"

Some tunings are better than others, but my simulations for the EWS invariably produce situations where the pitch near the antenna is cramped. I'm just not seeing any magic associated with the parallel tank + EQ, just an endless supply of mistunings. I own an EWS, and my experience with it, qualitatively anyway, bears this out. The tuning headaches alone have probably turned away droves from forming a positive view the Theremin.

When properly tuned, the EWS has sensitivity that is very similar to my capless / tankless designs (~4 %F/pF) and has very similar linearity, so these types of arguments against tankless (whether for digital or analog designs) don't really apply.

" - Dewster

I can see what you are saying - but I think there are several possible red herrings.. and in my expierience, this is the one area where simulation and reality, for some reason I dont fully understand (but I suspect its to do with the inductors) gives nearly meaningless results a lot of the time.

The idea of simply energising an antenna LC has been done - effectively using a large "EQ" inductance together with a small capacitance at the antenna (or only using the antenna capacitance) as effectively a series LC "tank".. And then there are the conventional parrallel LC tank circuits without and series "EQ" LC circuit, where the the tank (paralell) capacitance is varied by player proximity..

As I see it, neither of the above has any "compensation" mechanism, there is none in theory, there is none in practice.

You say "I own an EWS, and my experience with it, qualitatively anyway, bears this out." - I suspect that there is a reason why you are not seeing any improvement in linearity - not sure what it is (wrong EQ inductance / tuning / whatever) but my expierience is that there is always SOME (albeit often marginal) improvement in linearity with a correctly tuned dual resonant (seperate tank and EQ resonators) topology.

My "visualisation" of operation is non-mathematical.. I am often stressing that theremins operate on capacitance change - and this is always true with regard to the player - antenna interface... But I actually see the operation at the tank side (on a dual resonator topology) as variable inductance - Effectively, it is change in the inductance of the tank (because the antenna resonator is acting like a variable parallel inductance across the tank inductance) this effective (or, as I have called it in the past, "virtual" inductance) is governed by the tuning of the EQ resonator, which is controlled by antenna-player capacitance.

There is a huge range of possible values for tank L and C for any given operating frequency - but for a given operating frequency the possible value for the EQ inductance is constrained by the available antenna capacitance.. It seems to me that best operation is obtained when the tank capacitance is large, and the tank inductance is small (for example, in the order of 2 to 3nF with tank inductance in the order of 100uH) rather than where the inductance is large and the capacitance is small (for example, C = 180pF, L = 680uH)

IMO, it is the selection of the values for these components (not just the values, but the type / quality - and also the physical components such as antennas connectors wire etc), and selection of operating frequency, which determines performance in terms of linearity and sensitivity.

IMO, some form of equalization is essential for a reasonably playable conventional analogue heterodyning theremin, where the audio output frequency is directly proportional to antenna - player capacitance.

And yes, poorly designed theremins with tuning problems will, I am sure, have put a lot of people off the instrument, and is probably the reason why the theremin (or at least playing them or developing them) only appeals to a certain "type" of person.

IMO, as long as one stays with the basic topology invented by Lev (as in, a fixed frequency beating with a players capacitively controlled variable oscillator) one needs to correct the entirely natural non-linear response one gets - the capacitive relationship is inverse square, the human pitch response is exponential - the two cannot naturally give an output frequency which sounds linear..

**But we dont need to stay with Lev's topology..** Your capless AFE looks ideally suited to what you are doing - you can correct the data and provide a linear output through digital means. I am doing something similar by generating a voltage which I "equalise" through analogue means and then use to drive voltage controlled heterodyning (conventional)theremin modules..

Provided we can get repeatable data from the player-antenna proximity, and this data does not drift or distort, we can manipulate this data as we choose and use it in whatever way we want.. Analogue or digital, I believe this is the topology for future theremins.. It enables all the complex / impossible (for Lev's topology) tasks such as register switching or multiple simultaneous voices, to be implemented with ease.. Given a consistant signal corresponding to player-antenna distance, we can correct this signal to compensate for its natural law / non-linearities, and "map" this to the required law - whether this be an exponential output (to directly drive the pitch) or a linear output to drive pitch generators with an exponential law - and we can do this over the whole range - right from the antenna to the 60cm or wherever we set the 0 frequency point.

But, IMO, going back and trying to re-invent the original is probably folly - or it certainly has been an extremely expensive folly for me.. IMO, the most exciting discovery was how Lev's front-end really worked - But, while not entirely empty, even the promise this seemed to hold has evaporated a bit.

I think that Lev's topology will be with us for a long time to come (it is still by far the lowest cost and most elegant simple solution) but it has difficulties - I believe that you (and I, if I can be bothered anymore) have everything required now to overcome these difficulties using post-antenna (after the AFE) equalization / linearization.

Fred

Added -> There are other equalization methods employing feedback and / or oscillator coupling, and there are some theremins which I suspect employ shemes like this.. but I have never got my hands on a Tvox Tour or a Burns - its the Tvox Tour I am most interested in, because the designer assured me it did not use antenna equalization, and its damn good IMO!

BTW - this is just a brief visit - am moving home, getting divorced, trying to salvage my business and get work - and probably wont even have much internet access for the next month...