Bouncy sound in my etherwave

Posted: 11/27/2020 10:04:04 PM

From: Italy

Joined: 5/26/2019

Hi thereminworld friends, I wanted to let you hear the sound that my etherwave is producing, it had happened to me several months ago for a few minutes, but now it is constant, there seems to be a continuous intermittent jump in frequency.
Has anyone ever heard this sound? some idea?

Posted: 11/28/2020 1:47:16 AM

From: Northern NJ, USA

Joined: 2/17/2012

I would look at both the fixed and variable oscillators before heterodyning with a scope.  Delay the trigger one full mains cycle (1/60Hz = 16.666ms; 1/50Hz=20ms) to cancel that out and only see intrinsic noise.  You might also look at the regulated voltages to see if any noise there coincides with the pitch jumping.  I'm thinking it's either a noisy regulator or ESD damage to the variable oscillator.  It could also be ground noise.

Posted: 11/28/2020 6:26:35 AM

Joined: 10/24/2020

Good advice from Dewster, but before you do that, check the power supply. This effect sounds *exactly* like my old 142 theremin when I was using the original power supply...

I know the etherwave uses a proprietary ps, but you might be able to rig up something using a bench supply.

Posted: 11/28/2020 6:39:00 PM

From: Italy

Joined: 5/26/2019

Thanks for your advice, my power supply is not original and has no problems, it powers the whole circuit correctly at 12v, I just tried to tweak the oscillators and it seems to work almost correctly except once it has jumped but for 1/2  second, the frequencies I use are: L5 = 296.300 
L6 = 292.700 
L11 = 492.000 
this is my ideal configuration that I use since I finished the construction of my etherwave and so I manage to have 6 octaves reaching 4300 hz the strange thing is that  it had been three days since I last played it (maybe he got angry) 
Thanks again

Posted: 11/29/2020 9:37:18 PM

From: Darmstadt, Hesse, Germany

Joined: 11/12/2020

If this is not an effect of a bad contact due to faulty switch or solder joint, it could be a radio beacon transmitting around the pitch oscillator frequency.
Does the problem still persist? Is the effect stronger at evening and night time?
When it is pronounced at night, it is sort of radio beacon induced problem; the EW Theremin pitch oscillator frequencies have to be changed to areas where the distortions by radio stations (beacons) are lower and do not disturb. In general, radio beacons can be checked using an AM radio at LW. In the mid of Germany we have many disturbing aeronautical digital radio beacons, causing such pitch jumps when transmitting close to the pitch oscillator frequencies (e.g. I receive a digital data radio beacon at 291kHz and a Morse code radio beacon at 297kHz).
Radio induced disturbance is pronounced, when the pitch antenna sensitivity is set very high (when as much as possible octaves shall be available). I suggest to use a setting of less octaves (change of pitch oscillator frequencies and bending of antenna wire ‘capacitor’); the instrument can therefore be played much more easily and the sensitivity to radio disturbance is greatly reduced.

Posted: 11/30/2020 9:54:58 AM

From: Italy

Joined: 5/26/2019

Thanks for the advice Neutrodon I will investigate to verify if there could actually be something in the area that could affect my theremin on the frequencies I mentioned, even if I have been playing since March and have never encountered similar important problems, for now everything is ok  !  Hi

Posted: 11/30/2020 9:58:53 PM

From: Berlin Germany

Joined: 4/27/2016

My selfbuilt theremin has a pitch oscillator frequency of about 390 kHz. If tuned into the zero beat range and the volume vca is set to maximum loudness, a strong white/pink noise occurs, but also a weak airport beacon morse signal can be heard. 

I thought until now I had a shielding problem, but as Neutrodon explained, receiving the beacon is probably due to the high Q of the antenna circuit.

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