static electricity spark now etherwave is silent

Hooray! My EWS is fixed (I think). After the static discharge, and with generous guidance from all of you here, I ended up replacing what seemed to be the potentially sensitive components of the volume antenna circuit: D1, LM13600, L11, Q6 and Q7 (and also purchased/installed ESPE01 while I was at it). It seems to be back to what it was like before the spark of death. However in the process of testing and tuning, I notice that, when the jumper is across C28 and the instrument is at full volume that way, it is about twice as loud as when it's operating normally (even after tuning L11)...in other words it ordinarily seems weak and muted. I'm wondering if that's normal? Thanks everyone for your help with this. Now I have to learn how to play the thing.

Bob Klips

Columbus, Ohio USA

There seems still something to be wrong. Shorting C28 should give you 6dB below max volume. What is the maximum negative voltage which you can obtain directly behind D1 by tuning L11?

Thank you very much, Thierry! I agree. It seems so dull and mute, and the volume control is a bit sluggish. It may have been this way before the ESD; I am new to Theremins and wouldn't have noticed. Plus i don't have a proper amp yet (Moog "Theremin" amp is on back-order.)  

I get -5.6 v with the black lead clamped to the foil and the red one touching the right-hand side of the diode D1. 

Again, much appreciated. 

Bob 

My Jaycar Theremin MK2 is singing again.  It was indeed the pitch FET that blew.  I've worked in electronics for over 30 years, and that is honestly the first part I can recall destroying with static - especially an in-circuit part!  The 2N5484 seems to be obsolete now, so I substituted a 2N5486.  Seems to work fine. 

I was toying around with using a fatter antenna for the pitch, about a 1/2" diameter lamp rod, and performance seems immediately improved over the telescoping whip.  The main advantage I see with the telescoping whip is for tuning compensation when moving the device.  I suspect changing the volume antenna from a solid plate might improve the volume performance, too.  I also decided to not mount the internal speaker.  Besides, the tone is far more oboe-like (to my ears) when played through my homebrew tube guitar amp.

Thanks for a most interesting group!  Enjoying reading through the various topics.

Joe

" I've worked in electronics for over 30 years, and that is honestly the first part I can recall destroying with static" - Cephus

Most equipment isnt designed as badly as theremins are! - two antennas going to sensitive circuitry with no protection - the surprise for me is that so few seem to fail!

A neon between the antenna and earth will reduce the the risk substantially. With the S/C /Jaycar design the extra capacitance of these components can be easily adjusted away.

Fred.

A neon between the antenna and earth will reduce the the risk substantially. With the S/C /Jaycar design the extra capacitance of these components can be easily adjusted away.

Fred.

Yes, when I ordered the replacement FETs from Jameco, I also ordered some NE2 bulbs just for that purpose. 

Now that I know the Jaycar Theremin works, I'm ready to make improvements.  A different case will have to be among the first things to consider.

Joe

...an update re: my ESD-zapped EWS...After replacing a few sensitive parts and still getting only marginal performance on the volume side, I threw in the towel, happily, when I saw that I could get a new replacement PCB for $99. The parts supply vendor just sent me a notice that it's been shipped, so I ought to be up and running by week's end. Thanks for all the advice, Theremanics! 

Bob in Columbus, Ohio USA

" I saw that I could get a new replacement PCB for $99. The parts supply vendor just sent me a notice that it's been shipped" - Bob Klips

Thats real interesting! Would be great if you could tell us who sells these boards! Also, it would be real interesting to hear that it all works ok!

Best of luck,

Fred.

 (ps - I am interested in buying yoir old dead board.. I really need to get my hands on a genuine EW board and not rely on impressions gained from my constructions - I am happy to replace all the components if needed, and finding the path of the ESD damage would be educational anyway..)

Hi Fred.

The board came from http://www.instrumentalparts.com/

search under "Etherwave" and it comes up on page 2. 

...I think they just got it (drop-shipped?) from MOOG, because it is coming from North Carolina...

Thanks but I think I'll hold on to my old one. I messed it up a bunch de-soldering, and maybe I can fashion some nice pitch-only sparemin. 

Bob

Thanks Bob - Ive ordered a board.. at £71 inclusive of postage its by far the cheapest way I have found of getting a real EW board to play with... Just couldnt bring myself to part with the price of a kit (£329 from Guitar Centre being the cheapest I could find) particularly as I dont need PSU or case etc..

This should enable me to fully test some ideas I have for a comprehensive add-on / upgrade board - and adding protection and powering from battery via a custom SMPS, and exploring adding my mixed signal waveshaper and perhaps even register switching ..

Apart from which, I have never got on with any real  EW I have played, and found its "feel" almost impossible to play - I have wanted to explore what it is that makes this particular instrument so hard for me (I havent had this problem with prototypes I built using almost identical circuitry).

Fred.