Theremin pitch changing over time

Posted: 11/29/2010 2:50:11 AM
petitegeek

From: Kyoto, Japan

Joined: 11/29/2010

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 :)
Posted: 11/29/2010 6:43:02 AM
Thierry

From: Colmar, France

Joined: 12/31/2007

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)
Posted: 3/20/2020 3:20:38 PM
RLN Theremin

From: France

Joined: 3/15/2020

Hello Thierry, I know it is a very old post, but I read that you always let your etherwave switched on (day and night?); isn't it dangerous for the circuit? I ask this because living in a very old building the electric current is not up to standart I think and there are often variations (noticeable on electric bulbs for example when you turn on other devices) which makes me ask if it doesn't wear or damage my etherwave circuit in the long term? Thank you

Posted: 3/20/2020 4:47:34 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

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.

Posted: 5/21/2020 3:21:52 PM
austin

Joined: 5/17/2020

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

Posted: 5/21/2020 3:40:24 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014


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

Posted: 5/22/2020 12:48:28 PM
ILYA

From: Theremin Motherland

Joined: 11/13/2005

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.


Posted: 5/22/2020 12:54:46 PM
ILYA

From: Theremin Motherland

Joined: 11/13/2005

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!

Posted: 5/22/2020 1:04:48 PM
Valery

From: Russia, Saint-Petersburg

Joined: 6/6/2016

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

Posted: 5/22/2020 1:14:14 PM
ILYA

From: Theremin Motherland

Joined: 11/13/2005

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

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