WS: Phoenix Electrodeum Build

Posted: 6/29/2019 2:12:07 AM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014


WS786873 Said: "So he's a spring that acts as an inductance? I am in China"

After 15 years I am not quite sure what is going on. The Electrodeum spring to me acts like a resonating LCR circuit with capacitance to surrounding environment as the dominating factor. It creates an ideal linear pitch field in a way that simplifies theremin design as seen in video below. No added inline tuning coils are necessary for precise easy play. This approach probably has little value elsewhere but is remarkable when experienced, it is a phenomenon. 

Christopher   




Posted: 7/3/2019 5:53:22 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014


Would You Want The Volume Control To Add More Character?

I have developed biases over the years that get in the way of my own research as I think things like bass walking as fun but silly, maybe even pointless.

With a theremin we basically work in two dimensions, generate a sound and control the amplitude of that sound. We might even think we are shaping the sound; there is a human illusion factor working.

What makes the theremin special for me is it does something beautiful from a very simple principle. Over the years I have said if you need to add reverb to improve your sound it is already lost as reverb becomes your sound. I guess if you listen to reverb long enough you will think it is nicer than what you had before.

In my sample below I do what I think of as organic shaping of her voice at the mixer/detector. This is all natural as it truly develops from Nature, not a cheap post processing trick that sounds thin and tin like buried in too much reverb.

The reason I never attempt a tune is I am tone deaf, a C or D sounds the same to me, some people are not very nice. 

Christopher

Posted: 7/4/2019 3:54:47 PM
DreadVox

From: The East of Netherlands

Joined: 6/18/2019

Hi Christopher,

Your 'helical/coiled antenna' is kind of intruiging. Way back in my teenage years I made a tiny 'stealth crystal radio' that I oftenen listened to in the evenings when I couldn't fall asleep yet. It may not even have had a tuning circuit and what came out was the stongest station, in my case Radio Luxemburg. The circuit was a coil on a ferrite core, a germanium diode, a few capacitors and a piezo-earbud. The tubing of a central heating radiotor as 'ground/earth' and as antenna a couple of meters of electrical wire that was kind of folded back and forth on a wooden ceiling beam and a coil, handwound on a piece of PVC pipe, which as I understood would make the antenna wire appear longer than it physically was to the crystal radio circuit.  Antennae for WiFi and mobile phones also often incorporate a helical/coiled part, to be able to better match an antenna that's shorter than 1, 1/2 or 1/4 wavelength.
A coiled/helical antenna or antenna part could be seen as mainly a coil/inductance, but between the windings if there is a small air gap there is also capacitance,
and so it probably has some pattern of its own resonances, and to the connected circuit it 'looks' a lot longer/taller than it physically is.
In the common forms of pitch rods on theremins, the antenna is very short relative to the wavelength of the variable oscillator, so it doesn't couple to it in the sense of a transmitting or receiving antenna and in practice acts as one of the plates/electrodes of a capacitor, of which the surroundings, including the body/arm/hand/fingers of the player form the other half of that (variable) capacitor.

The electrodeum helical antenna, to the theremin circuitry appears as a significantly longer/taller antenna than the conventional pitch rods, and I understood that you also use a somewhat higher frequency for the reference and variable oscilators. All in all the helical antenna gets closer to match the oscillator as an antenna in the transmitting/receiving sense. Perhaps in practice the result is a more lineairly spread pitch field, I can describe what I see as the differnces, but lack in depth technical knowledge to predict/understand to what kind of differences in behaviour and playability they lead. What role the resonances of the helical antenna plays and what would be the best way the variable oscilator and a helical antenna are combined/matched in terms of frequencies would be an area to explore further.

As to reverb, being used just a tiny bit is very helpful for keeping playing in tune, as you can still hear the soft trail from the previous note, acurately intoning the next tone interval becomes easier. Very 'wet' reverb should be used very sparnigly if at all (when it matches what is played) as a 'special effect'.
When playing in a room/venue with some natural ambient reverb it is not needed to add artificial delay, but in an acoutically 'dry' environment just a touch of reverb is immensely helpful, especially when practicing/playing melodically and unaccompanied. The finetuning of reverb usually would be to adjust it to the point where you just can consciously hear it present, and which while adjusting you would think is the right amount and then adjusting it to half that level,
so its harldly perceivable, but you do year a difference from when you turn it off. This is enough to help give it some 'breathing space and time' and to help the intonation in pitch changes and jumps while playing.
Overdone, reverb muddies up things and can have the reverse effect of playing becoming sloppier instead of helping with getting intonation more precise and harmonious. As with many things theremin-related, the less is more adagium is also valid for the use of reverb when playing in a less than ideal acoustical space.

Posted: 7/4/2019 5:09:23 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

"A coiled/helical antenna or antenna part could be seen as mainly a coil/inductance, but between the windings if there is a small air gap there is also capacitance, and so it probably has some pattern of its own resonances, ..."  - DreadVox

Scientifically, capacitance between windings isn't a real thing due to the very slight phase difference between adjacent windings.  However there can be real C between the ends of the coil (if the coil is at or near resonance).

"... and to the connected circuit it 'looks' a lot longer/taller than it physically is."

True.  The screen door spring I tried a long time ago is 1/2" in diameter and 425mm long.  There are 6 turns / 10mm or 0.6 t/mm, * 425mm = 255 turns.  L = pi * D, so there is ~40mm length per turn, * 255 turns = 10.2m length.  A "standard" Theremin antenna is maybe 0.35m, so the spring is approx. 30 times longer.  Plugging the coil dimensions into Inca, I get 24uH.  Measuring it with my LC meter I get 31.27uH.

"In the common forms of pitch rods on theremins, the antenna is very short relative to the wavelength of the variable oscillator, so it doesn't couple to it in the sense of a transmitting or receiving antenna and in practice acts as one of the plates/electrodes of a capacitor, of which the surroundings, including the body/arm/hand/fingers of the player form the other half of that (variable) capacitor."

A high Q antenna uses a physically short element (sometimes with a "capacitance hat" on top) coupled to a coil.  To put "short" in perspective, the wavelength of 1MHz is 300m long.  So the screen door spring is 10/300 = 1/30 of a wavelength @ 1MHz, which is quite short.  So it isn't a good RF emitter, and is acting largely in the capacitive domain (like any other Theremin antenna).

"The electrodeum helical antenna, to the theremin circuitry appears as a significantly longer/taller antenna than the conventional pitch rods, and I understood that you also use a somewhat higher frequency for the reference and variable oscilators. All in all the helical antenna gets closer to match the oscillator as an antenna in the transmitting/receiving sense. Perhaps in practice the result is a more lineairly spread pitch field, I can describe what I see as the differnces, but lack in depth technical knowledge to predict/understand to what kind of differences in behaviour and playability they lead. What role the resonances of the helical antenna plays and what would be the best way the variable oscilator and a helical antenna are combined/matched in terms of frequencies would be an area to explore further."

More perspective: if the spring antenna intrinsic C is ~10pF (measured via my LC meter, and a good ballpark figure in general) then the resonant frequency with 30uH would be about 10 MHz, or at least an order of magnitude above the frequency of the oscillator driving it, so I don't see a lot to explore here.  AFAIK, no one else has reported that this particular antenna geometry is more linear than any other, so we only have the inventor's claims.  And the inventor ironically hates engineering, so take that for what it's worth and good luck to y'all.

Posted: 7/4/2019 5:52:11 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014


When I post at TW my hope is it is entertaining or even funny to the mob. My 40 year career was in printing not engineering of any kind, I learn as go. If I pronounce a word like piezo or germanium incorrectly get over it.

dewster … good stuff (thank you), funny my bargain LCR meter I ordered said it was left next to a mailbox in Jersey City, NJ did you have anything to do with that? It was shipped from China not California as the ad said.

Dew said: “AFAIK, no one else has reported that this particular antenna geometry is more linear than any other, so we only have the inventor's claims.  And the inventor ironically hates engineering, so take that for what it's worth and good luck to y'all.

Somebody might chime in.... hello hello  calling CQ CQ CQ

Not quite true, I still use a slide-rule and never owned a cell phone, it got us to the moon! 

I build in a modular fashion so sections can be easily swapped out with improvements. What most builders may not have recognized is my modular sections can adapt to what they are building also. If your vacuum tube theremin build does not sound like Clara Rockmore then you need to study what I am doing and go hybrid.

New builders should make a pitch only at first and expand this build in the future into something that performs better than the $6500 Epro.

The most important aspect in theremin design is the two RF oscillators must not know the other one exists. If they talk to one another you want it to be a conversation you control (wave shape) or you end up with them screaming at one another. (Bad Marriage)

You should view sound in two parts, the low end wave shape (throaty) and a high end (lady vocal) for even harmonics.

I think the finest theremin available today without doubt is the EtherWave Standard, I think the wood box is the best part of design.


Christopher

My first theremin was two AM Radio Transmitters with a crystal detector, today it is still not that much different.


Posted: 7/5/2019 8:02:47 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

I guess my future question should be … with the snap of your fingers “would you swap out the guts of your EWS for the theremin experience below?” I have shared these results for over ten years and exactly how it is done. There are some dedicated to keeping my results from you.

If you buy a new EWS for $500, gut the dam thing and add my parts for an extra $100 and Sell it for $1600, you have my blessing! Get the ball rolling.

What irks me is when a new builder thinks he can swap out parts to build it cheaper when a theremin will kick the ass of most engineers.

When I use the phrase “Perfect Pitch Field Linearity” it baffles some in how I can claim this. I never met a musician to give me proper feedback. In theremin design there is only simple knowledge that separates a standard from a master pro. In my design there are no special coils and a single 1N914 for the mixer detector.

For 2020 my thought was I will send my original design to the place it was originally invented 5000 miles away. My two boards were pulled out of the shipping box with little setup and it was a wow moment.

Always ask every designer "Can She Sing?"

Christopher

This is the warm up before the actual playing begins. Are the musical notes linear and where he expects to find them?

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