Static killed my Jaycar theremin - help fixing please!

Posted: 1/19/2009 12:41:08 AM

From: Wall, NJ, USA

Joined: 1/19/2009

I got a Jaycar theremin kit for Xmas, and built it with no problems. I had just plugged in the power pack and was playing with no problems. I took off my jacket and then while playing I touched the pitch antenna, felt a static discharge, and it died! I'm sooo disappointed... how do I figure out what component got fried?

Right now if I turn up the volume all the way, I hear a faint, high sound, and if I move my hand around or touch the volume plate, the pitch changes.

I've read that it's likely this fried a transistor, but which one and how do I test? There transistors are the cylindrical "D"-shaped pieces with the 3 legs right? Marked 2N5484 and BC548? 4 of them?

Can anyone lend a hand? is there a way to ground it to prevent this from happeneing again? Thank you.


Posted: 1/19/2009 7:18:53 AM

From: London, UK

Joined: 6/5/2007

Hi John

Ouch, that was unlucky. Looking at the circuit diagram, I would suggest you look at Q2 which is one of the 2N's.
But really it could be anything.

Where abouts are you?

Posted: 1/19/2009 12:16:04 PM

From: Escondido, CA

Joined: 2/6/2008

The most likely case are the JFETs. They are the most static-sensitive parts in that theremin.

Posted: 1/19/2009 8:09:27 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

I can confirm that Kees Enkelaar himself felt these problems were most likely the 2N5484 transistors. His theremins are modified Jaycar's.

It's not a bad idea to keep one or two spares on hand for any Jaycar/Kees Enkelaar theremin owner.
Posted: 1/20/2009 1:08:51 AM

From: Wall, NJ, USA

Joined: 1/19/2009

OK, I'll try and replace the 2N5484's - Radio Shack's site doesn't seem to have them, any other place you guys can recommend to get them from? I googled and came up with this place ( The numbers look right... I'll probably get a bunch of other replacements too (BC548), just to make the order worth it.

Thanks for the help guys!
Posted: 1/20/2009 3:44:28 PM

From: Escondido, CA

Joined: 2/6/2008

Yes, Mouser is a good supplier. Digikey is also a good place to get parts from.

Posted: 1/20/2009 5:59:44 PM

From: Colmar, France

Joined: 12/31/2007

If you have difficulties in finding the 2N5484 you may try the european type BF245 which has matching specifications.
Posted: 1/22/2009 4:52:40 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

.. And connect a small neon bulb between the antenna and ground for both antennas.. These are the NE-2 type with no resistor fitted..
This will prevent most future ESD (Electrostatic Discharge) problems, and cost under £1..

Provided the neon is wired close to the antenna connection, and the grounding lead is as short and fat as possible (low inductance and resistance) and connected to a good grounding point (the power supply input ground for example) tuning should not be significantly changed by this modification, as these neons have low capacitance.

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