Hello, some friends and I are building the EM Theremin by Moog and we are running into some issues. Please if anyone in this forum have built this theremin can you please share some advice on what to look for and what to avoid. This is for a class project and we have to complete it before the end of the semester.
One big issue that we are currently facing involve the pitch antenna range. We followed the procedure in Moog paper as far as construction but need help with the antenna.
this is an image of our antenna fixture we use for testing. https://www.dropbox.com/s/2bg6g7yq79f73hz/20120831_130019.jpg
I read up some things mentioned by Thierry here http://thereminworld.com/Forums/T/28530/antenna-tuning?Page=3
He mentions that the VPO frequency should increase (+5kHz or so) when the antenna circuit is connected to it. This doesn't seem to happen in our case. We are using an 18'' antenna with diameter 3/8'' as suggested in Moog's paper.
Please any help will be appreciated.
Your photo is worth a thousand words!
I am not the brightest bulb in the group as I designed my theremin through metaphysical guidance. Your layout is beautiful but I would expect at least two more IF cans. I wish we could have spoke earlier in your approach to theremin building.
Good luck, if Thierry chimes in he is a genius that I am a bit jealous of. LOL
Edit: On the enlargement I see the extra two tuned inductors I missed.
Thanks RS Theremin for the reply.
"Your layout is beautiful but I would expect at least two more IF cans."
what do you mean by IF cans?
Also, I just noticed that connecting the antenna with the linearization inductors already connected drops the frequency of the VPO by 3kHz. Any idea if this could mean something?
In the old days the coils today commonly used in theremins were called Intermediate Frequency Transformers. That would be that chrome looking square tuning inductor.
I wish I could help more but I only know my own design as I am not an engineer rather a kitchen table tinkerer.
Come on dewster these students need good assistance not us.
You as a Shaman would rely on magic given to you by earthly spirits maybe after cutting a chickens throat and dancing around where by the Metaphysician has direct communication with the big man. Plenty of room for us to get along. (-'
Now don't go get your doll and start sticking pins in it! LOL
"One big issue that we are currently facing involve the pitch antenna range. We followed the procedure in Moog paper as far as construction but need help with the antenna." - antman
What's the issue exactly?
"Now don't go get your doll and start sticking pins in it! LOL" - RS Theremin
*poke* Feel that? Or *poke* that? Don't make me hit you with the spirit stick...
As Thierry pointed out in another forum post, when you connect the antenna circuit to the VPO it should raise the VPO's frequency about 5kHz. I tried this with my VPO set at 257kHz and my antenna disconnected (connected just the four linearization inductors). This infact raises the frequency of the VPO to about 260kHz. But when I connect the antenna in the VPO drops back to 258kHz immediately and the device only operates from 0 - 1kHz.
What I'm trying to say is that the pitch range isn't where it should be (0-3kHz) instead it is at 0-1kHz. Also in order to get a response, the hand has to be pretty close to the antenna.
We are using a 18'' soft copper tube antenna with a diameter of 3/8''.
Is the pitch antenna located several feet away from other significant metal objects?
Your pitch and volume antennas look kind of closely spaced.
Try clipping a short wire like an alligator jumper to a scope lead and lay this maybe 6" to a foot away from the pitch antenna. Using a plastic tool, adjust the pitch oscillator for maximum amplitude on the scope. Then adjust the local oscillator to give you the audible response you're looking for. That might get you close. IMO you're shooting in the dark tuning the EW without some kind of field strength indication. I should also add that I don't have tons of analog Theremin experience, though I do own an EWS.
"Is the pitch antenna located several feet away from other significant metal objects?" - dewster
We've been testing in the lab and at home where we can have a nice open space but the same thing happens.
"Your pitch and volume antennas look kind of closely spaced." - dewster
The picture I showed earlier is just for testing. When we test the pitch we take the volume antenna off. We haven't begun complete testing on the volume side yet.