics to see how it worked.  I just did the best I could from the measurements I could get on the outside.

Here's a diagram of my headshell connector.  The biggest difference between mine and the Technics is a snap ring holding on the locknut.  This is because my tonearm is a larger, and having to match this larger diameter on the connector, I couldn't slide the locknut on through the back.  On the Technics, the locknut is secured by a shoulder on front of the connector body.

Functionally, my design works the same.  The only problem is the snap ring sometimes rotates and blocks the pin slot.

Now let's get into the build.  First I turned down and drilled the piece for the connector body.  The Body had to accept the 8mm headshell, so I started the hole with a 5/16" drill.

Next, I bored the hole to size.  Here I was test fitting it with the first failed version of the insulator, which I'd accidentally made out of fiberglass.

I then hacksawed the pin groove because I didn't feel like slotting it with a 1/32" end mill.  Here I'm sanding the groove.

Test fitting it with the headshell.  It's not very visible in the photo, but the pin did fit into the slot.

Now for the locknut.  I began with a piece of aluminum, bored it, and threaded the interior with a rectangular groove tool.  The coarsest thread setting on my lathe was still finer than the Technics' locknut, but that wasn't really important, just as long as the threads didn't overlap.

I then turned and knurled it as best I could.

Comparing it with the Technics locknut.  Dimensions also shown.

Machining the snap rings.

I then could assemble the connector body.

Test fitting it with the tonearm and headshell.

I turned the contact pins from some brass screws I had lying around.  It was challenging to machine such a small diameter without the material flexing.  The pin diameter was .050" and the head .075".  In the right of the photo, the second failed version of the insulator can be seen.  This one was made from wood.

Half the reason I kept failing at making the insulator was because I was trying to wind the springs myself from some pen springs, which didn't work.  I'd also changed the design a few times, originally intending to use a piece of rubber instead of actual springs, which also didn't work.  It wasn't until I special ordered springs the actual size I needed that I could complete the final version of the insulator.

I also needed a decent piece of material.  My first attempt was that piece of "plastic" I found in the street which didn't work because it was actually fiberglass.  I next attempted wood, but was unable to hold the spring hole and counterbore dimensions.  My success wasn't until I used actual plastic, nylon I think.  Here I've completed the insulator and am test fitting the springiness of the pins.

Next Step - Finally Assembly

Previous Step - Tonearm Linkage

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