Possibly a "new" theremin topology, and links to related background

That’s interesting Thierry as our fly-back transformers used 15,734 Hz horizontal rate which makes sense because Europe would use a different vertical two frame interpolation per sec rate to avoid hum bars in the picture from 50 vs 60 Hz

Often these transformers were easy to troubleshoot, just smell the back of the cabinet. That's what I would hope for as subtle minor power supply issues can be very difficult to trace back to the power supply. This would become the standard power supply method and made portable TV's more portable.

I was once sitting in a small aluminum folding chair and thought I would wipe the dust off the back side of the picture tube, knocked me out of my chair. DC shock is a bitch over AC, not to mention the time I picked up a DC motor controller on the bench using the aluminum fins on both sides as handles, you only do that once whether you live or die? LOL

Christopher

"Then I have a BIG problem with spam - I believe that someone is deliberately signing me up to spam lists, I get at least 200 spams a day, and 80% of them are utter filth.. Its not just normal spam - someone is signing me up to porn sites and the like."  - FredM

You're not alone, I get that too.  Have Outlook setup to only put contact list email in the inbox, the rest goes to the twit bin (which I must sort through with a fine toothed comb).

"Another advantage of fixed frequency is that one can implement a SMPS (switch mode power supply) locked to the master frequency - this way the whole instrument can be powered from a low voltage (8V to get a good regulated 5V) which powers the oscillator, and this drives the SMPS to give +/- 15V internally.."

For my designs I've been thinking about synchronization between the DPLL sampling rates, the audio output sampling rate, and the LED PWM rate.  The more these things can be locked together the less likely terrible interaction between them.

"That was the first generation of TVs where either everything would work or nothing at all because a failure in whatever circuit section would shut down the line oscillator, disabling the complete power supply."

;-) .. Yes, that is the down-side!

It was just an "aside" and not at the same critical level as a flyback transformer in a TV .. I plan to have most things (all the RF oscillators and related PLL logic in particular) running at 5V, and in fact theres possibly no need for any other supplies - its just that having a good stable +/- 15 or +/- 12V would enable use of available circuits.. I am thinking here more of the readers and possible implementers of the ideas in this thread.. People like Ruslan who may have a theremin that operates on +/- 12V, and want to drive its audio stages from upside-down oscillators built based on stuff floated here -

Debugging should be a lot simpler than debugging a flyback TV, because one should have your 5V stuff either running or not, and a split power source either running or not.

But thanks Thierry - Its always useful to be reminded and learn lessons from past technical problems!

As an aside, (LOL ;-) I am actually looking at a "simple" transformer driven from the MO or related fixed frequency, possibly in resonant mode, rather than a SMPS - Even when synchronous, SMPS can still be noisy due to the varying PWM.

Fred

"For my designs I've been thinking about synchronization between the DPLL sampling rates, the audio output sampling rate, and the LED PWM rate.  The more these things can be locked together the less likely terrible interaction between them." - Dewster

If I am correct, I believe your digital theremin operates with constant frequency antennas (?)

If this is the case, it could be worth our while to collaborate, and if possible decide a frequency both designs should work with.. If we do this, then we should be able to use a lot of each others designs rather than both be designing essentially the same sub-circuits..

Also, if operating with a common frequency, we could synchronise our theremins - I think the requirement for multiple theremins close together is probably small, but where I see it could be a big advantage is in tutoring situations - A teacher could have a number of students close together all playing synchronised theremins.. Also, from a sales / marketing perspective, compatibility could be a plus.

One of the reasons I am going this route is that I have other instruments I deem likely to be more commercially viable - these are "continuum" type instruments and electronic wind instruments using capacitive sensing, and I obviously want these to all be synchronous.

Perhaps we need to pick a number (MO frequency) carefully and establish this as a standard.

At present I am looking between 200kHz and 500kHz - I had sort of set about 377kHz as optimal, but any frequency I can derive from division of 24MHz is usable - Dont want to go  below 200kHz (makes filtering sum components more difficult, and inductors start to get way too big) and dont want to go above 500k because speeds start to get difficult (particularly if I use PWM shaping) - but between those almost anything would do.

I have absolutely no idea if there is an optimal frequency in terms of other established frequencies that may be in use - this is something I was going to check - but perhaps someone into radio could advise.

Fred.

RE: COPYRIGHTS ETC:

Oh - just to advise folks.. I have registered Ether-Zone as umbrella name for my proposed theremin and related  products, and this one would probably be the EZ-T1 or the EZT-Pro (or even the EZ-Pro, but I am a bit worried that this may be too close to another theremins name, and think I need the "T" to differenciate between Theremins, surface controllers and EWI's) .  I have ether-zone.com but theres nothing there yet.

One other thing - Ideas, once they are published (and provided they are not patented) are placed in the public domain, and are free for everyone to use or whatever - This does NOT apply to copyright though - What I publish (schematics etc) remains my "property" and no one can copy or replicate these without my permission.

I herebye give permission for anyone to use my copyrighted material for their own, NON-Commercial use (if you make more than 2, I would regard this as commercial), and to copy schematics or whatever for purpose of education or technical advancement provided I am named as the originator - For any other use you must obtain permission from me.

I am really not fixated by money or profit - its just that I dont like being ripped off.. I would be pleased for someone to manufacture my designs, and would be happy if a small percentage of profits was paid to me or donated to a charity of my choice.

"How would you rate the "upside-down" modification of e/w, if all I need is to completely get rid of "ghost tone" problems?" - Ruslan

I am no expert (at all) on the EW -

First, the "upside down" topology is not that simple - it COULD be applied as a modification to something like the EW, but would lose most of whats at the EW's front end if one wanted to implement electronic linearization - and even if you stayed with the series antenna linearization, it wouldnt be an easy mod.. Tuning would need to be modified (the PLL CV would need to drive the "reference" tuning and some summer fitted to enable manual tuning, and the volume circuit would need complete redesign to use the common master frequency..

I had looked at a possible mod board for the EW, but decided it wasnt worth thinking about - the advantages (adjustable linearity and span in particular) could not be achieved without MAJOR rework - and a mod board would be at a level where one may as well replace the whole EW board and do the whole "upside down" theremin in one hit.

So if you have ghost tones from your EW, probably best to get advice from Thierry.

Fred.

Dewster ,

Just thinking about synchronising theremins etc..

I intend to have a "Sync" signal at 32.768kHz (from a watch crystal) piped to all theremins etc, and from this, each theremin generates its synchronous MO as an integer multiple of this frequency (see posting 11/28/2013 1:56:55 AM here)

I am thinking that any synchronised integer multiple of that frequency should be ok for the MO of other theremins if the signals from the antenna were filtered to remove anything above say 20kHz..

Is this thinking correct? - As I see it, if one had one theremin running at say 196.608kHz 32.768*6) and another at 229.376kHz (32.768*7) any  "ghost" would be at 32.768 kHz - And if everything above 20kHz was filtered, there shouldnt be a problem....

Available frequencies (kHz) would then be:

  And any of these frequencies could be selected for synchronous theremins or parts (antennas etc) of any given theremin or related synchronously coupled instrument.

Even better would be to restrict frequencies to 2*32.768kHz so the closest one would get is 65.536kHz:

But my choices would be to select even multipliers, as this makes getting equal square waves simpler if one doesnt mutiply with a large divider:

262.114 or 327.68 are the most likely choices for me. 

?

Fred.

Just a few examples :
131.072 => will interfere with tVox tour pitch 
163.84 => will interfere with Henk and RCA pitch
196.608 => will interfere with Keppinger Mark I pitch
262.144 => will interfere with Moog Series91 pitch
294.912 => will interfere with Moog EW Standard/EW Plus/EW Pro pitch and completely fuck up Henk volume
etc, etc, etc...

LOL ;-)

Thanks Thierry ;-)

"294.912 => will interfere with Moog EW Standard/EW Plus/EW Pro pitch and completely fuck up Henk volume"

Your use of english is expanding! I like it ;-) - no silly "*" to replace the "u" as I often do! ;-)

ok - I was thinking more in terms of compatibility with synchronised theremins, and setting a standard for these - After all, an EW will interfere with another EW etc.. But you do bring up something important here.. At present there is the ability to select almost any frequency in the >200kHz <500kHz range -

What would be the best frequency/s - as in, what would you choose if selecting one? - as in, a frequency least likely to interfere with theremins presently in use..

Having a fixed frequency will mean that "my" theremin will have a different kind of interference mode with others (except for other FF theremins like the 91) - I suspect that other theremins (variable frequency antenna) if "picked up" by mine will produce pitch variations / variable ghost tones etc, but that other theremins "recieving" mine will have a continuous ghost tone (beating with their reference) or a tone which follows their pitch (beating with their VFO) or both.

I am not too worried though - if people want to play theremins in close proximity, they will just have to build or buy ones complying with the Ether-Zone specification ;-) 

Fred.

What about:

229.376,

327.68,

360.448

393.216

?

I could work easily with any of those.. Actually, could get anything if I use a PSoC (which I will)  to multiply the 32k by 1464 up to 48MHz, and then divide the 48MHz down to some fractional multiple of 32k.. I only selected the above to make life easier for anyone wanting to use a 4046 or similar PLL that would then output an integer multiple of the 32k defined by a small divisor.

Perhaps its not worth bothering about - The PSoC is a cheap 8 pin part that does everything - cheaper than building a board with 4046 and dividers.. I could sell the programmed PSoC for about £15 and freely provide the obj code for anyone wanting to program their own.

Or perhaps not.. Perhaps I select some frequency difficult to produce with PLL and have some other essential function in the PSoC, and force people to buy the PSoC - That way, if I get an order for 100 PSoCs I know someone is manufacturing my theremins! ;-)

Its all a fantasy anyway really - no one is going to build this fucking thing!  Just who do I think im kidding!  - This will just be one of those "projects" which will be looked at by multiple theremin wanna-be developers and builders, who may pick some (mostly irrelevant) meat off the bones, but go back to their safety zone of what they are used to.. If I dont put this into production, it will just remain as a bunch of bytes just taking up space on the WWW.

Fred.

Rusian said: "How would you rate the "upside-down" modification of e/w, if all I need is to completely get rid of "ghost tone" problems?"

I am learning basic theremin electronics but have probably experienced every issue a theremin can throw at someone and still maintain sanity.

My theremin design uses a stand alone independent volume control which is the same as two theremin's standing side by side sharing the same wall-wart and I have overcome any cross talk conflict by design.

My Op Amp on the pitch side amplifies the signal 100x which makes it very sensitive. Fred helped me recognize noise in my sound a while back. My volume side use PWM so the noise level must remain below the threshold of driving a simple 555.

If the ghost tones go away when using batteries on your EtherWave Standard my experimental fix would be to put a 100 ohm resistor in series with the +12v connection above each oscillator section. Add a 470 uf capacitor below the 100 ohm at the positive side of the osc circuit to the negative rail. This is a very low current spot and this extra filtering can work. I use this added method in my theremin designs to completely filter out noise using even the cheapest 12v switching wall-warts. Split power supplies are an engineer thing to make things complicated, often not needed. That is what makes battery powered busking more complicated with the EWS.

I have discovered as Thierry has often stated a well tuned EWS has very good linearity.

For those just passing by the EtherWave Standard has the ability to be an excellent theremin buy. In today's market of choices it is the only theremin I recommend.

Christopher