Several posts appeared while I was preparing this reply to Dewsters post -
Ilya - Great work producing that schematic ! ... This looks to me like confirmation that the issues Dewster found re linearity are likely to be the instrument to blame and not a grounding issue.. Extremely low antenna voltage simply doesnt give good far-field sensitivity and tends to compress the near field from my experience.. The antenna inductor shown IS NOT a series eq inductor, its simply a ferrite HF suppressor, and will not elevate the antenna voltage or provide any linearization.
I assumed the IC was a dual BJT because I believed what Moog had implied (something I wont ever make the mistake of doing again) that the design of the front end was based on the etherwave.
MAJOR RANT STARTS HERE ;-) =====>
I agree wholeheartedly with Wilcos comments:
"
So I am not happy with the Theremini. Not for myself, as a thereminist in the largest sense of the word, and what is more, not for the theremin community. Because of the lower price, I think many potential theremin players will prefer to buy the cheaper Theremini, but they will not experience what a theremin truly is, and quickly set it aside as a toy for Halloween or at a party, but they will not consider buying a ''real' theremin afterwards.
Lastly, I very much wish Moog Music would not present the Theremini as a serious instrument, for the new generation of theremin players. The world has enough conformity as it is. And listening to the Clara Rockmore CDs as they suggest in the manual does not help, because even she wouldn't be able to play a theremini like that.
"
But having now seen Ilya's schematic, I would be harsher.. Moog have been telling LIES IMO ! - They effectively told us that the theremini had an etherwave derived front-end - IT DOESNT HAVE ANYTHING EVEN REMOTELY RESEMBLING THE EW FRONT END!! - what it has is the cheapest, crudest, nastiest oscillators probably ever placed into any production theremin!. I see no analogue reference oscillator, and presume this is either entirely numeric, or output from the DSP.. It wont drift in sympathy with the antenna oscillator.
Also, antenna direct to the input of a CMOS inverter! No ESD protection whatsoever! .. Wear ESD straps when assembling the toy, then ship it with bloody great conductor (antenna) that plugs directly to a hi-Z input of a CMOS gate - are they morons???? - or do they just not give a shit? "Dont bother 'bout ESD - people wont notice the difference between a dead theremini and a live one anyway ;-) "
Moog went out of their way to mislead people about the nature of the theremini - I have seen numerous people on other forums expounding that 'fact' that the theremini had a heterodyning voice - false legend deliberately seeded by Moog.. And such is the faith and awe some folks have for Moog that I have been called a "troll" when I have simply stated that a heterodyning voice isnt available from the theremini.
If Moog had wanted to kill the theremin, to reverse everything Bob achieved in keeping this instrument alive and 'real', well, they could probably not have done any better at achieving that goal than they have with this theremini travesty.
"I think many potential theremin players will prefer to buy the cheaper Theremini, but they will not experience what a theremin truly is, and quickly set it aside as a toy for Halloween or at a party, but they will not consider buying a ''real' theremin afterwards."
"I very much wish Moog Music would not present the Theremini as a serious instrument, for the new generation of theremin players."
Wilco, You have, sadly, said all that there is to say about this TOY
All Moog needed to do to really boost the theremin and advance it, would have been to take the best from Bob's great designs, and package these in a low cost high end instrument.. If they can pack a pile of costly complex circuitry into a toy, for the same money they could have produced a damn good real theremin at least in the class of the EW+, perhaps better.
And whilst I have never been a huge advocate for digital theremins, I do believe good digital theremins are possible and imminent - Moog may well bring this direction into disrepute by producing something so inferior to what is easily achievable now with digital, that folks wont be interested in even trying another digital theremin (or as Wilco fears, any theremin) after experiencing the theremini.
END OF MAJOR RANT <=====
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MINOR RANT ? ===>
"My sweeps weren't 100% scientific, and I had to do them without being able to hear the audio as my PC was hogging the headphone jack, but yes, that kind of latency behavior was pretty obvious when I could hear what I was doing. " - Dewster
Actually, doing the movements without hearing the audio may give more scientifically accurate results - Its almost impossible when actually hearing the sound to not use this as feedback, creating a closed-loop compensation mechanism... The fact that " that kind of latency behavior was pretty obvious when I could hear what I was doing." just underlines how bad its likely to be IMO - almost confirming a full-span TC of perhaps >250ms.
"There's no way you could do anything even vaguely percussive on it but you could likely play regular stuff (if you don't mind staying up close and personal with the pitch antenna). "
Perhaps another way of saying this is that if you limit your hand (and related pitch) movement to a small area of the the field, particularly the area close to the antenna - or stay within a couple of octaves (20cm?) within the most linear area of the field, you might (me being uncharitable ;o) just about manage a recognizable tune at 80BPM - And as you can probably move the required notes into this 'playable' zone, you should be able to "play" most things that dont traverse more than a couple of octaves.
As I see it, it comes down to the speed at which change in capacitance is "registered" and the resolution of the derived value - Pitch is a bit of a red herring, but its the only measurable output from which we can guess or deduce the other.. Unlike an analogue theremin where the audio is directly derived from capacitance change (or more precisely change to the oscillator frequency/s) the digital theremin 'invents' the pitch from a processed version of the oscillator frequency/s...
In these terms, my comments about "octave error" etc are incorrect - if two octaves were spread over the whole pitch field it would take the >250ms or whatever to change the pitch by 2 octaves, but if 7 octaves were in the field, it would take the >250ms or whatever to change the pitch by 7 octaves (and therefore perhaps only 50ms to change the 2 octaves in the required playing area).. So for rapid pitch change that needed to be low latency one would want to cram as many octaves in the field as you could get away with, and play in a small area of the field, limited to one or two octaves.
"I'm holding my arm out and sweeping it in a semicircle by twisting my body so that my hand and the pitch antenna are closest about 1/2 way through the sweep, so as to produce the smoothest change I can. "
Its not possible to derive any linearity plot from just the sample - and what I say next needs to be taken as entirely speculative with a high probability of being wrong..
I have found that the sweeping action you describe tends to give better linearity on crude theremins than the 'standard' (correct) method of outstretching the arm / hand towards the antenna - I have actually used this as a playing 'style' - its the way I play theremins like the Jaycar / Silicon Chip and derivations thereof. I think there is a practical geometric / mathematical reason - One is forming a changing angular capacitance between the body/arm/hand and the pitch antenna, and I think this gives more rapid rate of capacitance change in the far field, and reduces rate of change in the near field.
Having listened to many sweeps of crude theremins done in this way, and used this as a rough guide to tuning and improving the linearity (particularly on my 16 H1's) - and if my memory serves me reasonably well, what I am hearing on your sweeps is extreme* non-linearity - there should be much more change in the far-field (bass) even from the crudest LC front end driven with sufficient current (ie antenna voltage) with a well grounded player.. And the change in the near field is way too extreme.*(Note: It may be that because I have always been listening while doing these sweeps, I was unconsciously applying 'closed loop' correction - I will have been doing this to some extent no matter how hard I tried to stop myself... In the light of this it may be that, had I heard recorded sweeps I had done without being in "the loop" they may have sounded as 'bad' as your sweeps do.. )
If this is due to the Theremini design, then IMO there's not much point in exploring this instrument further.. The only thing I will suggest though is that you ensure that your ground coupling is good.. Wrap some wire 'round your leg and connect it to the ground screw - just to confirm matters... One possible reason for what I am hearing is an ungrounded player capacitively coupling to both the antenna and the thereminis internal ground / power cable as they get close to the instrument - a dipole capacitive sensor if you like... This can happen with even the best theremin if the player (or theremin) is inadequately coupled to ground.
Fred.