NEW UK DESIGNED & BUILT THEREMIN with volume loop & pitch rod etc

[All theremins have two* "antennas" determining pitch and volume - one of these is usually invisible (and common to both pitch and volume) and it is ground! ]

Why on earth (pun intended) would anyone design a "theremin" that can work on battery power, knowing that this is a technical nonsense! Even when using grounded AC power on the theremin, the use of a battery powered amp can cause issues. Hence a completely battery-powered setup is just looking for trouble, unless you play barefoot on the ground :-)

"Hence a completely battery-powered setup is just looking for trouble, unless you play barefoot on the ground :-)" - rogue

No.. This is not the case!

It is EASY to create an adequate "ground antenna" from something as simple as a length of audio cable.. See the  Battery Supply for EW ? (condensed and meaningful posts) -> Particularly the post with a heading:

"Re: Grounding / Earthing.." and the post by ChrisC which pastes the EW battery modification from Moog, and my following posting headed : "RE: Grounding / Earthing :: vs :: EW TRM Instructions."

In fact, "barefoot on the ground " doesnt help with a battery theremin unless its ground is connected to "ground".

The whole "Battery Supply for EW ? (condensed and meaningful posts)" thread has been as much, or more, about grounding as it has on the power supply side - which is a bit of a shame IMO, as the grounding is a subject that should not need this kind of exposition in a forum like this - Understanding the effect of ground is fundamental and essential for theremins - battery or mains powered.

Battery or mains driven also, essentially, require the same "conditions" which are not always obtained on a mains theremin unless care is taken.

The theremin is not a keyboard one can just plug and play, and expect optimum performance without any understanding of the mechanisms.. 

(I have a LOT of emails from people with grounding problems on mains powered theremins - many from parts of the world where wiring standards are, well, sub-standard.. Russia tops the list of enquiries I get** - and it seems that many setups are effectively "floating" - the mains "ground" connection in the sockets simply isnt connected.. IMO, this is shocking [pun intended] - but it is a fact of life - This is a hidden danger which only shows up when an instrument goes 'live' and electrocutes the operator, or when one connects an instrument like a theremin which depends on ground for correct operation.

I am fearful about giving advice in these situations - If one has mains equipment where their "ground" connections are all linked together, but where this does not connect to a "true" ground return, then if any of this equipment goes 'live' the whole lot goes 'live'.. If one has a conductive mat connected to this floating "ground", this mat will go 'live' in such an event - and the potential for a fatal accident is greatly increased.. So my advice always is to sort out the grounding problem unless one is only using a battery supply for ANY and ALL equipment connected to the floating "ground")

If you dont understand capacitance and the basics of how it works with regard to playing (and this includes understanding that you are acting as a variable capacitor between two "coupling elements" - one being the theremins antenna/s, the other being the THEREMINS INTERNAL "ground" or "0V" - and that this "internal ground" needs to be connected somehow to a large external "antenna" - as in, either all stuff connected to "real" ground, or some large conductive "coupler") , you are unlikely to know how to achieve optimum functioning of your theremin, and likely to be clueless when things (which can be easily fixed) go wrong.

Fred.

** I have actually been asked by Russian theremin promoters to design a theremin to overcome their problems related to grounding - offered real money for design of a battery powered theremin that will work without needing to rely on the mains supply or grounding provided by the mains outlet, and which is intrinsically safe..

What they want is impossible - As soon as the theremin is connected to anything powered by mains, even if it is running off its own battery supply and has its own ground mat or other ground - player coupling mechanism, its "ground potential" will be determined by the "ground potential" of whatever it is connected to..

Sure, I can get the theremin to work and have good player coupling - But I cannot do anything to ensure safety unless whatever is connected to the theremin is safe. . Alas, for the price they want to sell these theremins, I cannot even make a 555 based battery theremin anyway ;-) .. I believe they are now looking at buying LV-3 's.. Or at least they wanted me to get one and reverse-engineer it.. I refused.

One other "aside" needs to be mentioned..

Back in the "old days", almost all audio equipment had internal power supplies and ground connection.

These days - largely due to the rules and expense of certifying internal power supplies and connections, most equipment has seperate power supplies - wall warts and horrible things like that.

These "warts" usually provide a low voltage supply to the equipment, and it is rare for there to be any connection to ground.*

The above has advantages and disadvantages.. The BIG advantage is that there is ALMOST no way the equipment can OUTPUT a lethal voltage - If there is a failure at the wart, the wart will blow up - but it is most unlikely (particularly with UL rated supplies) to ever couple directly to the incoming mains.

The disadvantage is that the instrument is "floating" - Its ground potential will be set by whatever its ground (usually through the audio screen) is connected to on other equipment.

IF the theremin is correctly grounded, THEN all "wall wart" powered equipment connected to it will be grounded. If however the theremin is not grounded, all "wall wart" powered equipment connected to it will be floating unless some item connected to it is grounded.

"Floating" is ok - As long as the coupling of this "floating ground" to the player is large enough and reasonably constant.

*It should also be noted that even some equipment with internal power supply and a 3 pin mains power connector, may not implement a ground connection - open it up and one finds the mid terminal has nothing connected to it.. All you have is connection to a nasty internal "wall wart".

"LOL, I had to look up "I keed, I keed" ;-)"  - FredM

I can heartily recommend the DVD "The Best of Triumph the Insult Comic Dog".  Just got the CD/DVD "Come Poop With Me" which is a hoot.

Back to grounding, I imagine a high voltage, small value cap (~1000pF, >2MOhms @ 60 Hz) in series with whatever Theremin ground connection might increase human safety?  It would still be floating in a DC sense, but I believe one only needs a good AC ground at the operating frequency (generally hundreds of kHz)?

If I ever actually get around to making a Theremin, I intend to supply an explicit grounding point, kind of like they used to do for record turntables.

[EDIT] And isolating the audio out(s) via transformer(s) might be a good thing as well, no?  It could help roll off any RF on the outs too.

"Back to grounding, I imagine a high voltage, small value cap (~1000pF, >2MOhms @ 60 Hz) in series with whatever Theremin ground connection might increase human safety?  It would still be floating in a DC sense, but I believe one only needs a good AC ground at the operating frequency (generally hundreds of kHz)?

If I ever actually get around to making a Theremin, I intend to supply an explicit grounding point, kind of like they used to do for record turntables." - Dewster

Correct - A high voltage capacitor in series with the player's ground mat or whatever, will protect against any mains conduction path to whatever its connected to..

But there is a wee (as opposed to "Come Poop With Me" ;-) problem... Whilst the (capacitor isolated) grounding terminal, or anything connected to it, wont kill you, If the equipment is live, and doesnt have a ground connection (which should cause the mains fuse to blow) then this could still kill you.

The most fatal connection is RA to LL (Right arm to Left leg).. If you are standing on a mat directly connected to floating "ground" which is 'live', then there wont be any conduction path between the mat and the live theremin.. Both will be live.. Watch out if you step on any "real" ground though.. This is also true if the mat is isolated with a capacitor.

Another "wee" problem relates to ESD.. If one has any ESD protection device on the antenna, this will shunt the HV spike to the theremins ground.. If this "ground" is only connected to "real ground" via a capacitor, then this capacitor will probably need a voltage rating of kV's.. So you would need to have a HV shunt device across this capacitor - something which trips at say 500V so that it doesnt allow mains through, but below about 1kV so that you can get a 1kV rated capacitor..

In all, I think it can get a bit OTT.. To me, a direct "ground" connection looks as safe as an isolated one - its one of these situations where you cannot cover every scenario.. If one has a 'live' mat and touch a "real" ground you would get electrocuted. If you have a grounded mat and touch a live surface, you will get electrocuted.. Capacitor isolation prevents either of these cases - But doesnt prevent any of the other possible scenarios.

Galvanic isolation (insulation) of any "ground antenna" object (such as a conductive mat) and direct connection of this to the theremins ground connection is probably the best compromise I think.. ESD will simply raise the potential of the floating ground, so protection will still work, and other possible problems will be no worse by having this "ground antenna".

Fred.

I want to be able to use the LV-3 as a full battery/remote unit so I can show people what I am bangin' on about re. theremins. Just set up anywhere sort of thing. I have the LV-3 on its 9v battery working through a Zoom G1XNext guitar fx box which is also on an internal battery source then running into the small 'Marshal' amp stack copy which is again on an internal 9v battery. A fully portable rig. Not going to need to protect your hearing with this amp.................oh, the way I play though it might be advisable!!!

Now the pitch antenna has to be fully clockwise to give a just-about reasonable field depth. This is a shift of about 25% over normal. I emailed John Woodley (Mr Lost Volts himself) to enquire what could be done about this.

Here's his reply without the attachment showing the circuit board as it is the first section you might all be interested in:-

I screwed about a 4 foot length of speaker wire to the ground post on my battery operated Roland Mobile Cube and wrapped it around my ankle.   It seems to work just fine with my Subscope and the rig behaves very well.

I am not sure do I understand what "progressively non-linear" means. (I assume that is how the field of this instrument is described.)

Is a linear field something like: ('x' represents a note, '-' physical space in between)

High x-x-x-x-x--x--x--x--x--x---x---x---x---x---x low 

If so, does the progressively non-linear mean something like?

High x-x-x--x-x--x-x-x---x-x-x--x--x----x---x---x-----x low

If not, could someone give me some sort of "visual" representation of a linear and a progressively non-linear field?

No, this is progressively non-linear (constantly decreasing tone spacing):

High x-x-x-x-x--x--x--x--x--x---x---x---x---x---x low

Linear on a theremin means constant tone spacing as on a keyboard.

Hi Puukorva,

The musical relationship is exponential - if one starts at a low note, and wanted one semitone higher to be say 1cm closer to the antenna, one would need the frequency at this closer point to be 1.05946 times the frequency of this starting note.. A linear musical relationship for the above would be that each cm closer would have a frequency 1.05946 times higher than the preceding note.

I believe that with "progressively non-linear" some other relationship would be applied - and due to physics and the way theremin oscillators are tuned, this tends to compress the distance between notes as the hand approaches the antenna.

Capacitance seen by the antenna increases rapidly as the hand approaches it - More rapidly and with a different function than the exponential increase required for musical linearity - and this results in compression of the intervals.

The whole mathematical balancing act, as far as I understand it, is about taking an extremely non-linear antenna capacitance vs distance relationship (which is highly progressively non linear) and bend this towards a perfect musically linear exponential frequency - distance relationship.

Oh, BTW - the 1.05946 is no mystery majik number, - each octave is twice the frequency of its lower octave, and (for the 12t ETS) there are 12 semitones, so the multiplier is 12th root of 2. If one had a 6 tone ETS scale, the multiplicand would be the 6th root of 2, (1.1225) .. As the theremin is infinitely microtonal though, I feel that equally spaced octaves is probably a better way to define linearity - provided that there is no distortion anywhere in the resulting curve... it all comes down to the same in the end.

Fred.

ps..

I think I need to confuse matters a wee bit just to make one thing clear -

Distance is, in terms of discussing linearity, quite valid.. However, in terms of playing, I do not believe it is actually the most important issue. The real issue is something unseen and which IMO requires a somewhat different thinking, its CAPACITANCE.

Capacitance is what determines the pitch, not distance alone - it is determined by distance, plate area, and dielectric.. Variation in any of these will affect pitch. Dielectric doesnt vary much and you have no control over it, but you have control, to some extent, over area - the shape of your hand reletive to the antenna -  the "wider" this is, the greater the capacitance, and the higher the note.. Distance may be the primary pitch determining component, but one can easily get an octave change in pitch at some positions in the playing field by changing the hand shape* or using "arial fingering" and fine pitch control is far better implemented in this way rather than using arm-controlled distance.

*Changing the curvature or wideness of the hand tends to act simultaneously both on area and distance, and the actual capacitive components acting on pitch when one say clenches ones fist without moving the arm can be quite complex. For example, with the arm not moving and the hands position not changing, bending the fingers will move the nearest part of the hand further from the antenna - decreasing capacitance and lowering pitch.. howvever, the bending of the fingers will also increase the area which increases the capacitance.. the result is that the pitch will drop less than if one kept the hand straight and moved the arm so that the nearest point was the same as if one had bent the fingers..