EM Theremin Build Completed

Thanks to all of you here, you can add me to the list of successful EM Theremin builders.  Without the information and help that has been provided here it may have just ended up being a failed adventure. So I want to thank you all. Those who had problems, asked for help and especially those that took the time to help others.

Here's the finished unit. I had just enough leftover maple around to make the case and used 3/8" aluminum rod for the pitch and volume antenna.

Not sure where I found the PCB layout. It was for a moog all-in-one that I had found about a year ago. I believe it was intended for a EW but the part locations were the same. It included the headphone amp and Of course after making and drilling the board I found out that the pin outs were wrong for the 2N3904 transistors so had to cross collector and base pins. It also seems to have been laid out for a leftie since the volume antenna was on the right side of the board. That's why I had to run the control wires over the board.

Here is what it sounds like played through my homemade ax84 tube guitar amp with two 10" Celestion's.

Sound Sample

The only thing that I'm not sure of is since I added the microphone flange on the bottom of the cabinet I can no longer adjust for zero beat and walk away without it going up in pitch. Another way to explain is that when I rotate the pitch knob clockwise to zero beat and continue turning it raises the pitch and moves zero closer to the antenna. Is this normal?

Joe

Hey the date is Pi day: 3.14.15, sharp as a marble.

Zylo, very nice build and you demonstrated your results with a sound byte, bravo!!! I hope you do not become possessed or obsessed to join the never ending journey of trying to find the most musical sound and then there is the authentic fat sound of some early classics. You do got the skills, keep up the fine work.

"The only thing that I'm not sure of is since I added the microphone flange on the bottom of the cabinet I can no longer adjust for zero beat and walk away without it going up in pitch. Another way to explain is that when I rotate the pitch knob clockwise to zero beat and continue turning it raises the pitch and moves zero closer to the antenna. Is this normal?"

The above almost seems normal if L6 has room to adjust the Null where you want it. I have my EWS setup so the Null has no locking point, it just rolls over to the other side. This prevents unwanted audio waveform distortion/pulling on the low end. I use a Mute switch when walking away.

PS: It was 90° f here today, sat outside trying to get some rays, my grandkids have commented on my pasty white legs.  0-:

Christopher   

Christopher, Thanks for the compliment.

"I hope you do not become possessed or obsessed to join the never ending journey of trying to find the most musical sound and then there is the authentic fat sound of some early classics."

Ahh, chasing that elusive sound.... Know what you mean. 20yrs. ago I wanted to learn to play the guitar, bought Strat copy and began to learn but wondered why it didn't sound anything like I heard on the radio? so I bought a Les Paul copy. That didn't help... tried changing a pickup, tried making a pickup. Tried making effects and buying speakers. Before you know it I was building complete guitar bodies, necks etc.... 

"The above almost seems normal if L6 has room to adjust the Null where you want it."

Null was a little too far from the antenna for me so I tried to retune. At first I was having no luck, but then found once I had L5 better tuned I just had to "tweak" L6 less than 16th or 32nd of a turn. Now I can adjust the tuning pot and walk away again without a sound. I find it helpful so I don't sound any worse than I am :)

Grandkids are the best, tan those things before you blind them!

Joe

Beautiful case Zylo!  But that wire bundle running over the volume side chokes connecting to a board actually on the volume side looks like it could possibly cause trouble.  I'd endeavor to keep extraneous circuitry as far away from the pitch and volume antennas - including the antenna chokes - as possible.

It also seems to have been laid out for a leftie since the volume antenna was on the right side of the board. That's why I had to run the control wires over the board.  - Zylo

Perhaps the board was meant to be mounted in the top of the enclosure rather than the bottom?

Thank you Dewster.

"But that wire bundle running over the volume side chokes connecting to a board actually on the volume side looks like it could possibly cause trouble."

The board is the power supply so the bundle is regulated supplies and ground. I was concerned too and hoped twisting would reduce any problems. Actually when I was retuning yesterday, with my hand in the mute range over the volume loop, I could move it slightly and tune in a faint spring training broadcast. It's not loud and you have to turn the amp up a lot to hear it. (If I was a fan it would be a plus.)

"Perhaps the board was meant to be mounted in the top of the enclosure rather than the bottom?"

Hadn't thought of that, it would work. 

looks nice! What kind of tuning coils did you use?

Wannes, Thanks.

I used Toko A7BRS-T1040Z 100uh from Digi-Key. I even used it for L11 the volume coil because I was having trouble finding the correct value. Figured I'd first see if there was enough adjustment and if not I'd remove a few turns. (Bought two sets just in case.) I was able to get in range with the slug almost fully backed out so I ended up removing about? 5 turns I think it was. I first tried about 10 but it bottomed out so had to put 5 turns back. Worked out good and it's at about mid range now.