Jaycar kit volume weirdness

Posted: 4/26/2012 3:09:35 AM

Joined: 1/14/2011

Hi all,

I've been fiddling with my Mk1 Jaycar theremin lately, I've applied Maxie's mods, built a different cabinet and tuned it. Pitch-wise it's reasonably playable, but the volume circuit's giving me trouble.

The transition from quiet to soft is quite abrupt and in the transition zone, there's a "put-put-put" sound. I replaced the 2k-ohm trimpot with a 25-turn version and this helped a bit, but I'm still getting the noise.

I'm using the original pitch antenna that came with the kit, I replaced the volume plate with an 8cm diameter circular antenna I pirated from a TV antenna, but it's probably still a bit small.

Any help would be most appreciated :)

Posted: 4/27/2012 4:53:10 PM

From: Colmar, France

Joined: 12/31/2007

How behaved the volume response before applying all the mods and changing the volume antenna?

I hope that you did it systematically, building first the theremin kit as originally designed, then applying one mod after the other, so that we can virtually go back step for step in order to find the problem...

Could you also put a picture of your new volume antenna online so that I can make a rough estimation of its static capacitance?

Posted: 11/16/2012 4:44:44 AM

Joined: 1/14/2011

So sorry it's taken me this long to reply, but life got in the way :)

I did build the kit as originally designed, but then applied all mods at the same time, so I haven't done things ideally. The original volume control also had a very small range, but didn't cause the "sputtering" sound.

I've attached pics of the board mounted in the box with the lid open and the assembled box.

Pat's Jaycar in box

Pat's Jaycar, box closed


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