Goals for a TW Theremin

Just realized the implications of Thierrys "The original VCA is pulled up to maximum level to allow an already waveshaped but unattenuated audio signal."

Using the other VCA (call it VCAX) to generate a CV would therefore leave you without a usable VCA for audio - You would need to add a VCA driven from the CV generated from VCAX, in order to get volume control from the antenna..

Gordon, IMO, your aversion to CV's is making life real hard for you! - You could have simply had a CV output and a direct audio output (pre-VCA) and supply voltages all coming out on a 5 pin connector, and an external box containing as many VCAs and CV driven interfaces as you needed.. Fitting a CV controlled "portentiometer" into such a box would have been a doddle, and would have given you access to cheap simple connection to effects units etc.. Just because you have CV doesnt mean you nust buy a MoogerFooger or little Phatty! ;-)  Your EW would have been nearly standard, and wouldnt have ended up like an ancient analogue telephone exchange! ;-)

Fred.

Hi Thierry, ;-)

You were too quick for me - I deleted my "grumpy old man" comment quickly, but obviously not quickly enough! LOL.

Yeah - I can see the difficulties you must have had - But in terms of linearity etc, I think that for Gordons application, its not too critical - the CV will be driving some unknown effects unit with unknown charactaristics - getting the external equipment to track the dynamics in the same way as the volume response is most unlikely to happen no matter how much care one took over "linearity".

In my view, taking a buffered CV out is the basic starting point if one wants your theremin to control any external equipment, and, in my view, if one opts to have any other configuration (VCA's or whatever) inside your theremin instead of going the CV route, one will sooner or later find oneself severely limited by this choice.

And, IMO, Gordon has hit this barrier.

Fred.

I think that answers my question. Thank you. :-)

When I wrote "Also, I have a theremin volume module already, built into my etherwave, courtesy of Thierry. It would be good if we could make it work with that." I should have been clearer in my intent, and added "This is not a thing I have to have at all costs, but if it is possible to make a simple adaptor which will allow my to experiment with the idea without further modification to my etherwave then I could report back whether it is a facility that I find useful or not without distracting anyone too much." 

I have already provided plenty of distraction to you, Fred and Thierry, and am happy to accept that I have reached an impassable barrier. And I have learned a little more about my instrument along the way, so I am not disappointed by the outcome.

(Oh, and I totally would have to buy a slim phatty etc. When a door opens I can't resist rushing through it...)

"I have already provided plenty of distraction to you" - GordonC

No problem! - I come here for distraction, LOL ;-) - And I think this was an important matter to bring up, in terms of this thread.. When and if a TW Theremin is designed, these are the kinds of issues which need to be thought about carefully.

Alas, you are beyond help, LOL - Unless we could devise some kind of CV which couldnt be made to work with anything costing more than £100 or so ;-) ... Whilst the MoogerF and Phatty are lovely pieces of kit, I think much of the appeal in your music comes from the fact that the sounds you produce are hugely different - Listening to your creations, I do not hear instrument used in the hackneyed way one hears in many compositions - I dont hear sweeping Moog filters or TB303 bass lines - And, much as I love those instruments, hearing music which has them "in yer face" can get tiresome..

Fred.

 "i thought you gave me back my PSU at one of Lydia's workshops. I have one just like it and I don't remember buying a duplicate. :-)" - Gordon

Thats probably why I havent been able to find it! LOL ;-)

"...and continue working on my Theremin Developers Reference manual and try to make some money from publishing that.."   - FredM

Fred, I can't imagine anyone more qualified to write such a book than you!  It would very likely give you huge gravitas in the community.  No pressure, but put me down for the first copy!

Have you given any thought to the editing process?  Books that don't run a formal editing gauntlet can be hit-or-miss.

Now all you need to do is clone yourself multiple times, teach them, and build that transporter device! :-)

"Have you given any thought to the editing process?  Books that don't run a formal editing gauntlet can be hit-or-miss." - Dewster

No - I havent actually thought much about any details like that.. This "project" sort of started because I found myself getting lost in my own output - duplicating work because I had lost files and things like that.. The more I tried to structure things, the more chaotic it was becoming..

So I thought I would organise my filing system like a book - top level sections (folders) with major topics, then sub topics, then "chapters" etc, with a seperate reference section containing links and articles etc..

It was originally just for me .. But the process got me thinking - and I have started writing book "chapters" within the folder "chapters" - I am old school - I remember the contents of physical books far more easily than remembering which folder I put the 200th simulation of a theremin oscillator in.

Fred

 "No pressure, but put me down for the first copy!" - LOL ;-) I had counted you as one of the 30 people on this planet who might be interested in the book! .. I would certainly like you to read it and give advice etc before it went public.. In fact, I dont intend to go much into digital stuff - but perhaps this would be a serious ommission.. I think there is probably a requirement for a contribution by someone better with digital than me, and can think of no-one better for this task than you!

"I would certainly like you to read it and give advice etc before it went public.."  - FredM

I would be honored to do so.

"In fact, I dont intend to go much into digital stuff - but perhaps this would be a serious ommission.. I think there is probably a requirement for a contribution by someone better with digital than me, and can think of no-one better for this task than you!"

Thanks!  I intend to organize my thoughts and design process in some form of written manner.  It could perhaps be integrated into / tacked onto yours.

I just discovered the site last night and started getting really intrigued by the Lev Oscillator discoveries and the RCA style with FETs work being done over in the Circuits Scratchpad. Then I found this thread and it looked like something great was in the works. It seems I might be too late though.

Personally, I love the idea of an "open hardware" theremin design. I think the comparison the the Arduino is particularly apt. I've got an Arduino that's not being used for much of anything at the moment, but I still feel it was a great purchase.

I've been somewhat interested in building my own synths for a while now, and have thought about bulding a theremin for my brother (who finds them fascinating). I think there is a definite place in the world for this project. Most theremins I've seen online are either really expensive, built out of modular synth bits (nothing wrong with that, but even more expensive), or cheap junk. My brother's a drummer and aspiring techno producer. I don't see the theremin as becoming a main instrument of his, thus there's no point in a really expensive setup. But he's got enough musical chops to appreciate something nicer than some 555s and a photocell.

Personally, I think the modular approach is the way to go. Even if you want a single board solution (which I'm sure many do), I think that design wise, the modular approach is better. To that end, I think Fred is right in saying that interface standardization is probably the most important thing at this stage. (Or brand protection...)

Some standards already exist and should be leveraged. CV is at the heart of modular synths and should be used where appropriate. This will allow much experimentation with different VCAs and such not. Clearly, audio should be whatever it is that professional equipment expects. (I know it comes on quarter inch phono jacks or five? pin connectors, but beyond that, not much. Clearly, I'm new at this.) I don't think MIDI is especially relevant. (If you want MIDI, use CV and get a converter box, they're commercially available.)

Clearly there are a lot of other standards that need to be specified. For instance, power. Personally, I'm in favor of a single sided supply (for simplicity), but being expected to play nice on some level with third party modular gear might require a double sided supply. Then there's other stuff I've got no idea about (though Fred sketched out a list).

The direction I'm thinking of heading in is very modular. Starting with a simple FET Lev Oscillator (like those built by Chobbs and Dominik) design seems like a solid first step. If I understand it correctly, three such oscillators (two for heterodyning and one for volume) could form the core of an RCA-style instrument. My theory is that one layout could be developed that (with the correct build) is suitable  for all three (or two if an alternate volume system is employed). This should help with the ease of the build and reduce number of distinct parts on the BoM. (Somebody please correct me if I'm horribly wrong here.)

Then the question becomes: "What else is needed?" Power/grounding, antennas, tuning/linearizing, and an amplifier come to mind.

But I think therein lies the beginning of the answer as to what interfaces are needed. What is needed to wire together the three oscillators and the rest of the parts into a functioning theremin? Those are the interfaces (it seems to me) that need defining.

Perhaps I'm looking at it the wrong way, but the symmetry of basing the machine around a core of three (nearly) identical oscillators is quite appealing. Of course, I'm sure there are a lot of subtleties I'm missing. I would appreciate it if those of you who know more about this than me could offer your own thoughts on this idea.

First, Welcome to TW !  ;-)

"I just discovered the site last night and started getting really intrigued by the Lev Oscillator discoveries and the RCA style with FETs work being done over in the Circuits Scratchpad. Then I found this thread and it looked like something great was in the works. It seems I might be too late though" - Karatorian

No - Never "too late"..

This was to be a collaborative project - Just because I will not be participating in the "project" does not mean its "dead".. Anyone is free to continue it.

I am developing some "clone" stuff based on Lev's designs which I will make public once fully tested etc.. This stuff will be published at Element-14 under my copyright and probably trademark to protect it from abuse, or "passing off" by a certain person or persons, but anyone will be alowed to use / modify the design to suit their purposes.. They just wont be able to use my name or the "name" of the project unless they comply with the specification, and abide by the rules.

Fred

"What is needed to wire together the three oscillators and the rest of the parts into a functioning theremin? Those are the interfaces (it seems to me) that need defining."

Agreed - for any collaboration, this is where one starts.. A proposal for this was going to be my next contribution.. Someone else needs to do this now.

The theremin designs I will publish will not be a collaborative project - Quite honestly, there is A LOT more effort involved in managing a collaboration than there is just initiating a design and rolling it out - I had thought of starting a collaboration at Element-14, but the issues of copyright and ownership, and the process of selecting / rejecting contributions and defining a structure contributors would be happy with - well, just too much hassle...

What follows is just me "venting" - If you like reading bile, go ahead! ;-)

Even when someone submits a junk circuit they pick up on the web, and asks for an opinion on it, If an engineer who knows what they are talking about does give an opinion, some idiot hobbyist will turn it into a reason to assault* that engineer.. (look - I do understand this.. I have done the same on the subject of music theory which I know nothing about - Jumped in to "defend" someone against a "nasty unjust attack" from someone whose musical understanding I could not touch in a million years - but I have not done this with the object of proclaiming that my knowledge or expierience or "insight" was superior)  So sorting through circuits submitted, and trying to reject ones which do not work / have deficiencies / are crap, and do this diplomatically in a way which wont cause bad feeling - well, I aint up to that job or hassle!

(*I have just noticed that the original assault on me in the above has been deleted and replaced with extracted quotes from other threads which have no relevance to the initial assault by him ..)

Yeah - Ive had a GUT FULL!    The big mistake I made was to think of the theremin community as a "community" - Its not! - It is just a "tag" for people who have some interest in the theremin - Other than that one tiny shared interest (and in some cases the stronger interest in music / music technology, which is probably a less fragile "bond"), we have NOTHING in common - Oh, one may find "members" with which one has more in common - but no more so than one finds in any gathering - apart from interest in theremins, I have as much in common with a crowd waiting for a train at the station as I have with a crowd of theremin devotees.

The only other common thing we share is that most of us are mad to some degree or other... But the same is probably true for the crowd at the station!

;-)

Now that the kerfuffle over the "Theremin that dare not speak its name" has died down to a dull roar (and at the risk of reigniting this one) the recent posts regarding the Moog Melodia make me think more than ever that a simple v1.0 TW Theremin could be done.  I deeply regret that I pushed more complex approaches in this thread, as most noobs are likely looking for something along the lines of the Melodia for their first construction project.

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So:

• single transistor LC pitch oscillator
• single transistor LC local oscillator (for the pitch side)
• single transistor LC volume oscillator
• volume detected via LC filter
• single diode mixer
• single transistor output stage

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What I don't like about Melodia circuit:

• complex proprietary coils with taps and movable slugs
• likely quite sensitive capacitive tuning / trimming method with tiny valued variable capacitors
• no voltage regulation

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I think coils are what stop a lot of experimenters dead in their tracks, and the more complex / hard to find / hard to construct they are the deader the tracks.  Those tiny valued trimmer caps look like trouble procuring and adjusting too.  Is there a simple way to use fixed value coils here and trim them with, say, a variable resistor - and do so with wide enough range and in not to temperature sensitive a manner?  FETs might be easier to use in the oscillators, likely obviating the need for low impedance taps on the coils.

Outside of a few RF chokes, is there a way to "junk box" this circuitry so that it behaves dependably and reliably, and is easily within the reach of just about anyone who wants to build it?  IMO the drivers here should be simplicity of design and ease of part availability, while maintaining a high level of performance in the face of inevitable component substitutions and the like.