"Build the EM Theremin" - altered component placement - comments?

tinkeringdude, the jack-plug solution is good. because it  gives you a good diameter for your brass tube, you might use  for the loop antenna. bending a nice loop is easier with a inner diameter of about 10,12 mm (depends on the plug).: my sister bent one for me out of a 4mm brass tube,for the open.theremin,and  she knows her stuff, and complained about the smallness. she did it by the 'sandfilled' version and used some very fine sandblasting powder. you probably know how it's done. this method prevents 'knickse', kinks and bucklings.... so one end of the loop needs a plug and the other end might go just so into the side of the case. if you place the female plug a bit more inside the case instead of right at the case, then the case supports the antenna further more.(does this make sense or is it just gibberish?) i could pm you a german solution, if you like.

but first sget your electronics working. with more or less proper antenna sizes attached maybe build something like a provisory testsite, so you can still adjust placement of the final hardware,(pots, panel, powerplug, wires antenna etc.), and do the troubleshooting,if necessary,on your circuit much easier. i'm actually at about the same stage of tinkering, with a theremax-kit. it's one of the most funniest theremin i've built, so far. ;-) if you like i can post a pict of my testsite.

I think I understood what you mean :-)

How critical is it to match the antemma diameter & length with the moog specs? And why is the antenna not a straight "U" but has a larger diameter "bottom" ?

And also important: how far away should I position the theremin from conducting objects in my alas not quite huge apartment with plenty of metal window frames, some keyboard stands and too many cables on the floor? ^^

As long as I don't have a mic flange, I guess I'll put it on a wooden chair, although that one also has some screws in it, heh

I think I understood what you mean :-)  oh,wich part? lol.

a wooden chair or a small non conductive materialized table, wood, seems quite a good suport for coarse tests. just make sure, that the volume antenna is free. the screws won't screw up too much.;-) page 15 of the original assembling manual:"..36" to 42" high... no objects on the table within a foot or two of the theremin...away from walls and other large stationary objects". get it working first and tune it more accurate on a mic stand when you cleaned up your room (and solved the mic stand.)  just joking. the more free space around, the better of course. cables on the floor are not so critical. or how do you connect it to the amp?

i wish i could come up with a good bedtime story about why a loop. i does not need to be a loop. you could form it differently, like on the tvox. but you'll get a different field. there's quite some information around here, also about the proper sizes and explanations of the relation diameter/length for the antennas. and it's affection on playing. go as close to the original as possible, just to keep it simple. ca.12mmØ,about 42mm length?

Oh gee, now I'm getting confused about the antenna coils I ordered.

I saw the values in this thread:
http://www.thereminworld.com/Forums/T/29260/confirmation-of-part-values-for-etherwave-build

on both sides (pitch, volume), he left the 4th coils out.
So pitch is in sum 30mH instead 40mH and volume is 10mH instead 12.5mH compared to the original.
Meanwhile I have seen several other threads also talking about using only 3 coils like the newer commeraial boards do - but the value sums there always were like the original, i.e. 40 and 12.5.

Can anyone shed light on this? Is the list in above thread actually wrong, or is the lower overall inductance an improvement?

EDIT:
Oh, so here Thierry explicitly mentions the values:
http://www.thereminworld.com/Forums/T/28429/etherwave-component-help?Page=2

(in the other thread it could have been an oversight)

So what will this do, the lower values?

UPDATE: It (mostly) works!!! :-D

Pitch & volume are tuned (thanks to Dewster's buffer circuit I did the rough part with oscillosscope, would have gone mad otherwise considering the coil range I guess :-D) & I can play it (well, not quite yet, haha!)

The only thing that seems not to work is the brightness control - it has no audible effect whatsoever.
The waveform control does, it changes the tone from a pulsy waveform (full counter clockwise) to rather pure sine (clockwise) - so it's not like my guitar amp is totally cutting the high end or anything.

Any hints on how to debug that?

Here's a quick photo for now (good that you can't see the whole case, it would display my lack of woodworking skills & workshop / tools ;-) )
http://postimg.org/image/4fdulrgkf/full/

The small perfboard roughly in the middle contains Dewster's bass mod in SMD form, plugged on with pin headers. The jumper on top mixes the buffered oscillator signals - or not, if removed it allows to view both signals separately on scope.

The reddish cans are the coils I talked about.
The board is a custom layout - I used the smallest board size allowed by Bilex-LP, a bulgarian PCB manufacturer, which is 120 x 80 mm², to drop the price. I also omitted soldermask. Such the price for 2 PCBs was just ~ 32€, e.g. 16,- EUR for one! Beat that, heh! (I'm going to treat the PCB with an insulation spray to protect the traces, one that can still be soldered through if necessary, as soon as the thing works 100%)
Also, my case is only about 39cm wide instead the ~45cm of the EM specs - not so much by choice but because that one weekend when I felt like building this, I happened to have spare wood parts of that size at hand *g*

As soon as everything works:
If anyone cares, I could upload the layout somewhere & reference to the Chech (?) ebay seller who still sells these coils, since this appears to work and the price is nice!
All three coils are the same, adjustable 45..100µH - still worked also for the volume antenna, although mine is currently far thinner than spec, 3mm or so brass wire.
(The provisorial pitch antenna is a wooden 8mm diameter stick, with a layer of doubly adhesive tape + aluminium foil, held in place by those two green clothing-pegs *g*)
That my layout works may well be due to luck than anything else, considering this is my first PCB layout ever.
If the second build, the one for a pal who also wants one, also works, Icould imagine, though, that someone might be interested - I've seen mostly considerably more expensive BOMs (incl. PCB cost) for bulding an Etherwave than mine!

Ah, yes, it dawned on me that having the audio jack on the right, i.e. the shielded cable close to the pitch antenna, was not so smart, but that's not the final front panel :-)

UPDATE #2:

Turns out the volume pitch knob didn't work either. Due to the terminal of that resistor in my schematic CAD software (and therefore, also on PCB) only hovering over the line that connects other components of that net, but not being connected - I saw that only when zooming in there.
As the great philosopher Homer used to say: D'OH!
And the brightness control, that resistor had one end invisibly somewhat loose.

Now basically everything works - well I haven't masured the linearity, have to read up on tried & proven procedure there next weekend... ^^

One maybe problem has surfaced, though:
Sometimes the first time I hit the power switch, the circuit will make no sound. Changing nothing tunig or body distance (to antenna) wise but just switching off / on again "solves" it.
Is that such an oscillator hiccup that's mentioned in some threads here?
What could be causes? Me using other coils than the toko ones, with some parameters other than inductance differeing? Or indeed the changed PCB layout?
Well, as long as turning it on a second time reliably solves it, this may be acceptable I guess.

Hah, I just  have to mention that I'm quite pleased with the sound of this thing. Works quite well with the low impedance input of my cheap e-guitar tube amp. Especially when switching to the distortin channel and add some spring reverb :-D (Now I have disgusted the classical players? ^^ Mind you, I'm much into classical music, too)

"One maybe problem has surfaced, though:
Sometimes the first time I hit the power switch, the circuit will make no sound. Changing nothing tunig or body distance (to antenna) wise but just switching off / on again "solves" it.
Is that such an oscillator hiccup that's mentioned in some threads here?
What could be causes? Me using other coils than the toko ones, with some parameters other than inductance differeing? Or indeed the changed PCB layout?"  - tinkeringdude

It really could be just about anything.  Layout, coil Q, coupling, etc.  Try touching either antenna to see if that brings it back to life.  I wonder if you alter the variable pitch LC tank tuning a bit if that might statistically change things?  The tank can theoretically pull a lot of current if slightly mistuned.  It could also be the volume side I suppose.  If you catch it in the "off" mode you might want to poke around and see if things are working up to the VCA.

If you catch it in the "off" mode you might want to poke around and see if things are working up to the VCA.

Heh, yeah I still have the wire in there on the diode that connects to C28 with a little clamp to put it against GND to disable volume attenuation.
And since I used your buffer circuit - I might even be able to look with the scope if one of the pitch oscs is misbehaving without influencing it.

I'll also examine the layout to see whether the traces are a bit close where this matters - the guide what kind of trace clearances one should use at what voltages on the PCB manufacturer's site indicated that 12V (or in some places 24V) may be a bit high with no soldermask - and I haven't put the insulating spray on yet.

Ah - and might it be worhtwhile to remove all the unused copper "eyes" on the antenna boards? So many isles with no defined potential maybe a bad thing?

"I might even be able to look with the scope if one of the pitch oscs is misbehaving without influencing it."  - tinkeringdude

You can bring a scope probe a couple inches from each antenna to see if the associated oscillator feeding it is running.

"Ah - and might it be worhtwhile to remove all the unused copper "eyes" on the antenna boards? So many isles with no defined potential maybe a bad thing?"

Most likely not a problem.  I'm not saying there's nothing to it, but the whole "get it away from metal!" thing is kind of overrated.

Ah, good hint with the probes near the antennas!

Most likely not a problem. I'm not saying there's nothing to it, but the whole "get it away from metal!" thing is kind of overrated.

On the other hand - the metallic & grounded front panel does make sense, not just because metal panels look nice? Mine is currently not metallic (well, the pots are grounded). I would imagine that having this grounded big metal plate between the two antennas gives them a certain base capacitance, from a key position, that would "decouple" the influence on one antenna by the hand that is supposed to play the other one, since that plate is 1) more conductive, 2) more grounded and 3) closer to the opposing antenna than the hand - does that make sense? Anyway I was feeling that in my current setup, it's not "decoupled" enough. (having the antennas 6cm closer together than original specs may also play a role)