Help with em theremin construction

how long should the connecting wire from the last inductor to the antenna be?

Kind of short I'd think.  In the EWS it's a few inches.

Is the wood that makes up your antenna mount good and dry?

Ya' know, I've always thought that wood was a rather poor choice of materials to mount an antenna to.

Both my Kep and my Termenator will use plastic mounts made from cheap, Walmart kitchen cutting boards. A trick I picked up from Tesla coil builders.

"Kind of short I'd think.  In the EWS it's a few inches." - dewster

My connection now is about 1'' or so and i'm still getting the same issue; when the antenna is connected the oscillator frequency goes down by about 2kHz (1kHz from the null frequency of the oscillator).

"Is the wood that makes up your antenna mount good and dry?" - dewster

Yea its pretty dry. Right now I've taken the top piece off so only the pitch antenna section of the mount will be used (volume part off)

Both my Kep and my Termenator will use plastic mounts made from cheap, Walmart kitchen cutting boards. - w0ttm

We plan on using acrylic for the final enclosure hopefully that isn't a problem.

What I'm wondering is how many people on this forum have built a working EM theremin?

"What I'm wondering is how many people on this forum have built a working EM theremin?"  - antman

Don't look at me.  Did you try the tuning method I described earlier?

What I'm wondering is how many people on this forum have built a working EM theremin?

I have! - 2 of them actually  and Ive  also built a few stand-alone versions just the volume circuit to use as a proximity sensor for some interactive sculptures... (works great - at least 2-3 ft range!)

I can guarantee you that the schematic is good!   ;)

My advice- build  a cabinet and put the PCB inside ,  then try tuning the volume.  

None of my EM's  seemed to  like bench testing - the volume especially was always a problem and drove me crazy.   loose flopping wires are no good.   once I had everything all boxed up...the volume would behave as expected... shrug? 

Hope this helps

Charlie

"Did you try the tuning method I described earlier?" - dewster
Yea I tried it, still no improvement.

"My advice- build  a cabinet and put the PCB inside ,  then try tuning the volume." -chobbs

This sounds like a good idea that I can try.

Chobbs, did you have any difficulty getting the pitch antenna to work with a good range?

Also, in a previous thread Thierry says the following

"When working with the default values (pitch oscillators at around 285kHz or 278kHz without antenna circuit) the resonant frequency of the antenna circuit will be ways too low which will limit the pitch range and worsen the linearity. That's why Bob Moog decided in the final release of the EM which was then called Etherwave to reduce linearization inductance to 30mH and to make the antenna circuit tunable by bending the wire which leads to the antenna above a grounded aluminum foil (thus adding some static capacitance)." - Thierry

Whats the deal with the aluminum foil? Is this really used in the etherwave to improve pitch range?

"Whats the deal with the aluminum foil? Is this really used in the etherwave to improve pitch range?"  - antman

Welcome to the real Theremin World!

If i recall properly, yes the pitch worked, but not completely right until it was all boxed up and the wires were all tidy.  

The foil is grounded and its proximity to the pitch wire  is a way to adjust the range/ note compression.  Improve Range might not be the words - can change whether you get about 4-5 octaves or 5-6 octave.   

The top of my pcb is a ground plane where traces are not present (with a few millimeter spacing). Is there a certain height away from the board that the inductor coils have to be?