The Theremin Temple

I didn't think of that. I usually have a low impedance source to drive them.

I also made a mistake in the schematic. The two parallel caps should be in the feedback loop. The knee is much sharper then.

Hi All,

Fred I can now trash my audio signal and then resurrect it. Right now this is standard theremin audio from a transistor osc, single diode detection.

Though this approach hides the signal I need for my research, I know many of you use this technique. The theremin is fed to a power amp and uses a microphone transducer to give total isolation to the digital recording, only problem is picking up acoustically the unwanted lawn mower next door. Also I made this sample stereo recording and added a bit of digital reverb.

I hope the aliasing (good call dew) is on vacation.

Testsample3  .mp3 220k

Christopher

Edit: Invis do I hear a Talking Machine, sounds good, they mostly have the same sound characteristics. (-'

Jason links seem to be adding themselves, how does this originate?

Hi Christopher,

Yes - Driving an analogue audio amplifier from the theremin, then recordring the speaker with a microphone, does give total isolation from the HF (provided the microphone lead, soundcard etc doesnt pick up radiated HF bypassing the amplifier / speaker / microphone isolation) ..

Provided one isnt using a class D amplifier or switch mode PSU for your amplifier, there is nothing to alias with any HF coming into the amplifier - and the speaker and microphone (and frequency response of the amplifier) will ensure that you aint going to get any HF signal to be aliased by the sound card.

The above is effectively creating an electro-mechanical filter, with the unwanted* side effect of microphonics and coloration .. These *unwanted effects may in fact be "wanted" from a musical perspective, but in terms of developing theremins which others can use / build they are certainly unwanted - Because the results you demonstrate can only be repeated by duplicating wour complete setup exactly.. Much the same way as I believe that to have a RCA theremin which sounds like the "original" one needs the power amplifier and speaker.

In our modern environment, when we provide an electronic musical instrument  (or designs / construction details for these) we must design with specifications to make it compatable with the wide range of equipment it could connect to - and a large number of these devices are going to be digital - Soundcards, Effects, class D amplifiers etc.. We cannot expect people to drive an amplifier and use a microphone to interface to such equipment.

If we make recordings using a microphone, people will (rightfully) be upset if, when they buy or build our design, and connect this to their sound card, what they hear bears no resemblence to our sample and is cluttered with aliasing artifacts etc.

My previous notes about building a filter box etc, were purely from a development perspective, for use with noisy prototypes in the noisy lab environments -

When we have the 'product' we want, the next step is to ensure that the signal from our instrument is clean, and works without problems with digital equipment it will be driving - And this could involve adding some of the filtering incorperated into the lab "isolation box" into the product. Usually a simple low pass filter on the output stage is enough to attenuate any HF to acceptable levels.

I suppose the gist of the longwinded blurb above is that I think you may be going in the wrong direction with the electromechanical approach - If it was just for you, fine - but if you are guiding your selected "wizards in training" into the dark arts of theremin sorcery, then you need to master the dark art of simple filters so that the (really quite simple to kill) aliasing demon is defeated first.

Fortunately, the art of filters has been distilled into ready-to-use decoctions, so you really dont need to master the killer arts like maths.

Fred.

Fred said: "I suppose the gist of the long winded blurb above is that I think you may be going in the wrong direction with the electromechanical approach"

Everyone uses the electromechanical approach or they would never be heard!

My reference to this is, I have never attempted a final sound. When I record direct theremin to sound card without Fx's it is for research purpose and I will continue this method. I need to know what is going on in the audio signal.

I mentioned my audio signal was 1v p-p or more as I have an adjustable output pot. The question is if 25 micro-volts RF is large enough to cause trouble. My board design has four active spots for RF filtering if necessary. The first passive stage seems to take care of it. The TL082 dual Op could have a feedback pf capacitors if it was necessary and pads have been left open to mount this component. I like using HF feedback to dampen the signal so it begins to quiet above 1 kHz, it acts like an automatic volume control attenuating the highs so they are not so piercing.

RF is another reason theremins need a good earth ground, the RF must go somewhere. I actually use a weak field strength today around the antenna so volume and pitch do not talk to one another. I can put the antennas 4" apart and they ignore one another.

In my early days my theremin use to pick up external noise like appliances switching on, microwave?  Today I do not have this issue, I wonder if a weaker magnetic field around the pitch antenna is related? There are other fascinating things about the pitch field still left for newbie discovery.

There are tradeoffs one must make in circuit design, the worst is running out of real estate if size is a factor. LOL   Like I was adamant about using Radio Shack, today the compulsion is to use 3" x 6" boards because of the clad board full size when purchased is 6 x 12. That's 4 boards.

w0ttm I have enjoyed using those RS 1:1 ratio audio transformers but found the loose wiring to be a pain in the butt.

Today I was contacted by a new wizard in training from TW, so the schedule is full. Anyone that built my past RS Illusion is a hero in my book. (-'

Christopher

Perhaps try this -

Take the output from your theremin into a HIGH PASS filter which gets rid of most of the audio..

Shove this signal into your soundcard, and you will probably be able to crank the volume up and hear the aliasing..

something like:

Theremin Out ->---C1 -----+------- C2------- + --------> To Soundcard

                                     R1                     R2

   Ground --------------------+-------------------+----------

with values to taste.. but C1 = C2*2   R2 = C1*2 is usually ok

C1 = 1n, C2 = 470p, R1 = 4k7, R2 (total - include resistance of soundcard input or experiment) = 10k

Produce a low frequencty from theremin Say 440Hz, which should be attenuated by about 80dbs with this filter..  its harmonics, if they exist, being attenuated progressively less, at the 12th harmonic, its level will be attenuated by about 40 db's.. So with a sine-like waveform you shouldnt hear audio

20kHz will only be attenuated by about 12 db's, and 44 kHz  by about 6 db's - so if any frequencies above 20kHz are producing the ghosts, with the above you should REALLY hear these ghosts... and only ghosts.

Fred.

Fred said:“In our modern environment, when we provide an electronic musical instrument  (or designs / construction details for these) we must design with specifications to make it compatible with the wide range of equipment it could connect to - and a large number of these devices are going to be digital - Soundcards, Effects, class D amplifiers etc.. We cannot expect people to drive an amplifier and use a microphone to interface to such equipment.”

My theremin board was designed around the simplicity of components I originally found at Radio Shack. I think when I started I viewed a theremin as a joke and over time developed a sort of an affection. (lonely old man syndrome)

The evolution of my designs began with the Ultimate, Ultimate 2, Ultimate 2c, the Illusion and now the enigma. Each design was a spin off of the previous. The enigma has had Revision A right through Rev V. Each time I think of something that makes it more practical. Things like using on board 1/8” stereo jacks instead of wire terminals. The main goal here was to eliminate loose wiring as found in the Theremax spider web.

Another type of theremin isolation I discovered early on was using the LED/Photo-Transistor which is still possible with my current design as a $10 off board plug-in if necessary. I have one stereo jack on board currently that supplies voltage and the audio signal. Its main purpose is to drive the independent volume control board.

This method not only isolates RF from getting to the digital sound card, in its own way it enhances the audio sound. I don’t want to go back to tube/valves though my current design is very good.

One Opto and one resistor is all that is needed for a isolated microphone level, another OP for Line-level.

This original sound byte (2004) below uses opto-isolation for its sound enhancement; I never had a chance to feed it into an amp speaker and microphone recording for a big sound. This is theremin to sound card direct and only your computer speakers enhancing it. I just purchased my amp and mic the past month.

Early Sample .mp3  220k

I have found over the years that RF uncontrolled can climb all over the place, even a hundred feet away.!#$%   I think Greg was running into this problem.

Christopher

Feeding the audio output to drive a LED, then coupling the light to a photodetector, will get rid of a lot of potential HF problems - particularly if slow LEDs and / or slow photodetectors (such as cadmium ones) are used.. RF certainly wont get through .. and with cadmium detectors high frequency audio wont get through..  This technique is effectively implementing a filter based on the frequency response of the coupling components - it will also 'distort' the waveform, because the transfer function of these components will be non-linear.. How much, and what kind of distortion will be produced, will depend on the circuitry..  To design an opto-coupler for Hi-Fi audio is no trivial task - virtually impossible unless one first digitises the audio, or unless one uses two matched opto-couplers, one to transmit the audio, and the other to feed back the "recovered" (isolated) audio to the "transmitter" so that a closed-loop can be implemented and the signals corrected.

Fortunately, one does not often need to do the above for audio (I am not talking about digital here - with digitised audio, opto coupling is standard, one can buy everything needed off-the-shelf these days - but - this sort of coupler will produce aliasing exactly as your souncard does if presented with frequencies greater or equal to 1/2 its sampling rate)

One of my first "real" jobs in analogue was on exactly this kind of problem - back in the days before one could buy integrated isolation amplifiers (and when LED / Transistor opto isolators were only just starting to appear) and I had to design isolated amplifiers for medical equipment, and was told to use optical rather than transformers like everyone else was using.. Hell, what a nightmare it was! The next job I took was with digital electronics, which (back in those days) was far easier!

I am bunged up with a stinking cold at the moment - ears and nose and sinuses clogged, so whatever I hear is questionable right now - if I heard ghosts, they could be due to mucus rattling about, and as I dont hear them - well - it doesnt mean they arent there.. but it sounds clean (a bit muffled - but thats probably my ears! ;-)

Fred.

Hi all,

If a master thereminist approved that what they hear is musical and could be played then why would anyone want to introduce digital into the design to create a tone. The theremin is about reaching for the past in a simple way.

The sound of enigma .mp3 310k

I just had a funny thought, if Coalport is not in communion with Clara Rockmore then I am not in communion with Lev Sergeyevich. I am then just a table top tinkerer.

I have builders, but the theremin was never for me to play. )-:

Christopher

"if Coalport is not in communion with Clara Rockmore then I am not in communion with Lev Sergeyevich." - Christopher

LOL ;-)

That, to me, says it all.. The great questions of the universe, reality, existance, immortality summed up in one simple sentance! And it all hangs on the meaning of the words "in communion with.."

Fred.

Oh hell! - I wanted to just leave it at that.. but what I wrote has kept bugging me.. "in communion with" - just this feeling that I was missing something "important" or had got something "wrong"..

Now I think I may know what this "something" is - but to  explain it is going to take another long metaphysical spiel - I really need to cut back on these before I get the rep of being away with the fairies - LOL ;-) So I will try to make this brief.

Back in my "escape" thread (life, the universe etc) I told this SF story about being dematerialised then rematerialised, and questioned whether there was any "real" continuity between the "I" that "I" was proir to being dematerialised and the "I" post rematerialization.. The question boiled down to  >> If an EXACT duplicate of "me" came into being, would that entity be "me" <<?

IF the answer to that question is "Yes", THEN it begs a further question - If an entity "came into being" which (in terms of brain wiring and thought processes etc) was 50% identical to me, would that entity be "me" in any way or to any degree?

Is this perhaps what "communion with" is about - ? If you have enough "in common" with some other person, and learn from, observe, absorb and "emulate" this person to a degree that some of "what you are" is identical or extremely close to what this other person is or was, does this other person "live on" in any "real" way in you?

I dont know (and cannot even guess at) the "answers" to the above - But I think that in most (if not all) cases this is an area where self-delusion is likely to be extreme.. I remember making a posting here on TW (which I deleted) where I projected MY concept of the 'personas' of two members, and made comments as if I knew them.. The clear reply from one of these members woke me up to how presumptious I had been to even imagine that I knew these people at all.

I think most (if not all) of the time we "commune" with ideas about people that are mostly our fictions - we bring these fictions "to life" (and here is another side-discussion.. Are we actually "creating" these ficticious characters and "bringing them to life" within "us"? Are the myriad of different "Jesus"es people create, because they have been saturated in differring fictions about him from childhood, and taught to emulate him, actually "real" and "made flesh" - is this why there are so many  "Jesus"es  in mental institutions ?) -

I think that the more we know about the person, the easier it is to "commune" with them - It may be that those who clearly and unambiguously expose themselves, their thoughts, their ideas, their creations etc, have more chance of being more accurately "embodied" and "living on".

Which is another damn good reason why I must stop posting so much! ;-)

Fred.