Battery Supply for EW ? (condensed and meaningful posts)

Very interesting!  He says he used 3 sheets....were they added one by one until the necessary effect was achieved?  It sounds heavy!

"Very interesting!  He says he used 3 sheets....were they added one by one until the necessary effect was achieved?  It sounds heavy!" - Bisem

Yeah, certainly sounds heavier than aluminium foil which, from a capacitive perspective,foil is just as good...

But, Aluminium foil isnt any good for a structural assembly - So if he wanted a robust heavy assembly, heavy plates would serve a double role.

I doubt that "tuning" the size would make much difference.. One wants more than 50pF capacitance, ideally 100pF or more - Two main things affect capacitive coupling, one is area, the other is distance.. Increasing distance between plates decreases capacitance in an inverse square manner, so having a large plate 50cm from the players legs is probably going to be less effective than the thereminist standing on a small plate.. Particularly if their shoes have a high dielectric constant (Product idea * High K shoes for thereminists ;-) LOL .

But whatever - it really isnt difficult to achieve 100pF coupling to the player.. The messier you are with laying tha cables (particularly by the player) , the more likely you are to have good coupling.. But there are loads of ways to create good player ground coupling.. Find a way which gives adequate coupling for you particular situation, stick with that, and you should be fine.

I don't understand the structural advantage.  Isn't the wood case strong enough?   It seems that if anything having the extra weight inside would make the whole box more vulnerable to damage if accidentally dropped since he travels with it so much.

BTW I have the same amplifier as Thomas but plan to build a case around it without dissembling it so that I don't void the warranty.

I tried a wire attached to the the amp and a small metal stake pushed into my lawn which worked perfectly, however it does limit one to a grassy area.  Perhaps a spring clamp attached to a lamp post or a metal fence?

Hi Bisem,

"I don't understand the structural advantage. " - Bisem. 

I was just guessing.. assuming there must be a reason for adopting this method of ground coupling.. To me personally, the idea of vertical plates at the theremin to facilitate ground coupling to the (quite distant - say 50cm) player seems like a daft idea.. But I dont know the whole story.

Have you tried just running a long audio (screened) lead on the ground 'round / close to where you stand when playing the theremin? Something like a good quality 5m audio lead connecting the theremin to the amplifier, but looped in front of the theremin as close to the player as possible usually does the trick.. Just keep as much of the cable close to the ground as you can - that way there is capacitive coupling to "real" ground as well as direct capacitive coupling to the player.

"Perhaps a spring clamp attached to a lamp post or a metal fence?" - Yes, this should help, if they are available - Lamp posts in particular should be well grounded..

But IMO (as you have probably seen from my above posts, LOL ;-) I believe that the simplest and most reliable solution, which is not dependent on finding any "ground terminal" or place to stick a stake, and is ideal for real-world busking situations, is to construct a conductive mat of some kind.. One can buy conductive flooring but it isnt cheap and sometimes has higher resistance than is ideal for theremins.. But you can buy copper and aluminium adhesive tapes on Ebay quite cheaply, or thin sheets of copper, bronze or aluminium.. connect a wire to this, paint it with some rubber/non-slip coating or stick some thin self adhesive vynl covering to it, and you are sorted and able to play your portable theremin anywhere in the known universe..

About 1 sq metre with the player standing anywhere on it should give more than adequate coupling - you could probably get away with less than half that size..

If you want absolute certainty, a seperate wire connected to the mat with a conductive strap on it you could strap to your ankle, covers all eventualities (like if you were wearing peculiar shoes or playing on stilts, LOL ;-) but in normal circumstances, the mat will do the job.

But try it first - a sheet of aluminium foil and some self adhesive plastic book covering material allows you to quickly knock a test mat together.. Make it 1m square (or bigger) to start, take it to the worst situation you can find, try it.. Then if its ok, cut this mat back in steps until it ceases to be effective.. You now know the minimum size... A real mat should probably be at least twice this minimum size.

Fred.

*The only problem with aluminium foil is that its difficult to get a good electrical connection to it - I use copper tape with conductive adhesive - solder to the copper, stick this to the aluminium.. A crude quick way for temporary connection is to take copper braid or wire and mush this up with the aluminium foil, then put some staples to lock this in place.. But this connection is unreliable.

There was no question of "structural advantage". Thomas wanted a "closed" and "invisible" solution and the inox sheet does work for him.

Although I told him that only 1 sheet would be enough, he added other ones "to increase the grounding mass" because he is an electrician. You know, one of these guys who think that all above 50Hz is RF and all below 10A is parasitic current...

" You know, one of these guys who think that all above 50Hz is RF and all below 10A is parasitic current..." - Thierry

LOL ;-) ... I knew there must be a "good" reason why !  ;-)

As soon as one thinks in terms of "mass" one is in trouble!

Fred, you have given me some good ideas to play around with but I am not sure I know what you mean by "peculiar shoes" and didn't I mention that I play while dancing on stilts? LOL!

"Fred, you have given me some good ideas to play around with but I am not sure I know what you mean by "peculiar shoes" and didn't I mention that I play while dancing on stilts? LOL!"

You know, in the 5 years of meeting thereminists and dealing with wanna-be thereminist enquiries, it wouldnt surprise me at all if you werent joking ;-)

... Which is why I added the "conductive strap on it you could strap to your ankle"..

Now, dont tell me you have  non-conductive artificial limbs ;-) .. Apart from that scenario, I hope I have covered everything this loony club can throw at me! ;-) 

(If the stilts are longer than about 10cm, you may find 3 vertical metal panels at the theremin are a better way to get ground coupling .. Or a bunch of metalized helium balloons connected with wire tied to the theremins output socket.. Get enough balloons and transporting the rig could also be less back breaking - but remember, this only works on earth or planets where there is an atmosphere - and the towel wont help.) 

Fred.

I will use aluminium stilts.   I understand that helium is becoming very scarce on the planet earth right now!

http://www.independent.co.uk/news/science/a-ballooning-problem-the-great-helium-shortage-8439108.html

OFF TOPIC !  " I understand that helium is becoming very scarce on the planet earth right now!"

Yes - Been going that way for quite a long time.. The USA selling its stocks off at absurdly low prices...

I actually thought it was worth buying the stuff as an investment - certainly would have been wiser than investing in theremins! I actually suggested this to my brother (who runs a party super store and buys / sells loads of helium) - that rather than sell the stuff he could probably make more long term by just holding onto it... He just laughed, but bought a few more large cylnders... Then, in the London riots, his store was burned down and these helium bottles exploded..

But the thing which I do not understand at all is this.. The situation (rapid depletion of stocks with no way to replenish these stocks rapidly, if at all) has been known for a decade.. But all those science projects and medical equipment owners did nothing.. They could have bought stock at bargain prices..

So we will end up with mountains full of linear accellerators and billions of dollars / euros of equipment which will be redundant, and hospitals with unusable scanners..

Oh well - At least we found the Higgs Boson before we ran out of helium..