Shielded Jack

[astronomicum]

Just finished a restoration of an Omega (Japanese) guitar amp from the late 50s. The amp is equipped with a shunt jack prior to the output driver circuit to redirect the preamp out (called Output). I had a persistent 9mV hum traced to this circuit. Yes, not bad, but annoying. And while rewiring the jack with shielded cable did not get rid of the hum, bypassing it did. Feeling the issue was the jack itself, or maybe more accurately, the jack position, and since removing or moving the jack was not an option, I went looking for a shielded shunted jack. Well, you probably know how that turned out.

So I decided to see if I could put one together. I found some good quality shunted square body jacks on E-bay, and out of aluminum flashing, razor blade, Dremel, and micrometers, constructed a shield. To my delight, after installing the jack, the amp now has only 3mVs of hum.

Something to keep in mind for the toolbox.

[Willabe]

Very nice work. 

Switchcraft used to make/sell a shielded 1/4" jack.

It was in their catalog.

[Willabe]

Very nice work. 

Switchcraft used to make/sell a shielded 1/4" jack.

It was in their catalog.