Thankyou everyone for your replies! All have been thoroughly read, digested and appreciated.
* Coalport - "It shouldn't [hum]. Sounds like you may have a grounding problem. This can happen if you have your theremin or any of its components (amp, speaker etc.) plugged into peripherals (computers, FX boxes, splitters, etc.) that are plugged into different AC outlets. You might try plugging everything that has any contact with the theremin into the same power bar."
I have computer/monitor from one wall socket, and then (wait for it): electric drums, mixer, theremin, electric piano, phone charger, hard drive from another splitter - although I turn on/off as required.
http://keaneshaped.co.uk/mp3s/thereminhum.mp3 < that's what I hear - the fade to silence is when I move my hand towards the volume bar, suggesting it's coming from the instrument.
* Coalport - "Chris, exactly what do you mean by "linear" and "non-linear"?"
My primitive understanding is that the Etherwave Pro has 'good' linearity, whereby the interval of an octave is X cms, both at high pitch and low pitch. 'Weak' linearity would mean the gaps between intervals are greater at the lower end, but get closer the higher the pitch.
So my logic as a violinist/guitarist goes that I'm used to the physical intervals being different, so non-linearity makes perfect sense. Therefore I wouldn't want a Etherwave Pro as the spacing would be counter-inituitive(...?) Am I barking up the wrong tree completely here? Is linearity seen as a good thing, bad thing, or personal thing? (Personally, I'm quite happy with my Etherwave Standard, although I've not tried anything else for any period of time!)
* Coalport - "it is a bit like putting the Rolls Royce "Spirit Of Ecstasy" hood ornament onto your Volkswagen"
Interesting analogy! I see what you're saying, but it wouldn't strictly be an exact replica of any previous instrument, more the general shape and style of the earlier instruments. I love her personality, but wish she'd present herself more like Audrey Hepburn than Lady Gaga...
* Lucita - "The Etherwave manual says to let it warm up for about 10 minutes for the oscillators to stabilize. Mine needs about 10 minutes or else the sensing distance changes rapidly during that time."
Ah yes, the manual. I've downloaded it once (it didn't come with my 2nd hand instrument from ebay), but I must read that again! I definitely noticed some change in the first few minutes.
* Thereminstrel - thanks for your recommendation of the Wavefront Classic - you make it sound very appealing!
In my opinion, it's got 'the look', and the tone is great - I love that deep brooding sound. Brass/string sounds good to me! Many thanks for your YouTube compilation of Wavefronts also.
How does the linearity and feel compare to the Etherwave Standard - would I be lost and have to re-learn what little I've picked up? Are people generally in agreement with Etherspiel?
Also, how much of a DIY job is it to convert it to a lefty? (I am the least practical person in the world. After my dad). Does it require cutting/drilling, or just unscrewing?