Build Project: Dewster's D-Lev Digital Theremin

I haven't tried any opamps but I may have to go there.  I do need something to work with a load as low as 25 ohms, and I was hoping to find an 8pin replacement assuming that this went obsolete because it was superseded and not because of lack of demand.  I've got 77 of these in my stock, which should cover the theremins I want to build for myself.  But I'm looking out for you here too, and I know that once the D-Lev gets going you'll be building theremins like Lucy on the cake factory assembly line! (Note:  that reference is really even before my time, but not by that much).

.the dog ate my homework... though I am quite anxious to get it into player's hands.

What would they want with your dog? Accompaniment? "Owuuuuuuuuuuuuu!"

D-Lev "Pro" - The Final Chapter

After an extended summer hiatus to finish some other projects, snow is on the ground and theremin season is here again.  One of the things that occupied me for a good portion of the summer is a CNC milling machine conversion project that was nearly finished but kept getting pushed out because of other projects that themselves could have benefited from having it up and running, so it was time to finish that.  I also made some progress on a coil winder that is needed to finish my Moog Melodia inductors, but the winder is evolving in a different direction than when it started and will take some time to complete.  My first priority around the first of November was to finish the D-Lev project, and now that it is finished this post will hopefully wrap it up.

Since it has been a while since I first posted about this project, I should probably give a short synopsis on how this started and why it looks like it does, and why I want to distance myself from it a bit. My tastes have changed quite a bit since I first started building the copycat Etherwave-Pro cabinet for a different theremin project.  This was started at a time when I was actively seeking to find a used EW-Pro, but the ever-increasing collector prices put me off that idea.  At this time I really liked the Pro cabinet design (except the blocky rear cabinet) and decided it would be fun to build one, and the project quickly progressed to the point where everything was largely complete except for drilling out the front panel (thankfully).

When Dewster's D-Lev design came along I decided (after successful prototyping) to put this exciting new digital theremin into the cabinet instead, which required some creative adaptation of the design to fit the large wood knobs and some other cutouts that were already in the cabinet. All of the modular circuit boards were designed to fit into this cabinet while still being generally usable for other enclosure styles.  The last batch of board revisions have been on my bench since spring, and with the completion of the the audio/spdif-decoder board, the last missing element, the D-Lev "Pro" project is finished except for updating with the latest FPGA load and software*.

*Eric, if you are watching, I'll need some direction on this.

The Disclaimer

At this point our informal plan was to begin making some more refined demo videos showing the versatility and range of the D-Lev, but I've become increasingly disappointed that I chose to use the fake EW-Pro cabinet as a flagship platform of sorts for the D-Lev.  As far as that particular cabinet design goes, I am so over it that I don't really want to have it visually associated with the D-Lev in any way.  I have found the D-Lev design to be quite enclosure-agnostic, at least compared to analog theremins, but it really needs to be seen demonstrated in its own distinctive (yet producible) enclosure design worthy of the contents.  So while I will probably be posting audio clips from my newly completed theremin, I don't expect to be making videos that might misrepresent what the D-Lev is.

From now on I hope to come up with something more creative for the next enclosure designs.

Here are a few final photos of the finished product. The first is the front view with the tuner visible off to the upper left; nothing new here...

And a rear shot of all the pretty custom boards.  I actually like the way the layout evolved, and there is plenty of room inside to keep good separation between the digital and the analog.  One feature that I had to remove was the circuit board for touch-sensitive knobs that lit LEDs on the LCD screen bezel.  On power-up it worked as it should and was extremely cool to see in operation, but due to some undocumented and/or misunderstood "feature" of the TTP-226 capacitive touch sensor IC, the sensitivity of the knobs would drift after about 30 seconds, resulting in erratic behavior.  It was unnecessary bling anyway and I'm not too sorry to have ripped it out of there.

Below is the audio/spdif-decoder board stack (center of picture, with white connectors) that was the final addition to complete the theremin.  The top board with all of the surface-mount components is the pcb stripped out of one of the widely-available Chinese optical/spdif decoders that come in small connectorized metal enclosures.  It is piggybacked on a custom stereo headphone amplifier board whose components are on the bottom. One assembly as seen here is a stereo digital-to-analog converter; one channel is for the main audio and the other is for pitch preview.  On each edge of the lower board are unpopulated pads for optional headers that allow stacking another decoder assembly on top if stereo main audio is wanted in addition to pitch preview.  If pitch preview is not needed then both channels my be used for the stereo main audio.  I had no interest in the stereo main audio, so I have used the second channel for pitch preview.

Features on the bottom panel are as follows (CCW from upper left) 1) 3.5mm jack for optional auto-calibration foot pedal, 2) 1/4" stereo jack, tip=main audio, ring=pitch preview, 3) 1/4" mono jack for pitch-preview, 4) main power switch (hidden by mic stand), 5) 1/4" mono jack for main audio, 6) RJ45 jack for the external tuner, 7) fuse, and 8) the AC power cord.  The two white objects at the top of the picture are nylon thumbscrews that lock the back panel in place.

And Finally, on an Unrelated Topic

I generally don't like to use 3D printing for anything other than hidden parts or prototypes because I am personally not fond of the inconsistent look of layer lines, even when printed with fine resolution.  But I learned of something this summer that may be a game changer and may be of interest to anyone who does 3D printing.  I use two slicer programs, Raise3D's IdeaMaker and Ultimaker's Cura, to generate gcode from 3D models for the printer.  I like IdeaMaker the best, but Cura 4.4 came out with an experimental feature called "fuzzy" that essentially adds noise to the x-y gcode coordinates.  This results in prints that have an attractive and consistent pebbly texture that nearly completely hides layer lines.  Some may not like this finish, but for the first time I feel that printed parts could be used in certain cosmetic applications on the theremin without having that characteristic printed look.

Here is a piece that I printed for use as an experimental pitch extension arm in lieu of PVC pipe for a possible theremin enclosure.  It is printed in PETG and the finish is tough as nails.  I like the possibilities here.

And this is a series of tapered telescoping tubes that could possibly be used for collapsible extension arms on a portable theremin (D-Lev Tour?).

So nice to see it completed.  Its really quite beautiful inside and out.  Thanks for sharing your process and results.

WOW! Looks like best theremin ever.

Looking forward for demo videos.

"The last batch of board revisions have been on my bench since spring, and with the completion of the the audio/spdif-decoder board, the last missing element, the D-Lev "Pro" project is finished except for updating with the latest FPGA load and software.

Eric, if you are watching, I'll need some direction on this."  -- pitts8rh

Will send you an email shortly...

"I've become increasingly disappointed that I chose to use the fake EW-Pro cabinet as a flagship platform of sorts for the D-Lev.  As far as that particular cabinet design goes, I am so over it that I don't really want to have it visually associated with the D-Lev in any way."

Yeow, that's some disclaimer!  Is it mainly the ergonomics of the EW-Pro that are a turn-off for you?  If so, what elements in particular are problematic? 

IIRC the EW-Pro cabinet wasn't designed by Bob Moog, who was perhaps at that point dealing with the brain tumor that would shortly take his life?  It's a really beautiful design, but strikes as an "artist's concept" sort of thing you might see at a car show, where style and flair tend to trump all practicality, and the car itself not intended for manufacture.

I've never even seen an EW-Pro in the flesh, but (will go ahead and rashly speculate anyway that) if I were building an analog Theremin in something like the EW-Pro cabinet, I'd probably mount both antennas lower in order to position the controls higher and easier to view.  And I'd probably angle the cabinet back some for even better viewing of the control panel.  And I'd probably locate the volume antenna even lower, so the player's hand wouldn't come anywhere near it when playing.  And I'd probably locate the pitch antenna farther away than the volume antenna.  Swap the antennas for plates and you've got the (tentatively proposed plate version of the) D-Lev tour!

(Blathering on and repeating myself some more) The ergonomics for electronic musical controllers are a really tough nut.  When you're replacing an acoustic instrument there's legacy ergonomics and people's training and expectation to take into account, which can narrow the design effort but also severely handcuff innovation.  When the interface is brand new the problem is in many ways much more difficult, as there are no up-front constraints to guide you towards the end result, so you have to come up with new ways of doing things, and do ergonomic studies of them - but you're free to spend the rest of your life innovating!  The Theremin is more in the first camp, though it doesn't have tons of players, and perhaps was never all that definite a "thing" in the first place.  (For my next electronic music project I want to design a drum controller / synth that you hold more like an electric guitar.)

"I had no interest in the stereo main audio, so I have used the second channel for pitch preview."

Pseudo stereo is something I wish I'd implemented earlier, but for a long while I was down a wrong path with the inharmonic resonator (my error was in mixing at the input rather than the output - it took fixing that and integrating an "xmix" control like I was doing for the other filters to finally make pseudo-stereo possible).  Pseudo stereo makes most voices more interesting to listen to, though it is somewhat problematic for the string voices as they rely on the mixing phase to produce a notch in the response.  Even if you're pitch previewing, you might want to use the pseudo stereo output for recording?

"And this is a series of tapered telescoping tubes that could possibly be used for collapsible extension arms on a portable theremin (D-Lev Tour?)."

Nice!  I like the texture!  Are those tubes machined on the inside?  What do you think of the long-term resistance to splitting / fracture, with the inner tube trying to expand the outer tube?  I suppose you could have reinforcement rings of some sort at the ends, and those rings could also keep the inner tubes from falling too far inside?

Awesome work!! please share the sound result with Thereminworld

My thanks to those that have shown interest in this project, and I'm pretty sure that Dewster appreciates your interest and comments as well .  I think we've both been taking a bit of a breather on this, but in our last discussions we had talked about trying to make some version of a D-Lev available for hands-on testing for anyone who might be interested.  That might be in the form of a loaner unit, but I should probably discuss this with Eric before saying too much unless he wants to open that topic up for everyone. 

I'm working on a few enclosure ideas that might be relatively easy to produce without having to resort to the standard mundane rectangular wood box, and it would be nice to see a loaner model housed in something more true to a final form factor. There also needs to be some user documentation put together that at the very least addresses setup of some of the key system parameters such as pitch and volume field size and linearity to fit the player's needs.  The extended topics of voice editing and synthesis could be deferred a bit since there should be a pretty representative set of "factory" presets available to start with.

As soon as I acclimate to this theremin a little more, I think it would be best to start a separate "Playing the D-Lev" thread (or something like it) to focus on the features and offer up some sound bites.  Although this unit has been generally playable in my shop for most of the last year, even while strung together out of various dangling pieces, my daily (or sometimes weekly!) practice theremin has been the Subscope theremin that Dominic made for me.  The Subscope has proven to be a favorite over the Etherwave for several reasons, one of which is the very comfortable volume response that I have not quite yet been able to emulate on the D-Lev, although I'm pretty sure that it's in there somewhere. I have also set the highly- configurable pitch response of the D-Lev to be more linear over a wider range than is attainable with either of the analog theremins, and that takes some adjustment period as well.

And as part of the boilerplate pre-apology/warning that I feel necessary to give before subjecting anyone to my playing , I will state again that I am a tinkerer, not a musician, and my theremin practice is spotty.  I sometimes go weeks between sessions, and most practice on the D-Lev has been while working on it in my shop with a scope or spectrum analyzer running. 

Try to listen to what the D-Lev is capable of doing, not necessarily just what you hear!

I'll follow up here if there are any project related questions, otherwise watch for the new thread.

And a few responses:

"Is it mainly the ergonomics of the EW-Pro that are a turn-off for you?" -Dewster

No, not really,  I've always like the vertical case with the extended pitch arm, although I think it was Coalport that commented a long time ago about the wobbly stand and the poor location of the controls before I even appreciated how correct he was.  I think it is a stylish design, but form was given priority over function.

What I am "over" is the copied enclosure which I know some might find plagiaristic and downright offensive.  I do this too much, where I find some kind of perverse pleasure in the challenge of trying to copy something accurately (search my website for "Zoltar" if you want to see insanity).  It is much easier to make something different and unique where you don't spend a lot of time trying to scale and judge dimensions and appearances.  I don't have enough time left to do this any more. I just see curved wood, and I think "Hmm, I could do that..."

"..And I'd probably locate the volume antenna even lower, so the player's hand wouldn't come anywhere near it when playing.  And I'd probably locate the pitch antenna farther away than the volume antenna.Swap the antennas for plates and you've got the (tentatively proposed plate version of the) D-Lev [i]tour!"[/i]

I agree, except for the plate antennas, but they can be user choice anyway.  I think you will recognize the enclosure CAD model that I'm working on!

 "Even if you're pitch previewing, you might want to use the pseudo stereo output for recording?"

Perhaps, and that is why I left room for stacked master volume pots and a second audio decoder assembly, and also why I have so many audio output jacks on the bottom panel.  Upgradeable!

"Nice!  I like the texture!  Are those tubes machined on the inside?"
No.  Smooth inside, as printed.

"What do you think of the long-term resistance to splitting / fracture, with the inner tube trying to expand the outer tube?  I suppose you could have reinforcement rings of some sort at the ends, and those rings could also keep the inner tubes from falling too far inside?"

The telescoping tubes are .060" wall printed using PLA filament, which seems appropriately strong for the application.  Ultimately I would use the higher temp PETG material for everything, but this was just a sizing experiment.  Splitting will not be an issue unless the theremin should fall over, and even then the tubes would likely telescope inward.  They are very solid when extended.

As far as loosening over time, I don't see that happening. I designed the tubes with a slight taper (.020") over their lengths to provide a tight friction fit when extended.  The grip of the texture between the tubes provides a very satisfying and reliable feel to the friction fit.  If you look closely you'll see that each tube has a slightly larger diameter ring at one end and is slightly necked down at the other end, so that even if all friction due to the taper failed (it won't) the tubes would come to a hard stop when extended.

The single tube with the Bezier contour in the other photo has a .150" wall and was overkill.  My thought with this was to have curved pitch and volume arms containing the SMD AFE boards inside but still using large inductors wound on printed bobbins that fit over the small diameter end.  You'll have to see what I'm talking about - it's basically the same function as a PVC pipe arm and large coil form, but with a little designer bling and without the PVC stigma.

This work is really impressive, especially the craftsmanship. I wished I could implement my project ideas so perfectly. 
Now I am curious about the new sound samples. 

Has a prototype ever been tested by one of the approved professional theremin players like for example Lydia Kavina, Carolina Eyck, Thorwald Jorgensen or Peter Pringle and have their critics and optimization suggestions (as musicians) been taken into account?

I'm sorry to have to ask this (rhetoric) question because I've seen a huge number of technically impressive and innovative theremin concepts over the last 12+ years, but none of them was ever adopted by one of the professionals... IMHO, any music instrument should be designed by a cooperation of engineers AND professional musicians, where the musicians should have the last word.