Replacing the oscillators in the Etherwave Theremin?

Hi. Long time lurker, first time poster here.

Like many others on this site, I have problems with sourcing the inductors to the EM Theremine. The antenna inductors seems solvable, but the trimming inductors is almost unobtanium. I was thinking, why not simply replace the oscillators with another design, like a Wien bridge or similar?

The fixed oscillators should not be a problem I think, but the function of the pitch- and volume oscillators is of course dependent on the response from the minute change in capacitance in the antenna circuit.

Has anybody tried to replace the oscillators altogether to a topology less dependent on special inductors, while keeping the overall architecture of the EM Theremine?

Sorry if I have missed any discussion of this. I have searched the forum but not found this very question addressed.

Thanks for the reply! At first I had a little trouble with decoding what you say, but if I understand correctly, in the later part of your post, you refer to this theremin: http://www.oldtemecula.com/theremin2020/peter/phoenix4-22.pdf ?

Yours seems *much* easier to build and if that is the one in your video, then I'm sold. I like the fact that the parts are "standard 1A" so to speak. No need for exotic parts with very special parameters to work, just plain old LM358. The only parts that is new for me is of course the transformers, but a quick check on Mouser indicated that there should be no problem to source them! And, ah, the LDR-optocoupler is also new for me, but I guess that in the worst case I can replace that with a handmade LDR-LED device(?). Edit: Maybe not. It seems to be a quite delicate and expensive part... Hmm.

99% of the parts are within 3 meters of where I'm sitting in my lab!

Stupid firefox. The mouser link worked fine in chromium. I must have confused the LED-LDR with another component, but now I see that it is both available and not expensive.

But, I'm confused by the schematics. According to the PDF the schematic is updated in January 2019, is that not recent enough? And it seems the pitch board appears twice, the only difference is the frequency? Or do the design calls for *two* boards? How is volume control? Maybe I'm blind, but I cannot find the volume antenna connector. Or, the thing is symmetrical with one board working with pitch, the other with volume? Seems so in your picture? (And is hinted at, in the description of each schematic page, but the silk on the PCBs in your picture both show "900 kHz")

Is there a reason that the build is over multiple boards and using only thru-hole components? Building from silk screen seems *very* hard, almost as building from Bill of Materials alone! Or do I misunderstanding? 

I'm an experienced electronics engineer, but that doesn't mean I cannot be very confused! I found the theory of operation: http://www.oldtemecula.com/theremin2020/theory/index3.htm but I'm still confused. Does it need an active antenna (Becker Electrodeum)? I keep finding mentions of "Phoenix Electrodeum" and "Phoneix 2020" and "RS Theremine". Samte thing evolved over time or totally different things?

My plan so far, after just a few hours of exploring this theremin is to create a single board using mostly SMD parts (for the passives, ICs and transistors) and thru hole for the transformers and other parts that only comes in this flavor.

I guess my most important question is this: Are there any pitfalls such as truly critical components? (Such as the tantalum capacitor. Nothing wrong with that, but a little unusual perhaps?). And I would love to see some clean pictures of the finished design in an operational state.

In my design earth ground, L3 & L4 & Q1 & Q2 and the Pitch Antenna are critical if you like the classic sound you hear.

If you want a theremin that is portable without using earth ground go with a digital approach.

If you want to single board it with surface mount parts then we must part ways. There is too much theory in explaining each of your changes and I must allow you to have your learning curve. Every part value and it's placement, especially the oscillators has purpose that cannot be ignored.

You could end up with something better, I hope so.

Christopher

Aha. Good thing I will stick with exactly those parts for L3 and L4 as you specify and Q1 and Q2 will still be MPSA42, but maybe in an SMD footprint. And yes, I understand the importance of ground and I'm not planning to make it portable. I would not exchange any values or parameters of the components, just footprints. I know very well that an "100n capacitor" is not just an "100n capacitor", but it also has a tempco, tolerance, an age curvature, vibration- and pressure dependence, "microphonics" (especially multilayer), etc, etc. I have never built a theremin before, but I'm no stranger to oscillating circuits and careful placement of components. But yes, a learning curve is expected. Thats one of the points really! If I just wanted a theremin, I would buy a kit or even a complete unit, but where is the fun of that?

What about the antenna? I can see that it may be a problem. I'm about 9000 km or (5400 miles) from California and used to the metric system! Even with international shipping it will be a real PITA at get one! How on earth did you found out that just exactly this spring would do the job? You must have tested many dozens of "things" for antenna? What is the "least bad" alternative?

What is the significance of having the 3.3u coil on the antenna and not on the PCB? (according to the picture on your site)

Edit: And what about the volume antenna? Where do it connect and how is its geometry?

I remove my posts above because I a firm believer in not clogging up the google database with nonsense due to ego driven “I wished it worked”. In our conversation my goal is to figure out if you have the drive in your gut to really do something original. Over twenty years I have helped a couple of hundred dreamers.

Charm, I will send to you (Europe) anything not available at no cost even all the Mouser Parts, and the Pitch Electrode. How this approach came about is not important but it works in a “startling” fashion, like Lev Sergeyevich must have been startled the first time he heard heterodyning.

Static discharge is a non issue in my design, a fatal flaw in most modern Theremins, I guess that is for the purpose of more sales. 
Probably not obvious my Pitch detector uses induction coupling of the two RF signals. This keeps them isolated from one another; over coupling is what causes the low end distortion of a EWS.

If I was to try something different it would be to use a different Pitch L1 & L2 coil, again these create the induction coupling to L3.  The ThierryMin gave me this idea with a var cap.  That guy is so dam smart, most of the time.

My Volume Control is much more sensitive than the standard design, this allows for further possibilities. You see the loop, for my design the wire inserts less than 4" or 10cm   The capacitive coupling insertion depth controls the sensitivity.

Edit: I build in a modular fashion so sections can be swapped out with improvements. Having the Volume separated from Pitch allows more comfort in how they are positioned. Have you ever met a Wounded Warrior Musician that lost hope?. Theremin design is a never ending project and more.

Edit2: Both 3.3mh choke/coils are mounted on the PCB    The Pitch Electrodeum is parallel tuned, unlike the series coils of the EWS

Edit3: To build on a single board with smd parts would be fine if you think you have the layout of a finished product, why not? Then again your first build should be done my way so you have a feel of what is going on.

Christopher   

All Theremins need a good ground, digital approaches are not exempt from this.  Hand capacitance needs a return path.

If you want to start from the basics, build something like the Thierrymin, and experiment with ILYA's Theremin simulator software.  Spicing and breadboarding oscillators can be fairly instructive, as can looking at LC phase shift on a scope.  I find the digital approach via FPGAs to be the most direct, though that's my background.

It seems that the Moog Kit is available again.
https://www.thomann.de/be/moog_etherwave_theremin_kit.htm

Some things starting to worry me. In your latest reply, and in the "theory of operation" page, you mention the inductive coupling between L3 and it sound like this is critical in the design. Is that the reason you imply that the placement of the components are critical? And, for instance, the P2 pot for timbre is only connected to the shield of L3? Nothing wrong with that of course, but doesn't that make things unpredictable?

My goal here is not to buy a kit/compete instrument (way to expensive), and nor is it to construct at theremin from ground up (lack of time). My quest at the moment is to dig up four theremins as Christmas gifts to three people (and then maybe doing something special or custom with the fourth one) and I looking for a construction that has easy to obtain parts and/or using parts I already have. Since I have all but a few (albeit critical) components I like this design (for its use of MPSA42, NE555, LM358, etc) but it is not obvious what terminal connects to where, and so on. Also, the picture you showed me had a silk screen with "900 kHz" on both boards, but in the schematics the second fixed pitch oscillator is marked with 750 kHz (the only difference I have spotted is different values of capacitor C8 and C36 and that indeed seems to be affecting the frequency).

You mentioned that I should build from slik screen instead of the schematics. Do you mean for the connections or the value of the components or the geometry? It would be unfeasible for me to draw the schematics from the PCB images (you specify "silk screen" but perhaps you meant the copper layers also?

Btw, Mouser ships to Sweden (where I live), so no problem there. And I don't want to bother you with sending me the springs (AFAIK the company do international shipping) if it isn't absolutely necessary.

Edit: The mouser link, is that a share or a copy? Haven't used that function before. I want to change (remove) some components but I obviously don't want to mess up *your* list.

Edit2: Eh? Where is the power on the variable and fixed oscillators? The first one marked "Fixed pitch, L2 oscillator" is connected to a pot with some mysterious mentions of "C-D is a port for panel mounted...". This may be little to messy for me.

"My goal here is not to buy a kit/compete instrument (way to expensive), and nor is it to construct at theremin from ground up (lack of time). My quest at the moment is to dig up four theremins as Christmas gifts to three people (and then maybe doing something special or custom with the fourth one) and I looking for a construction that has easy to obtain parts and/or using parts I already have."  - CharmQuark

Oh, that's very different.  Maybe try the Open.Theremin: http://www.gaudi.ch/OpenTheremin/index.php

Figuring out someone else's mysterious custom build from the PCB layout is beyond just about everyone, I don't think a month or so is enough time to do that in.