Need some help with pitch antenna inductors.

Hello Winter,

I did not want to seem cold so I will chime in. (-'

Why are you not buying commercially made 10mh coil/chokes? The frequency of a LC theremin is not critical between 200khz and 1mhz. Tune your osc circuit to match the antenna coils not the other way around. In my own research I have found the higher the theremin frequency the better which can eliminate antenna coils altogether. You're going to have so much thermal drift with the circuit approach you are using that antenna chokes should be the least of your concerns.

What you are doing now is getting your feet wet, finding out why so many fail at theremin design and talk talk talk. From this experience you will have great respect when you build a good design and there are not many. Are you after a controlled whistle or an authentic sound?  For a controlled whistle use a keyboard as the authentic sound is what puts the theremin in a league of its own.

If a theremin design requires noticeable reverb for the sound to be good it has already failed due to a lack of even harmonics.

Christopher

The simple question posed by this thread really cuts to the heart of Theremin oscillator design. 

You can use a parallel tank by itself operating at higher frequencies (where heterodyning makes up for the loss in sensitivity due to the tank parallel capacitance), or you can use a parallel tank with EQ inductor operating at lower frequencies (this gives a troublesome double tuned parallel / series LC which may have some linearizing effect), or you can use a series tank operating at any frequency (my designs use the antenna as the sole capacitance, but this makes the oscillator more complex).

You can pick the operating frequency to be above the AM band (like livio has done), below it (most Theremins), or smack dab in the middle of it (RS Theremin I believe).  I don't know how important it is to stay away from the AM band.  It may be more important to avoid the AM band for the volume side?

You can decouple sound generation from pitch detection (most digital Theremins) or not (most analog Theremins but not the EW Pro I believe).  Decoupling removes some of the "organic" nature of the Theremin (which may be good or bad), but allows one the freedom to adjust and correct for linearity, sensitivity, offset, etc. as well as other pitch effects (like the auto correction / quantization of the Theremini).

You have to pick a road and go down it a ways.

dewster said: "You have to pick a road and go down it a ways."

As an analog theremin builder I think you have to pick what sound you want to arrive at. That is why I always say get a sound sample to avoid disappointment. Sure there are digital add-ons if you don't like your original sound but is it authentic or would a keyboard do just as good if not better?

For me the theremin begins with the authentic sound, a changing eerie mystical "passion", not found in any modern day dry synth sounds using reverb as a Band-Aid! I am not saying that is a bad sound but we are losing touch with something that is very important to theremin which makes it unique, not a gestural controller using the Theremin name.

Sample.mp3  Would modern day Thereminists want this sound if I improved upon the noise in it?

If you are on the RS Theremin "black list" you might not get the sound to play. I apologize for that.

In the future I want to try a freq just above the AM Band using the dual RS 100 uh chokes I used in the past. They increased the linear octave depth of the pitch field even though it is good now.

In a natural linear pitch field you just stand further back from the antenna to play the lower notes, octave switching is not necessary. Also I have no thermal drift over a 10 degree F. room temperature change.

I have asked this before, if an analog theremin has a sound that can get Clara Rockmore's attention, is ideally linear and drift free, what does all this digital stuff add to the mix?  Always dead silence, watch! The original theremin principle is perfect with little to improve upon, it is a natural occurrence.

Christopher

"In the future I want to try a freq just above the AM Band using the dual RS 100 uh chokes I used in the past. They increased the linear octave depth of the pitch field even though it is good now."  - RS Theremin

Hold it now, I thought all of your designs were perfectly linear (because screen door springs, vinegar, toy beads, ...)?  You're confusing me.

"I have asked this before, if an analog theremin has a sound that can get Clara Rockmore's attention, is ideally linear and drift free, what does all this digital stuff add to the mix?"

Digital is capable of literally anything including nuance, detail, and unpredictability - like all things it's in the execution.  But I don't think it will ever be able to get Clara's attention, seeing as how she's dead and all.

They increased the linear octave depth of the pitch field even though it is good now."  - RS Theremin

Hold it now, I thought all of your designs were perfectly linear (because screen door springs, vinegar, toy beads, ...)?  You're confusing me.

---------

Now that is weird...how do you know about the toy beads? You owe me $50 and I will take you off the black list, I recognize you as playing an important role in theremin development though you have not demonstrated any physical or sound success to date. (-'  Let us all hear it can sound like anything.

When I use the term depth I mean more available octaves. In my linear pitch field there are no non-linear octaves, just more or less depending on the amount of energy at the pitch field. <= That will jerk someone's chain.

Christopher

Hi Christopher!
I'm not buying ready inductors because so far I've only found those toroidal ones, which are supposedly not good. 
Your theremin sounds very nice! What are those even harmonics you were talking about? 

Hello Winter,

Win: I'm not buying ready inductors because so far I've only found those toroidal ones, which are supposedly not good.

Hammond Coil  10 mh These may be good but I don't understand the application of them.

There are several different approaches to theremin design. I have not used inline pitch antenna coils and still get excellent results operating at 922 kHz. 9.22 is Faraday's birthday....hum?

Your theremin sounds very nice! What are those even harmonics you were talking about? 

A solid state theremin is often void of even harmonics unless certain circuit finessing is done. I have my own harmonic technique while a lot people rely on a lot of reverb to sound good. I use this simple Windows desktop program to evaluate harmonic balance and background noise.

SpecAn_2v9b.exe new version 2.9beta - May 2011

A little secret, that sound is from a hybrid tube/valve theremin. It uses a $5 vacuum tube which will last your lifetime and creates the authentic sound. Until the thousands of these in the world are used up it is the simplest approach. Tube/valves are pitch drift free!

The theremin journey is not easy so it is important that you proceed with your current project, hands on is the best way to  learn. You are a Theremin University Student in training.

Do you travel over to Vancouver Island for your job? Seems kind of far.

Christopher

"I have not used inline pitch antenna coils and still get excellent results operating at 922 kHz. 9.22 is Faraday's birthday....hum?"  - RS Theremin

Numerology aside, have you ever experienced any issues with the AM band regarding interference from strong broadcasts?

Dew said: Numerology aside, have you ever experienced any issues with the AM band regarding interference from strong broadcasts?

Unfortunately I live in a relatively RF dead zone, Fios is a blessing. I have never had anyone mention radio interference as an issue. Dana in Florida in our years together never mentioned picking up a station. I am certain it would happen if I had a 50kwatt transmitter in the backyard, but a bad audio connection will also do it if not bad fillings in your teeth. A neon gas globe within a few feet will flood the theremin with noise through the antenna.

I will tell you a significant observation I have made; I like your cold dry reasoning. I use to pick up the click from appliances around the house turning on. As you know the Hartley oscillator I use is a parallel LC off the collector. I have found connecting the antenna “I use” to the emitter of the exact same circuit eliminates the noise and works excellent. My theory is the antenna operating impedance is much lower off this connection. You will see a connection for this at the Ant- terminal on the pcb. Thermal drift on the Phoenix is stable due to the characteristics of the NPN transistor I use. The 2N3909 I used in the original builds was a horrible choice as practice will teach.

Because I am unable to technically describe things does not invalidate their existence.

I like Livio's thinking, you need to pay more attention as he does not ramble!

Christopher

Edit: I bet livio would understand what I am trying to say where the uninformed scream at me.

Hand capacitance at the pitch antenna does not work alone!

Thanks for that info RS!  I can clearly see large magnetic events going on in our house (the washer in the next room cycling, etc.) when observing resonance on my scope.  And I often see small amounts of random seeming noise of some sort which I assume is RF.

I'm sure some of it is my personality, but scientific reasoning appears cold from the outside because it must be divorced as much as possible from wants, desires, perceptions, etc. in order to bear any fruit, not because engineers endeavor to be kill-joys. Truths about nature may be valid from a variety of viewpoints, but beyond that they are non-negotiable.  I don't make the rules, nature does, and I'm just doing my best to understand them so that I can best work within them.  The more of a consensus there is the more people can work together and accomplish more.