Grounding and Alternatives.. Yes, a repeat performance! ;-)

From Here:

"bound to ground"

LOL;-)

Not strictly true though..

You dont actually need ground - you just need to be a capacitor 'plate' connected to the theremins 'ground'... We use ground because generally its the most common medium of conduction or capacitive coupling between the theremin / environment / player..

But connect the "ground wire" (from the theremin) directly to the theremin player, and the need for "ground" completely disappears! - You can have a battery powered theremin completely disconnected from "ground" provided the thereminist is connected to the 'ground side' of its circuitry.

Somewhat OT - TECHNICAL - And, astoundingly, controversial:

But its kinda risky saying something obvious like this here - because there are folks who turn it into pages of utter nonsense (will even paste pages from theremin instruction manuals where Bob Moog says the theremin must be connected to ground, Take Bobs words out of context, and say that as I am "contradicting" Bob, I must be talking BS)  and (effectively) claim that "ground" has special mystical qualities, and that unless you put stakes in the ground or otherwise ensure a physical connection to "real" ground, the theremin wont be a "real" theremin, and will lose its quality of sound.. All such claims are pure bullshit!

What the theremin sensing principle is, how it works, the basis on which the theremin world rotates is this:

There is a circuit comprising of an inductor and capacitor forming a tuned circuit. The capacitor sits across or in series with the inductor - one end of this capacitor is tied to the theremins "common" (0V)* the other end is connected to the antenna.. Another capacitor is across this capacitor, this capacitor is you,the thereminist, and your capacitive 'bulk' coupling to the antenna ... One end of you needs to be connected to the "common" so that you can be in parallel with the capacitor inside the theremin..

IF the theremins "common" is connected to ground, and you couple to ground strongly, everything works.. If the theremin isn't connected to ground or you dont couple to ground well, things dont work well.

IF however, you actually connect a wire between yourself (or have a separate plate from the theremins common which capacitively couples strongly to you)  and the theremins "common" then you are directly "in the circuit" and everything behaves, regardless of what else the theremins "common" is connected to, or even if this "common" isn't connected to anything other than you!

Fred.

*The above is a simplification in some cases - Sometimes the antenna coupling to the player is the only 'physical' capacitor in the circuit, and there are other "capacitors" formed between the antenna and the theremins board, or if the theremin is connected to ground, between the antenna and ground.

Also, ground is big - really really big! ;-) In fact, its Earth, and everything connected to Earth! .... So every theremin (like every conductive object within about a million miles of the center of earth) is coupled to "ground" in some measurable way... But none of this matters - If the thereminist is wired or strongly coupled to the theremins common.

(The above is the usual way theremins are operated)

To clarify the above crappy diagrams:

" i just don't like to  be bound to a instrument, but i guess a esd-wristband around the ankle would work?" - Xtheremin8

The coupling doesn't need to be extreme - you dont even need conductive connection, its capacitive connection that's most important.

Ok - I have no idea about how one has a theremin incorporated into a marching band ;-) .. But if the theremin was on a metal trolley of some kind (with the volume loop protruding over the side, not above some metal sheet ;-) then connecting the theremins common / 0V / ground to the trolly would give enough coupling to the player I recon.

If you configured a theremin to be worn as a pack against the body, and extended the antenna, you could have a truly portable instrument - would probably work better if built from a Jaycar or similar kit.. no point in even thinking about precision if one is moving the theremin.. ;-)

The only way I can think would suit 'marching' would be something like this:

EXTERMINATE!!!!

LOL ;-) Certainly should get some attention, particularly if the thereminist trips..

But perhaps just a pitch plate on one side and a volume plate on the other side would be better ;-) .. a sheet of aluminium or such on the player facing side of the instrument would provide more than enough 'ground' coupling- probably even this wouldnt be needed if the circuit board is near the player.

Fred.

Fred you are starting to concern me so I will be polite. The wire in the horizontal tube is as much a pitch rod as anything else and why I have gone with a horizontal pitch side.

If the kid is trying to look cool you ruined that 15 minutes of fame, if he wants a theremin whistle on-the-go he should get a slide whistle.

Christopher

"Fred you are starting to concern me so I will be polite. The wire in the horizontal tube is as much a pitch rod as anything else and why I have gone with a horizontal pitch side." - RS

Christopher.

A thin wire - as in, as thin as you can manage - the stuff they wind in IF transformers for example - has low capacitance.

I have actually done similar things to that shown above - I can have multiple antenna sockets, on left and right side of the theremin, without any problems - so as to facilitate left-handed and right-handed operation.

Capacitance is a function of AREA - thin wire has little area - thick wire has a load of area - replace the lead from an EW coil to the antenna with fine wire and you will mess up its tuning because it needs the capacitance relative to the ground foil, and the capacitance is hugely reduced if you use thin wire.

But you dont understand capacitance - You dont understand that the "antenna" is not an "antenna" in the usual RF sense, its a capacitance electrode - Even though this has been pointed out to you umpteen times in the friendliest way in the past - even though you have been shown that Lev Theremin never referred to them as "antennas" and in his patents specified them as capacitive electrodes.

In fact, you dont understand anything relevant to theremins... You think you are so great that you boast about never having looked at anyone else's theremin designs, you were dumbfounded when it was revealed to you that the big coils in Lev theremins were actually there for equalizing the response, and not stupidly large tank coils put there for decoration.

You mock players who use areal fingering, saying that its pointless, because theres a "bubble" 'round the antenna which gets 'pushed' by the finger, and therefore all that matters is how close the nearest finger is..

You talk absolute rubbish all the time - which is fine if you lay off those who have some basic understanding, and dont go disrupting every thread where someone is talking sense!

Why dont you check your facts before posting rebuttals to everything I say?  Cant you see that all you are doing is showing yourself up as the moron you are?

?

Fred

And you, who accuses everyone of having no sense of humor, failed to notice the Dalek reference..

Fred said: Capacitance is a function of AREA - thin wire has little area - thick wire has a load of area - replace the lead from an EW coil to the antenna with fine wire and you will mess up its tuning because it needs the capacitance relative to the ground foil, and the capacitance is hugely reduced if you use thin wire.

I agree completely with this statement above by you Fred, this is why I have a perfectly linear pitch field using the thinnest wire practical for the inside field and longer for the outside field pitch control. I have always said pitch field linearity is geometry not algebra. Don't complicate it.

I wonder if I could walk through an Airport with this.

On GROUNDING and particularly on use of battery supply for portable etherwave busking, this thread was an escape from the original which was disrupted by someone who knows nothing about theremins or electronics, and his sock puppets or other idiots..

http://www.thereminworld.com/Forums/T/28997/battery-supply-for-ew-condensed-and-meaningful-posts?Page=0

fred,

that device looks like a good weather version for a halloween costume. don't use it during thunderstorms in an open field !! lol

in fact: i know that capacitance area size relation to the playability of a theremin.(does that make sense? my grammar is so bad.) the tuningwire and the opposite foil in the ew explained some aspects of it quite well back then to me. also what part of the circuit i am. i define myself as the most variable last instance. ;-)  but your sketches remembered me to put some metallic plate or grid on my place behind the theremin in the studio, since i startet with a tromboneist who is also double the weight of me, and it's a bit crowded from time to time....! i also considered building a cheap as possible directional antenna shield, but that's a different story. since i know you experimented around with that, i have to reread some threads around here first, before i start any silly question.

Hi Dani,

My advice on a directional antenna shield is this - unless you are using a theremin designed from scratch (or one you have built and fully understand) forget it!

The shield must must have on it exactly the signal that the antenna has on it, and must be driven at low impedance so that capacitance it 'sees' doesn't change this signal or make it go unstable.

So for antennas with high voltage swings, its a LOT of trouble - you need a voltage supply capable of spanning the required output voltage (+/- 100V or more for some theremins) and a voltage follower with low loading on its input, capable of driving this voltage onto the shield.. And you can get a nasty shock off the shield if you touch it!

So really you need to limit the design to a theremin that has lower antenna voltage swing (say +/- 18V) and one can then quite easily supply the required voltage (say +/- 24V) and obtaining a suitable voltage follower isn't such a major headache.

So a parallel LC direct-to-antenna topology (like the SC / Jaycar) is a good easy way to start exploring shielding - but one really needs to get better linearity than these provide (although a focused field does seem to improve linearity quite a bit, so perhaps not..)

There are lots of really strange things one gets when playing with these shielded ideas - some I do not yet understand... The distance between shield and antenna does seem to have more effect on the performance than I can explain - but I think this could be due to delays or errors in the copied signal --- Its also a nightmare to debug, because one cannot easily see whats on the antenna without loading it.. And when loading it, even if the shield signal looks the same, you cannot verify that its the same when unloaded.

So unless you really need to do it, think carefully!

Where shielding does work a treat is if one has some large metal object that one needs to 'get rid of' - if this is insulated from ground, you can simply connect the shield to this object - the drive signal doesnt need to be nearly as accurate as if the shield is close to the antenna, and the capacitance effect from the object is hugely reduced.

Fred.

thanks fred.

i probably forget it.  or i build a zapper for the intruders. i once got zapped by a tv antenna. outch! so it seems a bit too adventerous for my knowledge on electronics. i wish you success  for your theremin. as far as i could imagine how it might sound looking at your schem. brilliant. but still a lot of work. so get busy instead of answering on my probably senseless posts..;-)

"And I assume a pitch preview wire in your ear could take care of this issue." - Rich

This is debatable - it certainly goes some way towards improving coupling, one is likely to get about 20pF from the metal in the earpiece for an in-ear plug, sometimes more, the cable is usually so thin and sometimes having quite high inductance, that it doesn't count for much.

An actual pair of slim headphones is certainly likely to be enough @100+ pf.  At HO2010 my client procured massive 'educational' headphones with bulky coiled cables for my theremins (so punters could play them when other exhibits were performing) and these were a real pain, because the field 'expanded' by about 1' when they were worn, and I had to go round and re-tune the instruments when ever headphones were required, and re-tune them when going back to loudspeakers.. Doing that for 16 instruments in about 4 minutes was the one real challenge I had there - ;-)

"Grounding" was an incessant problem at the show, and the reason I came up with the "ground antenna" scheme - the theremins were on chipboard plinths, and I lined the inside of these plinths with aluminium foil and connected the theremin grounds to this, and disconnected the grounds from "real ground" - All the problems vanished as soon as I did that - there had been some problems with theremins interacting with each other, and this stopped as soon as their grounds were independent.

Fred.