Build Project: Dewster's D-Lev Digital Theremin

Posted: 7/2/2019 6:01:58 PM

From: Minnesota USA

Joined: 11/27/2015

Thanks, Buggins.  The only recordings I have at this time are these two impromptu videos that I made with the prototype in the shop on New Year's Eve while I was looking at waveforms.  I was just playing around and decided to upload Auld Lang Syne in time before midnight, and as usual I regretted it after listening again.  With that pre-apology, here they are (the videos are also embedded in this thread a few pages back):


Male Voice:

The newly built "Pro" cabinet is still a few weeks from being finished (more boards to do), so I won't be making any recordings with that for a while.  The prototype is functionally the same though.

Posted: 7/3/2019 5:04:06 AM

From: Theremin Motherland

Joined: 3/16/2017

Thank you for samples!
Both instruments are awesome!

Posted: 7/3/2019 8:42:34 PM

From: Minnesota USA

Joined: 11/27/2015

D-Lev "Pro" Build Progress  Pt. 4

The separate tuner display that was used with the prototype worked out so well that I wanted to do the same with this new model.  I had some flame maple left over from when I formed the curved front panels, and I glued two pieces into a thicker block that would have the depth to accommodate the tuner board.  After completing about 80% of the machining the first time through a milling cutter shifted and destroyed the housing, so I had the extra fun of gluing up some new blocks and doing it all over again.  Even the second time my cut around the octave 7-segment display window was a little deep, and my grand plan to sand a curve into the front to match the theremin's panel was downgraded to a plan to just save the part.  I guess a flat front won't be so bad.

A steel back panel will be used again so that I can use the same magnetic mic stand mount for the tuner as before.  I've gotten accustomed to the break-away feature of the tuner for the numerous times that I have tripped over the cable.

Here is the hollowed out block with holes to let the LEDs protrude as before:

And everything slipped together to give it an admiration test before applying many more coats of lacquer:

Posted: 7/5/2019 4:20:36 PM

From: Minnesota USA

Joined: 11/27/2015

D-Lev "Pro" Build Progress  Pt. 5

Tuner Display Finished

After a nearly catastrophic incident while buffing the lacquer on the tuner housing ( I still say stationary power buffers are as dangerous as anything in the shop) I finished this thing up and called it good enough. As mentioned earlier the back plate is made of steel to stick to the magnets in the mic-stand holder that I made for the prototype.  I'm thinking of making some kind of arm that can clamp to the theremin's mic stand so that a separate stand won't be needed.  Another thing that might be practical would be to have a scaled up version of the display built into an angled floor pod (like a small stage monitor) and set out ten feet or so.

I went through a short period first starting out on the theremin when I believed that if there was any type of tuner display available that could respond quickly enough to pitch changes that playing would be much easier.  Then there was a longer period when I didn't want to have anything to do with visual tuners because they started actually getting in the way of hitting pitches by ear.  Now it seems that a combination of time and a little more experience, along with the practically instantaneous response and high resolution of the D-Lev tuner has resulted in a happy compromise.  I miss the ear-training benefits of the tuner when it's not there, but I know when to mostly ignore it while playing.  There's nothing out there that can match this volume and pitch monitor for speed.

Here's the magnetic mount:

The camera never shows light colors very well, but I like having blue LEDs for the four volume levels on the left and the constellation center on the right, with the rest white.  Eric seems to like all of his pitch LEDs to be white.  Each semitone step upward in pitch moves clockwise, alternating back and forth between the inner and outer circle of LEDs, and a single one lights when exactly on pitch.  But the beauty of this display is how the two LEDs adjacent to the center pitch LED come into play.  They act as pretty sensitive indicators of when you are slightly off pitch. And in normal playing if you can either hit a single LED alone or keep it and the two adjacent ones balanced in intensity with vibrato, you'll be sounding fine.

The "Qant" parameter (for Quantization) on the "TUNER" page can reduce the PWM flicker of these adjacent LEDs if you find it annoying, but with that you also lose the ability to finely discriminate when you are deviating from the true pitch.

This is the general idea of how I like to place the tuner off to the pitch side, although I prefer it well away from the theremin and a little further right.  Attaching it to the theremin stand would be convenient, but personally it just works best to have it in the same general direction as, but away from the pitch antenna (although a floor display would still work, I think).

Posted: 7/5/2019 7:28:44 PM

From: Northern NJ, USA

Joined: 2/17/2012

Lookin' really sharp Roger!  You've got me thinking that the tuner should be more in line with my pitch hand / antenna line of sight, as  I sometimes address the pitch plate a little off when concentrating on the tuner.  I play unaccompanied and with pitch correction most of the time, so it's hard not to rely 100% the tuner.  My "vertical" D-Lev tour mock-up has the pitch antenna closer to the tuner, which should help.

"After a nearly catastrophic incident while buffing the lacquer on the tuner housing ( I still say stationary power buffers are as dangerous as anything in the shop) I finished this thing up and called it good enough."

I hope the near catastrophe was for the wood, and not you personally!  (It's it seems it's always the most innocuous tools that people get hurt on most often.)

Posted: 7/5/2019 8:38:17 PM

From: Minnesota USA

Joined: 11/27/2015

Yes, it was the wood, although if you're gripping the work tightly you can get yourself involved too. The amount of energy in 10" 3600rpm buffing wheels is pretty high, and maintaining the point of contact between the wheel and the work without grabbing requires full concentration. There was no need to be using that or any machine for this job.  I ended up finishing the buffing by hand.

How is that mock up coming?  I'm ready for ya, or will be soon.

Posted: 7/6/2019 3:07:40 AM

From: züriCH

Joined: 3/15/2014

dewster & pitts8rh,
this sounds and looks pretty cool.
very nice woodwork. and the sound-samples are impressive !
will it ever be available as a Instrument or will it be more a diy-thing?
thinking out silent: (will it have midi features or cv outputs?)
so far: bravissimo signori.

Posted: 7/6/2019 8:45:24 AM

From: Minnesota USA

Joined: 11/27/2015

Hello xtheremin8,

Thank you for you comments.  I believe that Eric (Dewster) plans to sell some version of the D-Lev in a more easily manufactured cabinet or in some form of ready-to-go electronics  You may want to direct your questions or requests to Dewster directly in his thread or by personal message. I would venture to say that the whole purpose of his work is to make the theremin available to more users as soon as it is ready.  It would be helpful if you communicate your wishes.

Regarding CV outputs:  I have asked that question, and I believe it is possible to provide these outputs if there is sufficient demand, although I doubt that there would be a push to offer those features in a first release.

And for midi outputs, the answer is probably no.  I think the goal is to provide an adequate array of synthesis features within the D-Lev itself so that there would be less need to resort to an external midi-controlled synthesizer.  And using a theremin to control a midi sample player does not generally yield good results.  As you know, sampled instruments do not sound very realistic when undergoing pitch shifts of more than a few semitones.

But I would suggest that you please talk to Dewster directly if he does not respond to your questions here.  Thank you for your interest!

Posted: 7/6/2019 10:46:58 PM

From: Northern NJ, USA

Joined: 2/17/2012

"will it ever be available as a Instrument or will it be more a diy-thing?"  - xtheremin8

Available as a built instrument, hopefully soon - though "soon" for me can be a pretty vague thing.  I'm still tinkering around here and there with the software, then there are "factory" voice presets to come up with, I'm kinda lazy, the household to-do list is ever-expanding, the dog ate my homework... though I am quite anxious to get it into player's hands.

I'm not super interested in DIY as it can be really time consuming.  But I will always help those who seek info regarding implementation.

"thinking out silent: (will it have midi features or cv outputs?)"

Not this spin, and perhaps never.  CV out could be done with outboard DC DACs, or internal delta sigma (or perhaps some combo), though the FPGA is largely consumed (88%) and Hive main memory is also largely consumed (94%) as is the real-time.  MIDI out would likely be much easier, but MIDI isn't really designed in the first place for something like the Theremin which glisses all over the place.  Footpedal switch-type inputs are fairly trivial.

If there is a next spin (predicated on if there is a first spin that goes anywhere) I'd like to try my hand at reverb in a larger FPGA.

"so far: bravissimo signori."

Glad you're liking it!  That means a lot!  Roger's cabinetry skillz can't be beat...

Posted: 7/8/2019 2:37:08 PM

From: Minnesota USA

Joined: 11/27/2015

BTW, as mentioned previously I am planning to use the TDA1308 IC for my analog amplifier and headphone driver, but it is obsolete.  I have a bunch now, but it is probably not a good idea to use this going forward in a design.

Does anyone know of a suitable low-noise replacement for the TDA1308?

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