basic experiments

Posted: 7/23/2020 8:26:10 PM
JPascal

From: Berlin Germany

Joined: 4/27/2016

No it is not a sad theremin. A battery powered amplifier can be used, for example. 

Posted: 7/23/2020 8:29:41 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

JPascal said: "Is it really necessary to have a good grounding so that a theremin sounds undistorted and behaves the way you want it to?

The answer is: no. And even grounding is not required at all."


Then you have never discovered how beautiful an analog sound can be. The audio wave shape begins at the antenna/electrode working in harmony with earth ground. The performer is interacting with Nature and her natural forces, why it sounds alive.  Any theremin sound relying on reverb is spiritually dead.

JP If you post the most beautiful sound you have ever achieved it might reveal something, that there are other ways of doing things and why you believe as you do.

Dominik figured out the fundamentals of good sound long before I did. I was actually jealous of his success.

I do have a surprise at the end of next week, it is most likely my last build placed inside an EWS box. A completely original design with no specially wound coils. Too bad I do not have a local Thereminist that could test drive it for me. Once sent to somewhere in Europe, as a gift, I guess my journey is over.

Edit: Because Google likes TW, my boards are the Phoenix but the complete build in the box I call the Electrodeum after the pitch antenna. There is no other word like it and so in search google goes right to everywhere the word is found.

Don't worry Dew, I will be around to bother you. 

Christopher

Posted: 7/23/2020 8:48:24 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

JPascal, that's the way to wake everyone up!

I believe if you have enough stuff electrically "hanging off" of your Theremin that can serve as a big enough plate to be a ground.  Perhaps that's the effect that you're seeing?  "Enough stuff" might actually be better than an earth ground, as it may cause the mains AC field to cancel (common mode rather than differential).

Posted: 7/23/2020 8:50:13 PM
DOMINIK

From: germany, kiel

Joined: 5/10/2007

JPascal: i know i know. It just doesn't see earth and i kind of like the fact that theremins worldwide are plugged into mother earth. The ungrounded NOT :/

Posted: 7/23/2020 9:40:41 PM
DOMINIK

From: germany, kiel

Joined: 5/10/2007

Btw. JPascal, i like that contrabasson sound in the lower register. I have done some investigations as well and all timbres being interesting in the bass, sounded nearly unusable in the higher registers.

Posted: 8/14/2020 7:25:18 PM
JPascal

From: Berlin Germany

Joined: 4/27/2016

Some experience over the time.

There are three things that are easy to underestimate when building a theremin. 

One is the oscillator RF fields, which scatter into the other parts of the circuit via the highly inductive coils (magnetic) and the antenna (capacitive). 

Second, the antenna and coils themselves receive 50/60 Hz hum, which modulates the mixed signal. This leads to a splitting of all individual overtones into a central tone and side bands. 

The third known artifact is the coupling of the two pitch oscillators. When the beat frequency is close to zero, the frequencies "lock in" if proper buffering is not used. Playing bass notes is then impossible.

Of course there are fourth, fifth and more problems. But these three are really important in my opinion. 

Posted: 8/15/2020 2:10:34 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

"There are three things that are easy to underestimate when building a theremin. 
One is the oscillator RF fields, which scatter into the other parts of the circuit via the highly inductive coils (magnetic) and the antenna (capacitive)."  - JPascal

Yes, and with an analog Theremin there can be as many as six resonating inductors just for the axes.

"Second, the antenna and coils themselves receive 50/60 Hz hum, which modulates the mixed signal. This leads to a splitting of all individual overtones into a central tone and side bands."

I haven't investigated how to mitigate mains hum pickup and audio intermodulation in an analog Theremin, though I would like to hear people's thoughts on the issue.  On the D-Lev I've found significant hum conducted via the hand, and I've squashed it via notch and low pass filtering of the frequency number.  Another very effective digital method is to sample at 50/60Hz as this places a zero at the hum frequency and all harmonics and so really kills it (I do this when observing LC on the scope by delaying the sweep by 16.6667 ms).  In a simple Theremin (no EQ inductor) it would seem that L always has a low impedance return path to ground, so I would expect low hum levels.  It's obviously always best to quash this stuff at the source, rather than letting it in and dealing with the aftermath.

"The third known artifact is the coupling of the two pitch oscillators. When the beat frequency is close to zero, the frequencies "lock in" if proper buffering is not used. Playing bass notes is then impossible."

Coupling makes the far-field even more non-linear, but it can add interesting timbre to the low end.  It's too bad there isn't a way to decouple the timbre from the coupling.  Perhaps there is some sort of middle ground?  Could dividing the oscillators down keep them farther away from the coupling point?  But then you maybe don't get the timbre effect of coupling, and lose the sine as well.

A certain amount of oscillator coupling could be taking place via the power rails.

I think I would add a "zeroth" thing that is easy to underestimate: power supply regulation.  Most oscillators require a regulated supply for stable operation.  Thankfully this is trivial to do and quite inexpensive.

Posted: 9/29/2020 6:33:41 PM
JPascal

From: Berlin Germany

Joined: 4/27/2016

I had my first gig. A sunday soundpath performance arround a romantic forest quarry with church that my theremin and I were involved in. So I had to finish a first prototype of my theremin and it was sooo stressful because I didn't know if the little thing would be playable after putting in and soldering it into the box. Nothing was easy, the worst thing was that I had to split the pitch circuit board in two parts because of too much coupling.

Hardcore test was also the transport with an e-car (high volt, 100 kW), I was afraid about some jFets in the volume control. Not least the grounding. Would it be functionable with my simple grounding set? A 15 watt battery driven amplifier on site could not be tested before...

All was going well. Hundreds of people came, the bravest interacted with the pitch field and were interested in the causalities. I saw many happy faces.  


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