Theremin pitch changing over time

Hi there, I'm new to this forum so I'm sorry if someone has asked this already...

Does anyone know if there is a technique/tip to keep the theremin's pitch from descending over time? I've done some searching on Google and realize it's a common occurance (ie. the theremin is left on on 'silent' and at some point a low note starts sounding on its own.)

Does it ever stabilize? Are there certain models that do it more than others? I have an Etherwave Plus. Thank you in advance :)

The frequency deviation which is necessary to produce a low tone is less than 100Hz. Compared to the oscillator's free run frequency of about 285kHz it's just 0.035% which can already be considered as an insignificant value, especially if we are working with oscillators which should at the same time react correctly on smallest capacitance changes.

So it is normal that you have to retune your Etherwave Standard/Plus from time to time, especially during the 15min. warm-up phase. After the temperature of the transistors will have settled, the drift will be as minimal as cited above and that's ok.

If you have ever seen a violin soloist performing, you should have observed that he is also retuning his instrument between the different movements of a violin concerto. So what?

I personally minimize this effect by letting my Etherwave always switched on (its power consumption is also insignificant). I naturally switch the amplifier off when I don't play. Out of that you may hang the power or the audio cable over the volume loop (= Bulgarian version of the mute-switch)

Me lives in a 300+ years old house, too. I never worried about electricity since I know two things:
First, the Etherwave’s internal power supply section which complements and stabilizes what comes from the external transformer is relatively robust and can handle up to 40% over voltage for a few minutes.
Second, if something broke, I’d be able to fix it myself. But that wasn’t required in more than ten years.

If these statements don’t give you a good enough feeling, you might still go out and buy a small surge protector adapter, something which you put between the wall plug and the Etherwave power supply. These are normally sold to protect computers, but they’ll also protect your theremin.

Does it ever stabilize? 

I actually just did an experiment to answer this question. I ran an hour long recording because I was curious to see just how much the instrument changes pitch, and how long it takes to reach a stable pitch.

The range expands over the first 10 minutes, meaning your notes will go sharp. Even at the 40 minute mark, my Moog Etherwave Standard goes sharp by about a half step for the next 20 minutes. Low notes are more susceptible to going sharp, and high notes are a bit less likely to change pitch.

Full results here: https://youtu.be/qBE8igIiSGw

Austin, Excellent video production. A theremin is extremely sensitive and what causes the drifting after the so called warm up is the room temperature changes. By nature it could never be perfect but properly designed circuits can get ideal results. I consider ideal as holding A4 440 hz,  +/- 10 hz over a 1 degree F room temperature change. Interestingly vacuum tube theremins drift much less than solid-state.

Christopher

I do extracted the data from austin video and presented it as a graph.
If anyone is interested.

At the same picture I demonstrate the drift of Paradox MX which has air core coils.

Keep in mind that if Austin tunes the instrument to a low note (as I did in Paradox), the drift, expressed in musical terms, will be a few octaves!

Ilya, I did not notice such a large drift my MOOG ETHERWAVE PLUS...

Well, I quite admit  that the drift varies from one to another.

BTW,
does anyone know a freq meter application for PC with automatic logging feature?